Thesis Defence: Evolution of Critical Photoperiod in Codling Moths Subject to the Sterile Insect Technique

Ian Chambers, supervised by Dr. Rebecca Tyson, will defend their thesis titled “Evolution of Critical Photoperiod in Codling Moths Subject to the Sterile Insect Technique” in partial fulfillment of the requirements for the degree of Master of Science in Mathematics.

An abstract for Ian’s thesis is included below.

Examinations are open to all members of the campus community as well as the general public. Registration is not required for in-person defences.

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ABSTRACT

Codling moth is an invasive species in Canada that damages pomme fruit crops across the globe and has proven difficult to manage through the use of chemical sprays and the sterile insect technique (SIT). In my research I examine how codling moth populations may be evolving under the SIT to avoid management pressures. Photoperiod dictates the onset of diapause in codling moths and the SIT may be causing a change in the timing of diapause across wild populations by selecting for specific critical photoperiods.

Previous modelling of the SIT has failed to address how diapause might be affecting the efficacy of the SIT. Furthermore, no one has examined if the critical photoperiod distribution of a population, and therefore the mean timing of diapause, in wild codling moth populations might change under the selection pressure exerted by the SIT. I hypothesize that the SIT as is being applied in the Okanagan Valley, selects for longer critical photoperiods in wild codling moths, causing them to enter diapause earlier in the year and avoid the higher SIT pressures present in the warmer months of the summer. I developed two mathematical models incorporating the SIT and diapause as a function of critical photoperiod to investigate how the distribution of critical photoperiod within a population may evolve under the SIT. This approach aims to help understand why the SIT has not led to eradication of codling moths as originally predicted, and contribute to future management efforts. I find that the SIT may be selecting for longer critical photoperiods, causing a higher proportion of the population to enter diapause after the first generation.