Effect of species, age, and sex of tsetse on response to infection by Metarhizium anisopliae

Laboratory studies were carried out to determine the effect of sex and age on the susceptibility of tsetse, Glossina morsitans morsitans and G. m. cen tralis, to the entomopathogenic fungus, Metarhizium anisopliae. Both specie s of host flies were susceptible to fungal infection. Female flies were gen erally more susceptible than male flies. Three host ages (40, 20, and <1 da y-old) were used; the youngest group was most resistant to fungal infection . Interactions between species, sex and age were significant on many occasi ons. Age usually accounted for the largest variability in mortality, follow ed by sex. All flies of age 40 days died between 7 and 8 days after infecti on whereas some of the younger flies, especially age 0, lived longer than 1 0 days. Log(10) day probit (LDP) mortality regressions fitted well to most of the data sets. LDP slopes were significant and high, ranging between 4.3 and 12.8, indicating a generally high mortality rate of increase over days . The slopes differed significantly between species, sexes, and ages, but g rouping by age was more intra homogeneous than by species or sex. The 50% l ethal time mortalities (LT50) ranged between 4 and 7 days for age 0, 3 and 6 days for age 20, and about 5 days for age 40. Corresponding ranges of the LT95 were 8 to 20, 5 to 10, and 6 to 7 days for ages 0, 20 and 40, respect ively. The significance of these results in the fungal disease transmission by tsetse is discussed.