CHARACTERIZATION OF TOLYPOCLADIUM CYLINDROSPORUM (HYPOCREALES: OPHIOCORDYCIPITACEAE) AND ITS IMPACT AGAINST AEDES AEGYPTI AND AEDES ALBOPICTUS EGGS AT LOW TEMPERATURE

摘要

We examined the growth characteristics of Tolypocladium cylindrosporum IBT 41712 and its potential to infect eggs of Aedes aegypti and Ae. albopictus at a low temperature (15 degrees C). When grown on Sabouraud dextrose agar supplemented with yeast extract, the IBT 41712 formed white colonies turning to a slightly darker, off-white color when mature. The mycelia bore swollen conidiophores producing smooth-walled, oblong to cylindrical conidia with varying sizes, ranging from 1.5 to 3.5 mu m long. To determine the optimum temperature for the fungus, we cultured the fungus at eight temperatures (4 degrees C, 12 degrees C, 15 degrees C, 21 degrees C, 28 degrees C, 33 degrees C, 37 degrees C, and 40 degrees C) and measured the diametric growth. The optimum temperature for growth was 28 degrees C since it had the highest diametric growth rate (2.1 +/- 0.05 mm/day) and the fastest sporulation period (within 8-10 days of incubation). There was no fungal growth at the 3 highest temperatures (33 degrees C, 37 degrees C, and 40 degrees C) but plates incubated at 33 degrees C, when shifted to optimal temperature (28 degrees C), showed visible growth indicating that following incubation at 33 degrees C, the fungus remained viable. The IBT 41712 successfully infected mosquito eggs at 15 degrees C. Fungal treatment induced egg hatch on moist seed-germination paper and this effect was more pronounced in Ae. aegypti compared to Ae. albopictus. When treated eggs were immersed in dH(2)O 21 days posttreatment, larval hatch of both Ae. aegypti (control = 91%, 1 x 10(7) conidia/ml, fungal treatment - 0%) and Ae. albopictus (control - 85%, fungal treatment - 28%) was significantly lower in fungal treatment compared to the controls. The ability of the strain to grow in a wide temperature range, and effectively infect mosquito eggs and induce egg hatch at a low temperature warrants further investigation for its potential as a mosquito control agent targeting eggs that overwinter or undergo long diapause.