The impacts of plant species on the fitness of the tomato potato psyllid (Bactericera cockerelli) and the efficacy of its non-chemical management strategies

Important vegetables such as tomato and potato, among others are affected by Bactericera cockerelli (the tomato potato psyllid; TPP). TPP causes psyllid yellows on these plants. However, in the recent years, it was discovered to be a transmitter of the bacterium Candidatus liberibacter, which causes symptoms similar to psyllid yellows to be more pronounced. This causes zebra chip in potatoes, making them undesirable to consume. As a result, farmers are managing the insect with agro-chemicals. This has since disrupted the bio-control strategies for other pests in glasshouse in New Zealand. This study focused on learning more about the insect ecology and research non-chemical approaches to manage the pest. Several host plants of TPP are present in New Zealand, but the impact of these hosts on the ecological fitness (ability of the insect to adop to its environment) of the insect is limited. It was evaluated if TPP progeny development and survival were affected when their mothers transferred from non-crop to crop host species. TPP was reared on boxthorn (Lycium ferocissimum) and poroporo (Solanum aviculare) which are non-crop host species and potato (Solanum tuberosum) and tomato (Lycopersicon esculentum) which are crop host species. Adults were transferred from each non-crop to each crop host species and allowed to oviposit. Each life stage of the progenies was evaluated for survival (%) and development (time in days). Nymph eclosion was faster on tomato when their mothers were transferred from poroporo or boxthorn compared to if they were from tomato. Total development was faster for ‘poroporo to tomato’ than ‘tomato to tomato’. Total survival and development were also higher for ‘poroporo to tomato’ than ‘tomato to tomato’. In the third chapter, the coccinellid Cleobora mellyi, the parasitoid Tamarixia triozae, the mite Amblydromalus limonicus and the mirid bug Engytatus nicotianae, also ‘C. mellyi + buckwheat’ and ‘T. triozae buckwheat’ was eveluated in greenhouse conditions for the management of the pest. These have already proven to be useful in laboratory studies. A. limonicus significantly reduced TPP eggs. T. triozae reduced nymph numbers by almost a half, but this was not significant. Similarly, T. triozae, A. limonicus, C. mellyi and C. mellyi + buckwheat reduced TPP adults numbers by more than a half and T. triozae more than two thirds, but neither reduction was significant. The final research chapter determined in laboratory conditions how aphids colonise potato plants below mesh crop covers of different sizes which are currently used to exclude TPP from potatoes crops successfully. These mesh were touching or not touching potato leaflet. Aphid nymphs were able to breach all the mesh covers commercially available for field use. Aphids circumventing the mesh were not significantly affected whether the leaflet was touching the mesh or not. No adult was found feeding through the mesh. In conclusion, results obtained in this study showed that host transfer from poroporo to tomato of TPP adults had an impact on the development and survival of its progeny. Some BCAs reduced TPP numbers. However, the pest population was too high for the BCAs to reduce the numbers to a level that would not warrant the use of agro-chemicals. Mesh covers can be used to manage TPP but using a natural enemy to manage aphids below the mesh would aid in successful control. Smaller mesh sizes may obviate this, but the medium term economics of that action needs to be evaluated.