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BIOLOGICAL CONTROL OF AND BY ACARINA

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Overview

Distribution

Bdellidae

Acarina For Other Mite Control

Field Investigations

Cunaxidae

Ixodidae

Mass Production

Erythraeidae

Tetranychidae

Camerobiidae

Pyemotidae

Acarina for Armored Scale Insects

Cheyletidae

Stigmaeidae

Hemisarcoptidae

Eupalopsellidae

Associated Species

Taxonomic Ambiguities

Phytoseiidae

Marine Environment Acarina

Bionomics

Anystidae

References

 

Overview

          Phytophagous mites appear as pests in an array of agroecosystems, but have not been extensively discussed as a separate group for biological control. In most cases predatory mites are the key natural enemies of phytophagous mites. Gerson et al. (1990) were perhaps the first to elaborate on the Acari as a separate biological control category for armored scale insects. The following discussion relies extensively on their report:

Acarina for Biological Control of Phytophagous Mites

                (Ixodidae)

Dermacentor variabilis (Say), American dog tick.-- This species is widely distributed in the U.S. east of the Rocky Mountains, but is also found in California, Mexico and Canada (McMurtry 1977b). It causes irritation to dogs and sometimes to livestock. Its greatest importance is as a vector of Rocky Mountain spotted fever in the Central and Eastern U.S., and is occasionally known to vector tularemia. The life cycle may vary from 1-3 yrs. There is little activity during winter or in the warmest part of summer. Adults are most active in the spring and may live more than 2 yrs without food. This is the only stage known to infest humans, dogs and domestic animals. Small mammals, especially mice and rabbits, are considered to be the main hosts. Mating occurs on the host. After becoming engorged, they drop from the host, and the females deposit their eggs in protected places in masses of 4,00- 6,500 eggs after which the females die.

Eggs hatch into six-legged larvae, which attach to a passing host. After feeding for several days, they become engorged, drop to the ground and molt to the nymphal stage. When the nymph is ready to feed, it similarly seeks a host on which to attach. When the nymph has become engorged, it also drops to the ground where it molts to the adult stage. Both larvae and nymphs were observed to live over a year if food was not available (Smith, Cole & Gouck 1946).

Natural Enemies Sought.--In the U.S. a culture of the encyrtid parasitoid Hunterellus hookeri Howard (formerly Ixodiphagus caucutei du Buysson) was introduced from France where it was propagated and released on Naushon Island, Mass (Larrouse, King & Wolbach 1928). Small numbers of nymphs of D. variabilis parasitized by the French strain of H. hookeri were released on Capers Island, SC. in 1931 (Bishopp 1934). A larger effort was made on Martha's Vineyard Island, Mass, where an estimated 90,000 females of H. hookeri were released in two locations on the island during 1937-39. The strain of parasitoid used originated in Texas (Smith & Cole 1943).

In the season following the releases of H. hookeri on Naushon Island, immature parasitoids were found in a single nymph of the American dog tick and a single nymph of another tick species (Larrouse, King & Wolbach 1928). Subsequent surveys were made in 1940 by Cobb (1942) and in 1941 by Smith & Cole (1943). In both a few H. hookeri were found, but none was recovered from the American dog tick. Both this species and Ixodes scapularis Say were still observed in abundance; therefore, there was no evidence that any success was achieved on the island (McMurtry 1977b).

Bishopp (1934) reported recovery of the parasitoid from a single nymph of D. variabilis on Capers Island two yrs after release were made. In an assessment of results of releases of H. hookeri in Martha's Vineyard in 1937-39, Smith & Cole (1943) recovered no parasitoids from ticks in the release areas and observed no reduction in tick abundance that could be attributed to the parasitoid. A later report by Smith, Cole & Gouck (1946) also indicates that the attempt was unsuccessful.

Natural Enemy Biology.--Hunterellus hookeri is an internal parasitoid of wide distribution, having been recorded not only from North America but from Europe, Africa and South America (McMurtry 1977b). It was reared from several species of Dermacentor, Ixodes, Haemaphysalis, Thripecephalus and Hyalomma. The biology of this parasitoid was studied by Wood (1911), Cooley (1928), Cooley & Kohls (1933) and Smith & Cole (1943) summarized by Cole (1965).

The parasitoid oviposits in the body cavity of fed larvae and fed or unfed nymphs of the ticks (McMurtry 1977b). Oviposition may occur when the ticks are attached to the host animals. Apparently the parasitoids do not develop in the larvae or the unfed nymph, development proceeding after the nymph has become engorged. Overwintering may thus occur in the unfed nymph, with the parasitoids emerging the following spring after the nymph ticks have engorged with blood. The nymphs show no signs of parasitism until sometime after feeding on the host animals is completed. The period of development appears to be rather long. Cooley (1928) found that at 22°C. the average time from dropping of engorged nymphs from the host animal to emergence of adult parasitoids was 45 days.

A number of eggs is laid in a single host, and it was observed that more than one parasitoid may lay eggs in the same host. The parasitoid larvae seem to consume all of the contents of the body cavity of the host for successful transformation to the adult stage. Therefore, the size of the adult is inversely proportional to the number in a single host. An average of ca. 20 parasitoids emerges from a single nymph of Dermacentor andersoni Stiles or D. variabilis, and the highest number observed by Cooley (1928) was 73.

Dermacentor andersoni Stiles, Rocky Mountain Wood Tick.-- This tick is a vector of Rocky Mountain spotted fever, a rickettsial disease that can be fatal to humans, but is primarily a disease of wild animals. It can also harbor tularemia, another disease primarily of wild animals but also infectious to humans. This tick is also responsible for tick paralysis, which affects the motor nerves starting in the legs and gradually spreading to the rest of the body (McMurtry 1977b). It results usually if the tick feeds at the back of the neck or the base of the skull, and removal of the tick usually results in recovery. The species occurs in the western U.S., primarily in the Rocky Mountains and also in Canada. Spotted fever occurs in other areas also, but its chief vector there is the American dog tick, D. variabilis.

Eggs of D. andersoni are deposited on the ground. They hatch in springtime or early summer into six-legged larvae and climb onto grass or other vegetation where they wait attachment to passing animals, usually small rodents (McMurtry 1977b). When fully fed in a few days, the larvae drop to the ground to molt to the nymphal stage, which usually does not feed until the following spring, when they attach to small animals, become engorged and drop to the ground to transform to the adult stage. Although some adults may attach to hosts the same season, they seemingly pass the rest of the summer and winter in hiding and find a host the following spring. Mating takes place on the host, and when fully fed the female drops to the ground to deposit her eggs. Only the adult stage is known to attack humans and large animals (Cooley 1932).

Natural Enemies Sought.--In the U.S. a culture of the encyrtid parasitoid H. hookeri Howard, originating in France was started in Montana for colonization against the Rocky Mountain wood tick (Cooley 1928, Cooley & Kohls 1933). More than 4 million parasitoids were liberated during 1927-32, mostly in Montana but also in Colorado, Idaho and Oregon. Various methods were used, including release of adult parasitoids, scattering parasitized nymphs in grass and low vegetation, and liberating squirrels which had been infested with parasitized nymphs. The method of mass rearing the parasitoid on D. andersoni was described by Morton (1928).

Only one instance of recovery occurred in 1929, when a few parasitoids emerged from D. andersoni nymphs taken from squirrels captured in the Bitter Root Valley of Montana (Cooley & Kohls 1933). Cole (1965) cited from a personal communication from G. M. Kohls in 1963 that no reduction in the tick population was observed and no evidence had been obtained that the parasitoids were established in nature (McMurtry 1977b).

Other Ixodidae.--Alfeev (1940) reported on an experiment in which it was attempted to control Isodes ricinus (L.) and I. persulcatus Schulze in a 250-acre pasture in the province of Leningrad, USSR. H. hookeri, obtained from Montana in 1935 was propagated and 2,600 adult parasitoids and 38,000 parasitized ticks were liberated. No recoveries were noted (McMurtry 1977b).

           (Tetranychidae)

Tetranychus urticae Koch, Two-Spotted Spider Mite.--McMurtry (1977) noted that there is a long list of synonyms for this mite, the more common in the early literature being Tetranychus bimaculatus Harvey, T. telarius (L.) and T. multisetus McG. The mite is worldwide in distribution and has an extremely wide range of host plants including fruit trees, ornamentals, vegetables and forage crops. The mites increase to high populations causing stunting, drying of leaves and even defoliation. This mite usually overwinters as orange-red diapausing adult females, which do not feed or lay eggs until the following spring. Fertilization apparently takes place in the fall and at lower latitudes reproduction may occur throughout the winter (McMurtry 1977b).

The species is typical of most Tetranychidae in having egg, larva, protonymph, and deutonymph stages before becoming adult. it is arrhenotokous (virgin females produce male progeny, while mated females produce both sexes). A generation from egg to egg may be completed in 9 days. The rate of egg production at warm temperatures has been observed to be five or more per female per day, and the total number of eggs may exceed 100. This mite has not been observed to suspend itself on silken threads by which it can be transported by air currents, such as occurs with some other tetranychids. But, they can be dispersed by wind, although a higher velocity may be required (Baker & Pritchard 1953, Boudreaux 1963, Boyle 1957, Cagle 1949, Fleschner et al. 1956, Watson 1964).

Natural Enemies Sought.--The phytoseiid predator Phytoseiulus persimilis Athias-Henriot was introduced into Germany from Chile by Dosse (1958), who noted its potential for controlling T. urticae in glasshouses (Dosse 1959). From Germany it was dent to other countries of Europe (Bravenboer & Dosse 1962, Hussey & Parr 1965) and to Canada (Chant 1961) from where it was sent to the U.S. (Smith, Henneberry & Boswell 1963, Oatman 1965).

Due to most work with P. persimilis being in glasshouses or on annual crops outdoors, almost all results have been based on periodic releases rather than permanent establishment. In Germany Dosse (1959) showed that P. persimilis could increase rapidly and decimate populations of T. urticae in the glasshouse. The possibilities of using the predator were further studied by Langenscheidt (1966). In the Netherlands Bravenboer & Dosse (1962) reported that releases of P. persimilis on cucumbers in the glasshouse gave control of T. urticae that was comparable to 3-5 applications of insecticides or acaricides, but after the prey was eliminated the predator also died out. Bravenboer (1969) indicated that there are possibilities of practical application of this method for cucumbers, but that much information is still required before the practice can be recommended. But the use of Phytoseiulus appeared to have little possibility in flower growing because of the low damage tolerance to plants. In Great Britain considerable progress was made at the Glasshouse Crops Research Institute in Littlehampton, Sussex on the use of P. persimilis for commercial control of T. urticae on cucumbers in glasshouses. Experiments showed that when the predator was introduced at low population densities of the prey, the latter could be eliminated before leaf injury became serious (Hussey & Parr 1965). Larger tests showed that releases of P. persimilis over ca. 3 acres of glasshouse space resulted in successful control (Gould, Hussey & Parr 1968). One advantage was the generally severe leaf injury that cucumbers can tolerate without yield loss. Several methods of establishing a uniform pattern of control were tried, such as general inoculation with spider mites as well as predators and a banker method where infestations of the pest mites would be established on one plant in every glasshouse so that sufficient mites could develop to produce adequate numbers of predators for maintaining control over the entire glasshouse. In the U.S. Smith, Henneberry & Boswell (1963) observed that P. persimilis showed promising possibilities in the control of T. urticae on glasshouse ornamentals. However, the use of predators alone may be deterred by a demand for flowers free from pests or imperfections, and the possibility may be greater for an integrated control program (McMurtry 1977b). Commonly used pesticides were very toxic to the predators, but some were only slightly or nontoxic. Studies on annually planted strawberries grown outdoors in southern California showed promising results with releases of predators at the rate of ca. 300,000 per acre before the spider mite population exceeded one per leaf (Oatman 1965, Oatman & McMurtry 1966, Oatman et al. 1967). In central California this predator has been observed to survive the winter but permanent establishment was uncertain (McMurtry 1977b).

The life history of P. persimilis typically has an egg stage, a larval stage with three pairs of legs followed by the protonymph and deutonymph, each having four pairs of legs, and the adult. The period of development from egg laying to adult can be as quick as 4-5 days, which is more rapid than the rate of development of the prey, T. urticae, and also more rapid than most other species of Phytoseiidae (Bravenboer & Dosse 1962, Dosse 1958, 1959). The rate of oviposition may average as high as four eggs per female per day (Bravenboer & Dosse 1962, Dosse 1958, 1958; Laing 1968, McClanahan 1968, McMurtry 1977b). Although any stage of the prey may re readily consumed, Chant (1961, 1963) found that the adult predators prefer adult or nearly mature spider mites and that since the predator feeds directly on the reproductive units of the prey population, it should be better able to suppress the prey than one which feeds primarily on eggs and early immature stages.

The functional response by P. persimilis to increasing prey density studied by Mori & Chant (1966a) showed a domed curve of prey consumption with increasing prey density in a relatively simple experimental arrangement. It seemed that when prey were numerous there was a disturbance effect which reduced the predator's rate of consumption. The high mobility of P. persimilis appears to be an important factor in its effectiveness (Chant 1961). It quickly moves down the rows in strawberry plots, and is also able to migrate around barriers and over bare ground to invade control plots (Oatman 1965, Oatman & McMurtry 1966, Oatman et al. 1967). Combined with its high mobility is a marked ability to remain on and lay eggs only on infested leaves (Chant 1961, Oatman & McMurtry 1966). This predator is seemingly very dependent on spider mites for food, and therefore there is usually a marked response to a change in density of the host. Nutritive substances such as sucrose, honey, pollen and fish meal had no effect on longevity or reproduction (Laing 1968, Mori & Chant 1966b). The optimum temperature for reproduction was ca. 25-30°C (Bravenboer & Dosse 1962, Dosse 1958), but reproduction can occur at much lower temperatures (Böhm 1966, McClanahan 1968). Mori & Chant (1966a, 1966b) studied behavior in relation to humidity and found that activity of both predator and prey increased at low RH, whereas the prey avoided high RH but the predator did not. Prey consumption was highest at low RH.

Panonychus citri (McGregor), Citrus red mite.--This mite has also been noted as Tetranychus mytilaspidis Banks, T. citri McGregor, Paratetranychus citri, and Metatetranychus citri (McMurtry 1977b). Reports occur from North and South America, China, India, Japan, South Africa and Russia, but presumably are native to the Orient where citrus originated. It is considered the most important pest of citrus in California (McMurtry 1977b), but attacks other plants as well. P. citri feeds on leaves and fruit, causing a bronzing or silvering of the surface. High infestations can cause defoliation, which is enhanced under hot, dry conditions (McMurtry 1977b). One generation may be completed in 3 weeks during warm weather, and 12-15 generations may occur per year. An average of 96 eggs per female and an average longevity of 23 days at 24°C was reported in southern California, but other researchers reported a maximum of only 50 eggs. The life span and period of oviposition are considerably longer during cool months. There are commonly two peaks of abundance in spring or early summer and again in the autumn or early winter. During these periods the temperature may be most favorable, but the age of the foliage may also be an important factor (McMurtry 1977b). High populations can occur in some places at virtually any time of the year, however. All developmental stages can be found in midwinter in California and Florida, although in the colder areas of Japan it was reported that the winter is passed in an egg diapause. An important means of dispersal is air drift; adult females spin silken threads and are carried by air currents. This action seems induced when the foliage becomes unfavorable through excess feeding or other causes (Boyce 1936, Ebeling 1959, Ehara 1964, English & Turnipseed 1941, Fleschner 1953, Fleschner et al. 1956, Fukuda & Shinkaji 1954, Henderson & Holloway 1942, Jeppson et al. 1957, Muma 1961a, Munger 1963, Quayle 1912). Fleschner (158) reported other factors affecting the abundance of citrus red mite, such as predation, pesticides, water, soil, direct and indirect effects of climate and host plant genetics.

Natural Enemies Sought.--In the U.S. importation of predatory mites into southern California began in 1953 which resulted in the importation of several species of Stethorus from the Middle and Far East and Central America, and releases made in orchards infested with citrus red mite (McMurtry 1977b). Although one species, S. gilvifrons (Muls.) was recovered in large numbers several months after release, establishment did not occur (McMurtry 1977b). One species of the Phytoseiidae, Typhlodromus floridanus, was imported and colonized in 1955. This was followed by importation of 10 different species between 1961 and 1968. T. rickeri Chant was released in the largest numbers (ca. 1/2 million), and became established on lemon trees (McMurtry 1977b). But by 1958 this species disappeared from release orchards. Several other species of Phytoseiidae, especially Iphiseius degenerans, were recovered in large numbers during the season of release, but did not become established.

The life cycle of T. rickeri Chant is typical of the Phytoseiidae, having egg, larva, protonymph and deutonymph stages. No feeding occurs in the larval stages. At 22°C a generation is completed in 9.4 days, and an initial mating is insufficient for continued oviposition (McMurtry 1977b). The average rate of oviposition ranges from 0.7/female/day at 15°C to almost two per day at 24-27°C. Ovipositing females consume an average of 4.3 adult female hosts or 13.4 protonymphs of Tetranychus pacificus McG. per day at 24°C. Feeding and reproduction occur readily on a variety of tetranychid mites, including those which produce large amounts of webbing, such as T. pacificus, and those producing only a small amount such as Panynychus citri (McMurtry 1977b). The citrus rust mite P. oleivora is also a favorable prey species. However, the common native species of southern California, Amblyseius hibisci (Chant) and A. limonicus Garman & McGregaor, fed bud did not reproduce on this prey. In contrast to the latter predators, T. rickeri was found to be more dependent on mite prey for reproduction, although pollen, honeydew, and scale crawlers are fed on to some extent (McMurtry 1977b). Due to these biological differences, it seemed that T. rickeri would a significant addition to the predator complex on citrus in California if establishment were possible (McMurtry & Scriven 1964b).

Avocado Brown Mite, Oligonychus punicae (Hirst) [= coiti McGregor].--Presumably native to Central America and Mexico, this tetranychid is the most injurious pest of avocado in southern California (McMurtry 1977b). It feeds on foliage and causes a brownish discoloration and some leaf drop when at high densities (Ebeling 1959). A classical biological control program in southern california was initiated (Fleschner 1955, McMurtry 1961), with emphasis since 1961 on predacious mites of the family Phytoseiidae. The common native species seem to have certain limitations in their ability to attain control (McMurtry & Johnson 1966). Field releases of the imported predators were summarized by McMurtry (1977). No establishment of any predatory species was reported, however.

Other Pestiferous Acarina.--McMurtry (1977) reported that in the U.S. a stock of the phytoseiid T. rickeri was sent from California to Florida in 1962 and released against Texas citrus mite Eutetranychus banksi (McG.), six-spotted mite Eotetranychus sexmaculatus (Riley) and citrus rust mite P. oleivora, as well as the citrus red mite. Short term recoveries were made but there were no reports of establishment (Muma 1964). T. rickeri was also shipped to Texas from California where direct releases of several hundred did not result in establishment (McMurtry 1977b). In Israel several phytoseiid mites associated with citrus rust mite and tetranychids were introduced from Hong Kong in 1960 (Swirski & Schlechter 1961), and it was reported that one, Amblyseius largoensis (Muma) was recovered the following season on Convolvulus sp. ca. one mile from the release point (Swirski & Amitai 1961). Over 1/2 million A. largoensis were released, and establishment was thought to occur. Several species of mite predators were sent to Israel from California during 1960-65 (three indigenous species and two introductions from India), and Phytoseiulus persimilis of South American origin, was imported from Germany. Recoveries of P. persimilis and T. rickeri were reported (Rosen 1967).

Acarina for Biological Control of Armored Scale Insects

Mites and ticks (Acari) include a vast assemblage of small arthropods which rivals the Insecta in diversity of living habitats. They can be readily distinguished from insects by a reduction in segmentation, presence of four pairs of legs in adults, and the absence of compound eyes, antennae and wings. The Acari are separated into several subgroups, generally recognized at ordinal or subordinal rank. Three of these, the Astigmata, Mesostigmata and Prostigmata, include species that prey on or parasitize armored scale insects. These species included within 10 families may be divided into two functional groups: those for which biological data or claims for control are available and those which seem to be of lesser importance. These taxa are discussed separately, with families containing obligate or potentially important diaspidid parasites or predators considered first. Secondly, taxa occasionally associated with diaspidids and polyphagous predators will be mentioned. Finally, some mites which are often found in association with scale insects, but which do not appear to have any potential for control, will be noted.

Hemisarcoptidae.--The Hemisarcoptidae (Astigmata) is a group of small, soft-bodied mites associated with arboreal habitats such as polypore fungi, vertebrate nests, and subcortical habitats. The family may be recognized in the female by the position of the ovipore between or behind coxal fields IV, in the male by the presence of a median sucker anterior to the genital region and in all feeding stages by the sucker-like pretarsi which lack empodial claws (Gerson et al. 1990). Deutonymphs are characterized by the loss of pretarsi from legs IV, the reduction to a maximum of four setae of tarsi III-IV, and the presence of a single large pigment spot under the propodosomal ocelli. The genus Hemisarcoptes Lignières is the only genus in this family associated with armored scale insects, but all known species of this genus are obligate parasites or predators of diaspidid scales.

Species of Hemisarcoptes have been known as important generalized predators of diaspidids for >100 yrs and are found on many genera of host scale insects. Hemisarcoptes malus (Shimer) was not only one of the first mites described from North America, but was also the first mite utilized in a biological control program for insect pests (Shimer 1868, Riley 1973). Ewing & Webster (1912) stated that "it is quite evident that the oyster-shell scale [Lepidosaphes ulmi (L.)] is in many places kept in check by mites... Of these mites, the most efficient was Hemisarcoptes malus." Similar claims regarding the same pest in Canada were made by Lord (1947), and by Samarasinghe & LeRoux (1966). Kaufmann (1977) reported that Hemisarcoptes were the most efficient predators of the date palm scale, Parlatoria blanchardi (Targioni Tozzetti) in the Sahel region of Niger, West Africa. Claims of relatively high rates of predation affecting other economically important diaspidids were summarized by Gerson & Schneider (1981). A recent literature survey on the worldwide distribution of these mites shows non-specificity of diaspidid host preference. A surprising feature is that no records appear for one of the five major divisions of the Diaspididae, namely, the Odonaspidini (Gerson et al. 1990). Regardless of the enthusiastic reports concerning Hemisarcoptes, very little data is available on their biology and potential for biological control. Problems include taxonomic uncertainties, scattered information on distribution and bionomics, apparent uneven predation performance in the field, and lack of publications on mass production techniques.

Taxonomic Ambiguities.--Problems of misidentification and incomplete description are found in the literature on Hemisarcoptes. Shimer (1868) described the adults of the first species which he named "Acarus" malus, from Illinois. This species was apparently first noted by Riley (1873), but Riley mistook another mite for malus, and acrid mite of the genus Thyreophagus. This confusion most likely arose because these mites occur in association with many species of diaspidid scale insects, both are very small, and the general body forms are similar enough to be confused considering the optics of the era. This misrepresentation of malus led Lignières (1893a,b) to propose a new genus, Hemisarcoptes, for a species he described as H. coccisugus from France, while he regarded a species of what is now recognized as Thyreophagusas being identical with malus. The confusion of the genera Hemisarcoptes and Thyreophagus was recognized by Michael (1903) who correctly aligned the European species of Lignières (H. coccisugus) with its American cogener (H. malus). All researchers after Michael have regarded the European H. coccisugus as synonymous with the American H. malus despite the lack of detailed study. Contemporary workers have also had to rely on erroneous illustrations to distinguish species of Hemisarcoptes. The species H. coccophagus Meyer, described from South Africa, and H. dzhashii Dzhibladze, described from Soviet Georgia, were distinguished from H. malus only on the basis of very schematic figures of H. malus. None of these species is recognizable on the basis of the original descriptions.

More confusion regarding Hemisarcoptes concerns the dimorphic life cycle of these and other free-living astigmatid mites. The deutonmyph (second nymphal instar, or hypopus) of these species is highly modified morphologically and disperses by phoretic association with other animals. These deutonymphs are so morphologically divergent from the other life-cycle stages that association between stages is only possible through rearing or collection of moulting deutonymphs. Deutonymphs of Hemisarcoptes were first positively identified by Bartlett & DeBach (1952) in phoretic association with the coccinellid beetle, Chilocorus stigma (Say), in laboratory cultures in California. The specific identity of these mites in uncertain. Gerson (1967b) first described deutonymphs of H. coccophagus from laboratory cultures and natural populations in Israel. These deutonymphs were associated with the coccinellid, Chilocorus bipustulatus (L.). Thomas (1961) described a deutonymph collected from Chilocorus cacti (L.) in Texas, as Vidia cooremani. Gerson (1967b) placed this species in the genus Hemisarcoptes. The adults of H. cooremani (Thomas) remain undescribed. The species-level systematics of Hemisarcoptes on a worldwide basis is currently under study by O'Connor & Houck (Gerson et al. 1990).

Bionomics.--Hemisarcoptes coccophagus is most abundant in the field in Israel during summer, although winter activity also occurs (Gerson & Schneider 1981). Worldwide, Hemisarcoptes species seem to be quite resistant to extreme climatic conditions. In Canada H. malus is the major natural control agent of the oyster-shell scale during cold periods, as the mites may survive even when temperatures decrease to -34°C (Lord & MacPhee 1953). The other major natural enemy in these areas, the aphelinid wasp, Aphytis mytilaspidis (LeBaron) is killed at -25°C. Observations on H. malus in New York by Houck & O'Connor indicate that egg production continues throughout the winter (Gerson et al. 1990). In the other extreme, Hemisarcoptes coccophagus acted as "a most efficient predator" of date palm scale in the hot, dry climate of the Sahel region of Niger, while Chilocorus bipustulatus, which was introduced to control the pest, was rendered ineffective by the unusually harsh environment (Kaufmann 1977, Gerson et al. 1990).

Freshly laid H. coccophagus eggs hatch within 4-7 days at 21°C in the laboratory, and within 2-5 days at 28°C. Emerging larvae wander around the host scale avoiding strongly lighted sites, and settle down to feed. These usually progress through thee moults (to protonuymph, tritonymph and adult), feeding during each active stage. The adults mate and females produce an average of 16 eggs. A complete life cycle uninterrupted by a deutonymphal stage, requires ca. 26-28 days at 21°C, and 15-17 days at 28°C. The sex ratio is ca. 2 females/male (Gerson & Schneider 1981). Individual H. coccophagus which subsisted on insufficient food (i.e., moribund scales) as larvae or protonymphs went through a deutonymphal (hypopodial) stage in their development which was consequently quite prolonged (Gerson et al. 1990). The deutonymphs, which also serve to disperse the species, survived for 2-3 weeks in the laboratory at 22°C under saturation conditions (Gerson & Schneider 1982). In cultures of H. malus grown by Houck & O'Connor, deutonymphs have never been produced in one year and 6 months of continuous culture even though the scale hosts were allowed to completely desiccate. Since deutonymphs of H. malus do occur in field populations, they may be rare, or their appearance may require chemical or mechanical stimulation by the scale-piercing behavior of the Chilocorus beetles upon which the deutonymphs are phoretic (Gerson et al. 1990).

The deutonymph of H. coccophagus may be seen wandering among scale insect colonies, but it is most commonly encountered on Chilocorus bipustulatus in israel. Occurrence on the beetles followed a seasonal trend, peaking in late summer. By that time most beetles examined carried some deutonymphs, with an average of over 30 per beetle (max. 202) (Gerson 1967b). The deutonymphs lack mouthparts and do not harm the beetles, although heavily-laden Chilocorus appeared somewhat sluggish. Deutonymphs were evenly distributed on male and female beetles, indicating a similar attraction. This was later confirmed by choice-chamber experiments, which also demonstrated strong vector attraction for the deutonymphs, as 84.7% of all mites moved towards the Chilocorus-containing cells (Gerson & Schneider 1982). Species of Chilocorus are also predators of diaspidids, with the various beetle species attacking a wide range of scale insect taxa. The potential for defining the full geographic range for Hemisarcoptes can be evaluated in terms of the known ranges of the phoretic partner as indicated above. The affinity of Hemisarcoptes deutonymphs for Chilocorus beetles has been demonstrated by examination of museum collections of these and related beetle species, as first suggested by Gerson (1967b). O'Connor & Houck have examined specimens of 29 of the known species of Chilocorus in American museums, with 12 of these species yielding collections of Hemisarcoptes (Gerson et al. 1990). Examination of their scale-feeding beetles has yielded only one non-Chilocorus host for these mites, the related chilocorine species Axion tripustulatum (DeGeer). The only other reported host for these deutonymphs is the coccinellid Zagloba ornata Casey, and this record is from laboratory cultures (Sellers & Robinson 1950).

Distribution.--Hemisarcoptes species distribution may be estimated from the literature and records of mite deutonymphs obtained from museum collections. Knowledge of actual species distributions is encumbered by problems of identification. On the basis of specimens examined by Gerson et al. (1990), Hemisarcoptes malus is regarded as widely distributed in North America, probably corresponding to the range of its phoretic host, Chilocorus stigma. Hemisarcoptes cooremani is probably parapatric with H. malus, with a known range extending from southern Texas and California south through Honduras in association with Chilocorus cacti. In the Old World, the only recognizable species is H. coccophagus. This species has been verified from southern Europe (Spain), North Africa and the Middle East in association with Chilocorus bipustulatus and from eastern and southern Africa associated with C. distigma (Klug). Collections of Hemisarcoptes deutonymphs from other areas in western North America, Africa, India, Indonesia and the Philippines represent undescribed species. The specific identity of central European Hemisarcoptes remains questionable pending the examination of specimens. No deutonymphs have as yet been recovered from Chilocorus bipustulatus nor C. renipustulatus (Scriba) from this area. Also, the identity of Hemisarcoptes reported from South America (Flechtmann 1968, Fernandez 1973) must be reexamined. There are no species of Chilocorus native to this region, although C. bipustulatus has been introduced, probably from Europe, and is now widespread. There is a possibility that South American and European populations may be conspecific. Hemisarcoptes species are not yet reported from Japan or China, despite the diversity of species of Chilocorus in these areas. A large series of Japanese Chilocorus were examined by Gerson et al. (1990) without obtaining any Hemisarcoptes, although future collecting in these areas may reveal their presence. However, the absence of Hemisarcoptes from the Australian region may be predicted on the basis of the absence of Chilocorus species from that area (Gerson et al. 1990).

Field Investigations.--There have been no controlled experimental studies published concerning the field potential for biological control of scale insects using Hemisarcoptes (Gerson et al. 1990). The uneven field performance of these mites has been noted by several authors. Simmonds (1958) reported them to attack from 1-100% of the white peach scale, Pseudaulacaspis pentagona (Targioni Tozzetti), in Bermuda. Gerson (1967b) found that >70% of one population of the California red scale, Aonidiella aurantii (Maskell) were attacked by H. coccophagus in Israel, but that this rate dropped to ca. 20% later. Gulmahamad & DeBach (1978) recorded mite parasitism rates of 42-66% on the San Jose scale, Quadraspidiotus perniciosus (Comstock), in California during certain months, but scarcity or absence during others. Some of this variance in predation might be due to variable occurrence of mite predators (e.g., Cheletomimus berlesei Oudemans), slow dispersal rate of mobile stages, undetermined responses to chemical sprays, and seasonal shifts in temperature and moisture conditions. When living under optimal physical conditions and without chemical assault, as in laboratory populations of diaspidids, Hemisarcoptes mites may reduce population growth and actually endanger these scale cultures (Sellers & Robinson 1950.

Hemisarcoptes species usually occur in the field on or under ovipositing scale insects which may still continue to produce progeny (Gulmahamad & DeBach 1978, Gerson & Schneider 1981). Both female scale insects and their eggs are fed upon (Ewing & Webster 1912), although crawlers, second instar nymphs and prepupal male scale insects may also be less frequently parasitized (Gulmahamad & DeBach 1978). Feeding mites (usually more than one per scale) tend to take up the body color of their hosts (André 1942, Gerson 1967b, Kaufmann 1977). For example, Hemisarcoptes malus is bright purple on Lepidosaphes beckii (Newmann), red on Epidiaspis leperii (Signoret), and yellow on Quadraspidiotus juglansregiae (Comstock). This coloration often makes them difficult to locate (Gerson et al. 1990).

Regarding control potential, the effect of Hemisarcoptes species on their host scale insects appears to be cumulative; i.e., parasitized scale insects continue to deposit at least some eggs (Gulmahamad & DeBach 1978). Gerson & Schneider (1981) applied the following general rule to female scale insects parasitized by H. coccophagus: when fewer than five mites developed on a single host, its fecundity would be reduced. A scale insect attacked by five to 10 mites would fail to produce any progeny, while the feeding of more than 10 mites usually causes the death of the host. Scale insect species, size, age and sex, as well as mite species, may modify this generalization (Gerson et al. 1990).

The efficacy of Hemisarcoptes as biological control agents of scales was verified by two introduction projects. The apparent absence of these mites from western Canada suggested that they could be used there to control the oystershell scale. Introductions of H. malus from eastern Canada began in 1917, and 23 years later the mite was widely distributed and at times important in British Columbia. Turnbull & Chant (1961) rated this a successful biological control attempt. The other project took place in Bermuda, following an outbreak of Lepidosaphes newsteadi Šulc on cedar trees. Several natural enemies were introduced against this pest, including Hemisarcoptes malus. The mites were introduced as deutonymphs on the bodies of 235 coccinellid beetles, mostly Chilocorus spp. (Bedford 1949), and were subsequently found to attack the purple scale, Lepidosaphes beckii on citrus.

Hemisarcoptes mites are susceptible to many common pesticides. Sulfur and winter oil were quite detrimental to the mite, but DDT, lead arsenate, nicotine sulfate or summer oils had little effect under field conditions in Canada (Lord 1947). Sellers & Robinson (1950) who had to eliminate Hemisarcoptes from their laboratory cultures of diaspidids, used the acaricide Neotran with success.

Mass Production.--Mass and individual mite rearing methods were described by Gerson (1967b) and by Gerson & Schneider (1981), respectively. Large numbers of H. coccophagus were produced by growing diaspidids on potato tubers at 80% RH and colonizing them with deutonymphs obtained from elytra of chilocorus bipustulatus. Observations on individual mites were made possible by substituting the scale insects' shields with artificial covers. These consisted of a small amount of collodion dissolved in iso-amyl-acetate. A few drops of the resultant solution were placed on a smooth surface, and upon drying were used to cover young female scale insects whose original shields had been removed. Only a small aperture was left open, through which mites or their eggs were introduced. Use of the artificial shield made direct observations on these mites possible (Gerson et al. 1990).

Gerson et al. (1990) concluded that under certain conditions, especially when they are the only active natural enemies, Hemisarcoptes species may be important control factors of armored scale insects. However, this implies that they are not very efficient in the presence of other predators and parasites. The diversity of species of Hemisarcoptes, their close association with Chilocorus beetles, and their restriction to diaspidid hosts imply a relatively long evolutionary association among members of this community. Therefore, it is not surprising that the mites appear to be better adapted for coexisting with their diaspidid hosts than for killing them directly, since such long associations often tend toward reduced pathogenicity of the parasite. This evolutionary trend might also explain why scales parasitized by Hemisarcoptes normally produce at least some progeny, ensuring hosts for the progeny of the mites. However, deductions based on the natural biology of the mite- scale insect- Chilocorus community may not be valid in managed agroecosystems. Unpredictable performance, as has been reported for Hemisarcoptes, upsets control schedules and introduces unknown factors, detracting from the mites' potential for biological control. Future studies should strive to better understand Hemisarcoptes control performance in such managed systems. A sound systematic base is an obvious prerequisite; some of the unpredictability in prior studies may have resulted from the interaction or succession of more than one species (Gerson et al. 1990).

Camerobiidae.--The Camerobiidae (Prostigmata) are a small family of mites with long, "stilted" legs, a ventrally directed gnathostoma, weak palpi and looped peritremes. Species in one genus, Neophyllobius, have been reported to feed on diaspidid crawlers. McGregor (1950) quoted unpublished observations made by Pence, who noted that when attacking crawlers, the mites inject their prey with some opiate. The crawlers subsequently relax and allow their body juices to be sucked out. Meyer (1962) added to these observations, reporting that nymphs and adults of N. ambulans Meyer fed on crawlers of the California red scale, Aonidiella aurantii, but not on settled scale insects. The predator appeared to be rather scarce on South African citrus trees, and therefore Meyer noted that it was probably of no economic importance in natural control of red scale. A different opinion was by Richards (1962) who believed that a species of Neophyllobius was the principal predator of Quadraspidiotus ostreaeformis (Curtis) in New Zealand. The mites were very common wherever the scale insect was abundant, but no crawlers were actually observed consumed. In the laboratory the predatory mites were seen with their mouthparts inserted in adult scales, sucking them dry. Richards (1962) also thought the mites appeared to be injecting some relaxing chemical into prey, as the latter did not struggle.

Cheyletidae.--The majority of the prostigmatid family Cheyletidae are free-living predators, while others are ectoparasites of birds, mammals or rarely insects. Free-living cheyletids are slow-moving, yellow or orange and usually ambush prey. The morphological characteristic best defining the Cheyletidae is the prominent palpal thumb-claw complex, with the palptarsus bearing strong sickle and/or comb-like setae (Gerson et al 1990). These mites often occur on plants, and several species have been observed to feed on diaspidid crawlers. Cheletogenes ornatus (Canestrini & Fanzago) was observed feeding on crawlers in many parts of the world (Avidov et al. 1968, Gerson et al. 1990). The role of this predator in citrus groves in Israel was studied by Avidov et al. (1968). The mite was reared in plaster-of-Paris cells and fed crawlers of the chaff scale, Parlatoria pergandii Comstock. Females deposited <a dozen eggs throughout their lives under these conditions. Egg development took ca. 10 days, the larva and two nymphal instars another 47 days, and each molt required 2.5 days, total immature development taking 64 days. Oviposition started after another 25 days, indicating the total egg to egg cycle was about 3 months at 28°C. During this study, female mites consumed an average of 90 crawlers during their adult lives, which lasted an average of 43 days (Gerson et al. 1990).

Cheletogenes ornatus was reared on eggs of the olive scale, Parlatoria oleae (Colvée) (Zaher & Soliman 1971). It was reported that the predator's complete development took about 25 days at 29°C. Mites in that study produced an average of 16.8 eggs per female, and each female consumed ca. 170 scale insect eggs (males 125) and lived for 16.6 days. Such differences in life cycle parameters obtained in the two laboratory studies of this mite have also been reported for other species (Gerson 1985). Female survival is dependent on the ambient RH, and at 28°C, mites kept at 0% RH lived only 3 days, with the survival time at 21, 50 and 80% RH being 12.5, 14.5 and 26 days, respectively (Avidov et al. 1968). Starved females (at high RH and 28°C) survived an average of 16 days (range 1-33) (Gerson et al. 1990).

Exposure of C. ornatus females to citrus leaves dipped in several pesticides showed that the fungicide zineb had little effect on mite survival. The acaricide chlorobenzilate, however, was very toxic, causing almost total mortality 24 h post-treatment (Avidov et al. 1968). Field studies indicated that this predator was much more common on citrus bark (where diaspidids flourish) than on leaves or fruit. Mite numbers were usually low during winter, rising in summer and peaking during autumn. These observations, along with the laboratory data noted above, indicate that C. ornatus has two summer generations on citrus in Israel. Reproduction ceases during winter, probably in connection with female diapause.

Available information indicates that C. ornatus has a low rate of increase, a pronounced winter ebb and is difficult to rear in the laboratory. But it is a hardy species capable of survival under adverse conditions, and it is also the dominant acarine predator of armored scale insects on citrus. Avidov et al. (1968) recommended that efforts be directed at conserving the predator in the field.

Data on another diaspidid-feeding cheyletid presented by Wafa et al. (1970) show that adult females and males of Eutogenes africanus Wafa & Soliman consumed an average of 186 and 156 eggs of Parlatoria oleae, respectively. The life cycle at 29°C required ca. 31 days, and each female deposited an average of 16 eggs. Other cheyletids observed feeding on armored scale insect crawlers in the field include Hemicheyletia bakeri (Ehara) which feeds on the yellow scale, Aonidiella citrina (Coquillett) in Florida (Muma 1975) and Cheletominum berlesei (Oudemans) on the latania scale, Hemiberlesia lataniae (Signoret) in California (Ebeling 1959) and on Parlatoria spp in Israel (Gerson 1967a). Cheletominus berlesei has also been observed feeding on Hemisarcoptes mites associated with Lepidosaphes beckii in California (Gerson et al. 1990), with numbers of Hemisarcoptes negatively correlated with Cheletominum density. Additional cheyletid species, some as yet undescribed were observed to feed on various diaspidids on fruit trees in New Zealand and the Cook Islands (Gerson et al. 1990).

Eupalopsellidae.--This family of prostigmatid mites is characterized by very long palpi and chelicerae, a rather reduced palpal thumb-claw complex and the modification of the pretarsal empodia into two pairs of capitate raylets. Species in two genera are known to feed on diaspidids (Gerson et al. 1990).

Saniosulus nudus Summers is an active predator of crawlers of Parlatoria spp. on citrus in Israel. The prey is held by the mite's anterior legs as the predator inserts its cheliceral stylets into the crawler's body. Feeding may proceed for 30-40 min until the dried prey remains are pushed off the chelicerae. All active stages of this species feed on diaspidid eggs and crawlers. Second-stage nymphs and adults are also attacked but do not appear to be seriously affected (Gerson & Blumberg 1969).

Observations once a month in a citrus grove indicated that populations of S. nudus on bark peaked during late summer and then declined (Gerson 1967a). These mites have been subsequently observed feeding on various other species of diaspidids in Israel (Gerson et al. 1990). The species was experimentally cultured on Florida red scale, Chrysomphalus aonidum (L.), reared on green lemon fruits. The generation time of S. nudus was ca. 3 weeks at 24°C and 2 weeks at 28°C, the latter being less than half the time required for diaspidid generations. Each female produced 40-50 eggs, regardless of prior mating. Copulation itself is rather prolonged, with the female dragging the male around behind her. if introduced into laboratory cultures of armored scale insects, S. nudus may affect them to the extent that control measures must be implemented (Gerson & Blumbeg 1969).

Eupalopsis maseriensis (Canestrini & Fanzago) has also been collected from citrus bark in Israel (Gerson 1966). It is a rare predator, whose feeding habits are similar to those of S. nudus.

Phytoseiidae.--This family among free-living mesostigmatid mites is characterized by having 20 or fewer pairs of dorsal setae. Some species are efficient predators of phytophagous mites and have been intensively studied (Tanigoshi 1983). Several species of Phytoseiidae were collected near armored scale insects (Baccetti 1960, Muma 1975) but their role in such communities is uncertain. Typhlodromus baccetti Lombardini was a constant associate of juniper scales, Carulaspis spp., in Tuscany, Italy (Baccetti 1960). Mites gain access under the scales' shields, where they feed on the eggs. The predator overwinters as an egg, matures in May and undergoes two summer generations. It was considered a scale-insect predator of some importance. Other phytoseiid species have been observed to feed, oviposit and complete their life cycles when offered diaspidid crawlers as food in the laboratory (Tanigoshi 1983). Whether such diets are also used in the field, and to what extent, remains unknown (Gerson et al. 1990).

Other Predators / Parasites.-- Gerson et al. (1990) enumerate several other families in the Prostigmata, which are generally polyphagous predators or parasite, with diaspidids sometimes being included in their diets:

Anystidae.--Species in this family are fast runners which move about in a corkscrew or figure eight pattern (Muma 1975). These relatively primitive prostigmatid mites possess a palpal thumb-claw complex in which the palptarsus extends well beyond the tibial claw. Anystis agilis Banks was observed by Muma (1975) to feed on crawlers of purple scale, Lepidosaphes beckii, in Florida. Ewing & Webster (1912) noted that this mite is a common predator of oyster-shell scale, Lepidosaphes ulmi, crawlers and eggs.

Bdellidae.--Mites in this family have an elongate rostrum, with long palpi which terminate in strong setae and lack a palpal thumb-claw complex. Ewing & Webster (1912) reported species of Bdella and Cyta associated with and probably feeding on L. ulmi, and Muma (1975) reported Bdella distincta (Baker & Blalock) feeding on eggs and crawlers of L. beckii. The latter species appeared to be widely distributed in unsprayed citrus groves in Florida (Gerson et al. 1990).

Cunaxidae.--This family is morphologically similar to the closely related Bdellidae, differing in the form of the palpi which are raptorial and end in a claw. A species of Cunaxoides was reported by Baker & Wharton (1952) to feed on diaspidids.

Erythraeidae.--Species in this family are usually parasitic on various arthropods during their larval instar. The nymphs and adults are predaceous. The family may be distinguished by having numerous body setae, a palpal thumb-claw complex, and long, straight cheliceral stylets. Species in the genus Balaustium feed on various diets, from flower pollen to various insects including diaspidid crawlers (Gerson et al. 1990). These mites are also known to bite humans (Newell 1963).

Pyemotidae.--These mites are usually parasites of arthropods. Adult females have reduced palpi, capitate prodorsal sensillae, and a series of segment-like plates on the dorsal opisthosoma. Females are frequently physogastric, swelling enormously as they feed. Many pyemotid species of polyphagous parasites, feeding on a wide variety of arthropod hosts, often Lepidoptera or Coleoptera. Vaivanijkul & Haramoto (1969) reported that Pyemotes boylei Krczal parasitized Diaspis echinocacti (Bouché) in Hawaii. An undetermined species was found to parasitize females of Lindingaspis rossi (Maskell) in New Zealand. Rates of parasitism of the latter species ranged from 12-15% (Gerson et al. 1990).

Stigmaeidae.--Mites in this family have an ovoid or elongate dorsum that is usually covered by plate-like sclerites. They have a palpal thumb-claw complex and short, stylet-like chelicerae, but lack peritremes. Agistemus terminalis (Quayle) is a predator of the arrowhead scale, Unaspis yanonensis (Kuwana) in Japan (Ehara 2962). Another species, Agistemus floridanus Gonzalez, feeds on crawlers of A. aurantii in Florida (Muma 1975).

Associated Species.--Gerson et al. (1990) discuss mites of various taxa which are sometimes encountered under the shields of dead scale insects or may be found among live diaspidids without actually harming them. The most frequent and widespread associates are species of the asigmatid genus Thyreophagus (Acaridae). These are often erroneously called T. entomophagus Laboulbène, but probably represent T. angustus (Banks) or related species. The cigar-shaped, milk-colored mites have a strongly reduced dorsal setation, but retain pretarsal empodial claws. The confusion of these mites with Hemisarcoptes in early literature is common. Ewing & Webster (1912) claimed that these mites were found only under shields of dead Lepidosaphes ulmi, feeding exclusively on dead material. Other records from this habitat include those of Kosztarab (1963) and Muma (1975) from the U.S. and Williams (1970) from Mauritius. Gerson (1971) found Thyreophagus under various diaspidids in Israel and Canada, and reared them for several generations on a fungal diet. These mites have been commonly collected from various diaspidid species in the U.S. (Gerson et al. 1990), where gut-content analysis indicated fungi making up a large portion of their diet. They also have been collected from dead armored scales in New Zealand (Gerson et al. 1990). The deutonymph described as Thyreophagus (= Monieziella) brevipes by Banks (1906) probably represents that of Hemisarcoptes malus.

Another genus of astigmatid mites sometimes found in association with diaspidids is Tyrophagus (Acaridae) reported by Williams (1970) to be numerous among older scale masses of Aulacaspis tegalensis (Zehntner) on sugar cane in Mauritius. These mites are common saprophages in many situations and commonly contaminate laboratory cultures of other mite species.

A number of mites whose normal habitat is the bark of trees has been reported in association with scale insects. Species in several families of the order Cryptostigmata (= Oribatei) were reported in association with various armored scales in Ohio (Kosztarab 1963). These associations are probably accidental, however (Ewing & Webster 1912). Species of the prostigmatid family Tydeidae are quite ubiquitous mites sometimes associated with diaspidids. Ewing & Webster (1912) often found Triophtydeus (= Tydeus) coccophagus (Ewing) with L. ulmi and commented, "That this mite is predaceous upon scale insect or its eggs, there is but little doubt." But, in their words, "the case here is not so conclusive." Brickhill (1958) demonstrated that tydeids may complete their development and oviposit while offered spider mite eggs alone, but all eggs that had been fed on subsequently hatched. It is possible that even if tydeids, which generally feed on honeydew and sooty mold fungi, occasionally try to pierce diaspidid eggs, the latter remain undamaged.

Gerson et al. (1990) mentioned some perplexing observations in regard to associations with plant feeding mites. Ebeling (1948) noted that settlement of the citrus red mite, Panonychus citri (McGregor) (Tetranychidae) on citrus leaves rendered the latter unsuitable for crawlers of A. aurantii. This adverse effect was observed two days after mite settlement, and no crawlers survived on leaves which had been colonized by the mite 12 days or more. Gerson et al. (1983) found that the palm infesting tenuipalpid Taoiella indica Hirst may place its eggs only within colonies of the parlatoria date scale, Parlatoria blanchardi. Such eggs were found in 60.3% of scale colonies examined.

Gerson et al. (1990) concluded that a consideration of feeding modes allows a separation of those mites having some control potential into two groups, namely predators and parasites. Species of Hemisarcoptes and Pyemotes may be considered a parasite since host death, if occurring, usually occurs after long term feeding. All other important mites species are predators. Available data strongly suggest that at present species of the former group appear to be more promising as agents for the control of armored scale insects. This conclusion is based not only on the Hemisarcoptes data, but also on encouraging results of Bruce (1983) in regards to Pyemotes species used against stored food pests. Such results also serve to remind us that Acari can and should be used much more vigorously against insect pests. The overview of Acari as natural enemies of armored scale insects should serve to emphasize the paucity of information concerning such relationships. Claims that mites actually control diaspidid populations in the field are scarce, and mostly refer to species of Hemisarcoptes. It is sad that all too few mite enemies of armored scale insects have been recognized, collected, reported and considered by researchers, although some notable exceptions occur (Ewing & Webster 1912, Gerson et al. 1990). Gerson & van de Vrie (1979) noted that acarine enemies of armored scale insects are a group in regard to which most work is still done at the first, preliminary stage: recognizing the natural enemy.

Acarina in the Marine Environment

Mites inhabit broad habitats in the marine environment, where some species are associated with and/or attack other marine organisms, including marine mammals. Kenyon (1965) and Newell (1943-73) have specialized in these mites which include a vast array of species. There are only limited ongoing studies of their economic importance and use as biological control organisms.

 

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