Classical Biological Control of Arthropods in Australia

Farm Management,

Green vegetable bug (Nezara viridula [L.]) (Hemiptera: Pentatomidae) in Australian pecans

[Extract] The green vegetable bug, Nezara viridula (L.), is a cosmopolitan pest, possibly originating from the Ethiopian or Mediterranean region (Hokkanen, 1986). This pentatomid first appeared in NSW in 1916 and then spread to other states of Australia (Wilson 1960). Nymphs and adults feed on stems, petioles and fruit. In Australia a wide range of vegetables, fruit, agricultural crops (particularly legumes) and developing seeds, including macadamia (Ironside, 979), are damaged by this insect. In the USA, N. viridula is a major pest of pecans (Carya illinoensis [Wangenh.]C. Koch), causing "black pit", hich results in premature nut drop and black spotting in mature nuts (Turner, 1923). Polles et al., (1973) has shown that fourth instar nymphs and adults can cause nut abscission in cage experiments. However, only adults are known to occur in the tree crowns of pecans (Dutcher & Todd, 1983)

Host specificity in arthropod biological control, methods for testing and interpretation of the data

Potentially, the introduction of exotic natural enemies or mass release of biological control agents may lead to unwanted non-target effects. Whether or not such effects occur will depend mainly upon the host range of the biological control agent and the presence of non-target species in the areas of release and dispersal. To predict non-target effects, risk assessments for release of exotic natural enemies have been developed and applied during the modern era of biological control. Although methods to determine host ranges of natural enemies have been proposed during the past decades, decisions about release of exotic natural enemies are often still based on short-term decisions strongly influenced by financial benefit and tend to ignore environmental ethics, especially where risks are difficult to quantify. Here, we propose a framework for host-range testing of arthropod biological control agents, and suggest methods for evaluating possible effects on those non-target species considered to be at risk. Several factors should be incorporated into a host-range assessment, including literature and museum records, field observations in the area of origin, as well as physiological, behavioural and ecological observations and experiments. Usually, laboratory-based manipulative experiments will form the core of host-range assessments. In this chapter we concentrate on the question of how to determine host ranges. Several important considerations involved in designing host-range testing are presented. Next, a framework for step-wise host-range testing is given with levels of increasing complexity that should allow over- and underestimation of the host range of a biological control agent to be avoided. Finally, the interpretation of data obtained with host-range testing is discussed and conclusions are drawn about the importance of host-range testing within the framework of future biological control projects