THE EFFECT OF HUMIDITY ON GERMINATION AND INFECTION OF TERMITES BY THE HYPHOMYCETE, METARHIZIUM-ANISOPLIAE

The effect of relative humidities (r.h.) from 90 to 100% on germinatio n of a termite-active isolate of Metarhizium anisopliae (isolate FI25 and FI610) was studied using a liquid germinating medium to which the appropriate amount of glycerol had been added. Germination was increas ingly delayed at water activities equivalent to 99, 98, and 96% r.h. a nd completely inhibited at 94, 92, and 90%. Twenty-one isolates were t hen screened for germination at 96 and 100% r.h. All isolates showed d elayed germination at 96% r.h. but most isolates eventually gave a hig h final percentage germination at this humidity. Two isolates, FI527 a nd FI638, were markedly slower to germinate at both humidities. The su sceptibility of two species of termites, Nasutitermes exitiosus and Co ptotermes acinaciformis, to FI610 was tested at r.h. down to 86%-the l owest humidity at which the insects would survive. No consistent effec t of humidity on pathogenicity was detected. Mortality occurred over t he range range of humidities tested; sporulation from the disease-kill ed termites, however, occurred only at r.h. above 93%. It is concluded that the microclimate around living termites is usually sufficiently humid to ensure infection under most field conditions and that humidit y is unlikely to limit the efficacy of the fungus in controlling termi tes. (C) 1997 Academic Press.