Abstract
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.
Highlights
Throughout their lifetime, organisms have to cope with a large number of environmental challenges including parasite infections
Detrimental effects on fitness can occur as responses of gregarine-infected hosts exposed to suboptimal food conditions (Harry 1967; Zuk 1987b). These effects may be similar to responses of gregarine-infected hosts to sublethal insecticide exposure, because such exposure leads to a suppressed food intake, as shown, for example, in adults of the mustard leaf beetle Phaedon cochleariae (Coleoptera: Chrysomelidae) (Wolz et al 2021)
To understand whether the presence/absence of a biotic challenge can modulate insect responses to an anthropogenic environmental stressor, we investigated the effects of gregarine infection and larval exposure to a sublethal concentration of λ-cyhalothrin
Summary
Throughout their lifetime, organisms have to cope with a large number of environmental challenges including parasite infections. Sublethal concentrations of pyrethroids pose a threat to target pests and to non-target arthropods, which respond with locomotor deficits, a lower survival, and/or reduced reproduction (Desneux et al 2004; Ceuppens et al 2015; Charreton et al 2015) Such negative consequences of exposure to agrochemical pollutants may become even worse if insects are already challenged by other environmental factors such as parasites. Detrimental effects on fitness can occur as responses of gregarine-infected hosts exposed to suboptimal food conditions (Harry 1967; Zuk 1987b) These effects may be similar to responses of gregarine-infected hosts to sublethal insecticide exposure, because such exposure leads to a suppressed food intake, as shown, for example, in adults of the mustard leaf beetle Phaedon cochleariae (Coleoptera: Chrysomelidae) (Wolz et al 2021). We expected that detrimental insecticide exposure leads to a higher number of gregarines in the host
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