The susceptibility of Otiorhynchus sulcatus larvae to strains of Metarhizium anisopliae and Metarhizium flavoviride was studied at 15 and 20°C. Larvae were sprayed directly with aqueous suspensions of conidia. All strains tested proved highly infectious for larvae at 20°C, killing 95% or more of inoculated larvae at the two highest concentrations tested (4 × 10 5 and 4 × 10 4 conidia per cm 2 ) at 20 days. At 15°C, all strains infected larvae, but differences between strains were significant, with the best strain ( M. anisopliae no. 85) averaging 73% monality (LT 50 = 26.4 days) as compared with 42% (LT 50 = 51.9 days) for the next best strain ( M. flavoviride no. 88) at 4 × 10 3 conidia per cm 2 , 37 days after inoculation. At both temperatures, significant differences were found between strains with regard to their ability to colonize and sporulate on infected larvae. Sporulation Occured on 48% of larvae infected with the best strain ( M. anisopliae no. 85) vs. 8% of larvae infected with the least effective strain ( M. anisopliae no. 127) at 15°C (4 × l0 3 conidia per ml). M. anisopliae strain no. 85 is a promising candidate for use as a microbial control agent against O. sulcatus larvae at field temperatures below the optimum for this pathogen of 25°C.
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Soares et al. (1983) studied this question.
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