LB 25-264 - Seasonal pattern of pea aphid, Acyrthosipon pisum and three aphidophagous coccinellids in two alfalfa ecosystems: response to glandular trichome mediated resistance.

Background/Question/Methods:

The pea aphid is an oligophagous species that feed on several legume crops including alfalfa. In United States, alfalfa farmers grow cultivars with resistance to pea aphid, and other pests such potato leafhopper (Empoasca fabae) as a management practice. Potato leafhopper-resistant cultivars have glandular trichomes and, are one of the preferred cultivars since potato leafhoppers are the main alfalfa pests across the country. Although there is vast evidence that plant and crops with glandular trichomes can affect the behavior of natural enemies and increase mortality, the seasonal pattern, and interactions between non-target pests and their natural enemies is poorly understood in most of those systems. We strongly believe that “A Change is Gonna Come” through the designing of ecological studies addressing the interaction between glandular trichomes and non-target pests and its natural enemies under field conditions. To compare the seasonal pattern of pea aphid and its natural enemies in alfalfa ecosystems -with resistance and no resistance to potato leafhopper- we established a field study in a randomized complete block design with large plots of 100x100 feet of each alfalfa cultivar. From April to September in 2021 we placed sticky traps and collected weekly sweep samples through four growing periods.

Results/Conclusions:

A total of seven aphidophagous coccinellid species were identified being the convergent ladybeetle (Hippodamia convergens), the pink spotted lady beetle (Coleomegilla maculata), and the seven-spotted ladybeetle (Coccinella septempunctata) the more abundant in both alfalfa ecosystems. Weekly sampling of resistant and susceptible alfalfa with a sweep net in 2021 revealed significant reduced abundance of the seven-spotted ladybeetle (Coccinella septempunctata) , but no significant differences in pea aphid abundance in plots with resistant to potato leafhopper. While these results are from 2021, we will continue sampling in 2022-2023 to determine whether patterns in the abundance are similar. Trends through the four growing periods were similar in pea aphid and the seven-spot ladybeetle population with a peak abundance late in May, before the second cut of alfalfa in plots with resistant to potato leafhopper. Our findings will show the response of pea aphid, and abundant aphidophagous coccinellids to alfalfa cultivars with glandular trichomes; and will inform farmers and scientists about the potential long-term ecological impacts of host plant resistance in alfalfa ecosystems.