Determination of the functional response in the orb-weaving spider Araneus diadematus (Araneae: Araneidae) according to insecticide type

Orb-weaving spiders are abundant predators in agroecosystems and serve as key natural enemies for pest control. However, studies have demonstrated that many insecticides can negatively affect the predatory behaviours of spiders when exposed to sublethal concentrations, thus disrupting their biocontrol potential and subsequent ecosystem dynamics. Understanding how insecticides impact spiders is, therefore, of great importance.
This study investigated the effects of two conventional insecticides (thiamethoxam and deltamethrin), and a common biopesticide (neem oil) compared to a tap water control on the functional response of a common orb-weaver Araneus diadematus.
Spiders were collected from the wild and maintained under laboratory conditions in containers (20 × 20 × 5 cm) to allow for web production. Spiders were then exposed to one of the four treatments and Drosophila melanogaster were added to the webs as prey at densities of 1, 3, 5, 10, 20, and 40, with the number of consumed prey quantified after 16-h to determine the functional response.
Overall, A. diadematus exhibited a type II functional response when exposed to the control, thiamethoxam and neem oil treatments, with comparable consumption rates, search coefficients and handling times. This contrasted with deltamethrin-treated spiders which exhibited a type III functional response and a lower consumption rate of prey compared to the control.
This study demonstrates that deltamethrin, unlike thiamethoxam and neem oil, is capable of negatively affecting the biocontrol potential of A. diadematus. However, further research is required to fully understand the impact insecticides have on the predatory behaviours of orb-weaving spiders.