THE INFLUENCE OF TEMPERATURE ON THE SUSCEPTIBILITY OF VINE WEEVIL, OTIORHYNCHUS-SULCATUS (FABRICIUS) (COLEOPTERA, CURCULIONIDAE), LARVAE TOMETARHIZIUM-ANISOPLIAE (DEUTEROMYCOTINA, HYPHOMYCETES)

Mortality of Otiorhynchus sulcatus (Fabricius) larvae at 10-degrees-C, 15-degrees-C, 20-degrees-C and 25-degrees-C following treatment with 10(7) conidia ml-1 suspensions of six Metarhizium anisopliae (Metschni koff) Sorokin isolates was temperature dependent. In all cases, the LT 50s were inversely related to temperature, but the nature of this resp onse varied between isolates. Strain 101-82 was the most virulent isol ate at 25-degrees-C with an LT50 of 3.7 days, but it was the least vir ulent isolate at 15-degrees-C and it failed to kill any O. sulcatus la rvae at 10-degrees-C. In contrast, strain 159-83 had the lowest virule nce at both 20-degrees-C and 25-degrees-C, whereas it was the most vir ulent isolate at 10-degrees-C with an LT50 of 20.0 days. The mortality rates followed a similar pattern and were positively related to tempe rature in all cases with the exception of strain 159-83 at 25-degrees- C. Mycosis development was examined on larvae treated with strain 275- 86 and significant differences were obtained between all four temperat ures. Sporulation commenced after approximately 2.75 days at 25-degree s-C, but took nearly 11 days at 10-degrees-C. The infection rates also varied between temperatures; sporulation occurred on 98% of the treat ed larvae at 25-degrees-C, but only on 93%, 87% and 49% of the larvae at 20-degrees-C, 15-degrees-C and 10-degrees-C, respectively. The resu lts of these bioassays demonstrate that temperature has a significant effect on the virulence of M. anisopliae. The differences between fung al strains also emphasises the importance of selecting isolates for sp ecific situations on the basis of their temperature profiles.