Microbial Toxins in Insect and Nematode Pest Biocontrol

Abstract

Invertebrate pests, such as insects and nematodes, not only cause or transmit human and livestock diseases but also impose serious crop losses by direct injury as well as vectoring pathogenic microbes. The damage is global but greater in developing countries, where human health and food security are more at risk. Although synthetic pesticides have been in use, biological control measures offer advantages via their biodegradability, environmental safety and precise targeting. This is amply demonstrated by the successful and widespread use of Bacillusthuringiensis to control mosquitos and many plant pests, the latter by the transgenic expression of insecticidal proteins from B. thuringiensis in crop plants. Here, I discuss the prospects of using bacterial and fungal toxins for pest control, including the molecular basis of their biocidal activity.

Keywords: cyclic lipopeptide surfactants; innate immunity busters; insect ion channel modulators; pore-forming toxins; psychoactive compounds; ribotoxins; sterol homeostasis disruptors; uncouplers.

Figure 1

Insect resistant Bt-corn decreased pesticide use in US. (A) Percentage of Bt-corn acreage out of total corn planted between 1998 and 2011 (data extracted from [13]). (B) Insecticide use in maize (kg/ha and environmental impact quotient (EIQ) weights) during the same period as in A. (Figure reproduced from [14]).

Figure 2

A derivative of natural pyripyropene shows superior aphicidal activity. Of >40 derivatives tested, the derivative with cyclopropanecarbonyloxy groups at the C-1 and C-11 positions and a hydroxyl group at the C-7 position showed the highest insecticidal activity against aphids [70].