Variation in microclimate
Microclimate at the tower varied across the daily sampling period with temperatures highest and relative humidity lowest around midday and the early afternoon hours, although the time of peak temperature and nadir humidity varied by height (Fig. 3a, b). Mean temperature was highest at ground level at 11:30 (30.0 °C) when it was on average 0.2 °C hotter than at 9 m, whereas at 5 m and 9 m, it was highest at 13:30 (29.7 °C and 30.3 °C, respectively). The inverse was true for mean relative humidity, which was lowest at ground level at 11:30 (83.8%) and lowest at 5 m and 9 m at 13:30 (80.1% and 76.4%, respectively). Both variables showed substantial overlap in means and standard errors across the sampled heights during the morning hours, before diverging in the afternoon. For comparison, we extracted microclimate data from the corresponding sampling period in the BG-Sentinel trap study15, which revealed clear differences in temperature and humidity at each height sampled (Fig. 3c, d). BG-Sentinel traps were often hung beneath the forest canopy where it was considerably cooler and more humid than at the treefall gap, particularly at ground level.
Variation in microclimate by height and collection method. (a) and (b) show the mean temperature (temp,°C) + / − 1 standard error (S.E.) and relative humidity (RH, %) + / − 1 standard error (S.E.) for net collections made at the tower between 10:00 and 15:00 in this study. (c) and (d) show corresponding data extracted from the BG-Sentinel trap study15.
Community composition of diurnally active, anthropophilic mosquitoes
A total of 2146 adult mosquitoes representing seven genera and 34 species were collected using nets (Fig. 4a), of which 99.8% (2142/2146) were female and 99.7% (2140/2146) were identified to species level. Mosquito abundance was similar at ground level and 9 m but was slightly lower at 5 m, while species richness was higher at ground level (28 species), than at 5 m (18 species) and 9 m (22 species). Psorophora was the most abundant genus (1231 mosquitoes, 57.4% of the total catch), followed by Haemagogus (32.3%), and Sabethes (6.6%). The genera Limatus (1.4%), Culex (1.2%), Wyeomyia (1.0%), and Onirion (< 0.1%), formed just 3.7% of the total catch. In agreement with our BG-Sentinel trap collections from the same area (Fig. 4b), Ps. amazonica (82.4% of identified Psorophora) and Hg. janthinomys (97.3% of identified Haemagogus) dominated collections within their respective genera, while Ps. albigenu (16.8% of identified Psorophora) was also relatively abundant. Sabethes was the most diverse genus with 11 species collected, and Sa. chloropterus (32.4% of identified Sabethes) was the most abundant of these.
Relative mosquito species abundance (%) by height and collection method for net and BG-Sentinel trap collections. (a) shows the relative abundance of designated species collected using handheld nets, and (b) the relative abundance of designated species previously collected using BG-Sentinel traps15. Number of mosquitoes (n =) collected at each height listed at top of bar; number of individuals per species included in parentheses next to species name; *asterisk denotes species collected using both nets and BG-Sentinel traps; sp. = single species, spp. = potentially multiple species; genus and subgenus abbreviations follow Walter Reed Biosystematics Unit nomenclature36. (c) and (d) each show a dendrogram of PC1 from a principal components analysis of relative species frequency at each height sampled for respective species stacks. Panels (b) and (d) are reproduced from our previous study15 and reformatted for the current publication under a Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/).
The Morisita overlap index for specimens identified to species level (n = 2140 mosquitoes) showed substantial overlap in community composition between the sampled heights. However, elevated (5 m and 9 m) communities were more similar to each other (0.966) than they were to the ground level community (0.945 and 0.896 for 5 m and 9 m comparisons with ground level, respectively). These results were consistent with clustering based on principal components generated using the summed numbers for each species per height (Fig. 4c) and agreed with the results of our BG-Sentinel trap collections (Fig. 4d).
Comparing nets with BG-sentinel traps
When comparing handheld net collections in this study with those made using BG-Sentinel traps in the same area of the reserve15, there was a significant difference in relative genus abundance, pooled across height (Pearson’s chi-squared test, DF = 8, χ2 = 423.9, P < 0.0001) (Fig. 4). The relative abundance of Haemagogus was higher in nets than in traps, while for Psorophora, the reverse was true. The relative abundance of Sabethes was similar using both methods. When comparing the methods for individual species stratified by height, there was a significant difference in the relative abundance of Hg. janthinomys (DF = 2, χ2 = 22.7, P < 0.0001) which was collected in higher numbers at ground level compared with elevated heights in nets than in traps. There was also a significant difference in the relative abundance of Ps. amazonica (DF = 2, χ2 = 102.1, P < 0.0001), which was collected in lower numbers at ground level compared with elevated heights in nets than in traps. Small sample sizes precluded analysis of Sabethes mosquitoes at species level.
Species abundance by height
As expected, Hg. janthinomys showed significant stratification in abundance across the sampled heights when analyzed using data summarized by date and height (Kruskal–Wallis test, DF = 2, χ2 = 10.05, P = 0.007). Post-hoc Wilcoxon Each Pair tests revealed this species to be more abundant at 9 m than at 0 m (P = 0.01), but there was no difference in abundance between 0 and 5 m or 5 m and 9 m (P > 0.09 for both comparisons). In contrast, there was no significant stratification in abundance of Ps. amazonica or Ps. albigenu across sampled heights (P > 0.12 for both comparisons). Data were further summarized by morning (10:00–11:59) and afternoon (12:00–14:59) due to the differences in stratification of microclimate during these periods (Fig. 3a, b). This showed that Hg. janthinomys abundance was not significantly stratified in the morning (Kruskal–Wallis test, DF = 2, χ2 = 4.7, P = 0.1) when microclimate generally overlapped across heights, but it was in the afternoon as microclimate became more distinct (Kruskal–Wallis test, DF = 2, χ2 = 11.4, P = 0.003). Again, post-hoc Wilcoxon Each Pair tests revealed Hg. janthinomys to be more abundant at 9 m than 0 m (P = 0.001) in the afternoon, whereas comparisons between 0 and 5 m (P = 0.085) and 5 m and 9 m (P = 0.051) were not significant. Neither Ps. amazonica or Ps. albigenu showed significant stratification in the morning or afternoon sampling periods (P > 0.08 for all comparisons). Sabethes species were not included in analyses of abundance due to small sample sizes.
Lag to first approach
Lag to first approach was defined as the number of minutes that elapsed from the start of collections until the first mosquito of a given species was caught. If no mosquito of that species arrived during a particular collection, lag was set to 300 min (the full duration of collection). Lag to first approach differed significantly between heights for Hg. janthinomys (Kruskal–Wallis, DF = 2, χ2 = 6.4, P = 0.04), which arrived faster at 9 m than at 0 m (Wilcoxon Each Pair, P = 0.01), but did not differ between 0 m and 5 m or 5 m and 9 m (P > 0.1 for both comparisons). A linear regression showed that, across all heights, lag to first approach decreased significantly as Hg. janthinomys abundance increased (DF = 1, F = 52.1, P < 0.001), and the same pattern held when data from each height was analyzed separately (P < 0.005 for each analysis). As Hg. janthinomys abundance was higher at 9 m, this suggests that the difference among heights in lag to first approach is attributable to differences in abundance. When only considering collections in which least one Hg. janthinomys was caught, a multiple linear regression showed that lag to first approach did not differ by height but did differ by abundance (DF = 1, F = 16.7, P = 0.0001) and mean daytime temperature (DF = 1, F = 4.2, P = 0.04), with faster approaches occurring at higher abundance and higher temperature. Lag to first approach did not differ among heights for either Ps. amazonica or Ps. albigenu. Again, small sample sizes precluded analysis of Sabethes at species level. The mean time (+ / − 1 S.E.) to first approach for each species at each height is listed in Supplementary Table S4.
Species occurrence
Based on data summarized by date and height of collection, nominal logistic regressions revealed significant positive associations between several of the predictor variables and the occurrence of target species. Seven-day cumulative rainfall at a lag of 1 week (DF = 1, χ2 = 4.7, P = 0.03) was a significant positive predictor of Hg. janthinomys occurrence (Fig. 5), while height also had a marginal effect but was not significant in this analysis (DF = 2, χ2 = 5.1, P = 0.08). Rainfall at a lag of 1 week was associated with an increase in Haemagogus occurrence in our earlier study15. Date of collection (DF = 1, χ2 = 27.8, P < 0.0001), rainfall at a lag of one week (DF = 1, χ2 = 8.9, P = 0.003), and rainfall at a lag of four weeks (DF = 1, χ2 = 4.6, P = 0.03) were all significant predictors of Ps. amazonica occurrence (Fig. 5). Mean daytime temperature followed a similar but non-significant trend (DF = 1, χ2 = 3.3, P = 0.07) and height had no significant effect on the occurrence of this species. The association between Ps. amazonica occurrence and rainfall at lags of one and four weeks corresponded with our previous results15. Rainfall at a lag of one week (DF = 1, χ2 = 9.3, P = 0.002) was a significant predictor of Ps. albigenu occurrence, while height (DF = 2, χ2 = 5.0, P = 0.08) had a marginal but non-significant effect on this species which we had not previously analyzed15. Height was a significant predictor of Sa. chloropterus occurrence (DF = 2, χ2 = 14.5, P = 0.0007), but there was no effect of 7-day cumulative rainfall (Fig. 5). We had previously shown that Sa. chloropterus occurrence significantly increased with rainfall at a lag of 3 weeks15.
Rainfall and mosquito occurrence during the study period. (a) shows the cumulative weekly rainfall for the duration of the sampling period including four weeks prior to the start of collections. (b)–(d) show the weekly occurrence of Hg. janthinomys, Ps. amazonica, and Sa. chloropterus, while the number of mosquito sampling days per week is shown beneath the x-axis in panel (b). Occurrence was calculated as the percent of collections positive for a given species in a given week across all heights sampled, such that three collections were made each sampling day (one per each of three heights) and one to two days were sampled per week. Note that there was a sampling pause over the Christmas holiday (weeks staring 23 December 2019 and 30 December 2019).
Relationships between temperature and occurrence
BG-Sentinel trap collections had previously shown that Haemagogus and Sabethes species mosquitoes increased in occurrence with increasing temperature and decreasing relative humidity when analyzed at genus level15. In the current study, we found that these mosquitoes were mainly active between 26 °C and 33.9 °C when classified in ≈4 °C increments (Fig. 6), which were chosen to provide a balance between the range and sample size of each temperature class. Both Ps. amazonica and Ps. albigenu were more tolerant of lower temperatures (22–25.9 °C), while Ps. amazonica was the most abundant of the species collected at temperatures higher than 33.9 °C.
Relative mosquito species abundance by temperature and height for net collections. (a)–(c) show the relative abundance of species grouped in 4 °C temperature increments starting at 22 °C, while panel d shows species collected at 34 °C and above (maximum 38.6 °C). Number of mosquitoes (n =) collected and number of hours (hrs, rounded to one decimal place) that collections were made within each temperature and height class listed at top of bar; total number of individuals per species included in parentheses next to species name; genus and subgenus abbreviations follow Walter Reed Biosystematics Unit nomenclature36. Data were excluded for days where collections were made but iButtons malfunctioned.
When analyzing relationships between species occurrence and microclimate using data summarized at 15-min time intervals by date and height, a nominal logistic regression revealed a significant interaction in the impact of height and temperature on the occurrence of Hg. janthinomys (DF = 1, χ2 = 4.4, P = 0.036). Subsequent nominal regressions analyzing the effect of temperature stratified by height showed a significant positive effect of temperature on occurrence at 0 m (DF = 1, χ2 = 13.9, P = 0.0002) and 5 m (DF = 1, χ2 = 17.0, P < 0.0001), but not at 9 m (DF = 1, χ2 = 2.0, P = 0.157). Interestingly, the mean temperature for the intervals in which Hg. janthinomys was collected was 29.9 °C at all three heights. Nominal logistic regressions showed no effect of temperature on the occurrence of Ps. amazonica (DF = 1, χ2 = 0.3, P = 0.58) but did reveal an effect on the occurrence of Ps. albigenu (DF = 1, χ2 = 7.3, P = 0.007), which preferred cooler than average conditions. There was no effect of temperature on the occurrence of either Sa. chloropterus (DF = 1, χ2 = 2.0, P = 0.15) or Sabethes when analyzed at genus level (DF = 1, χ2 = 0.3, P = 0.59), although sample sizes were small (n = 44 and n = 132, respectively).
Community composition of mosquitoes in artificial and natural containers
A total of 2070 adult mosquitoes (50.9% female) representing seven genera and 11 species were reared from ovitraps, of which 99.9% were identified to species level (Fig. 7). In contrast to net collections, Culex was the most abundant genus (84.7% of the total catch), followed by Limatus (13.7%), Sabethes (1.3%), Wyeomyia (0.2%), Haemagogus (0.05%), Orthopodomyia (0.05%), and Toxorhynchites (0.05%). Collections in standard and fruit pod ovitraps were dominated by Culex urichii which comprised 75.2% of the catch in these containers, while Limatus flavisetosus (11.5%) was also relatively abundant. Mosquitoes reared from bamboo represented just 6.1% of the overall catch but included Sa. quasicyaneus (22 mosquitoes), Sa. batesi (5), and Hg. janthinomys (1), which were absent from other container types.
Relative mosquito species abundance by height and container type for standard, fruit pod, and bamboo ovitraps. Number of mosquitoes (n =) collected at each height listed above bar; number of individuals per species included in parentheses next to species name; *asterisk denotes species collected using both ovitraps and nets; genus and subgenus abbreviations follow Walter Reed Biosystematics Unit nomenclature36. Color scheme is consistent with previous figures.
Mosquito communities in standard and fruit pod ovitraps overlapped substantially when analyzed using the Morisita index at species level (Supplementary Table S4) but overlap decreased when comparing these traps with bamboo. When comparing heights for the combined standard and fruit pod ovitraps, there was substantial overlap at 0, 5, and 9 m, but this decreased slightly when comparing each height with 15 m. When comparing heights for individual container types (Supplementary Table S5), the standard ovitrap followed a similar pattern, but the fruit pod showed substantial overlap among all heights sampled. Bamboo communities were quite dissimilar when comparing 0 m with elevated heights, and those at 15 m were distinct from all other heights sampled, but this was based on a small number of specimens.
Source: Ecology - nature.com
