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1 Larvae of Thaumetopoea pityocampa (Lepidoptera: Notodontidae) develop throughout the winter, although their feeding activity and survival can be impaired by adverse climatic factors. The present study investigated the survival at low temperature of larvae originating from a population with range expansion in an alpine valley in Northern Italy. 2 The supercooling point of individually analysed larvae averaged at −7 °C. This value insufficiently described the cold hardiness of the larvae; 39% of the tested larvae were alive when returned to room temperature immediately after freezing. When larval colonies inside their nest were exposed to −17 °C for 1 h after gradual temperature decrease, survival was 70.4%. 3 Rearing of larvae in the laboratory at different day/night temperatures indicated an effect of cumulative chill injury on larvae. A logistic regression explained the relationship between negative thermal sum (h°C below 0 °C) received in the laboratory experiment and larval survival. A similar relationship was demonstrated between negative thermal sum and survival of larval colonies in the field. 4 In the laboratory experiment, some tested larvae were able to survive for up to 8 weeks without feeding depending on rearing temperature. As expected, feeding occurred only when larvae were reared at temperatures of 9 °C day/0 °C night. 5 We classify the larvae of T. pityocampa as being moderate freezing tolerant. The winter behaviour allows this species to track climate warming by a rapid expansion into those areas that become compatible with the insect’s development. [ABSTRACT FROM AUTHOR]

Larvae of the koinobiont endoparasitoid Glyptapanteles liparidis (Hym., Braconidae) need to suppress the immune responses of parasitized Lymantria dispar host larvae while maintaining them at high nutritional quality. We used the method of γ-radiation-induced pseudoparasitization to study the effects of the parasitoid's polydnavirus and venom in these processes. To achieve pseudoparasitization, G. liparidis females were irradiated in a cobalt-60 irradiator; such wasps injected during oviposition nonviable eggs along with polydnavirus and venom into the host. Glyptapanteles liparidis eggs or larvae were implanted into unparasitized or pseudoparasitized L. dispar larvae together with or without the parasitoid's teratocytes. Eggs or larvae of G. liparidis implanted into unparasitized hosts were readily encapsulated by the host hemocytes. The further development of the hosts was not impaired. Implantation into pseudoparasitized hosts prevented encapsulation; complete endoparasitic development, however, was only possible when also teratocytes were implanted along with parasitoids into the L. dispar larva. These parasitoids required longer to emerge from the host compared to natural parasitization, but they were able to complete metamorphosis into imagines. Analysis of trehalose levels in the host hemolymph and glycogen in host tissue revealed that G. liparidis polydnavirus/venom is responsible for an alteration of carbohydrate metabolism in L. dispar that is probably beneficial for the developing parasitoid. [ABSTRACT FROM AUTHOR]

Female Glyptapanteles liparidis (Hym., Braconidae) were irradiated in a caesium-137 irradiator; these wasps oviposit nonviable eggs along with polydnavirus and venom into the host (=pseudoparasitization). When Lymantria dispar larvae were infected with microsporidian species for which they are permissive or semi-permissive hosts, spore production was higher in pseudoparasitized than in unparasitized larvae. [ABSTRACT FROM AUTHOR]

Lymantria dispar (L.) (Lepidoptera: Lymantriidae) larvae can be infected in the laboratory with a variety of entomopathogenic microsporidia. In many cases, however, L. dispar is only a semi-permissive host for such infections. In this study, we analyzed changes in the melanization of hemolymph and hemocyte numbers in L. dispar larvae after inoculation with various entomopathogenic microsporidia. We compared the infections produced by microsporidia isolated from L. dispar and infections produced by isolates from other Lepidoptera to which L. dispar is only a semi-permissive host. Microsporidiosis induced a significant activation of the prophenoloxidase system leading to melanization; activation was highest when the pathogen caused heavy infections of the fat body, which was the case with two microsporidia originally isolated from L. dispar. Infection of only the silk glands or light infection of the fat body by two Vairimorpha spp. from other lepidopteran hosts elicited a lower response. Very light infections caused by a microsporidium isolated from Malacosoma americanurn were not accompanied by elevated hemolymph melanization activity. Heavy infections by Endoreticulatus spec. that remained restricted to the gut tissue likewise did not elicit melanization. One Vairimorpha spec. from U dispar induced a significant increase in total hemocyte numbers; the other infections led to temporarily decreased numbers. Microscopic examinations showed that parts of infected tissue were encapsulated by hemocytes. We conclude that measured alterations in hemolymph melanization and hemocyte numbers were likely to be induced by the damaging effects of heavy infections. Observed defense responses did not prevent the progression of infections. [ABSTRACT FROM AUTHOR]