EFFECTS OF TEMPERATURE, HUMIDITY AND INOCULATION METHOD ON SUSCEPTIBILITY OF SCHISTOCERCA-GREGARIA TO METARHIZIUM FLAVOVIRIDE

The effects of temperature on conidial germination and susceptibility of adults of the desert locust, Schistocerca gregaria, to four isolate s of Metarhizium flavoviride were determined. In addition, the effects of inoculation method (topical or spray), spore carrier (oil or water ) and ambient relative humidity (RH) on susceptibility of the locust t o the most thermotolerant isolate (Mf324) were investigated. There wer e differences among the isolates in the effects of temperature on germ ination of conidia after a 24-h incubation period. Over 90% of conidia of all isolates germinated after 24 h at 30 degrees C. In contrast, a t 40 degrees C, none of the isolates germinated for up to 72 h. Howeve r, there were differences in germination between the isolates at 35 de grees C. Locust mortality and disease progression were significantly a ffected by temperature. At both 25 and 30 degrees C, all isolates indu ced 98-100% mortality within 8 days; however, there were differences b etween isolates at 35 degrees C. None of the isolates caused significa nt mortality at 40 degrees C. Humidity and inoculation method had no i nfluence on levels of mortality in fungus-treated locusts. In contrast , carrier type significantly affected cumulative mortality. Topical oi l treatment resulted in higher overall mycosis than the three other tr eatments. Control mortality on the other hand was strongly affected by inoculation method and to a lesser extent by humidity and carrier. In these conditions, application of oil by spray was generally toxic at all humidities whereas topical application of water was most toxic at near saturation. The results of these laboratory studies demonstrate t he importance of strain selection, formulation and application method in the development of a microbial control agent against the desert loc ust. Low RH should not impede use of this fungus under dry conditions.