1. Cryptolaemus montrouzieri Mulsant (Coleoptera: Coccinellidae) is a native Australian ladybeetle that is produced commercially as a biocontrol agent. The beetle is released against soft scale insects and mealybugs on a variety of agricultural and horticultural plants, and is commonly accepted to be an effective generalist predator. This thesis explored the relationship between C. montrouzieri and its potential prey and host plants. These ecological and behavioural investigations provided a foundation from which to explore and expand upon current ecological theory surrounding diet breadth and the expectations of generalist predators.
2. A revision of C. montrouzieri literature revealed that records of field releases of this beetle in the primary scientific literature (equivalent to that screened by Web of Science) are rare (n = 13). Most of the releases documented here were considered successful (11/13), but in eight of eleven cases C. montrouzieri was released along with a parasitoid biocontrol agent. Interpretation of the contribution of C. montrouzieri is further confounded by a lack of quantification to support these claims of success (only 6/11 publications present data directly related to C. montrouzieri releases). This confounding experimental design and lack of data make it difficult to assess the biocontrol capacity of C. montrouzieri in the field.
3. A series of three C. montrouzieri field releases was designed to study the post release behaviour of the beetles and measure the impact of their feeding on pest mealybug (Planococcus citri (Risso)) numbers. The series compared the efficacy of C. montrouzieri released at three different life stages (egg, first instar larvae, adult), and under two different release strategies (caged or not caged with its prey). Adult beetles do not remain at the point of release (even in the presence of ample prey), larval C. montrouzieri have the most significant impact on pest mealybug numbers and beetles released at the egg or larval life stage can effectively control pest mealybugs. This efficacy of control is directly related to the reduced motility of these immature life stages.
4. Field release results were contrasted with monitoring data from 13 orchards sampled over two separate growing seasons. The monitored orchards were at coastal and inland locations of south east Queensland and all practiced integrated pest management through the augmentative release of C. montrouzieri. Planococcus citri pest numbers were substantially higher in coastal areas, but C. montrouzieri numbers remained relatively low across all sites. This monitoring further supported the assertion that adult beetles do not remain in orchards after their release, even in the presence of abundant prey.
5. Laboratory experiments confirmed C. montrouzieri feeding readily on a range of species in confined experimental settings. Cryptolaemus montrouzieri fed more readily on its native Pseudococcus prey than on the orchard pest Pl. citri. Adult beetles were resilient to starvation (over seven days), and fed readily on mealybugs in Petri dishes upon release. This has significance for the current transportation techniques of the beetles to their field deployment sites.
6. The natural associations of C. montrouzieri were characterised within the native range of the beetle in Queensland (the coccinellid species is indigenous to eastern Australia). Cryptolaemus montrouzieri and their potential prey were counted across seven plant taxa (Araucaria cunninghamii, n= 1722; Ar. bidiwlli, n= 332; Ar. heterophylla, n = 285; Ar. columnaris n = 112; Opuntia tomentosa, n = 653; Citrus spp., n = 2076; Annona atemoya, n = 212) over three years. Cryptolaemus montrouzieri showed a clear association with the native Australian hoop pine, Ar. cunninghamii, and the mealybugs on this tree (which are also native to Australia). This association was maintained across seasons and even in the apparent absence of prey. These results have significant implications for how we understand the behaviour of putatively generalist predators.
7. The interactions between adult C. montrouzieri and the range of plant and prey taxa identified during the field surveillance were tested in the laboratory using olfactometers. The patterns observed in the field were not observed in this setting. Citrus sinesis fruit (without Pl. citri prey) were actively avoided (n = 36, p < 0.05). No other specific responses to any one prey or host plant combination were apparent, despite other predatory coccinellids having been shown to respond to the host plant volatiles of their prey. Further investigation is necessary to identify the underlying cues and behavioural responses that determine the observed host/prey associations.
8. This investigation of the ecology and behaviour of C. montrouzieri indicated that the beetle did not fulfil the expectations of the term generalist with which it is almost invariably labelled. Predatory biocontrol agent literature was reviewed with a focus on the utility of the concept of generalist and current theories of diet breadth. A review of the broader entomological literature over the past 10 years shows most authors (52%, n = 157) use the term generalist (or polyphagous) without clarifying what the term means in their focal ecological setting. In those publications in which the term is defined the meaning varies widely, and no single definition can be generalised across ecological settings. This lack of clarity around the term generalist is mirrored in our current understanding of generalist theory.
9. In summary, biological control requires a theoretical framework, and the techniques, to exploit predatory insects that are reputedly generalist more effectively. The experimental data outlined in this thesis were combined with published studies on other generalist organisms to highlight the inadequacies of the concept of generalist and justify reanalysis of the underlying ecological theory. An alternative approach, based upon investigation of the prey and host plant associations of generalist predators within their native range, suggests that they exhibit predictable associations with a subset of organisms. This understanding will enable us to manipulate these predators for biological control more effectively.