Vermicompost-mediated host plant effects on generalist and specialist lepidopterous pest species

 

Vermicompost is the by-product (excreta) of earthworm digestion and has been shown to increase plant growth and production, as well as to a variety of arthropod pests. However, the mechanisms for this increased resistance are yet to be determined. The objectives of the present study were to evaluate possible antixenotic and antibiotic effects against two cabbage pests: the specialist Pieris rapae and the generalist Helicoverpa zea. Cabbage plants where grown in a commercial potting mix (Sun Gro Redi-earth) amended with 0 (control), 20, 30, 40 and 60 % vermicompost. Antixenosis was evaluated in choice assays where one leaf disc (2.5 cm diam) from each treatment was placed on moist filter paper in a petri dish (14 cm diam); the disks were placed equidistant from each other. Two 3^rd instar larvae where placed in the middle of the petri dish and allowed to eat the disks for 24 hours. The difference between initial and final weights of leaf discs and larvae were estimated. Oviposition preference was tested by placing one plant from each treatment in a 3ft x 3ft x 3ft cage with two mated pairs of adults; which where allowed to oviposit for 48 hours. The number of eggs on each plant where recorded and compared. Antibiosis was evaluated in no-choice assays by confining one 3^rd instar larva on a cabbage plant from the various treatments. Insects were allowed to feed until death or pupation. The data collected shows differing trends in preference and performance between treatments.

 

Key Words: Vermicompost, cabbage, plant resistance, Pieris, Helicoverpa, specialist, generalist