No abstract

The postembryonic changes of the external microstructure of the cuticle on the abdominal tergites and stemites of Cloeon sp. (Ephemeroptera:Baetidae) are described. An inventory of the structures as the aquatic nymph grows and becomes transformed into a terrestrial subimago and then an imago, is provided. It is found that sensillar diversity on nymphal tergites increases with development, but remains unchanged on the stemites. While nymphs and subimago possess various types of sensilla trichoidea, sensilla basiconica are apparent on the imaginal abdomen only. Furthermore, the scaled and spiny cuticle of the nymph becomes relatively smooth in the adult stages. The distinct changes which structure and distribution of the scales as well as marginal spines on the abdominal tergites and stemites of the nymphs undergo during development, must find a reflection in behavioural changes of the larvae. Finally, the taxonomic implications of the observed changes are discussed.

Early instar nymphs of the mayfly, Cloeon sp. were kept on an algal or a detrital diet at 20 + 1 C in the laboratory. A control group was not given any food. Nymphs kept on algae showed significantly (P = 0.001) higher growth both in terms of length and biomass than for those kept on detritus. None of the nymphs given algae or detritus died during the experiment, and 40 per cent of those fed algae and 20 per cent fed detritus reached maturity by the termination of the experiment. Food retention time as well as gill ventilation rate of nymphs feeding on algae were significantly (P = 0.001) higher than those feeding on detritus. It is probable that these two factors largely enabled the nymphs to survive as well as to grow and reach maturity, though relatively slowly, solely on a detrital diet. However, algae was clearly shown to be a superior food resource for Cloeon sp. nymphs.

A study on diversity and ecology of Plecoptera larvae was carried out at two small streams, Wahdienglieng and Umrisa of Shillong, Meghalaya, North-east India for the year 2014 and 2015. The total number of families and genera recorded during the study were 3 families and 8 genera. During the first year at Wahdienglieng, the Principal Component Analysis (PCA) revealed that the high weighted variables are total alkalinity, pH, electrical conductivity, water temperature and sand while at Umrisa, free carbon dioxide and electrical conductivity were strong variables. The next year at Wahdienglieng, PCA showed pH as the highly weighted variable while at Umrisa, the PCA indicated dissolved oxygen, water temperature and rainfall as influential variables. The CCA (Canonical Correspondence Analysis) dendrogram revealed that Indonemoura spp and Kamimuria spp have positive impact with sandy substratum in Wahdienglieng; while Amphinemura spp showed positive correlation with dissolved oxygen in Umrisa during the first year. In the next year, water temperature showed positive relation with Indonemoura spp and Tetropina spp at Wahdienglieng and Umrisa, respectively. The presence of Plecoptera larvae in these streams indicated that the water is unpolluted and the substratum type enabled the larvae to reside at various microhabitats with diverse species.

Post-embryonic developmental patterns of the lateral eyes of both male and female Cloeon sp. are described and compared with each other morphometrically on the basis of scanning electron microscopy. In the larvae number of ommatidia, ommatidial size, and total corneal surface area of the eye increase towards the subimaginal moult. It is then that clear differences between males and females begin to occur: while further increases in the number of ommatidia are recorded from the lateral eye of subimago and imago females (accompanied by decreasing facet sizes and interommatidial angles), males show decreasing numbers of ommatidia and total corneal areas in their lateral eyes as they prepare to leave the water. Consequently, the lateral eyes of a female are larger than those of a male imago. It appears that the enormous development of the dorsal eyes of the males has occurred at the expense of the lateral eyes. In male as well as female lateral eyes two major facet shapes are encountered: squares with rounded corners which are predominantly found in the central and upward looking areas, and hexagons which are dominating the lateral and ventral-facing regions. The different roles of the lateral eyes in male and female baetid mayflies is discussed in relation to their flights and the intriguing idea is presented that females might choose males with the largest dorsal eyes.