Search

Conidia of Metarhiziumspp. formulated in mineral oil (Propar 12) were bioassayed against adults of three acridids which are sporadic pests of pasture and crops in northern Australia. Each insect was treated by placing a drop of a suspension of conidia in oil under the pronotum and was then incubated at 29°C and observed daily. Eight isolates were screened against Locusta migratoriaand those found to be the most virulent were all M. flavoviride“group 3”. One of these “group 3” isolates, FI985 originally from Austracris guttulosa, was the most virulent, while three other genetically similar isolates from Africa also were highly virulent. With these four isolates, a dose of 50,000 conidiahsect caused 100% mortality in 8 d. Subsequent experiments were all with FI985. The LD50for adult L. migratoriawas 4,363 conidia (95% confidence limits: 987‐16,460) on a slope of 1.50 for the 9‐d mortality data and was 387 (68‐1,602) conidia on a slope of 1.11 for the 12‐d data. The spur‐throated locust, Austracris guttulosa, was more susceptible than L. migratoria—the LD50for 9‐d mortality was 413 conidia (227‐867) and, for the 12‐d mortality data, it was 92 conidia (43‐164) on a common slope of 1.59. The larger females died on average 1.5 d later than the males at each dose. A more limited test of the susceptibility of the giant grasshopper, Valanga irregularisshowed that this species was also susceptible to FI985. Taken together with previous data, this shows that FI985 could be used as a mycoinsecticide against all five of Australia's main acridid pests.

Conidia of an isolate of Metarhizium flavoviride, F1985 suspended in oil were sprayed onto mainly adult Phaulacridium vittatum(Sjöstedt) in field cages at two dose rates: 2 × 109and 2 × 108conodia/mL. Both rates were effective in killing all P. vittatumin the cages in 3 weeks, under the prevailing cool conditions. Samples of grasshoppers taken from the treated cages at 4, 8 and 14 d post‐spraying died within 1–6 d when placed at constant 26°C in the laboratory. Samples of foliage fed to healthy grasshoppers showed that some infections conidia persisted for 14 d. the results indicate that it may be possible to control P. vittatumwith an oil‐based spray of conidia of M. flavoviride.

An oil based formulation of an Australian isolate of Metarhizium flavoviridewas applied as an ultra low volume spray against nymphal bands of Chortoicetes terminiferain spring 1993. Up to 41% of sprayed locusts, sampled 1 d after treatment, died from the disease when incubated at 20‐28°. Field observations 21 d after spraying showed that the density of the treated nymphal bands was one‐third that of the controls.