Abstract
Interaction between insect herbivores and host plants can be modulated by endogenous and exogenous compounds present in the source of food and might be successfully exploited in Colorado potato beetle (CPB) pest management. Feeding tests with CPB larvae reared on three solanaceous plants (potato, eggplant and tomato) resulted in variable larval growth rates and differential susceptibility to Bacillus thuringiensis Cry3Aa toxin as a function of the host plant. An inverse correlation with toxicity was observed in Cry3Aa proteolytic patterns generated by CPB midgut brush-border membrane vesicles (BBMV) from Solanaceae-fed larvae, being the toxin most extensively proteolyzed on potato, followed by eggplant and tomato. We found that CPB cysteine proteases intestains may interact with Cry3Aa toxin and, in CPB BBMV from larvae fed all three Solanaceae, the toxin was able to compete for the hydrolysis of a papain substrate. In response to treatment with the JA-dependent plant inducer Hexanoic acid (Hx), we showed that eggplant reduced OPDA basal levels and both, potato and eggplant induced JA-Ile. CPB larvae feeding on Hx-induced plants exhibited enhanced Cry3Aa toxicity, which correlated with altered papain activity. Results indicated host-mediated effects on B. thuringiensis efficacy against CPB that can be enhanced in combination with Hx plant induction.
Highlights
The Colorado potato beetle (Leptinotarsa decemlineata Say, family Chrysomelidae, CPB) has proven to be an extremely difficult pest to manage because of its ability to develop insecticide resistance
Interaction between insect herbivores and host plants can be modulated by an enormous variety of both endogenous and exogenous compounds present in the source of food
We performed feeding tests with these three solanaceous host plants and, while CPB larvae reared on potato plants had a significantly higher weight than larvae reared on either eggplant or tomato plants, no statistically significant differences in weight between larvae fed on either eggplant or tomato plants were found (Table 1)
Summary
The Colorado potato beetle (Leptinotarsa decemlineata Say, family Chrysomelidae, CPB) has proven to be an extremely difficult pest to manage because of its ability to develop insecticide resistance. An environmentally sound tactic for the integrated pest management of important agronomic insect pests might be the use of host-plant resistance and microbial insecticides. Cry toxins delivered as conventional sprayable bioinsecticides or engineered in transgenic plants have been successfully used as bioinsecticides for decades. To exert their toxic effect, after ingestion by susceptible insects, Cry proteins are proteolytically activated by gut proteases and the active toxin binds to receptors located on the brush border midgut epithelium. Breakdown of the gut epithelium through a pore formation mechanism on the target membrane or an alternative cell death process involving the adenylyl cyclase/PKA signalling pathway have been proposed as responsible for Cry cytotoxic effect [4,5]
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