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. 2019 Aug 25:11:1179543319863417.
doi: 10.1177/1179543319863417. eCollection 2019.

Thermal Biology and Seasonal Population Abundance of Bactrocera dorsalis Hendel (Diptera: Tephritidae): Implications on Pest Management

Rebaone Motswagole  1 , Nonofo Gotcha  1 , Casper Nyamukondiwa  1
Affiliations

Thermal Biology and Seasonal Population Abundance of Bactrocera dorsalis Hendel (Diptera: Tephritidae): Implications on Pest Management

Rebaone Motswagole et al. Int J Insect Sci. .

Abstract

Since the first detection of Bactrocera dorsalis in Botswana in 2010, the establishment, spread, and response to prevailing Botswana microclimates under rapidly changing environments remain unknown. This study investigated the presence, seasonal population abundance, and thermal biology of B. dorsalis in Botswana. We measured B. dorsalis thermal tolerance vis critical thermal limits (CTLs) and lethal temperature assays (LTAs) to understand how temperature largely impacts on fitness and hence invasive potential. Seasonal monitoring results indicated B. dorsalis establishment in the Chobe district (its first area of detection). Trap catches showed continuous adult flies' presence all year round and high average monthly trap catches as compared with other districts. Furthermore, B. dorsalis was detected south of Botswana, including Kgatleng, Kweneng, South-east, and Southern districts. Critical thermal maxima (CTmax) to activity for adults and larvae were 46.16°C and 45.23°C, whereas critical thermal minima (CTmin) to activity for adults and larvae were 9.1°C and 7.3°C, respectively. Moreover, we found an improved CTmin for larvae at a slower ramping rate, indicating potential rapid cold hardening. The lower lethal temperature (LLT) and upper lethal temperature (ULT) assays revealed a reduction in survival at all the developmental stages as severity and duration of both temperature extremes increased. Microclimatic temperatures recorded in Botswana showed that environmental temperatures fall within the thermal breath of B. dorsalis activity measured here, indicating a potential conducive climate niche for the insect pest across the country, albeit other factors, e.g., host availability, play a significant role. These results therefore suggest that Botswana microclimatic temperatures aided B. dorsalis activity and invasion pathway are thus significant in mapping invasions and pest risk analysis, and may also aid in designing pest management strategies.

Keywords: Asian fruit fly; climate change; insect phenology; invasive insect species; population dynamics; thermal tolerance.

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Conflict of interest statement

Declaration of conflicting interests:The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Figures

Figure 1.
Figure 1.
Maps of Botswana showing the presence of B. dorsalis vis Chobe district, the area of first invasion and detection (A) and the current state of B. dorsalis distribution within the country (B).
Figure 2.
Figure 2.
Population abundance of B. dorsalis in (A) Chobe, Ngamiland, Central, and North-east and (B) South-east, Southern, Kweneng, and Kgatleng districts. Adults were baited using a pheromone lure in yellow Chempac bucket traps containing methyl eugenol pheromone lure.
Figure 3.
Figure 3.
The effect of different ramping rates and developmental stage (larvae and adults) on B. dorsalis critical thermal limits (A) CTmax and (B) CTmin. Means with the same letter(s) are not statistically significant. Each point represents mean ± 95% CL. Tukey-Kramer post hoc tests were used to separate statistically heterogeneous groups. CL indicates confidence level.
Figure 4.
Figure 4.
Summary results of the effect of high and low temperatures on the survival of different developmental stages of B. dorsalis at different temperature × time interactions: (A, B) upper lethal temperature assay results for adults and larvae, respectively; (C, D) lower lethal temperature assay results for adult and larvae, respectively. Error bars represent 95% CL. CL indicates confidence level.
Figure 5.
Figure 5.
Shaded microclimatic data from Kgatleng district (S24.56449; E0.26.16940) recorded during January - December 2016. Temperature was recorded using Thermochron iButtons (model DS1920; Dallas Semiconductor, USA) (0.5°C accuracy and 1 hour sampling frequency).
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