Associate Professor Cornell University Ithaca, New York
The intensification of agriculture has led to a surge in pesticide use, commonly resulting in increased pesticide tolerance among many pests. However, the presence of (semi-) natural habitats in the landscape has been hypothesized to protect generalist pests from developing insecticide resistance. Delia platura, a detritivore and generalist pest that affects germinating seeds and seedlings of various field crops, has been managed for many years by coating seeds with neonicotinoids. Although D. platura is commonly found in field crops, it also uses other crop and seminatural habitats. Our objective was to determine if D. platura populations vary in their insecticide tolerance along the gradient of landscape complexity. To do this, we first established the LD50 of D. platura to a Thiamtoxam (neonicotinoid) using a larval dip bioassay. This was done by submerging D. platura larvae (4–6 mm in length, 7–10 days old) for 20 seconds in different neonicotinoid concentrations and counting the survival rate after 24 and 48 hours, with larvae from a colony established in the lab 2 years ago. To understand if insecticide tolerance varies across the landscape complexity gradient, we collected ten different populations of D. platura across New York State that varied in the proportion of (semi-) natural habitat in the landscape. We then compared the insecticide tolerance using the previously established LD50 concentrations in a larval dip bioassay. Our results show that the different D. platura populations vary in their tolerance to neonicotinoids and that other factors can explain this variation.