2nd Place: Onion thrips host plant preference and performance are mediated by plant disease

Onion thrips (Thrips tabaci Lindeman) is a major insect pest of onions (Allium cepa) causing indirect damage through feeding and promoting pathogen infection. A new fungal pathogen of onions in Michigan is anthracnose (Colletotrichum coccodes), causing tan lesions on the foliage, and infecting bulbs, making them unmarketable. While thrips feeding promotes pathogen infection, it is unclear how host plant infection mediates thrips preference and performance. In a four-choice experiment, we tested thrips ability to differentiate between hosts based on health status with control (mock-inoculated), artificially injured, artificially injured + C. coccodes inoculated-symptomatic, and C. coccodes inoculated-symptomatic onion plants. Furthermore, we tested thrips ability to distinguish between hosts based on infection status in multiple two-choice tests containing combinations of control (mock-inoculated), C. coccodes inoculated-asymptomatic, and C. coccodes inoculated-symptomatic onions. Finally, we investigated thrips performance based on host plant infection status in a no-choice test which contained control (mock-inoculated), C. coccodes inoculated-asymptomatic, and C. coccodes inoculated-symptomatic onion plants. For each experiment, 5 adult thrips were added to the choice tests and 13 days later, we recorded the number of adult and larval thrips on each plant. The results from the four-choice test suggest that thrips prefer C. coccodes inoculated-symptomatic plants, and artificially injured plants. Results from the two-choice and no-choice tests indicate that thrips prefer C. coccodes inoculated plants over control plants and preform best on C. coccodes inoculated-symptomatic plants. These results suggest thrips distinguish between hosts and prefer and perform best on C. coccodes infected plants.