Abstract
Basal and plasticity of thermal tolerance determine abundance, biogeographical patterns and activity of insects over spatial and temporal scales. For coexisting stemborer parasitoids, offering synergistic impact for biological control, mismatches in thermal tolerance may influence their ultimate impact in biocontrol programs under climate variability. Using laboratory-reared congeneric parasitoid species Cotesia sesamiae Cameron and Cotesia flavipes Cameron (Hymenoptera: Braconidae), we examined basal thermal tolerance to understand potential impact of climate variability on their survival and limits to activity. We measured upper- and lower -lethal temperatures (ULTs and LLTs), critical thermal limits [CTLs] (CTmin and CTmax), supercooling points (SCPs), chill-coma recovery time (CCRT) and heat knock-down time (HKDT) of adults. Results showed LLTs ranging -5 to 5°C and -15 to -1°C whilst ULTs ranged 35 to 42°C and 37 to 44°C for C. sesamiae and C. flavipes respectively. Cotesia flavipes had significantly higher heat tolerance (measured as CTmax), as well as cold tolerance (measured as CTmin) relative to C. sesamiae (P<0.0001). While SCPs did not vary significantly (P>0.05), C. flavipes recovered significantly faster following chill-coma and had higher HKDT compared to C. sesamiae. The results suggest marked differential basal thermal tolerance responses between the two congeners, with C. flavipes having an advantage at both temperature extremes. Thus, under predicted climate change, the two species may differ in phenologies and biogeography with consequences on their efficacy as biological control agents. These results may assist in predicting spatio-temporal activity patterns which can be used in integrated pest management programs under climate variability.
Highlights
Abiotic factors such as temperature and relative humidity have direct effects on development, reproduction, abundance, biogeography [1,2] and survival of ectotherms [3], including parasitoids [4]
Initial colonies of C. sesamiae and C. flavipes were obtained from South African Sugarcane Research Institute (SASRI), South Africa and International Centre for Insect Physiology and Ecology (ICIPE), Kenya, respectively
An increase in duration of exposure to lethal low and high temperatures generally resulted in survival decrease for both C. sesamiae and C. flavipes adults (Fig 1A–D)
Summary
Abiotic factors such as temperature and relative humidity have direct effects on development, reproduction, abundance, biogeography [1,2] and survival of ectotherms [3], including parasitoids [4]. Temperature is considered the predominant abiotic factor affecting both herbivorous insects and their antagonistic biological control agents [5,6]. Since most insects have a limited ability to control body temperature, they have developed a range of mechanisms for survival under stressful thermal environments [9]. Failure to employ some compensatory mechanisms to survive these extreme temperatures may offset fitness traits, limited activity and poor performance of life-history traits leading to population decline and seldom species extinction [12]
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