Thermal tolerance of Cydia pomonella (Lepidoptera : Tortricidae) under ecologically relevant conditions

Chidawanyika, Frank (2010-12)

Thesis (MSc (Agric) (Conservation Ecology and Entomology))--University of Stellenbosch, 2010.

Thesis

ENGLISH ABSTRACT: Ambient temperature plays a key role in insect-physiology, -population dynamics and ultimately -geographic distribution. Here, I investigate the survival of codling moth, Cydia pomonella (Linnaues) (Lepidoptera: Tortricidae), which is a pest of economic importance in pome fruit production, to a wide range of temperature treatments. In this thesis, I first explore how temperature affects the survival and limits to activity of codling moth and secondly investigate if thermal acclimation can improve field performance of moths used in sterile insect technique control programmes under ecologically relevant conditions. First, I found that absolute temperature as well as the duration of temperature exposure significantly affects adult C. pomonella survival. Lethal temperatures, explored between -20 °C to -5 °C and 32 °C to 47 °C over a range of durations, showed that 50% of the adult C. pomonella population killed at -12 °C and at 44 °C after 2 hrs for each treatment. At high temperatures a pretreatment at 37 °C for 1 hr dramatically improved survival at 43 °C for 2 hrs from 20% to 90% (p<0.0001). Furthermore, high temperature pre-treatments (37 °C for 1 hr) significantly improved low temperature survival at -9 °C for 2 hrs. In sum, my results suggest pronounced plasticity of acute high temperature tolerance in adult C. pomonella, but limited acute low temperature responses. Secondly, low-temperature acclimated laboratory-reared moths were recaptured in significantly higher numbers (d.f. = 2, χ2 = 53.13 p<0.001), by sex pheromone traps, under cooler conditions in the wild relative to warm-acclimated or non-acclimated moths. However, these improvements in low temperature performance in cold-acclimated moths came at a cost to performance under warmer conditions in the wild. This novel study demonstrates the importance of thermal history on C. pomonella survival and clear costs and benefits of thermal acclimation on field and laboratory performance, and thus, the potential utility of thermal pre-treatments for improved efficacy in the sterile insect technique programme for C. pomonella control under cooler, springtime conditions. Finally, on a global scale, this study highlights that low and high temperatures could play a role in CM adult survival through direct mortality and thus, may influence, or have influenced in the pest, population dynamics.

AFRIKAANSE OPSOMMING: Temperatuur speel ‘n belangrike rol in die fisiologie, populasiedinamika en geografiese verspreiding van insekte. In hierdie tesis ondersoek ek die rol van ‘n wye reeks temperature op die oorlewing van kodlingmot Cydia pomonella (Linnaues) (Lepidoptera: Tortricidae), ‘n sagtevrug pes-spesie van ekonomiese belang. Ek ondersoek hoofsaaklik die effek van temperatuur op die fisiologie en fiksheid van kodlingmot, asook die mate waartoe termiese akklimasie (‘n mate van aanpassing) die veldgedrag van die steriele insek beheer-metode (SIT), d.m.v. kodlingot, in relevante omgewingstemperature kan verbeter. Ek het (i) gevind dat die temperatuur en duur van die temperatuur toediening ‘n betekenisvolle toename in volwasse C. pomonella oorlewing tot gevolg het. In die deel van die studie is temperature tussen -20 °C en -5 °C and tussen 32 °C en 47 °C ondersoek oor ‘n reeks van 0.5, 1, 2, 3 en 4 ure van duur. In kort lei -12 °C en 44 °C vir 2 uur onderskeidelik tot die uitsterf van 50% van die volwasse C. pomonella populasie. Indien die motte vooraf gehou is by 37 °C vir ongeveer 1 uur, is oorlewing by 43 °C vir 2 ure betekenisvol verbeter van 20% tot 90% (p<0.0001). Hoër temperatuur vooraf-blootstellings (akklimasie), by 37 °C vir 1 uur, het daartoe gelei dat lae temperatuur lae-temperatuur-oorlewings by -9 °C vir 2 ure betekenisvol verbeter het. Oor die algemeen het die resultate gedui dat hoër akute temperatuurstoleransie in C. pomonella bestaan, maar beperkte akute lae-temperatuur reaksies bestaan. Verder het lae-temperatuur akklimasie (laboratorium geteelde) motte ‘n betekenisvolle hoër getal hervangste deur geslagsferomone in koeler omgewings opgelewer (v.i. = 2, χ2 = 53.13, p<0.001) in vergelyking met warmer-temperatuur geakklimatiseerder motte. Hierdie verbeteringe in laetemperatuur reaksies vanaf lea-temperatuur akklimasie groepe is teen ‘n koste teen warmer reaksie-toestande in die natuur geïs. Hierdie eersdaagse studie demonstreer die belang van historiese temperatuur op die oorlewing van C. pomonella. Die kostes- en voordele van termiese akklimasie op veld- en laboratoriumpopulasie reaksies en die potensiële gebruik daarvan in die verbetering van steriele insek tegniek programme, onder koeler omstandighede, is uitgelig. Laastens, beklemtoon hierdie studie die belangrikheid van temperatuur as bepalende faktor van kodlingmot-oorlewing en die invloed daarvan op die vrugte-pes populasiedinamika.

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