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.

Ultrastructural characterization and comparative phylogenetic analysis of new microsporidia from Siberian mosquitoes: evidence for coevolution and host switching.

A survey of mosquito larvae infected with microsporidia was conducted from 2005 to 2008 in the Tomsk, Kemerovo and Novosibirsk regions of western Siberia, Russia. Twenty-one morphologically and genetically unique species of microsporidia were isolated from nine species of Anopheles, Aedes, Culex and Ochlerotatus mosquitoes including: (1) 14 proposed new species of Amblyospora (A. bakcharia, A. baritia, A. bogashovia, A. chulymia, A. hristinia, A. jurginia, A. kazankia, A. mavlukevia, A. mocrushinia, A. modestium, A. salairia, A. severinia, A. shegaria, and A. timirasia); (2) a newly proposed genus and species, Novothelohaniaovalae and; (3) six species of Amblyospora (A. flavescens, A. kolarovi, A. rugosa), Parathelohania (P. divulgata and P. tomski) and Trichoctosporea (T. pygopellita) from which gene sequences had not been previously obtained. Detailed ultrastructure of meiospores revealed unique cytological features associated with the length, arrangement and ratio of broad to narrow coils of the polar filament, comparative thickness of the exospore and endospore, and overall size of each species reaffirming their value in distinguishing taxonomic relationships. SSU rDNA sequences obtained from each species of microsporidia were unique when compared with GenBank entries. Phylogenetic trees constructed by Maximum Parsimony, Maximum Likelihood and Neighbor Joining analyses yielded similar topologies with a high degree of congruence between parasite and host at the generic level. Species that parasitize Aedes/Ochlerotatus and Culex mosquitoes segregate into distinct monophyletic groupings mirroring their host phylogeny, while species from Anopheles mosquitoes group as a sister clade basal to the entire group of mosquito-parasitic microsporidia as their Anopheles hosts cluster as a sister clade to the entire group of culicine mosquitoes. This provides strong evidence for host-parasite coevolution by descent at the generic level and limited host lineage switching between unrelated taxa. Among parasites of Aedes/Ochlerotatus and Anopheles mosquitoes, we found several instances where a single mosquito species serves as a host for two or more related species of microsporidia, an observation consistent with host switching and independent parasite speciation. Among the microsporidian parasites of Culex mosquitoes, we found only one parasite per host indicating a higher degree of host specificity and less host switching among parasites of this genus. Findings suggest a degree of host-parasite co-speciation with host switching occurring occasionally when the "normal" host is unavailable in the aquatic ecosystem. Frequency of host switching seems to be occurring in proportion to host relatedness and does not cross generic boundaries in this system.

What environmental factors are important determinants of structure, species richness, and abundance of mosquito assemblages?

Despite numerous ecological studies with mosquitoes, it remains unclear what environmental factors are the most important determinants of structure, species richness, and abundance of mosquito assemblages. In the current study, we investigated relations between these characteristics of mosquito larvae assemblages and environmental factors in a large set of different habitats. Particular objectives were (1) to rank the factors regarding their explanatory power, and (2) to quantify the contribution of major sets of factors such as habitat spatial/hydrological (H), water physico-chemical (W), and aquatic vegetation characteristics (V). Variance partitioning and forward selection based on ordinations and multiple regressions were applied to the data set on 79 water-bodies in southwestern Siberia covering a wide gradient of environmental characteristics and diverse mosquito assemblages. The results showed that richness and abundance inter-correlated poorly (r2 = 0.21), and assemblage structure, richness, and abundance depended on different sets of predictors. Explanatory importance of the three sets of environmental factors differed among the three assemblage variables: H, W, and V had equal importance for assemblage structure, while richness and abundance depended on H and V more than on W. The study showed that contradiction between the aims of conservation (support biodiversity) and mosquito control (reduce mosquito abundance) can be avoided, as relevant environmental factors can be used to define habitats with high richness and low abundance (i.e., high conservation value and low nuisance and disease transmission risk) for conservation activities, and conversely for control measures.