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

Verhoef FA, Venter GJ, Weldon CW - Parasit Vectors (2014)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Flies of Economic Significance Research Group, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa. arne.verhoef@zoology.up.ac.za.

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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Effect of test and acclimation temperature on survival of cohorts ofC. imicolaandC. 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.
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Fig2: Effect of test and acclimation temperature on survival of cohorts ofC. imicolaandC. 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.

Mentions: The interaction of LLT test temperatures and acclimation temperature had a significant effect on survival of both species (Table 1, Figure 2 A and B). Culicoides bolitinos acclimated to 24ˌC had the lowest LLT50 (−6.01ˌC), whereas those acclimated at 29ˌC had the highest LLT50 (−3.98ˌC). Parameter estimates relative to an acclimation temperature of 29ˌC were inspected and indicated that survival of C. bolitinos was significantly higher (p < 0.001) when acclimated at 24ˌC. LLT of those acclimated at 19ˌC and 29ˌC were not significantly different from each other. There was no significant effect of acclimation on the LLT of C. imicola. The LLT50 between acclimation treatments varied by 1ˌC, with the lowest estimated for 19ˌC (−4.39ˌC).Table 1


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

Verhoef FA, Venter GJ, Weldon CW - Parasit Vectors (2014)

Effect of test and acclimation temperature on survival of cohorts ofC. imicolaandC. 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.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4150952&req=5

Fig2: Effect of test and acclimation temperature on survival of cohorts ofC. imicolaandC. 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.
Mentions: The interaction of LLT test temperatures and acclimation temperature had a significant effect on survival of both species (Table 1, Figure 2 A and B). Culicoides bolitinos acclimated to 24ˌC had the lowest LLT50 (−6.01ˌC), whereas those acclimated at 29ˌC had the highest LLT50 (−3.98ˌC). Parameter estimates relative to an acclimation temperature of 29ˌC were inspected and indicated that survival of C. bolitinos was significantly higher (p < 0.001) when acclimated at 24ˌC. LLT of those acclimated at 19ˌC and 29ˌC were not significantly different from each other. There was no significant effect of acclimation on the LLT of C. imicola. The LLT50 between acclimation treatments varied by 1ˌC, with the lowest estimated for 19ˌC (−4.39ˌC).Table 1

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Flies of Economic Significance Research Group, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa. arne.verhoef@zoology.up.ac.za.

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.

Show MeSH
Related in: MedlinePlus