Hormonal Regulation Of The Vitellogenesis In An Ixodid Tick, Haemaphysalis Longicornis

Ticks are blood sucking arthropods and they are among the most important vectors of human and animal diseases. They have a super reproductive ability. Vitellogenesis and hormonal regulation are the hot topics, and they provide the theories for biological control of ticks.The morphological structure, weight and protein content of ovary in different developmental stages of female Haemaphysalis longicornis were investigated and the effect of 20E and JH III on vitellogenesis and Vg uptake into oocytes was tested by indirect double antibody ELISA in the current study. The main results were as follows:The morphological structure, weight and protein content of ovary in different developmental stages of female H. longicornis were investigated. Ovary was very thin and translucent white in hue through observing with a stereoscopic microscope at the mating stage, and became longer and thicker between days 0 and 2 post-engorgement. After considerable growth occurred to the ovary, it was completely covered with oocytes which were large, yolk-filled and reddish-brown. The ovary with its numerous bulging oocytes resembled an elongated cluster of grapes. This phase began at approximately day 4 post-engorgement and ended when oviposition started. Oviposition began at about day 5 post-engorgement; the ovary morphology was similar to that of day 4 post-engorgement, except that ovulated oocytes were visible in the lumen of the ovary and the oviducts. The number of the oocyte became much less and ovary became thiner and whiter obviously in hue after day 8 post-oviposition. Oviposition ended at about day 10 post-oviposition. Correspondly, the ovary weight was very low (0.867mg/tick) at the mating stage and then increased greatly after day 2 post-engorgement. Ovary reached the highest weight (30.540mg/tick) on the day of oviposition, afterwards, its weight decreased gradually. On day 8 post-oviposition, the ovary weight decreased to the lowest 3.667mg/tick. The ovary weight reached the highest percent (0.225%) of body weight (bw) on the day 2 post-oviposition and then decreased to 0.041% bw on day 8 post-oviposition. The protein content was low (33.504mg/tick) at the mating stage and then reached the peak (4069.000mg/tick) on the day of oviposition. Then it decreased slowly after the day of oviposition. The protein content declined to 72.455mg/tick at day 10 post-oviposition.Partially fed virgin female adults of H. longicornis ticks were injected with 20E (up to 10μg/tick), JH III (up to 10μg/tick), while they were attached and feeding on the rabbit host for 6 days, engorged mated ticks were also injected with 20E (up to 10μg/g bw) and topical applied with JH III (up to 100μg/g bw) on the day of engorgement to test the effect of 20E and JH III on vitellogenesis. Ticks on-host were examined 4d after injection. All of the ticks (20E; 10μg/tick) and (JH III; 10μg/tick) were died 2d after injection. Ovary (20E; 2μg/tick) was completely covered with oocytes which were large, yolk-filled and reddish-brown by observing with a stereoscopic microscope. However, Ovary of vehicle-injected tick was very thin and translucent white in hue. Ovary weight was significantly increaser in ticks treated with 20E compared to vehicle-injected controls. There was also a significant effect of 2μg/tick 20E on oocyte length compared to vehicle-injected tick. The fat body Vg content , hemolymph Vg concentration and ovary Vn content of ticks injected with 2μg/tick 20E is significantly higher than vehicle-injected controls. Ticks injected with JH III were not statistically different from vehicle-injected ticks. Engorged ticks injected with 20E or topical applied with JH III were not statistically different from vehicle-injected ticks. These results showed that 20E, not JH III,stimulated both vitellogenesis and Vg uptake into oocytes in partially fed virgin female ticks, and both 20E and JH III did not had statistically significant effect of stimulation on vitellogenesis in normal engorged tick H. longicornis.