Gregarines modulate insect responses to sublethal insecticide residues

Throughout their lifetime, insects face multiple environmental challenges that influence their performance. Gregarines are prevalent endoparasites in most invertebrates that affect the fitness of their hosts, but are often overlooked in ecological studies. Next to such biotic factors, a current common challenge is anthropogenic pollution with pesticides, which causes a major threat to non-target organisms that are readily exposed to lethal or sublethal concentrations. In a laboratory study, we investigated whether the presence of gregarines modulates the food consumption and life history traits of a (non-target) leaf beetle species, Phaedon cochleariae, in response to sublethal insecticide exposure. We show that the larval food consumption of the herbivore was neither affected by gregarine infection nor sublethal insecticide exposure. Nevertheless, infection with gregarines led to a delayed development, while insecticide exposure resulted in a lower body mass of adult males and a reduced reproduction of females. Individuals exposed to both challenges suffered most, as they had the lowest survival probability. This indicates detrimental effects on the population dynamics of non-target insects infected with naturally occurring gregarines that face additional stress from agrochemical pollution. Moreover, we found that the infection load with gregarines was higher in individuals exposed to sublethal insecticide concentrations compared to unexposed individuals. To counteract the global decline of insects, the potential of natural parasite infections in modulating insect responses to anthropogenic and non-anthropogenic environmental factors should be considered in ecological risk assessment.

Analysis of Bacillus thuringiensis treatment impact on microflora and cellulosolytic processes in southern chernozem

When using insecticides based on B. thuringiensis in biocenoses, the issues of their influence directly on plants and soil fertility are particularly relevant. The aim of the research was to study the direction of microbiological processes in the soil after processing potato plants with liquid spore cultures of entomopathogenic B. thuringiensis 792, 800, 810, 815, 857, 888, 902, 989, 994 and 0371 strains. The nature and extent of insecticide exposure were assessed by the quantity of microorganisms in the main ecological and trophic groups. It has been shown that soil treatment with B. thuringiensis strains 792, 854 and 989 influences the intensity of southern chernozem CO2 emission most actively, by 5.7-6.0 times. The studies made it possible to establish that B. thuringiensis strains 810, 854, 888 and 902 are able to exert the most active effect on the decomposition of cellulolose, increasing its activity by 93.7; 85.6; 82.0-93.7% to control. The statistically significant relationships study of correlation dependences made it possible to conclude that the treatment of southern chernozem with strains of B. thuringiensis 792, 800, 810, 854, 888 and 0371 does not have a destructive effect on soil microbocenosis.

Past insecticide exposure reduces bee reproduction and population growth rate

Pesticides are linked to global insect declines, with impacts on biodiversity and essential ecosystem services. In addition to well-documented direct impacts of pesticides at the current stage or time, potential delayed “carryover” effects from past exposure at a different life stage may augment impacts on individuals and populations. We investigated the effects of current exposure and the carryover effects of past insecticide exposure on the individual vital rates and population growth of the solitary bee, Osmia lignaria. Bees in flight cages freely foraged on wildflowers, some treated with the common insecticide, imidacloprid, in a fully crossed design over 2 y, with insecticide exposure or no exposure in each year. Insecticide exposure directly to foraging adults and via carryover effects from past exposure reduced reproduction. Repeated exposure across 2 y additively impaired individual performance, leading to a nearly fourfold reduction in bee population growth. Exposure to even a single insecticide application can have persistent effects on vital rates and can reduce population growth for multiple generations. Carryover effects had profound implications for population persistence and must be considered in risk assessment, conservation, and management decisions for pollinators to mitigate the effects of insecticide exposure.

Influence of temperature on spinosad toxicity in different populations of Plutella xylostella (Linnaeus)

Diamond back moth, Plutella xylostella (Linnaeus) is one of the major insect-pest of cole crops, causing high yield losses. In present study, larval populations of P. xylostella, collected from different regions of Punjab i.e. Amritsar, Kapurthala, Malerkotla and Ludhiana were exposed to different concentrations of spinosad at 15, 20, 25 and 30 °C for evaluation of LC values. The LC (Lethal 50 50 concentration) increased from lower (15 °C) to higher (30 °C) temperature for all populations of P. xylostella. Negative correlation was observed between the temperature coefficient and toxicity of spinosad towards P. xylostella populations, which decreased with increase in temperature. The LC 50 values varied among different populations of P. xylostella i.e. Amritsar populations with higher LC values 50 followed by Kapurthala, Malerkotla and Ludhiana populations. The temperature and insecticide exposure history both affected the toxicity of spinosad for P. xylostella. The information would be helpful in developing management strategies for P. xylostella according to prevailing environment conditions.