Population phenology, life table and forecasting models of tomato-potato psyllid (Bactericera cockerelli) and the efficiency of a selected natural enemy for its control

The tomato-potato psyllid (TPP), Bactericera cockerelli (Sulc) (Hemiptera: Triozidae) is an economically important crop pest that not only causes damage through its feeding but also transmits the bacterium, “Candidatus Liberibacter solanacearum”, which causes zebra chip disease in potato. TPP is also associated with psyllid yellows disease of potato, tomato and capsicum. Both zebra chip and psyllid yellows cause significant yield losses, plant mortality, decreased quality, and increased control-related costs. This insect invaded New Zealand in early 2006 and has now spread through most of the country. Laboratory and field experiments were conducted to determine the population development, phenology and life history parameters of the tomato-potato psyllid and to investigate aspects of its control, particularly in relation to using developmental parameters for preliminary forecasting models and investigate the efficacy and impact of a selected natural enemy. The temperature-dependent development of TPP was studied in the laboratory at seven constant temperatures (from 8 to 31°C) on potato and tomato. Developmental time in days for all stages on both host species were inversely proportional to temperature between 8 and 27°C but increased at 31°C. The lower developmental thresholds for total development of TPP were 7.1°C and 7.5°C reared on potato and tomato, respectively; and thermal constants of 358 and 368 degree days for TPP reared on potato and tomato, respectively. The optimum temperatures of TPP were estimated as 26.9°C and 27.1°C reared on potato and tomato, respectively. The upper temperature thresholds were estimated as 33.9°C and 34.1°C reared on potato and tomato, respectively. Life table parameters can be used to compare the population growth potential of this insect on different host plants, under different environmental conditions. These parameters can be used to project the population growth and stage differentiation for decision making for control of this species or for designing future studies on population dynamics. Life table parameters of TPP reared on potato were determined in laboratory conditions at 25 ±1оC, 50-60% RH, and at a photoperiod of 16:8 (L: D) h. A life table was constructed based on results obtained under unlimited food supply and a natural enemy free environment. The mean developmental periods for the egg stage, nymphal stage, and total development were 6.08, 16.94, and 23.02 days, respectively. The intrinsic rate of increase, the finite rate of increase, the net reproduction rate, the mean generation time, the life expectancy, the doubling time, and the fecundity of TPP were determined. The implications of these findings are discussed. Orius vicinus (Ribaut) has been reported to predate red spider mite, leafhopper, and thrips and is being investigated as a possible biological control agent for a range of pests in New Zealand. Because B. cockerelli is one of the prey of O. vicinus, it is of scientific interest to determine its potential for biological control of TPP. The functional response of the adult stage of the predatory bug, O. vicinus on egg, nymphal instars 1, 2, 3, 4, and 5 of TPP and its preference for two prey species: TPP (nymphal instars 1 and 2) and western flower thrips, Frankliniella occidentalis (Pergande) (nymphal instars 1 and 2), were determined. The resulting data were well described by both Type I and II functional response models for prey eggs and first and second instar nymphs 1- 2; and Type II for 3rd, 4th and 5th instar nymphs of TPP. While these results do not suggest that O. vicinus could regulate a TPP population under normal circumstances, the research suggests this species may reduce populations below economic threshold under circumstances of inundative release under cover in a glasshouse. The predator may have a greater biocontrol potential if release was timed to attack the eggs and smaller nymphal stages of TPP. The predator had a slight preference for thrips compared to the TPP at high densities of prey combinations, but despite that O. vicinus still responded strongly to TPP. The prediction of the first emergence and peak abundance can help researchers and growers assess insect population development more effectively for the application of chemical or cultural control measures or make other management decisions. Yellow sticky traps were used to determine the population development and phenology of the TPP over 5 site-years with respect to potato crops and in relation to ambient weather conditions. The relationship between field flight data and accumulated degree days was well described by both the Weibull and bimodal models. However, the bimodal model described the distribution of psyllid flight better than Weibull model. The occurrence of the first peak flight for the 5 site-years was between 722 to 749 degree days (DD) (above 7.1°C lower threshold) from a biofix on 1st November and the second peak occurred from 1189 to 1264 DD after the biofix. Although the bimodal model can provide precise predictions (within 6.6 days) for the first peak of adult psyllids in the field, it may not find practical application in potato crops in New Zealand due to low economic density threshold of this invasive insect species. Therefore, I anticipate improving the model by the incorporation of developmental parameters and events of immature stages of the psyllid based on long term data. Results in this thesis have provided essential biological data of TPP, such as the developmental rates and life history parameters. These results, along with an evaluation of the functional response of O. vicinus and its potential for biological control and preliminary forecasting models, augment the limited existing knowledge of the biology of TPP so that further research and current management of this psyllid species can be better targeted