Toxic Effects of Fine Plant Powder Impregnated With Avermectins on Mosquito Larvae and Nontarget Aquatic Invertebrates.

The toxic effects of an avermectin-impregnated fine plant powder (AIFP) against larval Aedes aegypti L. (Diptera: Culicidae), Culex modestus Ficalbi (Diptera: Culicidae), and Anopheles messeae Falleroni (Diptera: Culicidae), as well as selected nontarget aquatic invertebrates, were studied under laboratory conditions. The possibility of trophic transfer of avermectins (AVMs) through the food chain and their toxic effects on predaceous species fed AIFP-treated mosquito larvae was also evaluated. Among mosquitoes, Anopheles messeae were the most sensitive to AIFP, while Cx. modestus exhibited the least sensitivity to this formulation. Among nontarget aquatic invertebrates, the greatest toxicity of AIFP was observed for benthic species (larval Chironomus sp. Meigen (Diptera: Chironomidae), whereas predators (dragonflies, water beetles, and water bugs) exhibited the lowest AIFP sensitivity. AIFP sensitivity of the clam shrimp Lynceus brachyurus O. F. Muller (Diplostraca: Lynceidae), the phantom midge Chaoborus crystallinus De Geer (Diptera: Chaoboridae), and the mayfly Caenis robusta Eaton (Ephemeroptera: Caenidae) was intermediate and similar to the sensitivity of the mosquito Cx. modestus. However, these nontarget species were more resistant than An. messeae and Ae. aegypti. Solid-phase extraction of mosquito larvae treated with AIFP and subsequent high-performance liquid chromatography (HPLC) analysis of the extracts revealed an AVM concentration of up to 2.1 ± 0.3 µg/g. Feeding the creeping water bug Ilyocoris cimicoides L. (Hemiptera: Naucoridae) on the AIFP-treated mosquito larvae resulted in 51% mortality of the predaceous species. But no toxicity was observed for Aeshna mixta Latreille (Odonata: Aeshnidae) dragonfly larvae fed those mosquito larvae. The results of this work showed that this AVM formulation can be effective against mosquito larvae.

New genetic lineage within the Siberian subtype of tick-borne encephalitis virus found in Western Siberia, Russia.

Tick-borne encephalitis virus (TBEV), a member of the Flaviviridae family, is a causative agent of a severe neurological disease. There are three main TBEV subtypes: the European (TBEV-Eu), Far Eastern (TBEV-FE), and Siberian (TBEV-Sib). Currently, three lineages within TBEV-Sib have been recorded. In this study, the genetic and biological characteristics of a new original strain, TBEV-2871, isolated in the Novosibirsk province of Western Siberia, Russia were investigated. The strain has low neuroinvasiveness in mice. Phylogenetic analysis demonstrated that TBEV-2871 belongs to TBEV-Sib, but does not cluster with any of the TBEV-Sib lineages. The TBEV-2871 strain has 88-89% nucleotide sequence identity with the other TBEV-Sib strains, 84-86% nucleotide sequence identity with the TBEV-FE and TBEV-Eu subtypes and is genetically close to the subtype division border. The TBEV-2871 polyprotein sequence includes 43 unique amino acid substitutions, 30 of which are recorded at positions that are conserved among all TBEV subtypes. Strain TBEV-2871 and two similar but not identical isolates found in Kemerovo province, Western Siberia are separated into a new lineage tentatively named Obskaya after the name of Ob riber, in the vicinity of which the TBEV-2871 was first found. A molecular evolution investigation demonstrated that within TBEV-Sib, the Obskaya lineage likely separated 1535years ago, which is even earlier than the Baltic lineage.

Tick-Borne Encephalitis Virus Diversity in Ixodid Ticks and Small Mammals in South-Western Siberia, Russia.

UNLABELLED: The persistence of tick-borne encephalitis virus (TBEV) in nature is maintained by numerous species of reservoir hosts, multiple transmissions between vertebrates and invertebrates, and the virus adaptation to its hosts. Our Aim: was to compare TBEV isolates from ticks and small wild mammals to estimate their roles in the circulation of the viral subtypes. METHODS: TBEV isolates from two species of ixodid ticks, four species of rodents, and one species of shrews in the Novosibirsk region, South-Western Siberia, Russia, were analyzed using bioassay, hemagglutination, hemagglutination inhibition, neutralization tests, ELISA, reverse transcription with real-time PCR, and phylogenetic analysis. RESULTS: TBEV RNA and/or protein E were found in 70.9% ± 3.0% of mammals and in 3.8% ± 0.4% of ticks. The TBEV infection rate, main subtypes, and neurovirulence were similar between ixodid tick species. However, the proportions of the virus that were pathogenic for laboratory mice and of the Far-Eastern (FE) subtype, as well as the viral loads with the Siberian and the European subtypes for the TBEV in Ixodes pavlovskyi Pomerantsev, 1946 were higher than in Ixodes persulcatus (P. Schulze, 1930). Percentages of infected Myodes rutilus, Sicista betulina, and Sorex araneus exceeded those of Apodemus agrarius and Myodes rufocanus. Larvae and nymphs of ticks were found mainly on rodents, especially on Myodes rufocanus and S. betulina. The proportion of TBEV-mixed infections with different subtypes in the infected ticks (55.9% ± 6.5%) was higher than in small mammals (36.1% ± 4.0%) (p < 0.01). CONCLUSIONS: Molecular typing revealed mono- or mixed infection with three main subtypes of TBEV in ticks and small mammals. The Siberian subtype was more common in ixodid ticks, and the FE subtype was more common in small mammals (p < 0.001). TBEV isolates of the European subtype were rare. TBEV infection among different species of small mammals did not correlate with their infestation rate with ticks in the Novosibirsk region, Russia.

Phenological asynchrony between host plant and gypsy moth reduces insect gut microbiota and susceptibility to Bacillus thuringiensis.

The phenological synchrony between the emergence of overwintering herbivorous insects and the budding of host plants is considered a crucial factor in the population dynamics of herbivores. However, the mechanisms driving the interactions between the host plant, herbivores, and their pathogens are often obscure. In the current study, an artificially induced phenological asynchrony was used to investigate how the asynchrony between silver birch Betula pendula and gypsy moth Lymantria dispar affects the immunity of the insect to bacteria, its susceptibility to the entomopathogenic bacteria Bacillus thuringiensis, and the diversity in its midgut microbiota. The lysozyme-like activity in both the midgut and hemolymph plasma and the nonspecific esterase activity and antimicrobial peptide gene expression in the midgut were studied in both noninfected and B. thuringiensis-infected larvae. Our results provide the first evidence that phenologically asynchronous larvae are less susceptible to B. thuringiensis infection than phenologically synchronous larvae, and our results show that these effects are related to the high basic levels and B. thuringiensis-induced levels of lysozyme-like activities. Moreover, a 16S rRNA analysis revealed that dramatic decreases in the diversity of the larval gut bacterial consortia occurred under the effect of asynchrony. Larvae infected with B. thuringiensis presented decreased microbiota diversity if the larvae were reared synchronously with the host plant but not if they were reared asynchronously. Our study demonstrates the significant effect of phenological asynchrony on innate immunity-mediated interactions between herbivores and entomopathogenic bacteria and highlights the role of nonpathogenic gut bacteria in these interactions.

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.

VENOM FROM THE ECTOPARASITIC WASP Habrobracon hebetor ACTIVATES CALCIUM-DEPENDENT DEGRADATION OF Galleria mellonella LARVAL HEMOCYTES.

Ectoparasitoids inject venom into hemolymph during oviposition. We determined the influence of envenomation by the parasitoid, Habrobracon hebetor, on the hemocytes of its larval host, Galleria mellonella. An increase in both intracellular Са(2+) content and phospholipase C activity of the host hemocytes was recorded during 2 days following envenomation by the parasitoid. The decreased hemocyte viability was detected 1, 2, and 24 h after the envenomation. Injecting of the crude venom (final protein concentration 3 µg/ml) into the G. mellonella larvae led to the reduced hemocyte adhesion. The larval envenomation caused a decrease in transmembrane potential of the hemocytes. These findings document the suppression of hemocytic immune effectors in the parasitized host larvae.

Leaf surface lipophilic compounds as one of the factors of silver birch chemical defense against larvae of gypsy moth.

Plant chemical defense against herbivores is a complex process which involves a number of secondary compounds. It is known that the concentration of leaf surface lipophilic compounds (SLCs), particularly those of flavonoid aglycones are increased with the defoliation treatment of silver birch Betula pendula. In this study we investigated how the alteration of SLCs concentration in the food affects the fitness and innate immunity of the gypsy moth Lymantria dispar. We found that a low SLCs concentrations in consumed leaves led to a rapid larval development and increased females' pupae weight (= fecundity) compared to larvae fed with leaves with high SLCs content. Inversely, increasing the compounds concentration in an artificial diet produced the reverse effects: decreases in both larval weight and larval survival. Low SLCs concentrations in tree leaves differently affected larval innate immunity parameters. For both sexes, total hemocytes count in the hemolymph increased, while the activity of plasma phenoloxidase decreased when larvae consume leaves with reduced content of SLCs. Our results clearly demonstrate that the concentration of SLCs in silver birch leaves affects not only gypsy moth fitness but also their innate immune status which might alter the potential resistance of insects against infections and/or parasitoids.

The effects of defoliation-induced delayed changes in silver birch foliar chemistry on gypsy moth fitness, immune response, and resistance to baculovirus infection.

We tested the effects of defoliation-induced changes in silver birch, Betula pendula, foliar chemistry (delayed induced resistance, DIR) on the fitness and immune defense of the gypsy moth, Lymantria dispar. We measured larval developmental time, pupal weight, rate of survival to the adult stage, and five characteristics of larval immune defense: (1) encapsulation response; (2) phenoloxidase activity; (3) hemocyte concentration and (4) lysozyme-like activity in the hemolymph; and (5) resistance to infection by L. dispar nucleopolyhedrovirus (LdMNPV). The latter is an entomopathogenic baculovirus that often causes epizootics during outbreaks of L. dispar. We also measured the involvement of foliage non-tannin phenolic compounds in resistance of B. pendula to herbivory as well as the relationship between the compounds we identified and L. dispar development, growth, and survival. Leaves of B. pendula with previous defoliation history contained increased levels of myricetin glycoside, two flavonoid aglycones (acacetin and tetrahydroxy-flavone dimethyl ether), as well as one unidentified simple phenolic. The concentrations of two glycosides of quercetin, as well as the content of one unidentified flavonoid glycoside were significantly decreased under defoliation treatment. DIR of B. pendula retarded larval growth rate and increased lysozyme-like activity in the hemolymph, but did not affect encapsulation response, phenoloxidase activity, or hemocyte count. We did not find any DIR-mediated tritrophic interactions among birch, gypsy moth, and LdMNPV. After viral inoculation, the mean hemocyte counts in larvae reared on an individual tree correlated significantly with the survival of larvae reared on that same tree, indicating that hemocyte density in hemolymph might be associated with resistance to viral infection. We found a strong positive correlation between the concentration of 1-(4″-hydroxyphenyl)-3'-oxopropyl-ß-D-glucopyranose and L. dispar survival rate, which may indicate an unlikely role of this dominant non-tannin phenolic in B. pendula defense against L. dispar. Our study also shows that several immune characteristics of insects that function as barriers against different groups of parasites are differently affected by plant induced defenses. This underscores the importance of considering multiple factors when characterizing barriers to insect immunity.