Studies On Female Mating System, Reproductive Biology And Gene Transfer In Echinothrips Americanus And Thrips Tabaci

The reproductive biology is the basic knowledge to study pest reproductivecapacity and adaptation, which helps to understand pest occurrence, population sizeand dynamics in the field. Although thrips are minute insects, many species are knownas important agricultural pests globally. Onion thrips, Thrips tabaci Lindeman, is oneexample. In addition, invasive thrips pest Echinothrips americanus Morgan wasreported in Mainland China recently, posing a potential threat to ornamentals andgreenhouse crops. However, little is known about the reproductive biology of thesetwo species, such as mating system and the relationships between differentreproductive modes.In this research, we studied female mating systems in E. americanus and T.tabaci as well as the effects of mating and post-mating behaviors on their fitnessparameters. In addition, we compared the differences in fitness parameters betweenparthenogenetic and sexual females in arrhenotokous E. americanus and T. tabaci.Furthermore, different performance of arrhenotokous and thelytokous T. tabaci ononion and cabbage were demonstrated. Finally, we conducted behavioral, ecologicaland genetic studies to determine whether there is gene flow between arrhenotokousand thelytokous T. tabaci. The main results are as follows:1. In arrhenotokous E. americanus, the re-mating frequency in female adults wasextremely low during a30-day period, which suggested a single mating system.However, females suffered high rate of male harassment. Post-mating interactionsbetween females and males consist mainly of female resistance and male harassment.2. Mating behavior had beneficial effects on female fitness parameters inarrhenotokous E. americanus. Specifically, compared to parthenogenetic females,sexual females had significantly longer longevity and oviposition period and higherlifetime fecundity and survivorship. In addition, the duration of eggs from sexualfemales was significantly shorter than that from parthenogenetic females. Furthermore,the survival rates for eggs and first and second instars were significantly higher in offspring from sexual females.3. In arrhenotokous E. americanus, post-mating interactions significantly reducedfemale longevity, fecundity and survivorship. By contrast, increased access to malesdid not affect the ratio of female offspring. For males, mating dramatically reducedtheir longevity and survival rate. However, post-mating interactions with females hadno effects on the longevity and survival rate of mated males.4. In arrhenotokous T. tabaci, the majority of females mated multiply during theentire30days we tested and the mean mating frequency of females was2.3times,which indicated a multiple mating system. Females received high rate of maleharassment at all the ages we tested. Post-mating interactions between females andmales consist mainly of female re-mating behavior and male harassment.5. In arrhenotokous T. tabaci, mating was reported costly to females in terms ofreducing longevity and oviposition period and delaying the initiation of egg laying,although mating had no effects on the lifetime and daily fecundity of females.However, mating did not affect the survivorship and longevity of males.6. In arrhenotokous T. tabaci, post-mating interactions significantly affectedfemale fitness parameters. Mated females that continually exposed to males hadsignificantly longer preovipiosition period, shorter oviposition period, lower lifetimefecundity and survivorship compared with mated females housed individually.However, post-mating interactions did not affect offspring sex ratios.7. Host-related performance differences were reported in T. tabaci from tworeproductive modes. On onion, arrhenotokous T. tabaci performed better thanthelytokous T. tabaci, while on cabbage the opposite occurred. In addition, differenthost adaptation was found in different reproductive modes. Arrhenotokous T. tabaciperformed better on onion than on cabbage, whereas thelytokous T. tabaci performedbetter on cabbage than on onion.8. In gene flow section, we found that arrhenotokous males could mate withthelytokous females and there were no behavioral differences between arrhenotokousmales mated with arrhenotokous and with thelytokous females. Males did not have amating preference for females from either reproductive mode. Additionally, matingdid not affect fitness parameters of thelytokous females and their offspring.Furthermore, gene flow was also confirmed, although at a low rate, whenarrhenotokous males were crossed with thelytokous females. Most importantly, the presence of the transferred gene was confirmed in the next generation.In conclusion, E. americanus and T. tabaci had different female mating systems,which is consistent with the diversified female mating system in Thysanoptera.Additionally, the effects of mating behavior on female fitness were opposite in thesetwo species while post-mating behaviors had negative effects on female fitness of bothspecies. Finally, significant host-related performance differences betweenarrhenotokous and thelytokous T. tabaci and the detection of gene flow betweenarrhenotokous and thelytokous T. tabaci offer important knowledge of therelationships of these two reproductive modes in this species.