Evaluating vermicompost mediated host plant resistance as a sustainable alternative to manage agricultural insect pests
Vermicompost soil amendments have been reported to increase plant growth, yield, and resistance to pathogens, nematodes and arthropod pests. The mechanisms and factors responsible for this reported vermicompost mediated resistance to arthropod pests are yet to be determined. Therefore, the purpose of this study is to evaluate the plant defense mechanism against two chewing pests as well as generalists vs. specialists in each feeding group. Separate bioassays were developed and implemented to test for antixenosis (non-preference) and antibiosis effects against individual insect species.
To determine if the mechanisms responsible for herbivore resistance in vermicompost-grown plants were antixenosis and/or antibiosis we tested the effects of plants grown in various vermicompost concentrations on the preference (choice assays) and performance (no choice assays) of generalist (Helicoverpa zea) and specialist (Pieris rapae) lepidopterous cabbage pests.
Immature of both pest species tested fed equally well on all plant tissue presented, regardless of vermicompost treatment. We also noticed that Pieris rapae feed more when given young leaves than when given older leaves; whereas, Helicoverpa zea showed no feeding preference and fed indiscriminately of leaf age. Furthermore, P. rapae adults preferred the highest percentage vermicompost treatment over all other treatments for oviposition sites. Therefore, we conclude that no antixenosis effect was found for either species.
Data collected from immature performance bioassays, show strong antibiosis effects (lower survival rates) against P. rapae but not H. zea. This could be due to the different feeding habits of the two pests: P. rapae preferred to feed on the young leaves where H. zea grazed indiscriminately.
Impacts and Contributions/Outcomes
The results from current and previous research show that vermicompost can potentially be incorporated into pest management schemes for certain crops, such as cabbage. Furthermore for some pests (such as P. rapae) vermicompost-grown plants may be used as trap crops because females prefer to lay eggs on these plants, but their larvae perform significantly poorer when feeding on them. However, these are aspects that still need to be investigated under field conditions.
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