The neonicotinoid imidacloprid impairs the predatory performance and functional response of the jumping spider Helpis minitabunda (Araneae, Salticidae)

The neonicotinoid imidacloprid can cause lethal and sublethal effects in non-target organisms, including impaired behaviour, reduced fertility, disrupted locomotion, and reduced predatory performance in arthropods. Spiders are among the most abundant arthropod predators in terrestrial ecosystems, including agricultural ecosystems, yet the effects of neonicotinoids on the predatory function of jumping spiders remain poorly understood. The functional response of a predator describes how predation rates change with prey density and is key to understanding predator-prey dynamics. We tested whether acute exposure to a commercial formulation of imidacloprid at field-recommended concentrations alters the functional response of the Aussie bronze jumping spider, Helpis minitabunda (L. Koch, 1880). We compared the predation of treated (imidacloprid) and control (distilled water) spiders across five prey densities over a 9-hour observation period. Both treated and control spiders exhibited a Type II functional response. However, treated spiders showed more than double the handling time compared to controls, with no difference in attack rate, indicating impaired prey processing efficiency rather than reduced prey detection ability. Overall, treated spiders killed fewer prey than control spiders, and the mean realised predation rate at the highest prey density was more than halved. Control spiders killed more prey as prey density increased over the early observation periods (up to five hours), whereas treated spiders did not. Our findings demonstrate that acute exposure to field-relevant concentrations of imidacloprid impairs the predatory performance of the jumping spider H. minitabunda, which has potential implications for natural pest suppression by spiders in ecosystems where neonicotinoids are applied.