Adaptation Of Two Biotypes Of Aphis Gossypii On Different Host Plants In The Temperate And Tropical Regions

Aphis gossypii (Glover)(Hemiptera: Aphididae) is one of the most important insect pestsin agriculture and horticulture crops worldwide. In the course of adapting to different areas,hosts and other complicated environmental conditions; it has an extremely complex lifecycle,host specialization and different reproduction models. It has both parthenogenetic and sexualreproduction, and it was said that the former had a strong selective advantage over the latter.But did the cotton aphid have enough evolutionary motivation who only had parthenogeneticreproduction and led an autoecious life cycle in the tropical area? Does host-alternatingphenomenon exist in the nature? And what kind of connection with the feeding experience ofadults of aphid and the host choice to hosts? So far, there have been no surfeint and accurateanswers in the literature.It was reported that the cotton aphid had at least two specialized biotypes, one on cotton,and the other on cucurbit host plants. In order to determine the differences of fitness of thetwo biotypes of cotton aphid which belong to two specializations when the hosts changed, Iinitiated the studies with two objectives:(1) to investigate the adaptation ability on differenthost plants, and the preference and finite increase rates on10species of Cucurbtaceae withthe winged adults which were the natural form in the field; and (2)to determine the differencesbetween the adults which had feeding experience and without experience. According to theadults with or without feeding experience on cotton and melon, we divided the experimentaladults into4groups: C-WE, C-NE, M-WE and M-NE.The results were summarized below:In the experiment of host adaptation-no choice test, the longevity of the cotton biotypewith feeding experience(C-WE) is much shorter(39.83±2.88h) than the ones withoutexperience(C-NE62.58±3.50h) when they were transferred from cotton to melon plants. Andthat result had no statistic significant differences between the ones which had no food. Same,the longevity of the adults from melon (32±5.28h M-WE),(46.93±2.47h M-NE) were alsoshorter than the ones who were transferred to original host plants. The longevity of adultsfrom melon were longer than the ones from cotton. The group M-NE had longer survive time than the group with experience(M-WE). But the ones from cotton had no difference betweenthe ones with experience and without experience. In the same time, the offspring of the groupM-NE was highest（31.44±3.27）, and this result had statistic significant difference betweenM-WE (26.33±2.99). Otherwise, there were no significant difference between the ones withand without feeding experience from cotton.In the experiment of host adaptation-choice test, the adults from two hosts both hadstrong preference to the original host plants. And the feeding experience had no effect on thechoice to hosts. The number of adults on cotton from cotton group after48h was much morethan24h after adult introduction. That revealed that the adults had re-selection phenomenon.Also, the offspring of the group M-WE was higher than the group C-WE. The increasing rateof the group from melon was also higher than the ones from cotton. The group M-NE hadhigher increasing rate when they chose the same host than the group M-WE.In the olfactory experiment, the original hosts obviously affected the choice to the adults inthe re-selection process. Both of the two groups preferred to choose the original host plants,indicating that the plant volatiles did work in the selection process of the host plants. Moreadults of C-WE chose the new host-melon. And more adults of C-WE chose melon whenthey had to choose from melon and water, and melon and cotton. Interestingly, more adults ofM-NE preferred water rather than cotton plants. The time of adults of C-WE which crawlingto cotton (258.11±11.55s)was shorter than to melon (281.52±19.64s). But the time of theadults of C-NE was not different when they crawling to hosts or water. The adults of M-WEhad shorter time to choose cotton(242.21±11.14s) than to the original host melon(273.6±44.21s) when they chose cotton and melon plants. And the group of M-NE spentlonger time(366.43±53.04s) to choose cotton plants than to water(250.35±33.47s) when theychose cotton and the control water. Also, this group used shorter time to choose original hostmelon(281.60±18.24s) than the time to water.Comparison between the two groups, the adults of C-WE spent longer crawling time thanthe ones of M-WE. The adults of M-NE used significant longer time (366.43±53.04s)crawling to cotton plants than the ones of C-NE (209.61±2.24s).In the test of the preference of the aphids to different summer hosts including cotton and10kinds of Cucurbtaceae plants, we determined the preference and finite increase rates of thecotton and melon aphids on10hosts of Cucurbtaceae with the winged adults. The adults fromcotton significantly preferred hybrid squash and zucchini to other host plants in the first day.And the ones from melon chose most of the hosts including melon, cantaloupe, pumpkin,yellow squash, tornado and hybrid squash, but not cotton and zucchini. But, even the aphids from melon did not prefer zucchini; however, they could survive on this host well. We thinkthat zucchini should be the mutual host of the two aphid biotypes, serving as a bridge host ofthe two aphid biotypes.