Biocontrol of invasive tomato/potato psyllid Bactericera cockerelli: Effects of predatory mite, entomopathogenic fungi, diets and ants

Abstract

Global food production increasingly faces the problem of reducing the impact of a few widespread pests and diseases, without causing environmental harm from the overuse of pesticides. Biological control using predators and pathogens to control the pest offers one solution, but identifying suitable biological control agents and strategies to apply them is challenging. One such pest, the tomato/potato psyllid (TPP), Bactericera cockerelli (Šulc) (Hemiptera: Triozidae), is an important, difficult-to-control, agricultural insect pest of solanaceous crops in United States, Mexico, Central America and New Zealand. Although long-term use of chemical pesticides has resulted in insecticidal resistance, no alternative control strategies are available against TPP. The main purpose of this thesis was to develop a more effective control tool for TPP using biological control. I explored the effects of diet and habitat shelter on the performance of a generalist predatory mite Amblydromalus limonicus (Garman & McGregor) (Acari: Phytoseiidae), assessed interactions between TPP, entomopathogenic fungi (EPF), and predatory mites, and evaluated the effect of ants on the life table parameters and predation rates of A. limonicus on TPP. To find an alternative diet for the mass-rearing and preventative release of a predatory mite against TPP, I evaluated factitious and artificial diets on the performance of A. limonicus. Different diets significantly influenced survival rate, developmental time and reproduction of A. limonicus. A. limonicus had a faster developmental time and higher survival rate and fecundity when fed with Typha orientalis pollen than on punctured Ephestia kuehniella eggs and an artificial diet. Dispersed patches of pollen strongly increased the population growth of immature and female A. limonicus compared with aggregated patches when the mites fed on T. orientalis pollen under laboratory conditions. T. orientalis pollen resulted in a higher total number of A. limonicus in 7 days than E. kuehniella eggs. Greenhouse experiments demonstrated that the application of A. limonicus significantly reduced the total number of TPP on bell peppers after seven weeks compared with the control. Moreover, A. limonicus supplemented with T. orientalis pollen significantly maintained a higher number of predatory mites and reduced the mean number of total, eggs, and nymphs TPP on plants over 7weeks.So providing supplementary T. orientalis pollen in a crop system could enhance the control efficiency of A. limonicus on TPP. To identify other suitable candidate organisms that could form the basis of an integrated pest management strategy for the control of TPP in New Zealand, I screened 16 native strains of EPF against TPP adults and nymphs. The most successful fungus was BeauveriabassianaICMP8701, which induced high mortality and short median lethal times (LT50) values in TPP at 1×107mL-1 in 10 days. In the parental generation, the reproduction parameters of TPP adults were significantly reduced by two sublethal concentrations of B. bassiana. Physiological effects from the parental generation infected by B. bassiana (LC30) could be carried over to their offspring, significantly reducing developmental rates, and life table parameters of TPP. The integrated strategy of combining the release of predatory mites and EPF may further promote biocontrol of pests. To examine the compatibility of A. limonicus and B. bassiana, I tested the lethal and sublethal effects of B. bassiana on A. limonicus on TPP. A. limonicus females were susceptible to B. bassiana. Sublethal concentrations of B. bassiana (LC30) significantly reduced reproduction parameters and predation rates of F0 A. limonicus females. However, life table parameters, predation rates and population parameters of F1 A. limonicus were not influenced by sublethal concentrations (LC30). This result suggests that transgenerational effects of B. bassiana cannot be carried over to the F1 generation. Application of B. bassiana suspensions did not affect A. limonicus densities when they were combined in greenhouse conditions. The combined use of A. limonicus with B. bassiana suspensions resulted in significantly decreased TPP populations and greater plant biomass and fruit growth. Therefore A. limonicus and B. bassiana were compatible and could further improve the control of TPP. Predator cues can induce predation stress in prey that negatively influence survival, development, reproduction, and feeding behaviour of the prey. Hemipteran-tending ants such as Technomyrmex albipes can negatively influence the predation behavior of mites. This thesis also evaluated the effects of ant odour on life table parameters and predation rates of A. limonicus when feeding on TPP. Exposure to ant odour did not alter the development, survival rate and fecundity of A. limonicus. Consumption rates of TPP also showed a dimorphic response--predation rates increased in female A. limonicus, but not in males. To my knowledge, this is the first report indicating increased consumption rates by natural enemies exposed to the odour of a mutualist (ant) of the pest (TPP). My findings will fill some knowledge gaps regarding the development of commercially available biological control agents in New Zealand. T. orientalis pollen would be an effective alternative in solving the problem of mass-rearing of predatory mites and provided supplemental foods to maintain their populations in protected crops after release in the greenhouse in New Zealand. Based on the tested result, T. orientalis pollen might be registered as a commercial pollen product for predatory mites. Local strains of B. bassiana ICMP 8701 has the potential to develop as biopesticides against TPP for New Zealand. The simultaneous application of two agents provides a useful foundation for developing an IPM program for the control of TPP in particular and invasive alien pests in general. B. bassiana ICMP 8701 is compatible with A. limonicus. The combined application of two agents could overcome the shortcoming of individual agent and make crop protection more sustainable. The presence of hemipteran-tending ant odour did not influence the life table parameters of A. limonicus, but further improved its control efficiency. This finding may provide new insights into understanding tri-partite interactions involving a pest, its predator and a mutualist of the pest.