As part of a search for natural enemies of the gypsy moth (Lymantria dispar), virus-infected samples were collected near Toulouse, France. Light and electron microscope studies confirmed that the French strain is a multinucleocapsid nuclear polyhedrosis virus (MNPV). In vivo bioassays using the New Jersey strain of L. dispar, and comparing L. dispar MNPV (LdMNPV) strains from France, North America and Korea, showed that the French strain was the least active, whereas the North American strain had the highest activity. The viral efficacy of all strains was enhanced 200 to 1300-fold in the presence of 1% fluorescent brightener. The enhancement was highest in the American strain and lowest in the French strain. French LdMNPV (LdMNPVF) DNA cut with four restriction enzymes (BamHI, EcoRI, HindIII, and NotI) revealed minor fragment size differences, but many similarities when compared to the North American and the Korean strain. PCR amplification of a LdMNPV early gene (G22) was detected in the North American and the Korean strain, but not in the French strain.
The activity and number of protocerebral neurosecretory neurons of the dorsolateral group (L1, L2 and L2'), as well as the size of the corpora allata were investigated in 5th instar larvae of the gypsy moth (Lymantria dispar) from two populations (oak and locust-tree forests) fed one of two host-plants (oak is a suitable and locust-tree an unsuitable host-plant).
The monitoring of activity related cytological parameters and the number of protocerebral dorsolateral neurosecretory neurons revealed that differently adapted populations respond to nutritive stress differently. The activity of the L1 neurosecretory neurons in the protocerebra of the caterpillars is low in those from the locust-tree forest regardless of host-plant quality. The L2 neurosecretory neurons in the oak population become active when they were fed the unsuitable host-plant whereas their activity was high in locust-tree caterpillars regardless of the host-plant. A decrease in the number of neurosecretory neurons in a response to a novel food was noticed in both populations. The activity of the L2' neurosecretory neurons was similar in all caterpillars, but their number was increased in those from the locust-tree forest. The corpora allata of the locust-tree caterpillars were large whereas those of the oak forest caterpillars only increased in size when they were fed locust-tree leaves.
It is obvious that nutritive stress results in neurosecretory reorganization and changes in the titre of hormones that modulate the morphogenetic programme.
While the ultimate causes and adaptive significance of sexual size dimorphism (SSD) have been extensively studied, the developmental mechanisms behind this phenomenon have received little attention. Going through an additional larval instar may form a specific way of achieving SSD in arthropods. In the present study, the mechanisms of SSD determination of two lymantriid moths, with marked SSD, were studied. In both species, females tended to go through an additional instar compared to males, and form pupae that were more than twice the weight of the males. To reveal the role of an extra instar, larval growth was monitored in the laboratory and the growth parameters were analysed as dependent on sex and developmental type (number of instars). Prolongation of growth by means of adding an additional larval instar in females turned out to be the key mechanism in the determination of the highly female-biased SSD in the species studied. There is thus a developmental mechanism available that permits achieving a larger size by means of extending the growth period. This provides evidence against constraint-based evolutionary explanations for body sizes in insects. There was no considerable accumulation of SSD during earlier larval life when females went through more instars than males. In contrast, in those cases in which males and females had the same number of instars, SSD accumulated gradually during the course of several larval instars. Longer growing period turned out to be a crucial mechanism leading to the female-biased SSD even when instar number did not differ between sexes, although higher instantaneous relative growth rates of females also played a complementary role in the latter case. Within sexes, an additional instar was characteristic of initially smaller larvae, as predicted by the "threshold size" hypothesis.
The development of the solitary endoparasitic braconid Glyptapanteles porthetriae in gypsy moth larvae of different ages was studied. Host larvae were parasitized during the premolt to the 2nd instar (A-larvae), to the 3rd instar (B-larvae) or to the 4th instar (C-larvae), respectively. The percentage of successfully parasitized larvae decreased markedly with the age of the host at the time of parasitization. When parasitization occurred at the premolt to the second or third instar, parasitoid larvae successfully emerged at rates of 68% and 57%, respectively, in contrast to the 17% from larvae parasitized in the premolt to the fourth instar. In all three groups of parasitized larvae the final host instar was significantly longer than the corresponding instar of unparasitized control larvae of the same age. However, the growth and growth rate of parasitized larvae were reduced compared to control larvae. Due to the extremely low rate of successful development of G. porthetriae in C-larvae, parameters of parasitoid development were only recorded in A and B-host larvae. In both the parasitoid growth was slow during the first instar but rapidly increased during the second instar. Total developmental time of the parasitoid was significantly longer in B-host larvae, and the resultant cocoons were heavier than those that developed in A-host larvae, but proportionally fewer of the offspring were females. Within both groups the female wasps took significantly longer to develop than the males.
RNA interference (RNAi) technology uses dsRNAs to silence specific targeted genes by downregulating their expression. It has become a potent tool for functional and regulatory studies of insect genes and has potential to be applied for insect control. Though it has been challenging to generate effective RNAi in lepidopteran insects, in the current study this technology was applied to develop specific RNAi-based molecular tools that could be used to negatively impact the invasive lepidopteran forest pest, gypsy moth (GM). GM midgut-specific genes were selected for dsRNA design from larval transcriptome profiles. Two methods were used to produce specific dsRNAs, bacterial expression and in vitro synthesis, which were then fed per os to GM larvae. Depletion of uncharacterized gene targets known as locus 365 and locus 28365, or their stacked combination, depleted target transcripts in a sequence specific manner and resulted in 60% reduction in body mass. Treated GM females that were able to moult to the adult stage displayed an approximately two-fold reduction in egg masses. These have potential to be developed as molecular biopesticides for GM., Saikat Kumar B. Ghosh, Dawn E. Gundersen-Rindal., and Obsahuje bibliografii
The endoparasitoid Glyptapanteles liparidis (Hymenoptera: Braconidae) injects polydnavirus and venom together with eggs into its Lymantria dispar (Lepidoptera: Lymantriidae) host larvae during oviposition. We studied effects of these parasitoid associated factors by means of g-irradiation-induced pseudoparasitization. The application of radiation for sterilization of female wasps as a tool to study interactions between parasitoid associated factors and the host is demonstrated in this paper. When wasps were irradiated at doses ranging from 24 to 96 Gy and then allowed to oviposit into L. dispar larvae, temporary sterilization was produced. On the first day post irradiation they laid 99% sterile eggs, but fertility recovered partially during the following days. Irradiation had no negative effect on the lifespan of wasps, but total fecundity was significantly reduced. Pseudoparasitization of L. dispar by irradiated G. liparidis caused prolonged larval development with supernumerary molts before pupation in females, and higher pupal weights in both sexes. Only 8 to 20% of pseudoparasitized larvae developed into adults; 20 to 33% died as larvae, 55 to 65% in pupae. Abnormities, such as precocious formation of pupal antennal pads in larvae or incomplete sclerotization of pupal cuticle occurred. Pseudoparasitization impaired the immune reactions of L. dispar larvae. Encapsulation of implanted plastic rods by hemocytes was reduced and hemolymph melanization was significantly suppressed 3 and 5 days post pseudoparasitization.
The gypsy moth oophagous predator guild in the Mamora forest is an assemblage of many species whose succession in egg masses enhances the exploitation of this food source. Life history, biological Features and trophic capacities of predator species are described from field observations and laboratory rearing. Extreme diversity of diets, capacity to resist prolonged fasting and extended larval development with extra-instars enable them to survive on the cork oak when gypsy moth egg masses are absent. The 1986-1990 gypsy moth outbreak occurred in a forest part where unhealthy cork oaks are common. by providing abundant shelter for numerous arthropods these trees are beneficial to the oophagous predators which find there various and abundant food sources. This probably explains why egg predator activity in the infested area rapidly increased so that the pest outbreak collapsed.
While most theoretical models for the evolution of ageing assume that duration of pre-adult development does not affect the longevity, experimental data are still controversial and inconsistent. Here we examined the short-term and long-term pattern of pre-adult development time and longevity in populations of the gypsy moth (Lymantria dispar) originating from either oak forest (Quercus petrea), a suitable, or locust-tree forest (Robinia psedoacacia), a poor habitat. Using a full-sib design, we examined the genetic correlations between traits found in larvae reared on oak or locust-tree leaves. We detected only negative and insignificant genetic correlations, except for males from the Robinia population reared on oak leaves where the correlation was negative and significant. Our results also showed that a population living 40 generations in the locust-tree forest exhibited a significantly higher longevity than the Quercus population, whereas a significant difference between these two populations in pre-adult development time does not exist. The results are discussed in relation to the potential effect of stress selection in moulding the longevity of the gypsy moth.
The effects of tannic acid on mean values and genetic variation in fitness-related traits (mass, relative growth rate) and specific activities of digestive enzymes (total proteases, a-glucosidase and lipase), and genetic variation in their plasticity, were investigated in fifth instar larvae of Lymantria dispar L. (Lepidoptera: Lymantriidae) originating from two populations with different host use histories (oak and locust-tree). The two populations did not differentiate with respect to fitness-related traits, i.e. adverse effects of tannic acid were similar in both populations. However, Robinia larvae, which originated from the locust-tree forest, were characterized by higher total protease and lipase activity and lower a-glucosidase activity than Quercus larvae, which originated from the oak forest. Higher plasticity of lipase and lower plasticity of a-glucosidase in response to tannic acid were also recorded. Quantitative genetic analysis revealed mostly significant expression of genetic variation in the examined traits and trait plasticity, suggesting the potential for evolution of adaptive plastic responses to new environmental conditions and presence of a stressor. The genetic correlations observed between the environments significantly differed from “one”, which indicates there are no constraints on the evolution of trait plasticity., Marija Mrdakovic ... [et al.]., and Obsahuje seznam literatury