Role of juvenile hormone and allatotropin on nutrient allocation, ovarian development and survivorship in mosquitoes

Abstract

Teneral reserves are utilized to initiate previtellogenic ovarian development in mosquitoes. Females having emerged with low teneral reserves have reduced juvenile hormone (JH) synthesis and previtellogenic development. We investigated what role JH, allatotropin (AT) and other head-factors play in the regulation of previtellogenic ovarian development and adult survivorship. Factors from the head are essential for corpora allata (CA) activation and reproductive maturation. We have shown that decapitation of females within 9-12h after adult ecdysis prevented normal development of the previtellogenic follicles; however maximum previtellogenic ovarian development could be induced in decapitated females by topically applying a JH analog. When females were decapitated 12 or more hours after emergence nutritional resources had been committed to ovarian development and survivorship was significantly reduced. To study if allatotropin levels correlated with teneral reserves, we measured AT titers in the heads of two adult phenotypes (large and small females) generated by raising larvae under different nutritional diets. In large mosquitoes AT levels increased to a maximum of 45 fmol in day 4; in contrast, the levels of allatotropin in the heads of small mosquitoes remained below 9 fmol during the 7 days evaluated. These results suggest that only when nutrients are appropriate, factors released from the brain induce the CA to synthesize enough JH to activate reproductive maturation.

Fig. 1

Ovarian development in normal and decapitated females. The length of the terminal follicle of ovaries was measured from newly emerged females (I), and compared with the ovaries of 72 h old-females that were subjected to one of these three treatments: (II) Females were decapitated at emergence, (III) Females were not decapitated and treated with 0.5 μl of acetone, and (IV) Females were decapitated at emergence and immediately treated with methoprene (JHA) (500 ng/0.5 μl acetone). Each bar represents the mean ± SEM of at least 100 independent determinations of follicles dissected from three females. Values labeled with different letters are significantly different by Tukey’s test after ANOVA at P<0.05.

Fig. 2

Time of decapitation and ovarian development. The length of the terminal follicle of ovaries was measured in 72 h old-females after the following treatments: 0–24 h: decapitated at different hours after emergence; ND: non-decapitated; 0h+JHA: decapitated immediately after emergence and treated with methoprene (JHA) (500 ng/0.5 μl acetone). Controls (non-decapitated) were treated with 0.5 μl of acetone. Each bar represents the mean±SEM of at least 100 independent determinations of follicles dissected from three females. Values labeled with different letters are significantly different by Tukey’s test after ANOVA at P<0.05.

Fig. 3

Survivorship of decapitated females. Groups of 10–25 females were decapitated at different times after emergence and survivorship was evaluated every day. Each data point represents the percentage of insects alive.

Fig. 4

ELISA standard curve. Standard curve for Ae. aegypti allatotropin. Each data point represents the mean±SEM of three independent determinations of individual samples.

Fig. 5

Effect of nutrients on allatotropin levels. Allatotropin levels were evaluated by ELISA. Heads were dissected at different times after emergence. Values are expressed as fmol of AT in one head equivalent. Each data point represents the mean±SEM of three independent determinations of individual samples of five heads. Asterisk above each bar indicates the value is significantly different by Tukey’s test after ANOVA at P<0.05.