Does monogeny enable gall midges (Diptera: Cecidomyiidae) to regulate their sex ratio?

Abstract

Abstract. Monogeny, the production of unisexual broods by individual females, is widely recorded in gall midges (Diptera: Cecidomyiidae). Theoretical models propose that the adjustment of offspring sex ratio by females may pre-dispose the evolution of monogeny in gall midges however empirical studies in this field are superficial. Expressed more simply, monogeny may enable individual female gall midges to decrease or increase the number of male and female progeny they produce in response to changes in environmental conditions. Host quality/size is repeatedly reported to influence sexual investment in insects in terms of sex ratio adjustment. In this paper, we examined the sex ratio of the offspring of the monogenous predatory gall midge Aphidoletes aphidimyza attacking low and high abundances of the cotton aphid, Aphis gossypii. Two consecutive generations of female gall midges were presented with either a low or high abundance of aphids in each generation and the sex ratio of their progenies determined. There was no difference between the sex ratio of the progenies that developed on the high or low abundance of A. gossypii in the two generations. Apparently, the females did not regulate the number of female and male progenies, or adjust the numbers of male or female's eggs they produced in response to the changes in the abundance of prey. Results of this study do not support the theory of sex ratio regulation proposed for monogenous gall midges. It is likely that the skewed sex ratio in most species of monogenous gall midges is a consequence of differential mortality of male and female progenies under harsh conditions. The finding that male and female larvae did not differ in the number of aphids they require to complete their development supports this claim.

Quelques paramètres biologiques de Orseolia oryzivora H. & G. (<i>Diptera: Cecidomyiidae</i>) au Burkina Faso

“…Cecidomyiidae) une cécidomyie prédatrice des pucerons du cotonnier, Tabadkani et al (2012) ont conclu que les femelles ne régulaient pas le nombre de mâles et de femelles de leurs descendances en réponse au changement dans l'abondance de leurs proies. Selon Sanchez (2008), le règne animal possède un trésor de mécanismes à travers lesquels le sexe est déterminé et tous ces mécanismes sont représentés dans la classe des insectes.…”

When to estimate sex ratio in natural populations of insects? A study on sex ratio variations of gall midges within a generation

“…However, our results show that differential lifespan of sexes are sufficient to explain the occurrence of female biased sex ratio in natural populations of gall midges. The sex ratios of A. aphidimyza have been reported to vary from 45% to 72% females in both natural populations (Havelka & Zemek 1999) and laboratory or commercially reared colonies (Gilkeson & Hill 1986; Heimpel & Lundgren 2000; Tabadkani et al . 2012).…”

“…2004). Although, several studies have suggested that the sex ratio of A. aphidimyza in laboratory and commercially reared colonies is slightly male‐biased (Gilkeson & Hill 1986; Heimpel & Lundgren 2000; Tabadkani et al . 2012), some other studies propose a female‐biased sex ratio (47% to 72% females) in natural populations of this species (Havelka & Zemek 1999).…”

“…Aphidoletes aphidimyza is a general predator of over 65 species of true aphids and has been successfully used for biological control of several aphid species especially in greenhouses (Choi et al 2004). Although, several studies have suggested that the sex ratio of A. aphidimyza in laboratory and commercially reared colonies is slightly male-biased (Gilkeson & Hill 1986;Heimpel & Lundgren 2000;Tabadkani et al 2012), some other studies propose a female-biased sex ratio (47% to 72% females) in natural populations of this species (Havelka & Zemek 1999). During laboratory work, we found, unexpectedly, that the sex ratio of A. aphidimyza fluctuates remarkably, even within a day.…”