Australian fruitspotting bugs, Amblypelta nitida Stål and A. lutescens lutescens Distant (Hemiptera: Coreidae), are major economic pests of macadamia nuts in Australia. They are also pests of approximately a dozen other tropical and subtropical horticultural crops, and minor pests of many more. They are endemic to the east and northern coastal regions of Australia and as such are distributed across the entire growing region of Australia’s macadamia industry. Although the industry is reliant on synthetic pesticides for several major pests and diseases, including fruitspotting bugs, biological control of a major pest, the macadamia nutborer, Cryptophlebia ombrodelta Lower (Lepidoptera: Tortricidae), has been successful and is widely adopted. This success has set a precedent within the macadamia industry and provided incentive for research and development of other biological control agents for other important pests. In the early 1990s, a hymenopteran egg parasitoid, Anastatus sp. (Eupelmidae), was identified as having potential as a biological control agent for fruitspotting bugs in Australia, and in 2010, mass rearing began. No formal studies on Anastatus sp., apart from initial releases conducted after its discovery, had been done prior to this thesis.
A study on the potential for conservation biological control of fruitspotting bugs in macadamia orchards using habitat management was conducted over two years in northern New South Wales. Traditionally, trees in macadamia orchards are spaced such that the orchard canopy closes over when the trees reach maturity, shading out any existing ground-cover vegetation. In recent years, macadamia growers have been encouraged to adopt wider spacing and/or pruning techniques to increase light into their orchards for improved tree health and nut production. In this situation, common practice is to grow the shade-tolerant sweet smother grass in the mid-row; this provides ground-cover but does not increase floral diversity. In this study, open mid-row canopies, with resident, weedy, flowering mid-row ground-cover vegetation, were compared to closed mid-row canopies with no ground-cover vegetation in terms of a) pest and beneficial invertebrate abundance, b) predation levels of sentinel A. nitida eggs and c) levels of nut damage by A. nitida. The results showed a stark contrast between ‘light’ and ‘dark’ orchards; open canopy orchards (‘light’ orchards) harboured a significantly higher abundance of beneficial invertebrates than denser canopy orchards (‘dark’ orchards), whereas in ‘dark’ orchards the abundance of a major pest, the macadamia lace bug, Ulonemia concava Drake (Hemiptera: Tingidae), was significantly higher. Not a single fruitspotting bug was sampled during this experiment; however, damage levels to nuts were significantly lower in ‘light’ orchards compared to ‘dark’ orchards. Levels of predation on sentinel A. nitida eggs were variable and did not show any clear pattern that could be attributed to orchard management type.
Macadamia growers need information on when to implement control strategies to most effectively target fruitspotting bug populations throughout the macadamia season. The effect of temperature on the development and survival of A. nitida and A. l. lutescens at six constant rearing temperatures (10-35°C) was investigated. A. nitida and A. l. lutescens completed development from egg to adult at only 20, 25 and 30°C, with respective mean development times of 86.7, 63.5 and 29.4 days for A. nitida and 92.5, 64.7 and 30.8 days for A. l. lutescens. Lower developmental threshold temperatures and estimated number of degree-days for egg development above this threshold were 11.3°C and 420.2 degree-days for A. nitida and 14.1°C and 403.2 degree-days for A. l. lutescens. Similarly, no previous studies have investigated the biology of Anastatus sp. when developing in A. nitida eggs; understanding the effects of temperature on the development and mortality of Anastatus sp. is fundamental for mass rearing and release programs for control of Amblypelta spp. The effect of temperature on the development and survival of Anastatus sp. reared in A. nitida eggs at six constant temperatures (17.5-30°C) was investigated. Anastatus sp. was able to complete development at all six study temperatures with development times decreasing from 53.6 to 16.2 days at 17.5 through to 30°C. The lower developmental threshold temperature for Anastatus sp. was 15.0°C and the number of degree-days for pre-imaginal development above this threshold was estimated as 233.7.
In two field release experiments, the dispersal ability and level of parasitism by Anastatus sp. to sentinel eggs, with or without the presence of adult A. l. lutescens, was investigated. In both trials, parasitism of sentinel eggs was found in trees furthest from the release points; in a central row release trial this was 60m from the nearest release point. In a central point release trial, parasitism levels decreased with increasing distance from the release point; 10 m from the release point was the only distance at which sentinel eggs with a presence of adult A. l. lutescens were more attractive to Anastatus sp. than sentinel eggs without adult A. l. lutescens. The prospect of adopting habitat management to improve biological control of fruitspotting bug in macadamia orchards and the possibility of integrating this approach with strategic releases of Anastatus sp. is discussed.