UC Riverside

The mechanisms behind insecticide resistance are commonly thought to induce fitness costs in the absence of insecticides in the environment. However, it is still largely unknown how these fitness costs present themselves and what factors may influence the variation in cost on fitness due to insecticide resistance. To investigate this, I conducted multiple meta-analyses’ along with my own lab study on an insecticide resistant glassy-winged sharpshooter population. I first conducted a literature search and collected data on studies that tested for fitness costs associated with insecticide resistance. The data collected was then used to generate multiple meta-analyses’ to determine the overall effects of resistance on insect fitness indicated through different life history traits. Fecundity, juvenile development time, juvenile survival percentage, and male longevity were significantly reduced due to insecticide resistance. Juvenile development time was prolonged in resistant individuals compared to susceptible individuals; however, female longevity was unaffected by resistance overall. Results from the meta-analyses’ also indicated that there is no consistent trend between the magnitude of resistance and fitness cost. A lab study was also performed between field resistant and susceptible glassy-winged sharpshooter populations to detect any fitness costs associated with insecticide resistance. Glassy-winged sharpshooter fitness was significantly affected by neonicotinoid resistance. Individuals from the resistant sharpshooter population had a significantly reduced fecundity and adult lifespan compared to individuals from the susceptible population. Morphological features like tibia length and intraocular distance were larger in the resistant population compared to the susceptible population; however, there was no difference in wing vein length and dry weight between the two populations. This thesis provides evidence towards fitness costs associated with insecticide resistance that may be used to optimize existing resistance control strategies.