The effect of Cry proteins of Bacillus thuringiensis on the green lacewing (Chrysoperla carnea) was studied by using a holistic approach which consisted of independent, complementary experimental strategies. Tritrophic experiments were performed, in which lacewing larvae were fed Helicoverpa armigera larvae reared on Cry1Ac, Cry1Ab, or Cry2Ab toxins. In complementary experiments, a predetermined amount of purified Cry1Ac was directly fed to lacewing larvae. In both experiments no effects on prey utilization or fitness parameters were found. Since binding to the midgut is an indispensable step for toxicity of Cry proteins to known target insects, we hypothesized that specific binding of the Cry1A proteins should be found if the proteins were toxic to the green lacewing. In control experiments, Cry1Ac was detected bound to the midgut epithelium of intoxicated H. armigera larvae, and cell damage was observed. However, no binding or histopathological effects of the toxin were found in tissue sections of lacewing larvae. Similarly, Cry1Ab or Cry1Ac bound in a specific manner to brush border membrane vesicles from Spodoptera exigua but not to similar fractions from green lacewing larvae. The in vivo and in vitro binding results strongly suggest that the lacewing larval midgut lacks specific receptors for Cry1Ab or Cry1Ac. These results agree with those obtained in bioassays, and we concluded that the Cry toxins tested, even at concentrations higher than those expected in real-life situations, do not have a detrimental effect on the green lacewing when they are ingested either directly or through the prey.
We present a synthetic review and expert consultation that assesses the actual risks posed by arthropod pests in four major crops, identifies targets for integrated pest management (IPM) in terms of cultivated land needing pest control and gauges the implementation “readiness” of non-chemical alternatives. Our assessment focuses on the world’s primary target pests for neonicotinoid-based management: western corn rootworm (WCR,
Diabrotica virgifera virgifera
) in maize; wireworms (
Agriotes
spp.) in maize and winter wheat; bird cherry-oat aphid (
Rhopalosiphum padi
) in winter wheat; brown planthopper (BPH,
Nilaparvata lugens
) in rice; cotton aphid (
Aphis gossypii
) and silver-leaf whitefly (SLW,
Bemisia tabaci
) in cotton. First, we queried scientific literature databases and consulted experts from different countries in Europe, North America, and Asia about available IPM tools for each crop-pest system. Next, using an online survey, we quantitatively assessed the economic relevance of target pests by compiling country-level records of crop damage, yield impacts, extent of insecticide usage, and “readiness” status of various pest management alternatives (i.e., research, plot-scale validation, grower-uptake). Biological control received considerable scientific attention, while agronomic strategies (e.g., crop rotation), insurance schemes, decision support systems (DSS), and innovative pesticide application modes were listed as key alternatives. Our study identifies opportunities to advance applied research, IPM technology validation, and grower education to halt or drastically reduce our over-reliance on systemic insecticides globally.
Electronic supplementary material
The online version of this article (10.1007/s11356-020-09279-x) contains supplementary material, which is available to authorized users.
Toxicity and larval growth inhibition of eleven insecticidal proteins of Bacillus thuringiensis were evaluated against neonate larvae of Helicoverpa armigera, a major pest of important crops in Spain and other countries, by a whole-diet contamination method. The most active toxins were Cry1Ac4 and Cry2Aa1, with LC 50 values of 3.5 and 6.3 µg/ml, respectively. At the concentrations tested, Cry1Ac4, Cry2Aa1, Cry9Ca, Cry1Fa1, Cry1Ab3, Cry2Ab2, Cry1Da, and Cry1Ja1, produced a significant growth inhibition, whereas Cry1Aa3, Cry1Ca2, and Cry1Ea had no effect.
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