Combatting pesticide resistance in insects using botanical bio-synergists

Abstract

Over 600 species of pests have developed some level of resistance to pesticides, rendering many products ineffective and reducing the options for pest management. With increasing restrictions on future pesticide use and withdrawal of active ingredients, together with the decline in the rate of new insecticide discoveries, options need to be explored to extend the useful life of products currently available. Plant derived compounds (botanicals) have been shown to interfere with the activity of enzymes that detoxify insecticides and are involved in metabolic pesticide resistance in insects. The use of such compounds can increase the efficacy of insecticides, thereby reducing required application rates and/or counteracting metabolic resistance, allowing effective control to be restored without increasing application rates. In vitro enzyme assays and efficacy testing were used to evaluate whether botanicals could enhance pesticide efficacy against insect pest species associated with brassicas. These included cabbage stem flea beetle (Psylliodes chrysocephala), peach-potato aphid (Myzus persicae), diamondback moth (Plutella xylostella) and cabbage root fly (Delia radicum). Botanicals were tested in combination with selected plant protection products and efficacy compared to single product applications, using standard laboratory efficacy testing methods. Data showed that the efficacy of pyrethroids against field-collected P. chrysocephala, which have developed resistance against this pesticide group, can be restored when used in combination with some botanicals, such as neem oil. Pyrethroid efficacy can also be enhanced against M. persicae and P. xylostella when combined with lemongrass oil and garlic oil. Similarly, efficacy of Spinosad against D. radicum can be increased when used in combination with botanicals such as parsley-seed oil and thymol. Enzyme activity assays (esterase, glutathione S-transferase and cytochrome P450 monooxygenase) have also indicated that several botanicals interfere with the function of certain enzyme groups that detoxify insecticides, some of which correlates with the mortality data from the bioassays. Botanicals may counteract the metabolic resistance of some insect pests and thereby restore efficacy and/or allow the reduction of pesticide required for effective control, which could have implications for protecting oilseed rape and other high-risk crops.