Thermal limits of activity and survival in false codling moth, Thaumatotibia leucotreta (Lepidoptera: Tortricidae) : life-stage and ramping rate effects

Uys, Wilmari (2014-12)

Thesis (MSc)--Stellenbosch University, 2014.

Thesis

ENGLISH ABSTRACT: Knowledge of the factors affecting thermal limits of insects are of central importance to developing control, risk assessments and post-harvest pest management strategies. To better understand these limits, this study investigated life-stage-related variation in acute critical thermal limits to activity and lethal limits in larvae and adults of the false codling moth, Thaumatotibia leucotreta. The effects of variation in rates of cooling and heating on lower and upper critical thermal limits in both life-stages were also examined. I specifically tested the prediction, generated from dynamic ramping assays, that life-stages with a strong positive association between thermal tolerance estimates and ramping rate are predicted to show less pronounced hardening (acute plasticity) effects. T. leucotreta larvae generally survive at more extreme temperatures than adults, while adults can maintain activity over a broader thermal range; mean CTmin larvae vs adults: 10.5 °C vs. 2.3 °C; CTmax: 42.5 °C vs 42.4 °C (at 0.06 °C/min rates of temperature change); mean survival probability for 50 % of the population for 2 h exposure; LLT50 larvae vs adults: -12.0 °C vs -8 °C; ULT50 larvae vs adults: 49.2 °C vs 41.2 °C. In addition, larvae show a more pronounced negative effect of cooling rate on critical thermal minima (CTmin) and a stronger positive effect of heating rate on critical thermal maxima (CTmax) than adults, suggesting that adults are likely to be more thermally plastic. An independent test of this prediction supports the idea that T. leucotreta adults have a pronounced heat-hardening response, which likely facilitates their elevated CTmax under slower heating rates in dynamic assays. By contrast, larvae have less pronounced heat hardening responses (although higher basal tolerance), supporting the limited plasticity inferred from ramping rate variation in CTmax trials. Life-stage-related variation in thermal limits also varied depending on the choice of cooling/heating rate (some differences at one rate disappeared and vice versa). Life-stage-related variation in basal and plastic thermal tolerance further suggests there is a trade-off between these, even within a species. This suggests that hardening effects, and their variation among life-stages, could play a role in predicting the impact of heating rate variation under natural conditions. The results of this study are significant to understanding this species’ physiology and how field temperature variation may impact population dynamics.

AFRIKAANSE OPSOMMING: Kennis van die faktore wat termiese grense van insekte affekteer is van groot belang vir die ontwikkeling van beheer, risiko-evaluerings en na-oes plaagbestuur strategieë. Om hierdie grense beter te verstaan ondersoek hierdie studie lewensfase- verwante variasie in akute kritieke termiese perke aan aktiwiteit en dodelike perke in larwes en volwassenes van die valskodlingmot, Thaumatotibia leucotreta. Die gevolge van die variasie in die tempo van verkoeling en verwarming op die onderste en boonste kritieke termiese perke in beide lewens-fases is ook ondersoek. Ek het spesifiek die voorspelling, wat uit dinamiese aanloop toetse getoets was, dat die lewens-fase wat 'n sterk positiewe verband tussen hitte verdraagsaamheid gemiddelde en aanloop koers toon, ‘n minder uitgesproke verharding (akute plastisiteit) effek sal wys. T. leucotreta larwes oorleef beter by uiterste temperature as volwassenes, terwyl volwassenes aktief bly oor 'n breër verskeidenheid van temperature; gemiddelde CTmin larwes vs volwassenes: 10.5 ° C vs 2,3 °C; CTmax: 42.5 ° C vs 42.4 °C: (0,06 °C/min tempo van temperatuur verandering); gemiddelde (± 95 % fiducial perke) waarskynlikheid van oorlewing vir 50 % van die populasie na 2 uur blootstelling; LLT50 larwes vs volwassenes: -12,0 °C (-12,8 °C tot -11,4 °C) vs - 8 °C (-8,6 °C tot -7,2 °C); ULT50 larwes vs volwassenes: 49.2 °C (48,5 °C - 50,0 °C) vs 41.2 °C (40,5 °C - 41,9 °C). Daarbenewens toon larwes 'n meer uitgesproke negatiewe effek van verkoelings koers op kritieke termiese minima (CTmin) en 'n sterker positiewe effek van verhitting koers op kritieke termiese maksima (CTmax) as volwassenes, wat daarop dui dat volwassenes waarskynlik meer termies plastiek behoort te wees. 'N onafhanklike toets van hierdie voorspelling ondersteun die idee dat T. leucotreta volwassenes 'n uitgesproke hitte-verharding reaksie toon, wat waarskynlik hul verhoogde CTmax tydens die stadiger verwarmings tempo fasiliteer, soos gesien in die dinamiese toetse. In teenstelling hiermee toon larwes minder uitgesproke hitte-verharding reaksies (hoewel hoër basale verdraagsaamheid) ten ondersteuning van die beperkte plastisiteit afgelei uit oprit koers variasie in CTmax proewe. Lewens-fase-verwante variasie in die warm perke het ook gewissel afhangende van die keuse van die verkoelings/verwarmings tempo ('n paar verskille by een tempo verdwyn en omgekeerd). Lewens-fase-verwante variasie in die basale en plastiese termiese verdraagsaamheid dui verder aan dat daar 'n tradwisselwerkingtussen hierdie verdraagsaamhede is, selfs binne 'n spesie. Dit dui daarop dat die verhardings gevolge, en hulle variasie tussen lewens-fases, 'n rol kan speel in die voorspelling van die uitwerking van verhittings tempo variasie onder natuurlike toestande. Die resultate van hierdie studie dra by tot die huidige kennis van hierdie spesie se fisiologie en hoe natuurlike temperatuur variasie 'n invloed op bevolkingsdinamika kan hê.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/95769
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