A study of the relationship of potato tuber moth, Phthorimaea operculella (Zeller), to its habitat : A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in the University of Canterbury

During the latter part of the 1973-74 growing season, levels of damage to potato crops caused by potato tuber moth, Phthorimaea operculella (Zeller), were monitored by regular sampling. This revealed a significantly lower level of damage among tubers grown in sandy loam rather than silt loam. Similarly there was a higher proportion of infested seed grade tubers than larger table grade. As the haulms died off there was an increase in infestation among green tubers; this was the result of larvae moving from the haulms seeking alternative food sources. The 1974-75 season involved a more comprehensive study of tuber moth population growth and behaviour. This entailed the sampling of tubers and haulms for larvae and the use of suction traps; these were able to segregate the catch into specific time intervals and continuous recordings were made of weather conditions. This made it possible to study the relationship between abiotic factors and flight behaviour. Flight activity was found to reach its peak at dusk, and nightly catches were proportional to the total number of hours that occurred above 14°C. Fourteen degrees Celsius was found to be the field threshold temperature of flight. Although windspeed inhibited flight, the moths were found to fly in considerable breezes (up to 6 msec ⁻¹) and rarely left the boundary layer. At no time was there any detectable difference in the aerial density of tuber moths over the Ilam Hardy and Rua crops which are purported to be susceptible and resistant respectively. Six weeks after harvest the level of infestation among cull tubers had risen by 88%. This clearly shows the significance of discarded tubers as overwintering sites and the importance of a clean harvest. Laboratory work revealed there was no difference between infestation levels of Pentland Dell, (resistant), and Ilam Hardy tubers (susceptible), when subjected to identical infestation pressures. However it was shown that the three volatile components extracted from fresh potato leaves by steam distillation were capable of eliciting an excited response from adult moths, It is suggested that this highly volatile fraction ,could play an important. role in tuber moths' ability to detect crops. Field trials with a variety of compounds showed pyridine to be attractive to males and 3-ethyl pyradine attractive to females.