A major forest insect pest, the pine weevil Hylobius abietis, is more susceptible to Diptera‐ than Coleoptera‐targeted Bacillus thuringiensis strains

Abstract

BACKGROUND The pine weevil (Hylobius abietis) is a major forest regeneration pest causing high levels of seedling mortality and economic losses. Current management relies on silviculture, stem coatings and insecticides. Here we evaluated for the first time the effects of Bacillus thuringiensis (Bt) strains on H. abietis adults: two producing the Coleoptera‐targeted toxins Cry3Aa (Bt tenebrionis NB‐176) and Cry8Da (Bt galleriae SDS‐502), and one producing the Diptera‐targeted Cry10A (Bt israelensis AM65‐52). Choice and nonchoice assays using individual and mixtures of Bt formulations, containing these strains respectively, were conducted. RESULTS We found that Bt had toxic and lethal effects on H. abietis, but effects varied with strain and formulation concentration. The Diptera‐targeted Bt israelensis had the most negative effects on weevil weight, feeding and mortality (70–82% feeding reduction, 65–82% greater mortality than control), whereas the effect was lower for the Coleoptera‐specific Bt tenebrionis (38–42%; 37–42%) and Bt galleriae (11–30%; 15–32%). Reduced weevil feeding was observed after 3 days, and the highest mortality occurred 7–14 days following Bt exposure. However, we found no synergistic toxic effects, and no formulation combination was better than Bt israelensis alone at reducing consumption and survival. Also, pine weevils were not deterred by Bt, feeding equally on Bt‐treated and non‐Bt treated food. CONCLUSION There is potential to develop forest pest management measures against H. abietis that include Bt, but only the Diptera‐targeted Bt israelensis would provide effective seedling protection. Its Diptera‐specificity may need reconsideration, and evaluation of other Bt strains/toxins against H. abietis would be of interest. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Determination, distribution, and environmental fate of Bacillus thuringiensis spores in various honeybee matrices after field application as plant protection product

“…Although Bt strains are assumed to be selective on target pests, recent reports indicate cross-order effects (van Frankenhuyzen et al 2017). For example, the Coleopteran-targeted formulation can cause negative effects on Lepidopteran (Redmond et al 2020), the Lepidopteran-targeted formulation on Coleopteran and the Dipteran (Coyle et al 2000;Babin et al 2020;Nawrot-Esposito et al 2020), and Diptera-targeted formulation on Coleopteran (Tudoran et al 2020). Regarding the effects on bees, differences in the sensitivity of adult worker bees to different Bt products were reported (Brighenti et al 2007;Mommaerts et al 2010;D'urso V, Mazzeo G, Vaccalluzzo V, Sabella G, Bucchieri F, Viscuso R, Vitale DG, , 2017;Libardoni et al 2018;Potrich et al 2018;Steinigeweg et al 2021).…”

“…The most studied insecticidal toxins are Cry-toxins as δ-endotoxins affecting the susceptible insects after oral uptake (Bravo et al 2011 andBravo et al, 2017;Mendoza-Almanza et al 2020). Several reports regarding direct and indirect cross-effects of Bt formulations and their toxins across insect taxa and orders recently indicated the semi-specificity of Bt (van Frankenhuyzen 2017; Redmond et al 2020;Coyle et al 2000;Babin et al 2020;Nawrot-Esposito et al 2020;Tudoran et al 2020). Lepidopterantargeted formulation, containing Bta ABTS 1857, has demonstrated increasing mortality of adult and larvae of honeybees after chronic exposure under laboratory conditions (Steinigeweg et al 2021).…”

Comprehensive comparison of treatments for controlling the large pine weevil (Hylobius abietis) in Central Europe

“…Maturing weevils also feed on the bark of coniferous seedlings 18 , 19 . H. abietis adults cause high levels of seedling mortality and economic losses 20 . In Europe, H. abietis causes annual damage of almost 120 million EUR 21 .…”

Comprehensive comparison of treatments for controlling the large pine weevil (Hylobius abietis) in Central Europe

“…Hylobius abietis adults cause high levels of seedling mortality and economic losses 20 . In Europe, H. abietis causes annual damage of almost 120 million EUR 21 .…”

“…The depending on population density and weather conditions, H. abietis can kill 50 to 100% of seedlings at a site 11,22,23 . Current management relies on silviculture, feeding barriers, and insecticides 20 .…”