Cross-breeding And Reproductive Interference Between Two Geographic Population Of Ectropis Obliqua

Tea geometrid, Ectropis obliqua Prout (Lepidoptera: Geometridae), one of the most serious pests intea plantation, causes devastating leaf-losses on tea plants. E. obliqua, being morphologicallyindistinguishable, showed clear reproductive incompatibility, significant differentiation of susceptibilityto EoNPV and variable mitochondrial DNA sequences based on phylogenetic and inheritance analyses.These results suggested an existence of a complex of cryptic species with deep divergence andreproductive isolation in E. obliqua. To elucidate the relationships of E. obliqua, this study comparedthe biological characteristics between Yuhang population (YH) and Songyang population (SY). Weconducted the cross-breeding, population competition, reproductive interference and susceptibility ofEoNPV between the two populations. We also observed the mating interactions as an effort to examinethe behavioral mechanisms for the competition. The results are summarized as follows:1. Reproductive isolation between YH and SYThe hatchability, average larvae and pupua duration, survival to adult and percentage of normaladults of the two cross-breeding combinations were all very much lower than for intra-populationself-crosses. Moreover, the F1generation sex ratio of cross-breeding between the YH and SYpopulations was highly unbalanced, being1:4for the cross of YH♀×SY♂and1:27for the cross ofSY♀×YH♂. The survival rates of cross-breeding treatment were0.01%and0.51%, much less than thecontrols of51.25%and41.78%. To detect reproductive isolation level between the two E. obliquaclades, we conducted self-crosses of F1progenies of intra-population. Because of F1females and malesof the YH♀×SY♂cross not eclosion in three days, they produced no eggs without hatching. The F1hybrids of the SY♀×YH♂cross produced extremely few eggs with none hatching.2. Interspecific competition between YH and SYThe mating rate of YH females was significantly affected by the relative geographic populationdensity in the given treatment, while SY females mating success was not affected. The presence ofnonconspecific males and females could interfere the reproduction of mated females. Significanthatching reduction was observed in mixed cultures, and the pupation, emergence and normal emergencerate of F1and the female ratio in F1were also lower in mixed cultures than in pure culture. As a result,the F1offspring was significant reduction in mixed than pure culture. The difference of the variousnumbers of F1offspring was associated with the mixing of YH and SY. Comparisons among differentmix of populations indicated no significant differences in hatchability, progeny survival to adulthoodand female progeny ratio, and these parameters were lower when YH and SY populations were equallypresented. Furthermore, the population trend index of F1in of1:1trail with20.82%and its survival ratewas17.19%, which were the lowest. Again, these data indicated that the presence of mixed populationsaffects the female production, and least number of F1offspring produced when the two populationsbegan competition in equal numbers.3. Asymmetrical reproductive interference between YH and SY The percentage of conspecific mating of YH did differ significantly between the treatments.Addition of YH males into YH pair decreased the number of larvae slightly, but the negative effectbecame from distinct to significant as more SY males were introduced to the YH pair. In observationand comparison of total number of F1progeny reaching adulthood, increasing YH males by1,2, and3slightly, but not significantly, decreased the number of F1adults produced by YH pair. However, themore SY males were added into YH pair, the fewer F1adults were produced. Similarly, the proportion ofF1female progeny (sex ratio) was not significantly affected by any additional (1-3) YH males, but thesex ratio was significantly reduced with an increasing trend of negative influence as more SY maleswere added into the YH pair. The results indicated that SY males not only interfered mating andnumbers of F1progeny, but also reduced female ratio in F1generation. Reproductive interference wasalso examined by introducing different numbers (1-3) of SY males or YH males into SY pair. Resultsshowed that interspecific mating was not achieved for most cases, except for a combination of SY pairwith an extra YH male. This only interspecific mating group subsequent produced in the lowestnumbers of larvae and adults and female ratio in F1generation, but the influence didn’t reach significantlevel. Except for this group, adding more YH males and SY males to the SY pair didn’t show anynegative impact on mating and reproduction.4. F1generations of cross-breeding were sensitive to EoNPVThe results of laboratory bioassay experiment showed that SY had shown a series of resistancedegree to EoNPV, where YH and F1of cross-breeding were sensitive. The F1generations of YH♀×SY♂were altitudinal susceptibility with abnormally high mortality of97.8%after15days. The F1generations of SY♀×YH♂were91.6%after17days. Moreover, the LT50of YH was11.64days, and theLT50of F1of cross-breeding was shortened up to2days with10.12days and10.32days.