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COLOMBIAN DEFOLIATOR, Oxydia trychiata (Guenée) -- Geometridae

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A successful example of the use of an exotic parasitoid to control a native forest pest was the importation of the egg parasitoid, Telenomus alsophilae Viereck, from North America to Colombia in South America against a geometrid defoliator (Bustillo & Drooz 1977, Drooz et al. 1977, Dahlsten & Mills 1999). There are a number of interesting facets to the program since the normal geometrid host of the parasitoid in North America, the fall cankerworm, Alsophila pometaria (Harris), is in a different subfamily and genus than the target pest, Oxydia trychiata, in South America. The Colombian geometrid, O. trychiata, has a wide distribution extending from Costa Rica to most of the countries in South America. The moth has 3 generations per year and apparently is capable of normal development on introduced tree species (citrus, coffee, pine and cypress). There has been an attempt to establish exotic conifer species in Colombia for the production of pulp and paper. This previously unimportant insect became a pest in these pine and cypress plantations (Drooz et al. 1977).

The egg parasitoid, T. alsophilae (Scelionidae) has several biological attributes that are well worth noting since they may have influenced this unique cross genus introduction. First, its normal host, the fall cankerworm, feeds on several broad leaved trees but its host in South America feeds on conifers. This indicates that host plant odors or other differences between conifers and broad leaved trees are unimportant in host egg finding. There may have been a clue to this because the fall cankerworm feeds on several genera of deciduous hardwoods. The parasitoid is apparently easily to handle as changes in photoperiod and lack of cold in the winter did not interfere with development (Drooz et al. 1977). The climate at the origin of the parasitoid in Virginia (30° N. Lat., el. 370 m, mean winter temperature 2°C and mean summer temperature 24°C) compared to that of the release site in Colombia (6° N. Lat., 2340 m, temperature range 6° - 26°C with annual mean of 16°C) shows a shift from a temperate to a tropical climate although the extremes are about the same. The rainfall patterns in the two regions also differ. The ecological plasticity of this parasitoid is thus demonstrated, and in addition it is long-lived (>6 months) (Drooz et al. 1977).

The parasitoid may be easily reared, which is important to a biological control project (Drooz et al. 1977, Fedde et al. 1979), and eggs of another species of geometrid, Abbottana clemataria (J. E. Smith) are used because it could be propagated on artificial diet. Around 18,000 parasitoids were sent to and released in a pine plantation in Colombia between October and December in 1975 (Bustillo & Drooz 1977, Drooz et al. 1977). Parasitization rates on O. trychiata eggs were very high and by the time the parasitoid had undergone three generations in April of 1976 few adults could be found at normal emergence time. Only 13 egg masses of O. trychiata could be found and these were 99% parasitized. By May the outbreak was controlled when larvae could not be found in the area (Drooz et al. 1977). It is speculated that the parasitoid maintains itself on any of the four species of Oxydia or other geometrids in Colombia.

REFERENCES: [Additional references may be found at: MELVYL Library ]

Bustillo, A. E. & A. T. Drooz. 1977. Comparative establishment of a Virginia (USA) strain of Telenomus alsophilae on Oxydia trychiata in Colombia. J. Econ. Ent. 70: 767-70.

Dahlsten, D. L. & N. J. Mills. 1999. Biological Control of Forest Insects. In: Bellows, T. S. & T. W. Fisher (eds.), Handbook of Biological Control: Principles and Applications. Academic Press, San Diego, New York. 1046 p

Drooz, A. T., A. E. Bustillo, G. F. Fedde and V. H. Fedde. 1977. North American egg parasite successfully controls a different host genus in South America. Science 197: 390-91.

Fedde, G. F., V. H. Fedde & A. T. Drooz. 1979. Biological control prospects of an egg parasite, Telenomus alsophilae Viereck, p. 123-27. In: Current Topics in Forest Entomology. Selected papers from XV Intern. Cong. Ent., U. S. Dept. Agric. For. Serv. Gen. Tech. Rept. WO-8. 174p.