Environmental physiology of Eldana saccharina (Lepidoptera:Pyralidae) in South Africa : implications for pest management

[摘要] ENGLISH ABSTRACT: Eldana saccharina Walker (Lepidoptera: Pyralidae) is a stem borer and food crop pest of economicimportance. Temperature and moisture availability possibly influence E. saccharina distributionand abundance, however, the thermal biology and desiccation physiology of E. saccharina are notfully understood. Furthermore, physiological adaptation probably facilitates the invasion success ofE. saccharina into novel environments and this too remains unstudied. Here, the thermal- anddesiccation-trait variation of E. saccharina were studied and population responses were modelled.The results of this work provided insights into novel physiological outcomes of E. saccharina thatis coupled with its environmental climatic stress resistance, overwintering ability and populationfitness in general. In determining thermal limits to activity and survival of E. saccharina resultsshowed that chill coma onset temperature (CTmin) and critical maximum temperature (CTmax) of E.saccharina moths collected from sugarcane (Saccharum spp. hybrids) were significantly lower thanthose from Cyperus papyrus L. (CTmin = 2.8 ± 0.4 vs. 3.9 ± 0.4 °C; CTmax = 44.6 ± 0.1 vs. 44.9 ± 0.2°C, P < 0.0001 in both cases). These results holds important implications for habitat management(or 'push-pull') strategies in the sense that host plant may strongly mediate lower critical thermallimits. Results for pronounced variation in adult CTmin (± 4 °C) across the geographic range of E.saccharina in South Africa was found and it was significantly positively correlated with theclimatic mean minimum temperature. Slower developmental time in the most low-temperaturetolerant population suggests lower CTmin adaptation has come at a cost to fitness, but allows greatersurvival and activity in that environment. There are a significant reduction of phenotypic plasticityin the laboratory population and a strong genetic component to CTmin trait variation. Physiologicalacclimation within a single generation, during immature life stages, resulted in altered adult waterbalance physiology to enhance fitness. Results from a biophysical population model showed thatover-wintering life stage and climate significantly affected the number of E. saccharinagenerations, predicted stress, relative moth fitness and relative adult abundance. Larval overwinteringled to less generations and more frequent cold- and heat stress at a cold field sitecompared to a warm one. This in turn reflected on the relative adult fitness and –abundance. Larvalpresence predictions overlapped well with positive scout records averaged across a matrix ofsugarcane ages and cultivars. The results from this work are important on which to base integratedpest management strategies and are applicable to a large audience across agricultural landscapesand in the sugarcane industry of South Africa.

[发布机构] Stellenbosch University