Inbreeding is known to have adverse effects on fitness-related traits in a range of insect species. A series of theoretical and experimental studies have suggested that polyandrous insects could avoid the cost of inbreeding via pre-copulatory mate choice and/or post-copulatory mechanisms. We looked for evidence of pre-copulatory inbreeding avoidance using female mate preference trials, in which females were given the choice of mating with either of two males, a sibling and a non-sibling. We also tested for evidence of post-copulatory inbreeding avoidance by conducting double mating experiments, in which four sibling females were mated with two males sequentially, either two siblings, two non-siblings or a sibling and a non-sibling in either order. We identified substantial inbreeding depression: offspring of females mated to full siblings had lower hatching success, slower development time from egg to adult, lower survival of larval and pupal stages, and lower adult body mass than the offspring of females mated to non-sibling males. We also found evidence of pre-copulatory inbreeding avoidance, as females preferred to mate with non-sibling males. However, we did not find any evidence of post-copulatory inbreeding avoidance: egg hatching success of females mating to both sibling and non-sibling males were consistent with sperm being used without bias in relation to mate relatedness. Our results suggest that this cabbage beetle has evolved a pre-copulatory mechanism to avoid matings between close relative, but that polyandry is apparently not an inbreeding avoidance mechanism in C. bowringi.

The Asian corn borer, Ostrinia furnacalis (Guen ee) (Lepidoptera: Crambidae), enters facultative diapause as fully grown larva in response to short-day conditions during the autumn. Photoperiodic response curves showed a stable critical daylength of ca. 13.5 h at 25, 28, and 30°C, which is nearly identical with the critical daylength between 13 h 22 min and 13 h 27 min in the field. The incidence of diapause obviously declined during ultra-long nights (14-22 h scotophases) and DD (i.e., constant darkness). The required day number (RDN) for a 50% response differed significantly between short-and long-night cycles at different temperatures, indicating that the effect of one short night was equivalent to the effect of three long nights at 25 and 28°C. The third instar was the stage most sensitive to the photoperiod. Night-interruption experiments with a 1-h light pulse at L9:D15 and L12:D12 exhibited a broad trough of diapause inhibition. In experiments using non-24-h light-dark cycles, only the cycles containing a long night of 12 h resulted in high incidence of diapause, regardless of the duration of the accompanying light period, indicating that the duration of the dark period was of greater importance than that of the light period. The Nanda-Hamner and B€ unsow experiments in O. furnacalis did not show any rhythmic fluctuations with a period of ca. 24 h in their photoperiodic response curves; the incidence of diapause was low when the scotophase length exceeded 16 h. The rearing daylengths of 11 and 12 h evoked a greater intensity of diapause than did 13 h at 25 and 28°C. By transferring naturally overwintering larvae from natural conditions to a short photoperiod of L12:D12 or a long photoperiod of L15:D9 combined with 25°C, photoperiod appeared to have a significant influence on diapause development during the early phase of diapause. Field observations for 2 years revealed that pupation and adult emergence of overwintering individuals (50% responses) occurred in early May and mid-May, respectively.

The Asian corn borer Ostrinia furnacalis (Guenée) enters facultative diapause as fully-developed larvae in response to short-day conditions. As a consequence of geographical variation in photoperiodic response, moths from Nanchang (28 • 46 N, 115 • 50 E) enter diapause in response to short day-lengths (D strain), even at the high temperatures whereas moths from Ledong (18 • 47 N, 108 • 89 E) exhibit almost no diapause under the same conditions (N strain). In the present study, crosses between the two strains are used to evaluate the inheritance of diapause under different photoperiods at temperatures of 22, 25 and 28 • C. The moths, both reciprocal crosses and backcrosses, show a clear long-day response, similar to that of the D strain, suggesting that the photoperiodic response controlling diapause in this moth is heritable. However, the critical day-length for induction of diapause is shorter in hybrids than in the D strain. The N strain also shows a short-day photoperiodic response at the lower temperature of 22 • C, indicating that the N strain still has the capacity to enter a photoperiodically-induced diapause, depending on the rearing temperature. The incidence of diapause in all crosses is highest with D strain fathers or grandfathers and lowest with N strain fathers or grandfathers, indicating that the male parent has significantly more influence on the incidence of diapause of subsequent progeny than the female. The results obtained from all crosses under LD 12 : 12 h or LD 13 : 11 h photocycles at 25 • C show that inheritance of diapause in O. furnacalis does not fit an additive hypothesis and that the capacity for diapause is transmitted genetically in the manner of incomplete dominance.

It is widely accepted that the genetic divergence and reproductive incompatibility 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 Colaphellus bowringi was investigated by testing their mating preferences, mating latency, copulation duration, and reproductive performances of post-mating. In choice mating experiments, the percentages of matings were significantly higher in intra-population crosses than in inter-population crosses. Both isolation index (I) and index of pair sexual isolation (IPSI ) 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 intermediate in heterotypic matings 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.