Research

Tritrophic interactions in mixed vegetable crops

Abstract

Biological control is widely recognised today as a major component of pest management strategies, particularly where chemical control has failed or is seen to give rise to even more complex problems. As a sole method of pest control in a specific target crop, biological control is, however, seldom sufficient. It must therefore be integrated with other control tactics to obtain a successful outcome. The investigation of plant- insect interactions to the third trophic level has become very important in understanding and formulating a sustainable integrated pest management system in salad/vegetable crops production. The cabbage plant (Brassica oleracea), one of the widely cultivated edible vegetable in the Brassica genus, has continued to be faced with various insect pest mainly lepidopteran species such as the Diamondback moth, Large white butterfly, Small white butterfly, the Cabbage looper and many species of aphids mainly the Cabbage aphid and the Peach potato aphid. Control of these pests could be favoured by the presence of its naturally occurring enemies such as the Diamondback moth larval parasitoids( Cotesia plutellae and Macromalon orientale), the pupal parasitoids (Brachymeria excarinata and Diadromus collaris) and Apanteles sp.,the Vespid wasp and the Ladybird beetles. Their occurrence in nature alone cannot, however, be relied upon to reduce the level of damage on the cabbage plant. Plants vary extensively in chemical and physical traits that affect herbivore-carnivore interactions, and, as a result, changes in plant community structure and expression of plant traits can alter herbivore populations. Plant varieties and cropping systems have been shown to influence the fecundity, population density and the relative growth rate of insects pest of cabbages as well as their naturally occurring enemies. For instance, an intercrop of cabbage with tomato in the field has been shown to reduce the population of the Diamondback moth and other associated pest, it is therefore important to understand the mechanism for the control of these pests by the tomato plant. In addition, treatment of plants with environmentally safe plant derivatives such as jasmonic acid could lead to enhanced parasitism by the natural enemies, there is a need to explore this possibility in light of advancing its use in field cultivation. Research into the plant- herbivore interactions in the cabbage plant aims to compare known varieties of the plant and the differences in genotype colonization by the associated pest, the role of a non- host intercrop in disrupting the specificity of the response of the herbivore as well as the use of treatments with derivatives of plant metabolites to induce greater parasitism by the naturally occurring parasitoids. This is intended to propose an environmentally safe and agronomically beneficial component of the integrated pest management system for cabbage production as well as reduce the dependence on chemical control methods.

Description

Biological control is widely recognised as a major component of pest control.  This project investigates the interactions between plant resistance and crop phenotype as a means of enhancing biological pest control.

Funding Body

Niger Delta Development Commission

Lead Organisation

University of Ibadan