Evaluating vermicompost mediated host plant resistance as a sustainable alternative to manage agricultural insect pests

Evaluating vermicompost mediated host plant resistance as a sustainable alternative to manage agricultural insect pests

Summary

Vermicomposts are produced through the digestive action of earthworms upon organic waste and are a rich source of microbial diversity and available plant nutrients. Addition of low concentrations of manure- or food-based vermicompost to soil or potting mixes have been shown to increase plant growth and productivity. More importantly for the purpose of this study, vermicompost has been shown to reduce damage by, and populations of, pests such as pathogens, plant parasitic nematodes and a variety of arthropods including jassids, aphids, spider mites, mealy bugs, and caterpillars. However, the mechanisms responsible for resistance against this wide variety of insects has not been fully investigated. Therefore the effects of plants grown in varying vermicompost concentrations on the preference and performance of alate and apterous morphs of the generalist and specialist aphids Myzus persicae and Brevicoryne brassicae were evaluated.

Results from these studies show that vermicompost differentially affects that intra-species effects are morph-dependent. These data also show that vermicompost-mediated resistance effects are not dose-dependent and that lower concentrations result in greater resistance effects on insect preference and performance than higher concentrations.

Objectives/Performance Targets

1. 1) To evaluate potential negative effects of vermicompost treatments on the host preference of apterous and alate morphs of M. persicae and B. brassicae. 2)To determine if vermicompost-mediated resistance is due to detrimental effects on the performance and survival of the selected aphid species.

Accomplishments/Milestones

We evaluated the preference and performance of two cabbage pests: the specialist Brevicoryne brassicae and the generalist Myzus persicae on cabbage plants grown in soil amended with varying vermicompost levels. Plants were grown in a commercial potting mix amended with 0 (control), 20, 30, 40 and 60 % vermicompost. Feeding preference was evaluated for apterae (wingless) adults in leaf disc choice assays conducted in petri dish arenas. Aphids were released in the middle of the arena where the discs were placed equidistant from the center of the petri plate and each other. Alighting preference was also evaluated with alates by releasing them above canopy level in the center of a cage containing one plant from each treatment. Finally, apterae colonization ability was evaluated by confining 5 newly-emerged apterae to a single plant and allowing them to feed and reproduce for 14 days.

Impacts and Contributions/Outcomes

In a previous study conducted in our laboratory it was found that plants grown in vermicompost-amended soil showed enhance resistance against the generalist caterpillar Helicoverpa zea and the specialist Pieris rapae in Arabidopsis and cabbage, respectively. Furthermore, this resistance was determined to be due to antibiosis, based on poor caterpillar performance and significant mortality levels. Since aphids pierce and suck to feed on phloem within sieve elements of their host plants, the damage they inflict affects plants differently than damage from chewing mouthparts and; therefore, plant defenses activated by vermicompost are expected to affect aphids differently than lepidopterous larvae.

Results from this study show that vermicompost has no significant negative effects on the feeding preference of apterae of either species with any of the treatments tested. To the contrary, apterae B. brassicae showed a significant preference for vermicompost treatments over control leaf discs. Alate M. persicae preferred alighting on control plants over vermicompost-grown plants, but B. brassicae showed no preference towards any of the treatments tested. However, both aphid species deposited significantly more nymphs on control plants than on those grown in 20% vermicompost. Furthermore, plants grown in soil amended with 20% vermicompost significantly suppressed mass accumulation, as well as, numbers of adults and nymphs of both aphid species compared to controls. These data clearly show that vermicompost soil amendments can significantly influence pest aphid preference and performance on plants and that these effects are not dose-dependent, but rather species and morph dependent.

Altogether these studies suggest that vermicomposts may reduce the need for synthetic pesticides. This environmentally-friendly soil amendment has the potential to be easily adopted and incorporated into pest management programs for certain crops.

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