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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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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Fig3: 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).

Mentions: This study indicates that lower temperature limits may play a role in constraining the distribution of C. imicola. Modelling attempts often rely on a mean temperature threshold of 12.5ˌC to predict presence or absence of C. imicola[29, 45] as established by Purse et al. [46]. Peters et al. [45] on the other hand, found absence indicated by a mean temperature of 14.4ˌC and presence by a mean of 15.7ˌC. For the two years of weather data we analysed, Clarens had a mean annual temperature of 14.51ˌC, two degrees above the suggested thermal intercept suggested by Purse, but very close to that of Peters and colleagues. Furthermore, the suggested mean minimum temperature thresholds of Peters et al. (Absence: 9.4ˌC; Presence: 10.0ˌC) coincide strongly with the mean minimum temperatures of our study sites (Clarens: 8.67ˌC; Onderstepoort: 10.74ˌC). However, we propose that mean temperatures are only an indication of potential distribution, and it is extreme minimum temperatures reached that determine population persistence of C. imicola. The lowest temperature recorded for Clarens in 2012 was −8ˌC (Figure 3), with temperatures regularly below 0ˌC and often dropping below the LLT of adult C. imicola in winter. In tandem with a relatively high CTmin, it seems likely that the thermal environment in the areas surrounding Clarens may prevent adult C. imicola from surviving or establishing in any great abundance, concurring with the negative correlation found between C. imicola abundance and low winter temperatures [47]. In addition, it is highly likely that the low winter temperatures of Clarens and similar areas affect larval development and survival because the lower developmental threshold of larvae is ~11.75ˌC (calculated from [10]). Indeed, Baylis et al. [30] suggested that minimum temperatures determine the ability of the C. imicola to successfully overwinter as larvae (for one or two months [47]), as the larvae inhabit the O horizon and are easily affected by ambient temperature in the open habitats they prefer [31]. Furthermore, Legg et al. [48] suggested that median lower developmental thresholds are useful for determining phenology (and thus also distribution potential).Figure 3


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

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

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).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Fig3: 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).
Mentions: This study indicates that lower temperature limits may play a role in constraining the distribution of C. imicola. Modelling attempts often rely on a mean temperature threshold of 12.5ˌC to predict presence or absence of C. imicola[29, 45] as established by Purse et al. [46]. Peters et al. [45] on the other hand, found absence indicated by a mean temperature of 14.4ˌC and presence by a mean of 15.7ˌC. For the two years of weather data we analysed, Clarens had a mean annual temperature of 14.51ˌC, two degrees above the suggested thermal intercept suggested by Purse, but very close to that of Peters and colleagues. Furthermore, the suggested mean minimum temperature thresholds of Peters et al. (Absence: 9.4ˌC; Presence: 10.0ˌC) coincide strongly with the mean minimum temperatures of our study sites (Clarens: 8.67ˌC; Onderstepoort: 10.74ˌC). However, we propose that mean temperatures are only an indication of potential distribution, and it is extreme minimum temperatures reached that determine population persistence of C. imicola. The lowest temperature recorded for Clarens in 2012 was −8ˌC (Figure 3), with temperatures regularly below 0ˌC and often dropping below the LLT of adult C. imicola in winter. In tandem with a relatively high CTmin, it seems likely that the thermal environment in the areas surrounding Clarens may prevent adult C. imicola from surviving or establishing in any great abundance, concurring with the negative correlation found between C. imicola abundance and low winter temperatures [47]. In addition, it is highly likely that the low winter temperatures of Clarens and similar areas affect larval development and survival because the lower developmental threshold of larvae is ~11.75ˌC (calculated from [10]). Indeed, Baylis et al. [30] suggested that minimum temperatures determine the ability of the C. imicola to successfully overwinter as larvae (for one or two months [47]), as the larvae inhabit the O horizon and are easily affected by ambient temperature in the open habitats they prefer [31]. Furthermore, Legg et al. [48] suggested that median lower developmental thresholds are useful for determining phenology (and thus also distribution potential).Figure 3

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