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. 2014 Aug 20:7:384.
doi: 10.1186/1756-3305-7-384.

Thermal limits of two biting midges, Culicoides imicola Kieffer and C. bolitinos Meiswinkel (Diptera: Ceratopogonidae)

F Arné Verhoef  1 , Gert J Venter, Christopher W Weldon
Affiliations

Thermal limits of two biting midges, Culicoides imicola Kieffer and C. bolitinos Meiswinkel (Diptera: Ceratopogonidae)

F Arné Verhoef et al. Parasit Vectors. .

Abstract

Background: Culicoides imicola Kieffer and Culicoides bolitinos Meiswinkel (Diptera: Ceratopogonidae) are both of veterinary importance, being vectors of Schmallenberg, bluetongue and African horse sickness (AHS) viruses. Within South Africa, these Culicoides species show a marked difference in their abundances according to altitude, with C. imicola highly abundant in lower altitudes, but being replaced as the dominant species by C. bolitinos in cooler, high-altitude regions.

Methods: The thermal physiology of field collected adults of each species was determined to evaluate whether it could account for differences in their distribution and abundance. Critical thermal maxima (CTmax) and minima (CTmin), as well as upper and lower lethal temperatures (ULT and LLT) were assessed after acclimation temperatures of 19'C, 24'C and 29'C. Critical thermal limits were determined using an ecologically relevant rate of temperature change of 0.06'C x min(-1).

Results: Significant differences in CTmin and CTmax were found between acclimation temperatures for C. imicola and C. bolitinos. In C. bolitinos, the LLT of individuals acclimated at 24'C was significantly improved (LLT50 = -6.01'C) compared with those acclimated at the other temperatures (LLT50 = -4'C). Acclimation had a weak (difference in LLT50 of only 1'C) but significant effect on the LLT of C. imicola. When CTmin, CTmax, LLT and ULT were superimposed on daily maximum and minimum temperature records from locations where each tested Culicoides species is dominant, it was found that temperatures frequently declined below the CTmin and LLT of C. imicola at the location where C. bolitinos was dominant.

Conclusions: The distribution and abundance of C. imicola is likely directly constrained by their relatively poor tolerance of lower temperatures. Results for C. bolitinos suggest that the adult phase is hardy, and it is hypothesised that the thermal biology of other life stages could determine their range.

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Figures

Figure 1
Figure 1
Effect of acclimation on critical thermal maximum for (A) C. imicola and (B) C. bolitinos , and critical thermal minimum of (C) C. imicola and (D) C. bolitinos . In each case, the mean ± 1 S.E. is shown (n = 14). Means labelled with the same lowercase letter are not significantly different from each other at the 0.05 level (Fisher’s LSD).
Figure 2
Figure 2
Effect of test and acclimation temperature on survival of cohorts of C. imicola and C. bolitinos . Survival was assessed 6 hours after each cohort was exposed to the test temperature for 2 hours. (A) Survival at high temperatures by C. imicola; (B) survival at high temperatures by C. bolitinos; (C) survival at low temperatures by C. imicola; (D) survival at low temperatures by C. bolitinos. In each case, the mean ± 1 S.E. are shown (n = 5) for each test and acclimation temperature combination.
Figure 3
Figure 3
Daily temperature range for Onderstepoort and Clarens from the end of winter 2011, to end of winter 2013 (1 August 2011 – 31 July 2013). Horizontal lines represent thermal limits of C. imicola and C. bolitinos: ULT50 and CTmax of C. bolitinos and ULT50 of C. imicola (red); ULT50 of C. imicola (orange); CTmin of C. imicola (purple); LLT50 of C. imicola (magenta); CTmin of C. bolitinos (blue); LLT50 of C. bolitinos (light blue).
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