Darker eggs resist more to desiccation: the case of melanin inAedes,AnophelesandCulexmosquito vectors

Abstract

27melanin, mosquito, viability. 28 29 30 31 32 33 34 2 Summary statement: The ability of mosquito eggs of several species to resist differently 35 to dry conditions is investigated. In particular, it unravels why Aedes aegypti eggs survive 36 for several months outside water. Abstract 39 Mosquito vectors lay their eggs in the aquatic milieu. During early embryogenesis water 40 passes freely through the transparent eggshell, composed of exochorion and endochorion. 41 93 Curiously, the level of egg resistance to desiccation (ERD) varies among mosquito species 94 at the end of embryogenesis: while Ae. aegypti eggs can survive for at least 72 hours in a 95 dry environment (high ERD), those of An. aquasalis and Cx. quinquefasciatus in the same 96 condition can survive, respectively, for 24 hours (medium ERD) and 5 hours (low ERD) 97 (Figure 1C) (Vargas et al., 2014). Physical and biochemical features of these eggs were 98 investigated in order to identify traits related with these differences. Chitin content is 99 directly related to ERD levels while both egg volume increase during embryogenesis and 100 eggshell superficial density are inversely related to. Moreover, other yet unidentified traits 101 might also be relevant (Farnesi et al., 2015).102 4Although the melanization increases desiccation resistance of adult insects of different 103 orders (Kalmus, 1941; Parkash et al., 2009; Wittkopp and Beldade, 2009; King and 104 Sinclair, 2015) it is currently unknown if the same process occurs in insect eggs. We 105 investigated here if the intensity of eggshell pigmentation is related to desiccation 106 resistance phenomenon in mosquito vector eggs.