Prevalence of natural fungal mortality of black bean aphid, Aphis fabae Scopoli, on primary host and two secondary hosts
2002
Barta, M. | Cagan, L. (Slovak Agricultural Univ., Nitra (Slovak Republic))
During 2001 and 2002, Entomophthoralean infection of the black bean aphid, Aphis fabae Scopoli, was analysed on aphid's secondary hosts (field bean and sugar beet crops) and on its winter host, Euonymus europaea L in Slovakia. Entomopathogenic fungi attacking the black bean aphid were identified as Neozygites fresenii (Nlowakowski) Remaudiere and Keller, Erynia neoaphidis Remaudiere and Hennebert, Entomophthora planchoniana Cornu and Conidiobolus obscurus (Hall and Dunn) Remaudiere and Keller. E. planchoniana, E. neoaphidis and W. fresenii infected the black bean aphid on the winter host, the first one being predominant. In spite of strong infestation of the shrubs, the level of aphid infection was low. A proportion of infected aphids in the population did not exceed 5% in 2001 and 2% in 2002. Aphid colonies on field bean were affected with N. fresenii in 2001 and with W. fresenii, E. neoaphidis and C. obscurus in 2002. W. fresenii showed a potential for epizootic development of disease in dense colonies of the aphid, but cutting of the crop interrupted the disease development in the population. Therefore, the maximum proportion of infected aphids reached just 8.78% on field bean. Few individuals killed by W. fresenii and C. obscurus were recorded from the sugar beet in 2001, but during the next year strong epizootics of W. fresenii was found after a peak of aphid population. However, since the infection occurred late, when the economic threshold had been exceeded, the pathogens possibly did not play important role in a reduction of crop damage by the aphid. Natural outbreak of pathogens among aphid colonies is likely to indicate just a decrease in aphid populations after their peaks and does not bring about their extinction
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