Eggplant or aubergine (Solanum melongena) is a crop often attacked by the Colorado Potato Beetle (Leptinotarsa decemlineata), a major insect pest of plants from the Solanaceae family including potato, tomato and eggplant throughout North America, Europe and Asia. This insect pest is exceptionally destructive to crops and readily develops resistance to a wide variety of chemical insecticides, making research into alternative control methods vital. Now new research has revealed that the use of clover cover crops in agricultural fields of eggplants may provide an economically and ecologically viable method of Colorado Potato Beetle management that is as effective as chemical insecticides in regulating the beetle populations.
Numerous studies have shown that introducing habitat diversification into intensive agriculture systems can reduce the problems associated with insect pests by various mechanisms such as increased habitat and refuge for natural enemy populations and by reducing the colonisation of the crop by the insect pest. Cover crops such as clover are well utilised for their capacity to improve soil quality, but their potential use as a tool to help suppress insect pest populations is less well known.
Research lead by Dr Cerruti Hooks from the University of Maryland has investigated the impact of inter-planting eggplant with crimson clover (Trifolium incarnatum) to establish what effect this has on Colorado Potato Beetle numbers and the populations of insect predators which prey on the beetle. It was observed that significantly fewer Colorado Potato Beetles (adults, larvae and eggs) were found on eggplants cropped with crimson clover than in eggplant plots with no crimson clover. Additionally, there was no apparent impact of insecticide treatment on Colorado Potato Beetle numbers on eggplant inter-planted with crimson clover in comparison to plots without clover, suggesting that a winter cover crop of clover can be used to manage Colorado Potato Beetle without the use of insecticide sprays. Furthermore, the study team found that the proportion of Colorado Potato Beetle insect predators was greater in the eggplant plots that were inter-cropped with clover.
It is thought that these results can be explained by the beetle’s method of detecting its plant hosts. The beetle relies heavily on visual cues and chemical detection to locate its host plants. It is thought that the chemical odours emitted from the crimson clover disguise the plant odours of the eggplants which the beetles are trying to detect, making it more difficult for the beetle to find its host plant. In addition, the clover provides a habitat and nectar source for beneficial insects such as pollinators and predatory insects including natural enemies of the Colorado Potato Beetle, which are then able to more effectively control pest population numbers. As a nitrogen fixing plant, crimson clover is also beneficial in converting atmospheric nitrogen into compounds that can be used by the eggplants, and since it is a winter cover crop it begins to die back in the spring, so does not compete with the growing eggplants.
This research has shown that crimson clover cover crops can reduce and slow the colonisation of eggplant by the Colorado Potato Beetle and increase the number of insect predators. The findings suggest it may be more cost effective, practical and ecologically sustainable to use crimson clover as a management technique to control Colorado Potato Beetles on eggplant than repeated insecticide applications.
Hooks, C., Hinds, J., Zobel, E., & Patton, T. (2012). Impact of crimson clover dying mulch on two eggplant insect herbivores Journal of Applied Entomology DOI: 10.1111/j.1439-0418.2012.01729.x
Szendrei, Z., Kramer, M., & Weber, D. (2009). Habitat manipulation in potato affects Colorado potato beetle dispersal Journal of Applied Entomology, 133 (9-10), 711-719 DOI: 10.1111/j.1439-0418.2009.01429.x