# Sub-Lethal Toxicity of Bifenthrin and Acetamiprid Through Dietary Trophic Route: Effects on the Foraging Activity, Social Interactions, and Longevity of Apis mellifera L

## TL;DR

This study shows that low doses of two insecticides harm honey bee foraging, social behavior, and lifespan, even if they don't kill the bees outright.

## Contribution

The study reveals the sub-lethal effects of bifenthrin and acetamiprid on honey bee colonies via dietary exposure in natural field conditions.

## Key findings

- Higher doses of insecticides reduced foraging activity and social interactions in honey bees.
- Exposure to insecticides shortened adult bee longevity but did not affect immature developmental stages.
- The findings highlight the need for more precise pesticide application to protect pollinators.

## Abstract

Honey bees (Apis mellifera L.) play a vital role in the pollination of different crop plants but remain exposed to lethal and sub-lethal doses of pesticides which are used in different farming systems. This study investigated how the indirect individual dietary trophic exposure of two commonly used insecticides, bifenthrin and acetamiprid, belonging to two different groups (pyrethroid and neonicotinoid), affect bee colonies. Sunflower fields (Hysun-33) were subjected to different sub-lethal doses of these insecticides. After seven days of individual insecticidal treatments, twenty-seven bee colonies were introduced at nine different sites in these fields. The isolation distance between each site was not less than 3 km. The colonies introduced in the insecticide-free plots were considered as untreated control (T0). The results revealed that the bee colonies exposed to higher individual doses of insecticides exhibited less foraging activity, weaker social behaviors such as food sharing and communication, and shorter lifespans compared to the untreated control colonies. However, the growth durations of different immature stages of bees (egg, larva, and pupa) were not affected by the individual exposure of these insecticides. These findings suggest that even small amounts of pesticides taken through contaminated food can disturb the normal behavior and health of honey bee colonies. The results highlighted the need to use pesticides more precisely, especially by adjusting their timing and application methods, to protect pollinators that serve as an essential component of crop production and ecological sustainability.

Apis mellifera L. is an important pollinator of both wild and domesticated crop plants, thus greatly contributing to plant biodiversity and commercial agriculture. However, in field conditions, honey bees remain exposed to different pesticides which ultimately affect colony health parameters and their associated ecological services. In the current study, the individual toxicities of sub-lethal doses of two distinct insecticides (bifenthrin and acetamiprid) belonging to different groups (pyrethroid and neonicotinoid) were assessed against the foraging activity, social interactions, and longevity of A. mellifera. The bees were exposed to individual doses of both insecticides via the dietary trophic route through contaminated pollen and nectar under natural field conditions. Sunflower crop (Hysun-33) was sown at nine different sites with an isolation distance of 3 km, and was treated with different doses (1/2, 1/4, 1/10, and 1/20 of the recommended field doses) of both insecticides. However, the untreated control crop plots were not subjected to any chemical treatments (bee colonies received no insecticide, and served as the baseline for making comparison). Twenty-seven bee colonies were introduced in these sites after seven days of treatment applications. Significant differences were observed in the foraging activity of A. mellifera (including bees going out from the hive, returning foragers, and those carrying pollens). The fecundity, adult longevity, and social behaviors like trophallaxis and antennation were significantly lower in bees exposed to higher individual insecticidal concentrations. However, the hatching duration, larval duration, and pupal duration were not affected by the tested insecticidal treatments. Overall, these findings demonstrate that the dietary trophic exposure of sub-lethal doses of insecticides compromised colony activities, which is indeed a matter of concern regarding the existing pesticide application methods in different agro-ecosystems. Such impacts may ultimately impair the survival of colonies, particularly when bees remain exposed to these chemicals over an extended period of time. Therefore, future studies must consider the pesticide application techniques and their application timing to mitigate the direct and indirect negative impacts of pesticides on pollinators.