A Comparative Study Of Reproductive Mode Of Phenacoccus Solenopsis Tinsley

Phenacoccus solenopsis Tinsley is one of the most important pests in China in recent years. The pest has brought severe damage to cotton and other host plants. Risk assessment reveals that it’s a potentially dangerous pest of most regions in China. Cotton mealybug is omnivorous insect, and its host plant reaches 200 kinds. Many researches demonstrate that cotton mealygug can impaire many kinds of ornamental plants and economic plants severely, especially cotton.The reproduction mode of P. solenopsis is a controversial case in home and abroad. One point is that it can only be bisexual, cannot produce offspring by parthenogenesis. Another view is that P. solenopsis can produce offspring by both parthenogenesis and bisexual. So, I n order to clarify the reproduction mode of P. solenopsis, we studied the reproduction of the mealybug at the temperature:27±1℃, RH:70±5%, the light cycle L:D=12:12 in laboratory. After Multi-generational culture, we concluded that the reproduction mode of mealybug is deuterotoky and did detailed researches about biological characteristics, such as preoviposition, fecundity, sex ratio, the ratio of spawning parent and the mating times. Besides, we performed a preliminary study about sexual selection of male.The results are below:1. After developing the five generations of P. solenopsis which was kept in virgin, we found mealybug can produce both male and female offsprings. Therefore, the reproduction of mealybug is facultative deuterotoky as it can produce offsprings by both amphigenesis and parthenogenesis.2. Exploring the relationships about preoviposition, fecundity, the sex ratio of offspring and the ratio of spawning parent among each generation mealybug, which reproduction mode is parthenogenesis. We found in the former two generations only had one female adult which produce nymph, respectively. It added from the third generation, which the female adult produced nymph. After statistical analysis of the various data of five generations, we found that the preoviposition were 14 d,9 d,15 d,15.9 d and 12.2 d, respectively; fecundity were 412 eggs,587 eggs,356.7 eggs,342.9 eggs and 382.4 eggs, respectively; sex ratio were 1.2,1.0,1.1,1.2 and 1.2 respectively. There’s no significant difference among preoviposition, fecundity, sex ratio. However, the longer preoviposition is, the less fecundity will be. The ratios of the five generations of spawning female adults were 0.014、0.014、0.043、 0.16、0.07. Nympha stage and longevity of female were 13.1 d and 57.2 d, respectively. Nympha stage and longevity of male were 18.7 d and 20.8 d. There’s significant difference in the above aspects.3. Exploring the relationships about preoviposition, fecundity, sex ratio and the ratio of spawning parent among each generation by developing the three generations P. solenopsis, which the reproduction mode was bisexual reproduction. The results were:The preoviposition was 7.1 d,6.7 d and 6.6 d, respectively; fecundity were 251.1 eggs,825.3 eggs and 406.1 eggs, respectively; sex ratio were 1.1,1.2 and 1.2, respectively. Statistical analysis showed that fecundity had significant differences among three generations but there’s no significant difference about preoviposition and sex ratio. Longevity of female and male were 32.8 d and 20.8 d, respectively. There’s significant difference about longevity. The ratios of the three generations of spawning female adults were 0.90、0.95、0.95, respectively. It indicated that if the female was mated, then it can generally produce offsprings.4. Comparing the above experimental data between parthenogenesis and amphigenesis, we found there was significant difference about preoviposition, as the parthenogenesis was 14.8 d, the amphigenesis was 6.9 d. Besides, there was also significant difference in fecundity of the two reproductive modes and the longevity of female adults, as the parthenogenesis was 348.3 eggs, the amphigenesis was 494.1 eggs, the fecundity of amphigenesis is more than parthenogenesis. The longevity of parthenogenesis female adult is about 57.2 d while in amphigenesis is 32.8 d. At the last, it’s no significant difference about sex ratio of the offspring.5. Exploring sexual selection of male adults of P. solenopsis, we found when mating, female adults tilted tail slightly for the convenient to mate with male. When mating, male usually mated more than once, however, female generally mate once. Each time the average mating lasted 2.9 minutes, meantime, mating time does not vary with the number of mating.