A Review of the Potential Use of Entomopathogenic Nematodes to Control Above-Ground Insect Pests in South Africa

Entomopathogenic nematodes (EPNs), of the families Steinernema and Heterorhabditis, are insectparasites that have been successfully used as biological control agents of soil-based insect pests on theNorth American and European continents. The success of nematodes as biological control agents of the soilstages of pest insects has led to research into their use for control of above-ground insect pests. Laboratorybasedstudies have shown exceptionally good control, in most cases, against such pests as mealybugs,codling moth and leaf miners. As the life stages of the above-ground insect pests have not co-evolvedtogether with those of EPNs, they are, generally, more susceptible than the soil-based life stages. However,EPNs are susceptible to desiccation and vulnerable to UV radiation, so that ensuring their survival beyondsoil environments is problematic. The impetus to avoid environmental stressors can cause EPNs to seeksheltered, cryptic habitats on foliage, where their target insect pest (such as mealybugs) may be found.The current paper provides an overview of information on the application of EPNs as a biocontrol agentfor the control of insect pests above ground and on foliage, with particular reference to research done inSouth Africa

Grapevine Leaf Application of Steinernema yirgalemense to Control Planococcus ficus in Semi-field Conditions

The vine mealybug, Planococcus ficus Signoret (Hemiptera: Pseudococcidae), is a key insect pest of South African grapevine. The ability of mealybugs to avoid or resist the action of chemical pesticides has led to the investigation of alternative control methods, such as the application of entomopathogenic nematodes (EPNs). However, EPN application faces challenges, due to the maladaptation of EPN species to aboveground conditions. In this study, the ability of adjuvants to improve the control of P. ficus in grapevine using an indigenous nematode species, Steinernema yirgalemense, was investigated. A trial was performed to assess EPN survival on grapevine foliage, when applied in the morning (high humidity / low temperature) compared with in the afternoon (high temperature / low humidity). In a semi-field trial, the combination ofadjuvants Zeba® and Nu-Film-P® resulted in 66% control of P. ficus after 48 h, compared to the use of Zeba® alone (43%), and EPNs alone (28%). Additionally, lower concentrations of EPNs showed predictably lower mortality rates of P. ficus. Significantly, higher EPN survival was recorded at each time interval in the morning, compared with the corresponding interval in the afternoon. This study demonstrates the ability of S. yirgalemense, when applied with adjuvants and at an appropriate time of day, to control P. ficus on grapevine, under semi-field conditions