Wing symmetry and flight activity

We compared bilateral structures (wings) of flying versus non-flying insects in two lines of #P. megistus$ which differed only by their laboratory maintenance time : PM1 (more than five generations in insectarium) and PM2 (one or two generations under laboratory conditions). Insects were processed according to Schofield (1980) and observed through a period of 30 days. During this time the insects that had flight (gf, for "good" flyers) and their wings extracted for morphometry. At the end of this period the same number of insects that did not fly (bf, for "bad" flyers), were used as a control and submitted to the same analysis. Fluctuating asymmetry (FA) was estimated at nine distances (A, B, C, D, E, H, 1, 2 and 3). FA occurs as a result of random deviations in the developement of bilaterally symmetric traits, and is considered as a useful trait for monitoring stress in the laboratory and in natural environments (Parsons, 1990). For each sample, FA values were calculated for each character as the sum of the squared signed differences between sides divided by the number of individuals sampled, i.e., ((Li-Ri)2)/N). This is equivalent to index 5 of Palmer and Strobek (1986) which they state is best able to discriminate true differences in FA. As the index to estimate asymmetry is a variance, differences between samples were tested for significance using tests of homogeneity of variances (Ho : s1=s2). Due to low sample size, statistical analysis was not applied to PM2 females (only two individuals). The PM1 bf females (6 insects) were more asymmetric than their gf counterparts (5 insects) at four wings traits (2,3 in PM1 and 2 in PM2) (gf=7 insects and bf=7 insects). Conversely, one character out of nine was found more asymmetric in gf either from PM1 (character 3 for PM1 females and E for PM1 males) or PM2 males (character D). (Résumé d'auteur

The effect of laboratory maintenance of Panstrongylus megistus on its flight activity

In this study we compared two lines of #P. megistus$ which differed only by its laboratory maintenance time. PM1 (more than five generations in insectarium) and PM2 (one or two generations under laboratory conditions). The parameters studied were temperature (tp), humidity (hm), the weight/length ratios (nutritional status, w/l), isoenzyme electrophoresis at 7 locus (ME, GPI, LDH, ICD and alfa-GPD), as well as enzymatic activity of alfa-glycerophosphate dehydrogenase (alfa-GPD ac.), a crucial flight activity related enzyme. Insects were processed according to SCHOFIELD (1980) and observed througth a period of 30 days. The temperature and humidity were measured daily at the safe time, and the insects that had flighted, "good" flyers (gf), were also measured for the determination of the nutritional status. Muscle extraction was made for isoenzyme and alfa-GPD enzymatic studies. At the end of this period the same number of insects that did not fly, "bad" flyers (bf), were used as control and submitted to the same analysis. No isoenzyme difference was observed between gf and bf for the two populations. Main external factors influencing flight activity were w/l (PM1 P=0.0027; PM2 P=0.0209) and tp (PM1 P=0.0814; PM2 P=0.0118). However, PM1 and PM2 strongly differed with respect to alfa-GPD activity : it was the main difference found between PM1-gf and PM1-bf (P=0.0001), whereas it did not present any evidence for heterogeneity in PM2 (P=0.5995). We used two multivariate approaches to verify the differences between gf and bf (logistic regression and canonical variate analysis, CVA). Logistic regression was able to separate "good" from "bad" flyers of the old established laboratory strain (PM1) using as the unique parameter value the alfa-GPD activity (87 to 93% of correct attribution), while it reached lower scores (78 to 86%) in PM2, needing the combination of two or more parameters excluding alfa-GPD activity. (Résumé d'auteur