Neozygites fressenii (Zygomycetes:Entomophorales) as a mortality factor of the black bean aphid Aphis craccivora (Homoptera: Aphididae) in VISCA
2001
Villacorta, L.T. (Visayas State Coll. of Agriculture, Baybay, Leyte (Philippines))
The effect of Neozygites fressenii, with or without manipulation, on black bean aphid population was studied and the development of epizootictology in the aphid population was monitored for several cropping seasons. Findings showed that N. fressenii was constantly present in Aphis craccivora population in cowpea, bushbean and stringbean from 1 to 100% infection in a given aphid colony. The fungus was present in the field even at very low aphid population and at normally high day temperature of 31 deg-32 deg C. The disease incidence was dependent on the aphid population with correlation coefficient of 0.38-0.87. Heavy rains washed off the aphids thereby drastically reducing their population. The introduction of infected aphids as source of inoculum may hasten the development of the fungus and decrease the resulting aphid population by almost 30%. The lowest number of aphids were recommended on bean with some natural infestation of aphids prior to the introduction of two live infected aphids. The source of inoculum early in the season were infected with alatae, and conidia coming from the nearby vegetation per weeds. The information of resting spore may be related to high inoculum density. N. fressenii has been shown to be a very important mortality factor of A. craccivora which appear early in the season. The effect of this fungus can possibly be maximized by tranferring or introducing infected aphids in healthy aphid colonies to facilitate development of epizootic. To conserved this beneficial organism, farmers should be careful in using fungicide once infected aphids are noticed in the field
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