Correlation between wing measurements and dry body weight in ...

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Wing size and body weight in Oc. caspiusA. CarronWing characters r² Source Estimate t-valueWing length 0.77 Intercept female 1.846 19.914***Intercept male 2.067 10.539***Slope (body weight) 0.0018 7.879***Interaction (sex: body weight) NA 3.409 ns aWing width 0.89 Intercept female 0.609 15.859***Intercept male 0.503 12.245***Slope (body weight) 0.0005 5.858***Interaction (sex: body weight) NA 0.414 ns aWing surface area 0.76 Intercept female 1.004 7.077***Intercept male 0.891 -3.518**Slope (body weight) 0.0029 8.072***Interaction (sex: body weight) NA 0.039 ns aTable 1: ANCOVA results of the relationship of wing measurements (wing length, wing width and wingsurface (length x width) as a function of body weight and sex. ns (p > 0.05); *(p < 0.05); **(p < 0.01);***(p < 0.001). a F-value of the interactions was calculated using ANCOVA.multiplying the wing length and the wingwidth. Regressions between these threewing characters and body weight for bothmales and females were calculated andcompared.Materials and methodsDuring the summer of 2006, soil sampleswere collected from a known Oc. caspiusbreeding site in the Rhône delta insouthern France to obtain eggs forrearing in the laboratory. Sampling wascarried out using vegetation as anindicator of egg biotopes (Gabinaud,1975). Ascorbic acid was used to initiateegg hatching (Sinègre, 1974) and larvaewere reared to adult stage in thelaboratory at 28.4 ± 0.3°C, 52 ± 0.7% RHand 16:8 L:D.One day after emergence, 20 unfed adultsof each sex were killed, transferred toindividual 1.5 ml plastic vials, dried at60°C for at least 12 h, and weighed to aprecision of ± 1 µg using a MettlerToledo MX5 balance (Mettler-ToledoGmbH, Greifensee, Switzerland).Subsequently, the left wing wasremoved, and its length (from the axillaryincision to the wing tip) and maximumwidth were measured using astereomicroscope (Zeiss Stemi 2000C)coupled with the measurement softwareEllix TM (Microvision instruments,France). The normality of the bodyweight, wing length, wing width andwing surface (length x width) were testedusing the Shapiro-Wilk test (Zar, 1999).Analysis of covariance (ANCOVA) (Zar,1999) was used to assess the regressionbetween body weight and each wingmeasurement according to sex. Male andfemale body sizes were compared with at-Test (Zar, 1999). All statistical analyseswere done using R 2.4.0 software (RDevelopment Core Team, 2005).Results and DiscussionBody weight, wing length, wing widthand wing surface were normallydistributed (Shapiro-Wilk test, n = 40,p = 0.158, 0.771, 0.157, 0.692,respectively). The slopes of theregression for body weight and eachwing measurement (length, width andarea) were all significant and positive(ANCOVA, p < 0.01; Table 1, Figure 1ac).Moreover, as the interactions betweensex and body weight were not significant,the slopes between males and femaleswere not significantly different. Hence,an increase in wing size denoted anequivalent increase in body weight inmales and females.5
European Mosquito Bulletin, 24 (2007), 4-8.Journal of the European Mosquito Control AssociationISSN1460-6127; www.europeanmosquitobulletin.comFirst published online 30 December 2007(a)(b)(c)The intercepts of wing length, wingwidth and wing surface area in Oc.caspius were different between the sexes(Table 1). The wing length intercept wassignificantly higher for males than forfemales (Figure 1a). Therefore for thesame body weight, the wing length ofmale Oc. caspius is greater than forfemales. The intercepts of wing widthand wing surface were significantlyhigher for females than for males (Table1). Therefore for the same body weight,the wing width (Figure 1b) wassignificantly larger for females than thatfor males, and female wing surface wassignificantly greater than for males(Figure 1c).Nasci (1990) noted that the slopes of theregression between wing length and bodyweight were significantly differentbetween the two sexes for three mosquitospecies reared in the laboratory (St.aegypti, St. albopictus, and Cx.quinquefasciatus) and for five speciescollected in the field (St. aegypti, St.albopictus, Oc. triseriatus, Culexquinquefasciatus, Cx. salinarius). Resultspresented here for Oc. caspius weredifferent, and suggest that wing length isnot always greater in females. Althoughthe relatively low replicates (n=40) usedin this experiment could be criticized, thehigh r² of the ANCOVA suggests thatregression values will probably not bealtered by increasing the number ofreplicates, thus use of wing length aloneto estimate body size should be used withcaution in previously unstudied speciesFigure 1: Regression of wing measurements as afunction of dry body weight (µg) for males(triangle, dashed line) and females (circle, solidstraight line); a) wing length (mm), b) wingwidth (mm), c) wing surface (wing length x wingwidth) (mm 2 ). Regressions presented in eachfigure were calculated for each sex separately.Wing surface area was greater in femaleOc. caspius than in males, but theconverse was true for wing length incontrast to previous studies (Nasci, 1990;Agnew et al., 2000, 2002). As the bodyweight of the females were significantlyhigher than the males (t-Test, p < 0.01),these results suggest that using winglength alone to estimate body size, may6
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