Sex specificity in innate immunity of insect larvae

The innate immunity of insects has been widely studied. Although the effect of sex on insect immunity has been extensively discussed, differences in immunity between the sexes of larvae insects remain largely unstudied. Studying larval sex differences in immunity may provide valuable information about the mechanisms underlying the insect immune system, which, in turn, can be valuable for the development and improvement of pest management. Here we compared the antibacterial activity in both the midgut tissue and cell-free hemolymph of Lymantria dispar L. (Lepidoptera: Erebidae) females and males at the larval stage without and after a challenge by entomopathogenic bacterium Bacillus thuringiensis Berliner. We also evaluated the sex-specific mortality of L. dispar induced by B. thuringiensis infection. We find that antibacterial activity in the midgut is activated by infection, but only in females. Thus, sex differences in immunity can have important effects even before sexual differentiation at adulthood

Tubulinosema loxostegi sp. n. (Microsporidia: Tubulinosematidae) from the Beet Webworm Loxostege sticticalis L. (Lepidoptera: Crambidae) in Western Siberia

Adults of beet webworm Loxostege sticticalis were collected in Western Siberia in 2009 and 2010. A microsporidium was found infecting 12 of 50 moths in 2010. The parasite develops in direct contact with host cell cytoplasm, sporogony is presumably disporoblastic. The spores are ovoid, diplokaryotic, 4.2 × 2.4 μm in size (fresh), without a sporophorous vesicle. Electron microscopy showed: (a) tubules on the surface of sporoblasts and immature spores; (b) slightly anisofilar polar tube with 10–14 coils, last 2–3 coils of lesser electron density; (c) bipartite polaroplast with anterior and posterior parts composed of thin and thick lamellae, respectively; (d) an indentation in the region of the anchoring disc; (e) an additional layer of electron-dense amorphous matter on the exospore surface. The spore ultrastructure is characteristic of the genus Tubulinosema. Sequencing of small subunit and large subunit ribosomal RNA genes showed 98–99.6% similarity of this parasite to the Tubulinosema species available on Genbank. A new species Tubulinosema loxostegi sp. n. is established

Rock Microhabitats Provide Suitable Thermal Conditions for Overwintering Insects: A Case Study of the Spongy Moth (<i>Lymantria dispar</i> L.) Population in the Altai Mountains

Many insect species overwinter in various rock shelters (cavities and crevices), but the microclimates of rock biotopes remain poorly understood. We investigated the temperature dynamics in rock microhabitats where clusters of egg masses of the wintering spongy moth Lymantria dispar L. (SM) were observed. Our research objective was to find the relation between the ovipositing behaviour of females and the landscape features in different parts of this species’ range. Studies of the ecology of the SM are important from a practical point of view, as the moth causes significant economic damage to forests of the Holarctic. We found that the average monthly temperature of rock surfaces in the studied microhabitats was 2–5 °C above the average air temperature. More importantly, the minimum temperatures in these microhabitats were 4–13 °C higher than the minimum air temperature. These results help to reassess the role of the mountain landscape in the spread of insect species. Rock biotopes provided a significant improvement in the conditions for wintering insects. We believe that, when modelling the spread of invasive species (such as the SM), it is necessary to account for the influence of rock biotopes that may facilitate shifts in the northern boundaries of their range

Molecular sexing of Lepidoptera

We developed a universal method of Lepidoptera molecular sexing. The method is based on comparing the number of copies of the same gene in different sexes. Males of the majority of lepidopteran species have two Z chromosomes, whereas females have only one Z chromosome. Correspondingly, the number of copies of each gene located on this chromosome differs by two times between males and females. For quantitative estimation, we used qPCR. Via multiple alignment of the kettin (a Z chromosome gene) nucleotide sequences, we detected the most conserved fragment and designed primers with broad interspecies specificity for Lepidoptera. Using these primers, we successfully determined the sex of three lepidopteran species belonging to different superfamilies. The developed method is a simple, cost-effective and high-throughput technique for routine sexing. The sex of lepidopteran individuals can be examined at any developmental stage

A Comparison of the Vertical Transmission of High- and Low-Virulence Nucleopolyhedrovirus Strains in Lymantria Dispar L.

Baculoviruses can persist in insect host organisms after infection and may be vertically transmitted to the next generation, in which they may be reactivated. The goal of the present study was to compare the efficiency of the vertical transmission of high- and low-virulence strains and the subsequent reactivation of Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV) in the offspring of Lymantria dispar L. adults who survived after viral infection. As a result of parental infection, the fecundity of survived females, pupae weight, and fertility were significantly different compared to the untreated insects. However, differences in these parameters between high- and low-virulence strains were not observed. The prevalence of virus strains in the offspring measured by quantitative polymerase chain reaction also did not differ. When the larvae reached the fourth instar, they were starved to activate the vertically transmitted virus. The frequency of virus activation in the experiment was not dependent on the virulence of the virus strains. These results are helpful for understanding the strategy of virus survival in nature and for the selection of the most effective strains with transgenerational effects in the years following pest treatment

Tubulinosema loxostegi sp. n. (Microsporidia: Tubulinosematidae) from the Beet Webworm Loxostege sticticalis L. (Lepidoptera: Crambidae) in Western Siberia

Adults of beet webworm Loxostege sticticalis were collected in Western Siberia in 2009 and 2010. A microsporidium was found infecting 12 of 50 moths in 2010. The parasite develops in direct contact with host cell cytoplasm, sporogony is presumably disporoblastic. The spores are ovoid, diplokaryotic, 4.2 × 2.4 μm in size (fresh), without a sporophorous vesicle. Electron microscopy showed: (a) tubules on the surface of sporoblasts and immature spores; (b) slightly anisofilar polar tube with 10–14 coils, last 2–3 coils of lesser electron density; (c) bipartite polaroplast with anterior and posterior parts composed of thin and thick lamellae, respectively; (d) an indentation in the region of the anchoring disc; (e) an additional layer of electron-dense amorphous matter on the exospore surface. The spore ultrastructure is characteristic of the genus Tubulinosema. Sequencing of small subunit and large subunit ribosomal RNA genes showed 98–99.6% similarity of this parasite to the Tubulinosema species available on Genbank. A new species Tubulinosema loxostegi sp. n. is established

The effect of population density of Lymantria dispar (Lepidoptera: Erebidae) on its fitness, physiology and activation of the covert nucleopolyhedrovirus

After high population densities of insect defoliators there is often a dramatic decrease in their abundance due to various limiting factors. Here, we compared gypsy moth larvae (Lymantria dispar L.) reared singly and in crowded conditions. We compared a number of physiological parameters of these insects and the effect of L. dispar population density on the activation of covert baculovirus infections in the larvae. It was found that the population density of gypsy moth larvae did not affect the mortality due to the activation of the covert virus infection or the total mortality. On the other hand, solitary-reared larvae were heavier, took longer to develop, and showed a four-fold higher concentration of dopamine in their haemolymph than larvae reared in groups. Thus, we demonstrated that an increase in the population density of larvae per se facilitates some changes in fi tness and innate immunity traits but is not related to the activation of covert baculovirus infection. We suggest that an increase in population density does not increase the risk of epizootics triggered by the activation of covert baculovirus infection and that researchers should pay more attention to studying density-associated factors, such as starvation

The effect of mixtures of Bacillus thuringiensis-based insecticide and multiple nucleopolyhedrovirus of Lymantria dispar L. in combination with an optical brightener on L. dispar larvae

This study evaluated the efficacy of the commercially available insecticide Lepidocide based on Bacillus thuringiensis var. kurstaki and Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV) and their combination with an optical brightener to control L. dispar L. Efficacy against both second and fourth instar L. dispar larvae was evaluated, and the type of interaction between the tested components was determined using second instar L. dispar larvae. Most combinations of Lepidocide and LdMNPV containing a 5 mg ml(-1) optical brightener had synergistic effects, and their mixtures were most effective in reducing the number of second instar larvae. In contrast, mixtures containing Lepidocide and LdMNPV with an optical brightener caused significantly lower mortality of fourth instar L. dispar larvae than mixtures without Lepidocide. This result suggests that an increased concentration of Lepidocide in a mixture containing LdMNPV and an optical brightener leads to an antagonistic effect on insect mortality. The possible reasons for the differences in the observed effects of the components on the second and fourth instar L. dispar larvae may be associated with the resistance of fourth-instar larvae to the antifeedant effect of B. thuringiensis

Asynchrony between host plant and insects-defoliator within a tritrophic system: The role of herbivore innate immunity

The effects of asynchrony in the phenology of spring-feeding insect-defoliators and their host plants on insects’ fitness, as well as the importance of this effect for the population dynamics of outbreaking species of insects, is a widespread and well-documented phenomenon. However, the spreading of this phenomenon through the food chain, and especially those mechanisms operating this spreading, are still unclear. In this paper, we study the effect of seasonally declined leafquality (estimated in terms of phenolics and nitrogen content) on herbivore fitness, immune parameters and resistance against pathogen by using the silver birch Betula pendula—gypsy moth Lymantria dispar—nucleopolyhedrovirus as the tritrophic system. We show that a phenological mismatch induced by the delay in the emergence of gypsy moth larvae and following feeding on mature leaves has negative effects on the female pupal weight, on the rate of larval development and on the activity of phenoloxidase in the plasma of haemolymph. In addition, the larval susceptibility to exogenous nucleopolyhydrovirus infection as well as covert virus activation were both enhanced due to the phenological mismatch. The observed effects of phenological mismatch on insect-baculovirus interaction may partially explain the strong and fast fluctuations in the population dynamics of the gypsy moth that is often observed in the studied part of the defoliator area. This study also reveals some indirect mechanisms of effect related to host plant quality, which operate through the insect innate immune status and affect resistance to both exogenous and endogenous virus