Canadian Forest Service Publications

Developmental and reproductive responses of the spruce budworm (Lepidoptera.: Tortricidae) parasitoid Tranosema rostrale (Hymenoptera.: Ichneumonidae) to temperature. 2017. Seehausen, L.; Régnière, J.; Martel, V.; Smith, S.M. J. Insect Physiol. 98:38-46.

Year: 2017

Available from: Laurentian Forestry Centre

Catalog ID: 37464

Language: English

CFS Availability: PDF (request by e-mail)

Available from the Journal's Web site.
DOI: 10.1016/j.jinsphys.2016.11.008

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The temperature-dependent development and survival of immatures, as well as adult longevity and potential fecundity of the endoparasitoid Tranosema rostrale (Hymenoptera: Ichneumonidae) parasitizing spruce budworm Choristoneura fumiferana (Lepidoptera: Tortricidae) larvae was investigated under laboratory conditions at several constant temperatures ranging from 5 to 30 C. Maximum likelihood modeling approaches were used to estimate thermal responses in development, survival, and longevity. A model describing the effect of temperature on potential fecundity of the parasitoid was also developed taking oogenesis and oosorption into account. In-host and pupal development rates of the parasitoid increased with temperature up to 25 C, and decreased thereafter. Immature survival was highest below 20 C, and rapidly decreased at higher temperatures. Adult longevity decreased exponentially with increasing temperature for both males and females. Highest potential fecundity was reached at 10 C. Considering survival and potential fecundity, the parasitoid seems best adapted to cool temperatures below 20 C. Simulations of the life-history traits under variable temperature regimes indicate that temperature fluctuations decrease survival and increase realised fecundity compared to constant temperatures. The temperature-dependent fecundity model developed can be applied to other non-hostfeeding synovigenic parasitoids. The equations and parameter estimates provided in this paper can be used to build comprehensive models predicting the seasonal phenology of this parasitoid and spruce budworm parasitism under changing climatic conditions.

Plain Language Summary

This study carried out in a laboratory environment helped researchers model the impact of temperature on the development of the parasitoid Tranosema in spruce budworm (SBW) larvae, as well as on the longevity and fecundity of this parasitoid’s adults.

It was observed that the development of this parasitoid in SBW larvae increases with temperature until it reaches 25°C, after which it decreases. Parasitoid survival decreases significantly at temperatures above 22°C. The longevity of adult Tranosema decreases exponentially as temperature increases. This is true for both males and females. The highest fertility rate was observed at 10°C. It would therefore seem that these parasitoids are better adapted to temperatures below 20°C. Compared with stable temperatures, temperature variations decrease the parasitoid’s survival rate and increase its fertility rate.

The spruce budworm (SBW) is a native pest insect. Its outbreaks are the most significant natural disturbance in Canadian fir forests. Its parasitoids play a vital role in maintaining SBW populations at an endemic level between outbreaks. One such parasitoid, the Tranosema rostrale wasp, uses its stinger to lay an egg under the skin of SBW larvae. The larva that emerges from this egg then feeds on the internal tissue of its host.

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