Varying impact of neonicotinoid insecticide and acute bee paralysis virus across castes and colonies of black garden ants, Lasius niger (Hymenoptera: Formicidae)

Bumblebees prefer sulfoxaflor-contaminated food and show caste-specific differences in sulfoxaflor sensitivity

More than 30% of human food crop yield requires animal pollination. In addition, successful crop production depends on agrochemicals to control pests. However, agrochemicals can have negative consequences on beneficial insect pollinators, such as bees. We investigated the effects of an emerging class of pesticides, sulfoximines, on the common eastern bumblebee, Bombus impatiens. We performed a series of 96-hour toxicity tests on microcolonies of laboratory-reared B. impatiens. Our data showed that sulfoxaflor (SFX) is significantly less toxic to B. impatiens than historically used neonicotinoid pesticides, such as thiamethoxam. Further, for the first time, we found significant differences among castes in sensitivity to SFX; workers and drones were more sensitive than queens. These findings are notable because they reveal both caste and sex-specific differences in bumblebee sensitivity to pesticides. Interestingly, we found no evidence that bumblebees avoid SFX-contaminated sugar syrup. To the contrary, B. impatiens workers had an apparent preference for SFX-contaminated sugar syrup over sugar syrup alone. Overall, our investigation provides novel information on an important pesticide and may help inform regulatory decisions regarding pesticide use.

Neighbors sharing pathogens: the intricate relationship between Apis mellifera and ants (Hymenoptera: Formicidae) nesting in hives

Ants are ubiquitous and eusocial insects that exhibit frequent physical contact among colony members, thereby increasing their susceptibility to diseases. Some species are often found in beehives and in their surroundings, where they exploit the food resources of honey bees. This intricate relationship may facilitate the interspecific transmission of honey bee pathogens to ants, although ants themselves may contribute to spillback phenomena. The objective of this study was to assess the presence and abundance of honey bee pathogens in ants sampled from Italian apiaries. A total of 37 colonies within 24 apiaries across 7 regions were monitored. In total, 6 pathogens were detected in adult ants and 3 in the brood. In particular, the study revealed a high prevalence of honey bee pathogens in ants, with DWV, BQCV, and CBPV being the most commonly encountered. The brood also tested positive for the same viruses. Notably, all analyzed viruses were found to be replicative in both adult ants and ant broods. Furthermore, co-infections were prevalent, suggesting complex pathogen interactions within ant populations. Statistical analysis indicated significant differences in pathogen prevalence and abundance among ant species and sample types. The findings highlight active infection in both the ants and the brood, suggesting a potential role of ants as reservoir hosts and vectors of honey bee pathogens emphasizing the need for further research to understand the implications of interspecific pathogen transmission on ant and bee health.

Low concentrations of acetamiprid, deltamethrin, and sulfoxaflor, three commonly used insecticides, adversely affect ant queen survival and egg laying

Ants are key ecosystem service providers and can serve as important biological control agents in pest management. However, the effects of insecticides on common farmland ant species are poorly understood. We tested the effects of three commonly used insecticides on ants (Hymenoptera, Formicidae). The tested insecticides were acetamiprid (neonicotinoid; formulated as Mospilan 20 SP), deltamethrin (pyrethroid; formulated as Sanium Ultra), and sulfoxaflor (sulfilimine; formulated as Gondola). We tested two ant (Hymenoptera: Formicidae) species with different colony founding strategies, Lasius niger (Linnaeus, 1758) and Myrmica rubra (Linnaeus, 1758). We sprayed their queens with insecticides at concentrations recommended for use in foliar applications in agriculture, i.e., at 1.25 g L-1 (acetamiprid), 0.6 g L-1 (sulfoxaflor), and 0.875 g L-1 (deltamethrin). Further, we diluted the compounds in distilled water and tested them at 10%, 1%, and 0.1% of the field-recommended concentrations, and used distilled water as a control. We monitored the survival of the queens and the number of eggs laid. All three tested insecticides caused severe lethal and sublethal concentration-dependent effects. Even at concentrations three orders of magnitudes lower than recommended for field applications, significantly lower numbers of eggs were found in the queens' nests. The extent of the sublethal effects of acetamiprid and sulfoxaflor was concentration-dependent and differed between the two ant species. Besides bees and bumblebees, ants represent an important group of hymenopterans that are severely affected even by low concentrations of the tested compounds and therefore should be included in risk assessment schemes.

Virus transmission via honey bee prey and potential impact on cocoon-building in labyrinth spiders (Agelena labyrinthica)

Interspecies transmission of RNA viruses is a major concern for human and animal health. However, host-range, transmission routes and especially the possible impact of these viruses on alternative hosts are often poorly understood. Here, we investigated the role of the labyrinth spider, Agelena labyrinthica, as a potential alternative host of viruses commonly known from western honey bees, Apis mellifera. Field-collected spiders were screened for Acute bee paralysis virus (ABPV), Black queen cell virus, Chronic bee paralysis virus, Deformed wing virus type A and B (DWV-B), Israeli acute paralysis virus, Lake Sinai virus and Sacbrood virus. In a laboratory experiment, labyrinth spiders were fed with ABPV and DWV-B infected honey bees or virus free control food. Our results show that natural infections of A. labyrinthica with these viruses are common in the field, as 62.5% of the samples were positive for at least one virus, supporting their wide host range. For DWV-B, the laboratory data indicate that foodborne transmission occurs and that high virus titres may reduce cocoon building, which would be the first report of clinical symptoms of DWV in Araneae. Since cocoons are tokens of fitness, virus transmission from honey bees might affect spider populations, which would constitute a concern for nature conservation.

Buffered fitness components: Antagonism between malnutrition and an insecticide in bumble bees

Global insect biodiversity declines due to reduced fitness are linked to interactions between environmental stressors. In social insects, inclusive fitness depends on successful mating of reproductives, i.e. males and queens, and efficient collaborative brood care by workers. Therefore, interactive effects between malnutrition and environmental pollution on sperm and feeding glands (hypopharyngeal glands (HPGs)) would provide mechanisms for population declines, unless buffered against due to their fitness relevance. However, while negative effects for bumble bee colony fitness are known, the effects of malnutrition and insecticide exposure singly and in combination on individuals are poorly understood. Here we show, in a fully-crossed laboratory experiment, that malnutrition and insecticide exposure result in neutral or antagonistic interactions for spermatozoa and HPGs of bumble bees, Bombus terrestris, suggesting strong selection to buffer key colony fitness components. No significant effects were observed for mortality and consumption, but significant negative effects were revealed for spermatozoa traits and HPGs. The combined effects on these parameters were not higher than the individual stressor effects, which indicates an antagonistic interaction between both. Despite the clear potential for additive effects, due to the individual stressors impairing muscle quality and neurological control, simultaneous malnutrition and insecticide exposure surprisingly did not reveal an increased impact compared to individual stressors, probably due to key fitness traits being resilient. Our data support that stressor interactions require empirical tests on a case-by-case basis and need to be regarded in context to understand underlying mechanisms and so adequately mitigate the ongoing decline of the entomofauna.