Experimental insecticide applications change tomato pollinator assemblages and do not increase fruit production

One of the main threats to pollinators is insecticide application, many products widely used have lethal and sublethal (affects behavior, health, and fitness) effects on pollinators, and hence pollination. As sensitivity to such effects varies across species, insecticide application also changes the pollinator community composition within agricultural landscapes and hence affects the assemblages of crop pollinators. However, studies on the effects on native bees and their consequences on pollination services are lacking for many pesticides. Here, we use an experimental setup placed in four study regions (each with three blocks, with 15 experimental per block) to evaluate the effect of lambda-cyhalothrin pulverization on pollination and production of tomato (Solanum lycopersicum L.). Lambda-cyhalothrin is a pyrethroid insecticide highly toxic to the environment and commonly used in the tomato crops of Brazil, a crop that is pollinated by a diverse community of native bees. The effect of an alternative insecticide, classified as biological, on pollinators and pollination of tomatoes was also evaluated. For each experimental individual under each treatment, we collected data on the pollinator visitation before and after starting pulverization up to 23 days after the last application of pesticides. We also evaluated the effect of the three treatments on stigma pollen load, fruit, and seed production. We found that in all treatments (even control) visitation rate was higher before than after pulverization. During the spraying period, the plants sprayed with pyrethroid insecticide showed lower pollinator visitation compared to other treatments, these plants also ended with lower pollen deposition on the stigma. Paratrigona lineata was more susceptible to insecticide pulverization than other bee species. Recovery of visitation rates was detected after 23 days for all treatments. Despite the effect on visitation and pollen deposition, fruit and seed sets were similar among treatments. Overall, our results show that pyrethroid insecticide pulverization causes changes in the behavior of native flower-visiting bees. The mechanisms that explain these changes deserve further investigation, and further studies are needed to understand the large-scale effects of the use of pyrethroid insecticide on insect biodiversity and agricultural landscapes. As the biological insecticide had lower negative effects on bees, future studies that take into account both the effects on pest damage and pollination are needed to define more sustainable management approaches, minimizing negative impacts on biodiversity.