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Description & Statistics
Coccinellids are primarily predaceous as larvae and adults, but some species are phytophagous on green plants, others feeding on fungal spores. In the subfamily Epilachninae, mostly in genus Epilachna, there are several phytophagous species that cause serious injury to legumes, potato and other crops. Species in the tribe Psylloborini are fungus-feeders, and one species is coprophagous. Some species live in ant nests, and many feed voraciously on aphids, mites, scale insects and whiteflies and at times on thrips and other insects. Adults usually feed on the same prey species as the larvae. The entomophagous species are mainly predaceous on Coccidae, Aphididae and Aleyrodidae. Several species of Aiolacaria and Neoharmonia are effective predators on all immature stages of some chrysomelids, while other genera and species favor mites and Chermidae (Clausen 1940/1962). Coccinellidae are important to biological control, and many species have been successfully imported for the control of pest insects.
Among aphid- and scale-feeding species, thee is frequently a pronounced tendency to vary their diet, so that many will be found at times to feed on immatures of Hemiptera, Lepidoptera, etc. Some have been known to feed extensively at nectar glands of plants on sap, pollen, fungi, honeydew, etc. (Watson & Thompson 1933). This is especially obvious during times of normal food scarcity and seems to be a general habit among coccinellids. Chilomenes vicina Muls. feeds extensively on eggs and young larvae of cotton worm, Prodenia litura F. in Egypt during times of aphid scarcity (Bishara 1934). Neocalvia anastomozans Crotch consistently preys on the larvae of fungus-feeding Psyllobora, also a coccinellid (Camargo 1937). Both larvae and adults of Hippodamia tridecimpunctata L. in Japan feed on eggs and young larvae of the rice beetle, Lema oryzae Kuway during June and July, when the preferred aphid hosts are scarce. This coccinellid is rated as one of the most important natural enemies of that beetle (Kuwayama cited by Clausen, 1940). The ability to change diet is advantageous because it maintains the species during host scarcity. A definite tendency toward cannibalism in both larval and adult coccinellids serves the same purpose. Schilder & Schilder (1928) and Balduf (1935) provided early but still valid information on the food habits of Coccinellidae.
Effective use has been made of Coccinellidae in biological control, both classical and augmentative. The most noteworthy example is the Australian vedalia beetle, Rodolia cardinalis Muls., to control the cottony-cushion scale, Icerya purchasi Mask. and other related species in many worldwide areas (see separate discussion under CASE HISTORIES). Cryptolaemus montrouzieri Muls., an Australian predator of mealybugs, has been effective in reducing heavy infestations in a number of areas. Because of its size, it seems not too well adapted to prey on sugarcane mealybugs or other of similar habit which are protected by leaf sheaths. Cryptognatha noidiceps Mshll., from Trinidad and tropical America, was responsible for most of the complete control of the coconut scale, Aspidiotus destructor Sign. in Fiji. An undetermined species closely related to Cryptognatha, was imported to Cuba from Malaya in 1930 and was able to control heavy infestations of the citrus blackfly, Aleurocanthus woglumi Ashby, in just a few months. Azya trinitatis Mshll. was the most effective of a series of species introduced for the control of Aspidiotus destructor in Puerto Rico (Clausen 1940/1962). Generally, not much effect has ever been achieved against aphid hosts, however (Clausen 1940/1962).
For diaspine Coccidae control, coccinellids seem limited by certain physical characteristics of the scale covering. Species which have been completely or partially control all had a relatively thin and readily penetrated covering. Those scales with very thick and tough coverings, such as Chionaspis, Prontaspis and Lepidosaphes, are relatively free from attack. Coccinellid species that are very polyphagous among the light scale covering attack group, have been found unable even to complete development when limited to hosts having a heavy covering (Clausen 1940).
Entomophagous Coccinellidae are usually thought of as being wholly predaceous, but certain species are specialized to the extent that they may develop as solitary external parasitoids. This is found in some species that attack hosts much larger than themselves. Novius limbatus Mats., which attacks all stages of the very large Drosicha corpulenta Kuw. in Japan, is only a fraction of the size of the adult coccid female. There are times when the egg was laid under the scale and the resulting larva retained its feeding position on the body venter of a single host until mature and ready to pupate (Clausen 1940/1962).
How effective a coccinellid is in reducing the host population is related to the relationship of the larva to its host. The closer it approaches the habits of a parasitoid the more effective it is in biological control. Because of this quality, Rodolia is able to bring its host to low densities where it is held permanently. The egg is laid on the adult Icerya female or on the egg mass, and there is enough food material in the egg output of the one female to carry the larva to maturity. Therefore, the larva is spared the need to search for food, and the species is able to maintain itself in an exceedingly low host population density. The same condition operates in species which are effective against diaspine Coccidae and Aleyrodidae, although in modified form. These hosts even when relatively scarce, are gregarious and thus reduce considerably the necessity of searching for food. The adult beetle is an active flier and finds the food on which its progeny are to develop prior to oviposition (Clausen 1940/1962).
Aphid-feeding species such as Hippodamia convergens Guer., which also those which attack solitary Coccidae, often find difficulty in locating enough hosts in a low population to carry them to maturity. They are often effective in reducing heavy infestations, but usually only after crop injury has occurred, and their value is thus reduced. This may be overcome by spraying the environment with sugar substances that simulate a high host density (see work by Hagen et al. in section on Manipulation).
There are certain specific adaptations in host relationships that are of interest. Newly hatched larvae of Cryptognatha nodiceps under the covering of mature Aspidiotus scale usually find a number of eggs which have not be consumed by the parent beetle, and these provide its first nourishment. Following emergence from under the scale covering, it feeds mostly on 2nd instar larvae, while following the first molt, attack is extended to any stage of either sex of the host (Taylor 1935). Young larvae of Scymnus sieverini Weise feed principally on young scales of diaspine Coccidae, but the nearly full grown larvae prefer eggs. Rhizobius ventralis Er. larvae, which hatch from eggs laid underneath ovipositing Saissetia females may feed either on the eggs or on the female scale, but those which are free on the foliage attack only young scales (Clausen 1940/1962).
Adult coccinellids usually attack the same host species that serve as food for the larvae, even though a different stage may be favored. They chew their prey vigorously and devour all but the harder portions of the body, whereas the larvae usually bite out a hole in the body wall and suck out the fluid contents. In some cases a marked degree of pre-oral digestion occurs, in which the fluid contents are sucked out and repeatedly pumped back into the prey, thus effecting a rapid and thorough mixing with the digestive juices (Clausen 1940/1962).
The amount of food consumed is proportional to the predator's size. Clausen (1916) provided feeding records of a number of California coccinellids, which indicate that the 4th instar larvae of species of average size, such as H. convergens, consume ca. 50 aphids pe day and that adult females, if ovipositing, have very nearly the same capacity. The giant Caria dilatata F. larva of China consumes 400-500 bamboo aphids daily. Bishara (1934) studying Chilomenes vicina Muls, normally an aphid feeder, found it to destroy up to 22 eggs or 12-15 young larvae of Prodenia litura F. daily during times of aphid scarcity. This same rate was recorded for Coccinella undecimpunctata L.
Oviposition.-- The kind of host insect attack determines the manner and place of oviposition. Most species that feed on aphids, such as H. convergens lay their eggs in compact clusters of 10-50, the spindle-shaped eggs standing vertically on the leaf or bark surface. However, Synoncha grandis Thbg. spaces the eggs at intervals of several millimeters. When attacking aphids on pine and bamboo, Caria dilatata F. places the eggs in two rows, averaging a total of 28 in each group. When these are placed on pine needles, a mucilaginous ring is formed about the needle a few mm. below the mass of eggs (Liu 1933). This is though to provide a degree of protection from predators. Coccinellids that feed on red mites and some of the species that attack diaspine scales lay their eggs singly or in small clusters, and horizontally, in the vicinity of the hosts. However, the latter more often place them singly beneath empty scale coverings, the ovipositor being inserted beneath the margin, through a feeding hole that was made by the female, or sometimes through a parasitoid emergence hole. This kind of behavior is frequent among those species attacking scales that have a soft covering such as Aspidiotus destructor and related species. Species of genera Chilocorus, Scymnus, Cryptognatha, Pentilia and Rhizobius usually oviposit in this manner. Several species that attack Aleyrodidae consistently lay the eggs singly or in pairs within the pupal cases from which the whiteflies have emerged. In attacking lecaniine Coccidae such as Saissetia oleae Bern., that have a large egg chamber under the female's body, Rhizobius ventralis and others insert their eggs under the living host adult. The mealybug predators usually lay their eggs abundantly over the hosts, directly on the dorsum of the female scale or in one of the grooves on the surface of the egg sac (Clausen 1940/1962).
Reproduction.-- Reproductive capacity is usually relatively high, with 1,550 eggs secured by E. K. Carnes (cited by Clausen, 1940) from a female H. convergens during slightly more than 2 months. Swezey (1905) secured a max. of 944 from Callineda testudinaria Muls. It may be concluded that the aphid feeding species of genera coccinella, Callineda, Leis and Hippodamia lay the greatest number of eggs, which ranges from 500-1,000. Those which attack diaspine Coccidae, Aleyrodidae and red mites produce much less. The oviposition period is quite long, usually exceeding one month. In some cases it has extended over 3-4 months, but this is usually associated with lower temperatures and food scarcity. Oviposition rate is governed by the same factors, seldom exceeding 10-12 per day over an extended period even in the most prolific species (Clausen 1940/1962).
Mating usually occurs within 1-2 days after emergence, and fertile eggs are laid 7-10 days later. Older females that have had sufficient time for egg formation before mating will produce fertile eggs in a much shorter period of time, however. Virgin females of several species have been observed to lay a much smaller total number of eggs than mated females. However, unfertilized do not hatch, as they do in Hymenoptera. In many cases only a single mating is necessary to ensure fertilization of eggs deposited during the female's entire lifetime (Clausen 1940/1962)
Coccinellidae, or "ladybird beetles," is a large cosmopolitan family with ca. 252 genera and more than 3,000 species known. They occur in large numbers in most regions, and are the most often encountered of all predaceous Coleoptera. Important morphological characters of these "ladybird beetles" include a short clavate antenna; head recessed into prothorax; prothorax conspicuously narrower than elytral bases; tarsal formula 4-4-4, with the 3rd segment reduced; legs short and stout. The body is usually subhemispherical, the dorsum highly convex, the venter nearly flat; dorsum smooth. Their color varies from red or orange to black.
Developmental Stages.--Eggs of larger aphid feeding coccinellids are uniformly spindle-shaped and yellow or orange-yellow. Species attacking diaspine Coccidae, Aleyrodidae and red mites have eggs with their poles much more broadly rounded. They may be yellow, white or greenish-yellow, with the chorion often bearing minute reticulate markings. Eggs of Cryptolaemus montrouzieri are amber in color, those of Rodolia cardinalis are distinctly orange. There is a noticeable darkening of the eggs as they incubate. Just prior to hatching, the egg becomes almost black in species that have dark colored larvae, while in others it becomes grayish. Egg color is influenced to a considerable extent by the color of the host insects on which female beetles feed.
Larvae of larger aphid feeding coccinellids, such as Coccinella and Hippodamia, have variable color markings and bear a number of relatively short setae on their segments. This is also true of many species that attack Coccidae. In Chilocorus and related species, the larvae may bear large, branched fleshy processes on each segment. Others are white, with delicate setae. Many species of Hyperaspis, Scymnus, Cryptolaemus, etc. bear a heavy covering of white waxy material, which may be in the form of granules, slender threads, tufts or plates, depending on the species. These are produced as a glandular secretion. There seems to be a tendency among the species attacking mealybugs and other hosts having a waxy covering to bear a similar covering themselves. This is the result of feeding on hosts with a high wax content rather than as an adaptation for protection. However, some species developing on diaspine Coccidae have this heavy waxy covering while others on the same host do not (Clausen 1940/1962). Early work on the morphology and classification of coccinellid larvae may be found in Böving (1917) and Gage (1920).
Coccinellids usually have 4 larval instars, with exceptions being Pseudonycha japonica Kuris, which Iwata (1932) found to have 5, and Hyperaspis lateralis Muls. in which the autumn generation has only 3 larval instars contrasted to the normal 4 of the spring generation (McKenzie 1932).
They usually pupate in situ on the foliage or bark at the point where they had fed. However, Cryptolaemus montrouzieri frequently descend the tree trunk and pupates in masses in sheltered places thereon or in trash on the ground surface. Chilocorus similis and Chilocorus spp. and Cryptognatha assemble for pupation in large aggregations on the twigs, the lower sides of main branches and the trunk (Clausen 1940/1962). When ready to pupate, the mature larva fastens the caudal tip of the body securely to the substrate by means of a mucilaginous secretion. Aphid-feeding species generally cast the final larval exuviae almost completely, and it remains only as a collar or ring about the abdomen base. Rodolia, Cryptolaemus and some species of Curinus and Scymnus just effect a median split of the exuviae over the anterior body portion (Clausen 1940/1962).
Coccinellidae are relatively short life cycles, although they may be lengthened under adverse temperature and food conditions. Therefore, only records secured under optimum summer conditions are comparable. The minimum recorded time from egg laying to adult emergence was 12 days in Propylaea quatuordecimpunctata L. (Strouhal 1926), and most species require 20-35 days. The incubation period takes 2-6 days. The 1st and 4th larval instars are usually a bit longer than the intervening instars, and the four total 7-30 days, with an average of ca. 20 days. The pupal stage is 3-10 days, with an average of 6 days. Generations often follow one another in tropical climates, and a new brood may be produced each month. In temperate climates only 1-2 may be produced each season, which is related to when food is available even though temperatures might be ideal. For this reason a species that is limited to a host with an annual cycle and which is suitable for feeding for only a short period would itself have a minimum number of generations during the same period.
Overwintering is usually passed as adults in sheltered places, in large masses in mountain valleys, in smaller aggregations under tree bark, in piles of trash, beneath stones, etc., or singly in the latter locations. An exception is found in C. montrouzieri, which passes winter mostly as pupae in dried leaves or under tree bark, on which it develops. It persists only in subtropical regions where development during winter is not entirely inhibited, and some adult beetles may be found at this time (Clausen 1940/1962).
Coccinellids assemble in vast numbers in mountainous areas that ar far removed from their feeding and reproduction areas, which results from a pronounced migration tendency. In Hippodamia convergens of western North America, these huge colonies are present at certain spots every year, deeply buried in snow (Carnes 1912). However, often they may be found in mountain valleys during midsummer, massed on stones and usually near water under high temperature conditions. Such migrations and gatherings in large masses are attributed to several influences, among which are food scarcity, temperature and air currents. The choice of identical sites every year may be explained by the presence of large numbers of dead bodies, which are left in the spring after the colony, has departed and which provide a persistent odor that attracts the beetles in the following autumn. The occurrence of large aggregations of beetles in hibernating places in the mountains has been recorded in different parts of the world and is the normal habit of quite a few species in several genera. Dobrzhanski (1922) discussed the phenomena of gregariousness and migration in coccinellids, concluding that they have a physiological basis and are not related to food shortages. This was later substantiated by the work of Hagen et al. (see section on predators).
Further Discussion and Ecology
Coccinellidae is a family of beetles, known variously as ladybirds (UK, Ireland, Australia, Pakistan, South Africa, New Zealand, India, Malta, parts of Canada), or ladybugs (North America). Scientists increasingly prefer the names ladybird beetles or lady beetles as these insects are neither birds nor bugs. Lesser-used names include ladyclock, lady cow, and lady fly.
Coccinellids are small insects, ranging from 1 mm to 10 mm (0.04 to 0.4 inches), and are commonly yellow, orange, or scarlet with small black spots on their wing covers, with black legs, head and antennae. A very large number of coccinellid species are mostly, or entirely, black, grey, or brown and may be difficult for non-entomologists to recognize as coccinellids. Conversely, there are many small beetles that are easily mistaken for coccinellids, such as the tortoise beetles.
Coccinellids are found worldwide, with over 5,000 species described, more than 450 native to North America alone.
A few species are considered pests in North America and Europe, but they are generally considered useful insects as many species feed on aphids or scale insects, which are pests in gardens, agricultural fields, orchards, and similar places. Harmonia axyridis (or the Harlequin ladybug) was introduced into North America from Asia in 1988 to control aphids but is now the most common species as it is out-competing many of the native species. It has since spread to much of western Europe, reaching the UK in 2004.
A common erroneous belief is that the number of spots on the insect's back indicates its age.
The name "ladybird" originated in England where the insects became known as "Our Lady's bird" or the "Lady beetle".Mary (Our Lady) was often depicted wearing a red cloak in early paintings and the spots of the seven spot ladybird (the most common in Europe) were said to symbolise her seven joys and seven sorrows. Common names in other European languages have the same association (the German name Marienkäfer translates to "Marybeetle" or, literally, Mary-chafer). In the United States the name was adapted to "ladybug".
Coccinellids are typically predators of Hemiptera such as aphids and scale insects, though conspecific larvae and eggs can also be important resources when alternative prey are scarce. Members of the subfamily Epilachninae are herbivores, and can be very destructive agricultural pests (e.g., the Mexican bean beetle). While predatory species are often used as biological control agents, introduced species of ladybirds (such as Harmonia axyridis or Coccinella septempunctata in North America) outcompete and displace native coccinellids and become pests in their own right.
Coccinellids are frequently brightly colored to ward away potential predators. This phenomenon is called aposematism and works because predators learn by experience to associate certain prey phenotypes with a bad taste (or worse). Mechanical stimulation (such as by predator attack) causes "reflex bleeding" in both larval and adult ladybird beetles, in which an alkaloid toxin is exuded through the joints of the exoskeleton, deterring feeding. Ladybugs, as well as other Coccinellids are known to spray a toxin that is venomous to certain mammals and other insects when threatened.
Most species overwinter as adults, aggregating on the south sides of large objects such as trees or houses during the winter months, dispersing in response to increasing day length in the spring. In Harmonia axyridis, eggs hatch in 3–4 days from clutches numbering from a few to several dozen. Depending on resource availability, the larvae pass through four instars over 10–14 days, after which pupation occurs. After a teneral period of several days, the adults become reproductively active and are able to reproduce again, although they may become reproductively quiescent if eclosing late in the season. Total life span is 1–2 years on average.
It is thought that certain species of Coccinellids lay extra infertile eggs with the fertile eggs. These appear to provide a backup food source for the larvae when they hatch. The ratio of infertile to fertile eggs increases with scarcity of food at the time of egg laying.
Most coccinellids are beneficial to gardeners in general, as they feed on aphids, scale insects, ., and mites throughout the winter. As in many insects, ladybugs in temperate regions enter diapause during the winter, so they often are among the first insects to appear in the spring. Some species (e.g., Hippodamia convergens) gather into groups and move to higher land, such as a mountain, to enter diapause. Predatory ladybugs are usually found on plants where aphids or scale insects are, and they lay their eggs near their prey, to increase the likelihood the larvae will find the prey easily. Ladybugs are cosmopolitan in distribution, as are their prey.
Coccinellids also require a source of pollen for food and are attracted to specific types of plants. The most popular ones are any type of mustard plant, as well as other early blooming nectar and pollen sources, like buckwheat, coriander, red or crimson clover, and legumes like vetches, and also early aphid sources, such as bronze fennel, dill, coriander, caraway, angelica, tansy, yarrow, of the wild carrot family, Apiaceae. Other plants that also attract ladybugs include coreopsis, cosmos (especially the white ones), dandelions and scented geraniums.
Coccinellids are sensitive to most synthetic insecticides. If food sources are limited, oviposition is reduced. A larva uses its sharp jaws to crush an aphid's body and sucks out the aphid's juices
In North America, ladybugs usually begin to appear indoors in the fall. They leave their summer feeding sites in fields, forests and yards looking for a place to spend the winter. Typically when temperatures warm to the mid 60s Fahrenheit in the late afternoon, following a period of cooler weather, they will swarm onto or into buildings illuminated by the sun. Swarms of ladybugs fly to buildings in September through November depending on location and weather conditions. Also, homes or buildings near fields or woods are more prone to infestation.
The presence of ladybugs in grape harvests can cause ladybird taint in wines produced from the grapes.
Following a long period of hot dry weather in the Summer of 1976 in the UK, there was a marked increase in the aphid population followed by a "plague" of ladybirds, with many reports of people being bitten as the supply of aphids dwindled. Recent studies suggest that coccinelidae can also cause allergic reactions, such as eye irritation or asthma.
Balduf, W. V. 1935. The Bionomics of Entomophagous Coleoptera. J. S. Swift Co., NY. 220 p.
Brannon, L. W. 1937. Ann. Ent. Soc. Amer. 30: 43-50.
Stehr, W. C. 1930. Tech. Bull. Minn. Agr. Expt. Sta. 75: 1-54.
Timberlake, P. H. 1943. Hawaiian Planters' Record 47: 1-67.