Natural Occurrence Of Entomopathogenic Fungi On Cereal Aphids At Assiut: A Comparative Study Between Real Parasitism (Laboratory Observations) And Cadavers Count (Field Observations)

• M.A. A. Abdel-Rahman1, A. Y. Abdel-Mallek2, S. A. Omar2 and G. H. A. Hamam2
• ¹ Plant Protection Research Institute, Agriculture Research Center, Giza, Egypt.
• ² Botany Department, Faculty of Science, Assiut University, Egypt.

Abstract

The present investigation was carried out during two successive wheat-growing seasons (2000 and 2001). The impact of entomopathogenic fungi on cereal aphid populations was evaluated under natural conditions. The aphid began to appear on wheat plants early in the season during 22nd January when the plants were in the stem-extension stages. Thereafter, number of aphids increased gradually to reach a peak of abundance, when the plants were at flowering stage, during the first half of March. During the next three weeks, the number of aphids declined sharply. The insect was observed in few numbers during the third week of March, when the plants were at the ripening stage. In the field, mortality rate with the fungal pathogens (cadavers count) was observed from January 22nd up to March 22nd. The number of cadavers increased gradually to reach the maximum level during the second week of March coincided with the peak of cereal aphids. Concerning the number of infected aphids developed in the laboratory from alive aphids collected from wheat field, mortality rate fluctuated from the first week of February up to the third week of March. The maximum level of parasitism coincided with the collapse of aphid population. The rate of mortality by fungi in the field was always low as compared with that recorded from the aphid collected from the field and reared in the laboratory. At the peak of aphid populations, the rates of parasitism in the field were 24.67 and 12.01% as compared with 58.67 and 42.00% in the laboratory during 2000 and 2001 seasons, respectively. The infection of cereal aphids with the entomopathogenic fungi (laboratory observation), was always much higher than the infection rate in field observation, being 2.35 and 3.50 times higher at population peak during 2000 and 2001 seasons, respectively. Based on the regression model the effectiveness of entomopathogenic fungi on cereal aphids and the mortality rate can be predicted by looking for aphid cadavers on wheat plants.