Shovon Chandra Sarkar

The tomato potato psyllid, Šulc (Hemiptera: Triozidae) is a significant insect pest of Solanaceae. In early 2017, it was first detected in Perth, Western Australia. From the two years of field sampling, the predators collected represented a broad taxonomic range. The most abundant predator was green lacewing. Therefore, this study investigates the potential of the Australian native and commercially available green lacewing, Mallada signatus Schneider (Neuroptera: Chrysopidae), as a biological control agent for B. cockerelli. The effect of feeding on B. cockerelli on the development rate and survival, of M. signatus were evaluated. Further, a greenhouse cage study was conducted to determine the optimal density of M. signatus larvae needed to effectively control an established B. cockerelli population. The third instar larvae of M. signatus consumed over 75 B. cockerelli nymphs in 24 hours. Following the introduction of M. signatus larvae to caged tomato plants, eight M. signatus larvae per caged tomato plant decreased B. cockerelli population by 64 % at the end of the sampling. These results indicated M. signatus, particularly at the larval stage, are an effective biological control option for B. cockerelli, especially in greenhouse tomato cultivation. This research provides valuable insights for Australia's horticultural industry, offering an eco-friendly alternative to chemical pesticides.

The rise in insecticide resistance in various pest species, the risk of chemical residues, and the potential impact of insecticides on non-target species have led to the exploration of alternative methods of management. Biological control, which involves the use of natural enemies to help manage pest populations, has been the focus of considerable research efforts. However, in the case of a newly invasive pest in an ecosystem, there is the specific question of whether any of the resident natural enemy species in the region are capable of effectively utilising the new pest as a food source. In this context, generalist predators are likely to be promising options because their ability to adapt to a wide range of prey species. An invasive pest, tomato potato psyllid, Bactericera cockerelli (Hemiptera: Triozidae) was first detected on mainland Australia near Perth. It can cause significant losses to solanaceous crops via direct feeding and by transmitting the bacterium Candidatus Liberibacter solanacearum that causes zebra chip disease in potatoes, although this pathogen has not yet been detected in mainland Australia. Considering B. cockerelli’s demonstrated ability to develop resistance to insecticides, utilizing resident predatory natural enemies as biological control agents could make a valuable contribution to managing B. cockerelli. The species of B. cockerelli predators occurring in fields of Solanaceae in Western Australia were identified and the biocontrol potential of the two most abundant ladybirds, both generalist predators, were evaluated in laboratory and glasshouse experiments. Sampling was conducted in fields of different solanaceous crops to identify the species of generalist predators that occurred in the environment of south-western WA. The most abundant generalist predator was green lacewing (Neuroptera) followed by ladybirds (Coleoptera). To screen the field collected predators for those which had been feeding on the B. cockerelli, PCR primer pairs were developed. Individuals from 7 insect taxa were analysed for the presence of DNA of B. cockerelli. Coleopteran predators were most frequently detected with B. cockerelli DNA. Hippodamia variegata (Coleoptera: Coccinellidae), an introduced ladybird species, was positive in 70% of cases and an Australian native ladybird, Coccinella transversalis (Coleoptera: Coccinellidae), was positive in 65% of cases. The biocontrol potential of H. variegata and C. transversalis were investigated and compared. Both ladybirds could successfully develop and reproduce when feeding on B. cockerelli. In the greenhouse, the release of ladybird larvae significantly suppressed the development of the B. cockerelli population and positively influenced the plant chlorophyll content and biomass. Moreover, early life experience with B. cockerelli as a prey species significantly increased the preference of both ladybird species for the psyllid. The results of this study have the potential to contribute the implementation of sustainable pest management solutions for the invasive B. cockerelli. They also demonstrate the value of examining generalist predators as possible biocontrol agents for newly invasive species and point to the possibility of improving the impact of augmentative release strategies through early life exposure of generalist predatory insects to target pests. This may be particularly useful in cases of invasive pest species.