Biological Control of Insect Pests: Southeast Asian Prospects - EcoPort

4.12 Nezara viridula 219
Africa and two from northern Australia (Darwin and Kununurra). Although
a slightly higher level of parasitisation has resulted, the problem has not been
resolved (J. Turner, pers. comm. 1984; Clarke 1992a). It is notable that
N. viridula is seldom a pest except in regions where soybean is a major crop.
Turner (1983) showed that the rate of movement of T. basalis on soybean
Glycine max was a third of that on cowpea Vigna unguiculata, mungbean
V. radiata radiata, bean Phaseolus vulgaris, or sunflower Helianthus
annuus. The proportion of N. viridula eggs parasitised on soybean was down
to 25% of that on cowpea, mungbean and sunflower. Observations, since
contested by Kelly (1987), suggested that the arrangement and height of the
soybean leaf hairs, which are neither evenly spaced nor patterned, were
responsible for interfering with the waspsÕ searching activities and this
suggestion needs further investigation. Many soybean varieties have beeen
selected for cicadellid resistance, which is directly correlated with the
density, length and orientation of the leaf hairs (Broersma et al. 1972).
Sesame Sesamum indicum leaves were repellent to the wasps, and those that
did alight left immediately and engaged in vigorous grooming elsewhere
(Turner 1983). Thus the nature of crops in an area can materially affect the
success of biological control of the green vegetable bug.
In spite of the foregoing, a claim has been made (Clarke 1990, 1992a,b,
1993a,b, Clarke and Walter 1992), that, in Australia, Ôthere is little evidence
to support claims of successful biological control of N. viridulaÕ (Clarke
1993b). It is a mystery how such a view can be maintained in the light of the
abundant evidence, available to its authors, from Western Australia, South
Australia and coastal and southern New South Wales (Wilson 1960; Callan
1963; Ratcliffe 1965; Strickland 1979; Michael 1981; Field 1984;
Waterhouse and Norris 1987). Furthermore, until the 1970s, when
increasing plantings of soybean, in particular, have provided highly suitable
conditions for N. viridula populations to increase greatly in southern
Queensland and northern New South Wales, there were even publications by
entomologists in the Queensland Department of Primary Industries that,
with the exception of the Darling Downs, Ôcontrol of the pest has become
virtually unnecessary resulting from the introduction and establishment of a
tiny parasite É Õ (Passlow and Waite 1971) and Trissolcus basalis Ôhas
reduced the importance of Nezara viridula (L.) in coastal QueenslandÕ
(Smith 1977). The highly effective control progressively achieved over a
vast area of southern and Western Australia is in no way diminished in
validity by the fact that N. viridula is, indeed, an important pest in a much
smaller area extending from southeast Queensland, through central NSW to
northern Victoria (Clarke 1992a). Although it is most commonly associated
there with soybean (see later under Italy) it is also found on a range of other
crops, including grain legumes, tomatoes and beans.