Investigation into the use of entomopathogenic nematodes to control the mealybugs on pome fruit (Pseudococcus viburni)

The obscure mealybug, Pseudococcus viburni (Signoret) (Pseudococcidae), is one of the common and serious pests of apples and pears in South Africa. Increasing concern over the environmental impact, pesticide residues in fruits, resistance, and expense associated with frequent use of insecticide make

A fast screening was done to identify isolates of entomopathogenic nematodes with a high percentage mortality against P. viburni. Five out of the 16 tested isolates were selected as promising isolates for the control of P. viburni. From these five isolates, H. zealandica (J34) was selected as the most promising isolate to be used for further studies. The biological development of a steinernematid and a heterorhabditid inside adult P. viburni females was followed. The number of nematodes that penetrated; the development of the different generations; and the time and number of IJ that emerged, were noted. Heterorhabditis zealandica (J34) and S. yirgalemense (157–C) successfully reproduced in P. viburni.

The effect that three mealybug sizes have on infectivity was assessed. Adults and intermediates were more susceptible to nematode infection than crawlers. Nematodes were tested for their ability to locate and infect mealybugs on the surface, ovary and calyx of P. viburni field-infested apples. Results from the study indicated that the nematodes are capable of locating and infecting mealybugs, even in the ovaries of infested apples. To determine the lethal time and dose, mealybugs were exposed to 52, 73, 102, 143, and 200 IJ/insect for 12, 24, 36 and 48 hrs. The LD₅₀ and LD₉₀ values were 54 and 330 nematodes per insect, respectively and the LT₅₀ and LT₉₀ values were 30 and 62.5 hrs, respectively, were calculated.