Neem seed cake enhances the efficacy of the insect pathogenic fungus Metarhizium anisopliae for the control of black vine weevil, Otiorhynuchs sulcatus (Coleoptera: Curculionidae)

Neem seed cake enhanced the efficacy of the insect pathogenic fungus Metarhizium anisopliae for control of black vine weevil (BVW), Otiorhynuchs sulcatus (Coleoptera: Curculionidae) larvae in out door potted Euonymus plants. Both M. anisopliae and neem seed cake alone were effective against earlier instar larvae with the degree of control being dose dependant. Significantly higher conidial attachment was observed on larvae recovered from pots treated with combined application of M. anisopliae and neem seed cake (5 g/l of peat) suggesting that the neem seed cake increased larval movement and the subsequent acquisition of conidia. At higher concentration of neem seed cake (5 g/l), few BVW larvae survived whereas larvae recovered from neem treated pots (0.5 or 2.5 g/l) were less than half in body size and weight to that of untreated control suggesting that neem acts as growth regulator. Incorporation of neem seed cake or M. anisopliae in potting media did not influence adult BVW feeding or oviposition. Since neem seed cake products are considered safer than synthetic insecticides, the interactions we describe could easily be exploited to control insect pests in situations where no synthetic insecticides are permitted. Furthermore, enhanced efficacy of M. anisopliae at 100-fold lower doses (1 × 108 conidia/l of peat) in combination with neem seed cake would greatly benefit the grower by reducing the cost of the fungal BCA.