Spinosad and Mixtures of an Entomopathogenic Fungus and Pyrethrins for Control of Sitona lineatus (Coleoptera: Curculionidae) in Field Peas.

The pea leaf weevil, Sitona lineatus L., is an important pest of field peas and faba beans in most temperate regions. As no information is currently available on efficacy of biopesticides for S. lineatus control, laboratory bioassays were performed to evaluate the impact of biopesticides (spinosad, Beauveria bassiana strain GHA, pyrethrins, B. bassiana GHA + pyrethrins, and B. bassiana GHA + azadirachtin) against adults of this pest. The concentrations used in this bioassay were 0.1, 0.5, 1.0, and 2.0 times the lowest labeled application rate of each product. Results were further verified in cage experiments by assessing biopesticide effects on adult mortality and feeding damage in pea plants. The impact of biopesticides on mortality of larvae of two beneficial species, Chrysoperla carnea and Adalia bipunctata, was also tested in laboratory conditions. We found spinosad to be the most promising candidate, causing 100% adult mortality at high and medium concentrations. Beauveria bassiana and its combination with pyrethrins caused 60-62% adult mortality, but only at the highest concentration. In contrast, B. bassiana + azadirachtin and pyrethrins treatments caused only minimal adult mortality at all concentrations. In cage experiments, spinosad and B. bassiana + pyrethrins had significant effects on adult mortality and provided foliage protection from adult feeding. Conversely, the fungus treatment alone showed inconsistent performance. Beauveria bassiana and spinosad were generally harmless to C. carnea and A. bipunctata larvae, but B. bassiana + pyrethrins was toxic toward beneficial species. These results could help to improve integrated pest management programs intended to control S. lineatus.