Assessment of prey-mediated effects of the coleopteran-specific toxin Cry3Bb1 on the generalist predator Atheta coriaria (Coleoptera: Staphylinidae)

A laboratory study was carried out to assess the potential prey-mediated effects of Cry3Bb1-expressing Bt maize on the fitness and predatory ability of Atheta coriaria Kraatz (Coleoptera: Staphylinidae), using Tetranychus urticae Koch (Acari: Tetranychidae) as prey. The concentration of Cry3Bb1 toxin through the trophic chain significantly decreased from Bt maize (21.7 μg g−1 FW) to mites (5.6 μg g−1 FW) and then to A. coriaria adults (1.4 μg g−1 FW), but not from mites to A. coriaria L1–L3 larvae (4.1–4.6 μg g−1 FW). Interestingly, the toxin levels detected in A. coriaria larvae represent more than 20% of the concentration found in Bt maize, and the toxin was detected up to 48 h after exposure. To our knowledge, this is the highest level of exposure ever reported in a predatory beetle to the Cry3Bb1 protein. When A. coriaria larvae were reared on Bt-fed mites, Bt-free mites or rearing food, no significant differences among treatments were observed in development, morphological measurements of sclerotized structures and body weight. Moreover, no negative effects on reproductive parameters were reported in adults feeding on Bt-fed prey after 30 days of treatment, and survival was not affected after 60 days of exposure. Similarly, predatory ability and prey consumption of A. coriaria larvae and adults were not affected by exposure to the toxin. All together, these results indicate a lack of adverse effects on A. coriaria, a species commonly used as a biological control agent. The use of A. coriaria as a surrogate species for risk assessment of GM crops that express insecticidal proteins is discussed.

Effects of Bacillus thuringiensis Cry1Ab and Cry3Aa endotoxins on predatory Coleoptera tested through artificial diet-incorporation bioassays

Traditional approaches to studying the effects of genetically modified (GM) crops on beneficial insects involve either field assays, comparing insect population levels between control and GM crops or tritrophic bioassays with contaminated insects – usually larvae or eggs of Lepidoptera – as preys. Here, we report the results of a bioassay using an artificial diet, suitable for predatory Coleoptera, to supply Bacillus thuringiensis (Bt) solubilized Cry1Ab and Cry3Aa as well as trypsin-activated Cry1Ab to Atheta coriaria and Cryptolaemus montrouzieri adults and young larvae of Adalia bipunctata. Water, solubilization buffer and trypsin-treated solubilization buffer were used as controls. In total, 1600 insects were assayed. Assays showed a relatively low mortality rate in the controls, ranging from as low as 7% after 15 days (C. montrouzieri) to about 15–20% after five days (A. bipunctata) or 15 days (A. coriaria). For all three predators, there were no statistical differences between the mortality recorded in any of the treatment groups and the corresponding controls. These results indicate a lack of short- (A. bipunctata) and long-term (A. coriaria and C. montrouzieri) mortality associated with oral ingestion of Cry1Ab and Cry3Aa at the high dose tested (50 μg ml−1). We discuss the relevance of these findings for the ecology of beneficial Coleoptera and compatibility with Bt and GM Bt crops.

Compatibility of Atheta coriaria with other biological control agents and reduced-risk insecticides used in greenhouse floriculture integrated pest management programs for fungus gnats

Fungus gnats (FG) (Diptera: Sciaridae: Bradysia spp.) are economically important pests of greenhouse flowers. Larvae feed on root tissue and transmit a variety of phytopathogens. Atheta coriaria (Kraatz) (Coleoptera: Staphylinidae) is a new biological control agent (BCA) for FG. To support its successful use by the greenhouse industry, its compatibility with current integrated pest management (IPM) programs used in floriculture was assessed. This included investigations of prey preference, possible detrimental interactions with other soil-dwelling BCAs, and the toxicity to A. coriaria of registered and novel insecticides. Atheta coriaria showed little preference among eggs of different pest species or between pest eggs and eggs of the intraguild predator Hypoaspis aculeifer (Canestrini) (Acari: Mesostigmata: Laelapidae). It preferred FG 1st-instar larvae to larvae and pupae of other soil-dwelling pests. The entomopathogenic nematode Steinernema feltiae (Filipjev) (Rhabditida: Steinernematidae) was compatible with A. coriaria, but H. aculeifer mites fed on A. coriaria larvae. Insect growth regulators with limited contact activity (e.g., diflubenzuron) were compatible with adult A. coriaria and had minimal effects on larvae compared with other insecticides. Atheta coriaria can be incorporated into an IPM program for FG if harsh insecticides are avoided, but interactions with predatory mites, as well as its effectiveness against other greenhouse pests when FG are present, require further investigation.