Evaluation of food grade products for attractancy to potato tomato psyllid adults infected with or without Candidatus Liberibacter solanacearum : A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Agricultural Science at Lincoln University

Abstract

Tomato potato psyllid (Bactericera cockerelli (Šulc) (Hemiptera: Triozidae)) (TPP) is an insect, introduced to New Zealand in 2006, which causes significant damage to potato crops on the Canterbury plains of New Zealand. In this study three key aspects of integrated pest management, namely: trapping, biological control and identification of food grade attractants for utilization in a lure, were investigated. In addition, DNA integrity of TPP extracted off yellow sticky cards placed in vivo in potato paddocks was examined. A novel study of 75 food grade products were evaluated for attractancy to TPP adults. Choice testing using a Y-tube olfactometer found that a total of 16 products had attraction at ≥50% for “cold” TPP (i.e. insects with no infection of Candidatus Liberibacter solanacearum (CaLso)). Those attractants included: fatty acids (palm oil + lecithin granules; and macadamia nut oil + lecithin granules); glycerin flakes + lecithin granules; polysaccharides (xanthan gum, micro agar and iota carrageenan, primellose, fermented gelatin type B); disaccharide (trehalose) monosaccharide (xylose); amino acids (glutamine, methionine and valine) an alcohol (96% ethanol) and an acid (phosphoric acid). All of these products were subsequently evaluated for attractancy to “hot” TPP adults (i.e. insects confirmed positive by polymerase chain reaction (PCR) to CaLso). All the amino acids were marginally more attractive to “hot” TPP adults than “cold” ones: methionine (70% vs. 55% respectively), valine (65% vs 60%) and glutamine (55% vs. 50%). Similarly, primellose was also more attractive (60% vs 50% respectively). Xanthan gum, micro agar, trehalose and glycerin flakes + lecithin remained attractive (at 50%), whereas 96% ethanol (45%), iota carrageenan (40%), macadamia nut oil + lecithin granules (40%), phosphoric acid (35%), and palm oil + lecithin granules (25%) were all significantly less attractive than to cold TPP (P<0.01). Two insect traps were compared throughout the 2022/2023 season, the commonly used yellow sticky card and a novel 3-D printed yellow cup-trap, which was also designed to enable housing of an attractant lure. At low population numbers of TPP seen on the Canterbury plains (mostly only 1 or 0 per trap during 2022/23 potato growing season), both trap types were only partially successful in catching TPP. The highest number of TPP caught in late February/early March 2023 was 8 on a sticky card and 3 in a cup-trap. Inclusion of valine, trehalose and palm oil alone or in combination with each other in late summer did not improve efficiency of the cup-traps. To determine DNA integrity of TPP, an in vitro study of insects harvested from colonies raised in an acrylic sheet-covered greenhouse found that DNA of a single insect, captured off potato plant into a plastic vial, regardless of age, could be successfully amplified using PCR. In vivo studies found that at least 3 young, light-coloured, TPP adults must be combined in a pooled sample to successfully amplify their DNA. Pooled samples of 5 young TPP adults were placed on yellow sticky cards in vivo in a paddock in autumn. DNA of each pooled sample was then analysed using PCR on days 1 to 7, 10 and 14 in the field. DNA integrity was maintained up to 6 days under field conditions. This research successfully identified 13 potential products which show potential for use as an attractant lure, although performance in the field against low density populations was not strong. Field use of cone-shaped traps was the first in New Zealand, allowing the inclusion of a lure. In addition, TPP DNA extracted off yellow sticky cards over 1-14 days in the field, found reducing ability to detect TPP over time using PCR, leading to the recommendation that extraction was best done within 7 days, ideally 5 or more TPP as a pooled sample should be used for PCR extractions.