Canadian Forest Service Publications

Effects of seasonal variation in host quality and availability on parasitism by the egg parasitoid Telenomus coloradensis. 2013. Legault, S.; Hébert, C.; Berthiaume, R.; Brodeur, J. Entomol. Exp. Appl. 148:142-151.

Year: 2013

Issued by: Laurentian Forestry Centre

Catalog ID: 34928

Language: English

Availability: PDF (request by e-mail)

Available from the Journal's Web site.
DOI: 10.1111/eea.12086

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Hemlock looper, Lambdina fiscellaria (Guenée) (Lepidoptera: Geometridae), is one of the most important defoliator in North American forests. The common egg parasitoid Telenomus coloradensis Crawford (Hymenoptera: Platygastridae) plays a significant role as a natural control agent, with parasitism levels in spring typically higher than in fall. The objectives of this study were to quantify changes in host acceptance and reproductive performance of the parasitoid in relation to (1) host egg fertilization in fall, (2) host diapause status, (3) host embryonic development in spring, and (4) host deprivation during summer. Our results indicate that T. coloradensis do not have the capacity to develop in unfertilized host eggs, whereas early-diapausing eggs are more suitable for the parasitoid than post-diapausing eggs. Furthermore, the host physiological suitability decreases with embryonic development in spring. Finally, a host deprivation period during the summer tends to negatively affect the parasitic activity of T. coloradensis. These laboratory results confirm previous hypotheses concerning T. coloradensis seasonal ecology and contribute to a better understanding of the effect of hemlock looper egg physiology and availability on the reproductive potential of T. coloradensis.

Plain Language Summary

The hemlock looper, a native insect found throughout Canada, is considered a major defoliator of balsam fir in eastern Canada, and of hemlock in the western provinces. Outbreaks develop suddenly and spread swiftly. Severely affected trees can die within one season. The hemlock looper lays its eggs in September, and they hatch late in the following spring.

Parasites play a key role in the natural control of this insect, particularly Telenomus coloradensis, a small wasp that parasitizes the eggs of the looper. Researchers studied the effectiveness of attacks by this Telenomus.

This parasite can spend the winter in looper eggs either in larval or adult form. If they spend the winter in the adult state, the wasps resume their activity in early spring, as their adaptation to the cold prolongs their attack period. The researchers found that this wasp is very effective in spring, and much less so in the fall. The adults emerge at the end of July, but as there are no looper eggs before September, they enter a dormant state.

This new knowledge on parasitization by Telenomus coloradensis could be integrated into hemlock looper damage predictions.