Laboratory screening of entomopathogenic fungi and nematodes for pathogenicity against the obscure mealybug, Pseudococcus viburni (Hemiptera: Pseudococcidae)

Abstract

Pseudococcus viburni (Hemiptera: Pseudococcidae), the obscure mealybug, is a serious polyphagous, cosmopolitan agricultural insect pest that affects deciduous fruit production in South Africa. The presence of the mealybug in orchards results in significant damage to crops, with economic implications. The potential use of two entomopathogenic fungi (EPF) and entomopathogenic nematodes (EPN), as biological control agents against P. viburni, was assessed under laboratory conditions, using screening bioassays. The EPF isolates, Metarhizium robertsii (6EIKEN) and M. pinghaense (5HEID), tested at a conidial concentration of 1 × 107 conidia/ml, proved to be effective against the adult stage female mealybugs, causing 96% ± 6% and 91% ± 13% mortality, respectively, 7 days post inoculation, when incubated at 25°C with humidity levels of > 95%. Heterorhabditis indica, applied at a concentration of 200 infective juveniles per insect, was found to be the most effective EPN against P. viburni, causing 79% mortality, 48 h post inoculation, while incubated at 25°C. Further bioassays showed a positive correlation between insect mortality and conidial concentration as well as exposure time. The study represents the first report on the pathogenicity of multiple local and commercial EPF isolates to control P. viburni and several local EPN isolates against P. viburni.