The influence of female age on male mating preference and reproductive success in cabbage beetle, Colaphellus bowringi

The influence of female age on male mating preference and reproductive success has been studied using a promiscuous cabbage beetle, Colaphellus bowringi Baly （Coleoptera： Chrysomelidae）. In a simultaneous choice test, middle-aged females had significantly greater mating success than young and old females. In single pair trials, when paired with middle-aged virgin males, middle-aged females mated faster, copulated longer, and had greater fecundity and fertility than young or old females, while the longevity of males was not significantly affected by female age. This study on C. bowringi suggests that middle-aged females are more receptive to mating, which can result in the highest male reproductive success.

Host plant mediation of diapause induction in the cabbage beetle, Colaphellus bowringi Baly （Coleoptera： Chrysomelidae）

The cabbage beetle, Colaphellus bowringiBaly （Coleoptera： Chrysomelidae）, is a serious pest of crucifers in China, undergoing an imaginal summer and winter diapause in the soil. The effects of host plants on diapause incidence were tested in the beetle. The ratio of adults entering diapause was significantly low when they fed on the mature leaves of Chinese cabbage Shanghaiqin （Brassica chinesis var communis） than those feeding on Chinese cabbage Suzhouqin （Brassica chinesis var communis）, radish （Raphanus sativus var longipinnatus） and stem mustard （Brassicajuncea vat tumida） at 25℃ combined with 13：11 （L： D） h. Fewer adults entered diapause on young leaves compared to physiologically aged and mature radish leaves at 25℃ combined with 13：11 （L： D） h. The effect of host plant species on diapause induction was also evident under continuously dark rearing conditions or at different photoperiods. These experimental results demonstrate that host plant mediation of diapause induction exists in the cabbage beetle. However, at temperatures ≤20℃ or photoperiods of 16：8 （L： D） h combined with 25℃, all individuals entered diapause regardless of the host plants, indicating that the effects of host plants on diapause induction could be expressed only within a limited range of temperatures and photoperiods.

Laboratory evaluation of flight activity of the common cutworm, Spodoptera litura （Lepidoptera： Noctuidae）

The flight activity of Spodoptera litura in tethered conditions is evaluated using a computer-mediated flight-mill in the laboratory. The 3-4-day-old moths fly longer and farther than those of other ages. Male and female moths exhibit similar flight activity. Mating status does not influence the flight duration and distance of 2-day-old females. However, these two flight parameters with a 6-day-old mated female is significantly lower than that of tmmated ones. The optimum temperature for flight ranged from 16-24℃, whereas the optimum RH ranged from 60%--100%. During 72-h period, the total flight duration and distance of 1-day-old male and female moths were 19.6 h （± 5.8） and 83.3 km （± 28.4）, and 24.0 h （± 7.0） and 105.4 km （± 37.4）, respectively. These results indicate that S. litura has a great potential to undertake long-distance migratory flights.

Testing the rate isomorphy hypothesis using five statistical methods

Organisms are said to be in developmental rate isomorphy when the pro- portions of developmental stage durations are unaffected by temperature. Comprehensive stage-specific developmental data were generated on the cabbage beetle, Colaphellus bowringi Baly （Coleoptera： Chrysomelidae）, at eight temperatures ranging from 16℃ to 30℃ （in 2℃ increments） and five analytical methods were used to test the rate isomor- phy hypothesis, including： （i） direct comparison of lower developmental thresholds with standard errors based on the traditional linear equation describing developmental rate as the linear function of temperature; （ii） analysis of covariance to compare the lower devel- opmental thresholds of different stages based on the Ikemoto-Takai linear equation; （iii） testing the significance of the slope item in the regression line of arcsin（√p） versus tem- perature, where p is the ratio of the developmental duration of a particular developmental stage to the entire pre-imaginal developmental duration for one insect or mite species; （iv） analysis of variance to test for significant differences between the ratios of developmental stage durations to that ofpre-imaginal development; and （v） checking whether there is an element less than a given level of significance in the p-value matrix of rotating regres- sion line. The results revealed no significant difference among the lower developmental thresholds or among the aforementioned ratios, and thus convincingly confirmed the rate isomorphy hypothesis.

Comparison of sexual compatibility in crosses between the southern and northern populations of the cabbage beetle Colaphellus bowringi

It is widely accepted that the genetic divergence and reproductive incompat- ibility between closely related species and/or populations is often viewed as an important step toward speciation. In this study, sexual compatibility in crosses between the southern XS population and the northern TA population of the polyandrous cabbage beetle Co- laphellus bowringi was investigated by testing their mating preferences, mating latency, copulation duration, and reproductive performances of post-mating. In choice mating ex- periments, the percentages ofmatings were significantly higher in intra-population crosses than in inter-population crosses. Both isolation index （/） and index of pair sexual isolation （/PSi） indicated partial mating incompatibility or assortative mating in crosses between the two different geographical populations. In single pair mating experiments, XS females in inter-population crosses mated significantly later and copulated significantly shorter than those in intra-population crosses. However, TA females in inter-population crosses mated significantly earlier and copulated longer than those in intra-population crosses, suggesting that larger XS males may enhance heterotypic mating. The lifetime fecundity was highest in XS homotypic matings, lowest in TA homotypic matings, and intermedi- ate in heterotypic rnatings between their parents. The inter-population crosses resulted in significantly lower egg hatching rate and shorter female longevity than intra-population crosses. These results demonstrated that there exist some incompatibilities in premating, postmating-prezygotic, and postzygotic stages between the southern XS population and northern TA population of the cabbage beetle Colaphellus bowringi.