Life history responses of the small brown planthopper Laodelphax striatellus to temperature change.

Temperature is a key environmental factor in ectotherms and influences many life history traits. In the present study, the nymphal development time, sex ratio and wing dimorphism of the small brown planthopper Laodelphax striatellus were examined under the conditions of constant temperatures, naturally varying temperatures (or different generations), and different temperatures combined with different photoperiod. The results showed that from 18 to 28 °C, the developmental time of nymphs was gradually shortened with the increase of temperature, whereas the high temperatures of 30 and 32 °C in the third to fifth instar nymphal stages and high summer temperature of 28.8 and 29.7 °C significantly delayed developmental time and resulted in higher mortality of nymphs. In all treatments, the developmental time was longer in females than males. The nymphs took significantly longer time to develop in the short daylength of 12 h than in longer daylengths of 13, 14, 15 and 16. Differences in developmental time were also found between wing morph, with long-winged individuals being significantly longer than the short-winged individuals at lower temperatures and significantly shorter than the short-winged individuals at higher temperatures. In all treatments, the sex ratio was stable, approaching 1:1, without being affected by temperature, generations and photoperiod. Photoperiod and temperature had significantly influence on the wing dimorphism. Long daylength combined with different temperatures resulted in significantly higher proportions of long-winged morph, whereas the low temperatures combined with the short daylengths in autumn and winter resulted in significantly high proportion of short-winged morph. This study broadens our understanding of the life-history traits of this planthopper and provides basic data for analyzing the effects of climate change on the planthopper reproduction.

Partial reuse of circadian clock genes along parallel clines of diapause in two moth species.

Understanding the molecular basis of repeated evolution improves our ability to predict evolution across the tree of life. Only since the last decade has high-throughput sequencing enabled comparative genome scans to thoroughly examine the repeatability of genetic changes driving repeated phenotypic evolution. The Asian corn borer (ACB), Ostrinia furnacalis (Guenée), and the European corn borer (ECB), Ostrinia nubilalis (Hübner), are two closely related moths displaying repeatable phenological adaptation to a wide range of climates on two separate continents, largely manifesting as changes in the timing of diapause induction and termination across latitude. Candidate genes underlying diapause variation in North American ECB have been previously identified. Here, we sampled seven ACB populations across 23 degrees of latitude in China to elucidate the genetic basis of diapause variation and evolutionary mechanisms driving parallel clinal responses in the two species. Using pooled whole-genome sequencing (Pool-seq) data, population genomic analyses revealed hundreds of single nucleotide polymorphisms (SNP) whose allele frequencies covaried with mean diapause phenotypes along the cline. Genes involved in circadian rhythm were over-represented among candidate genes with strong signatures of spatially varying selection. Only one of two circadian clock genes associated with diapause evolution in ECB showed evidence of reuse in ACB (period [per]), but per alleles were not shared between species nor with their outgroup, implicating independent mutational paths. Nonetheless, evidence of adaptive introgression was discovered at putative diapause loci located elsewhere in the genome, suggesting that de novo mutations and introgression might both underlie the repeated phenological evolution.

Differentiation of Developmental Pathways Results in Different Life-History Patterns between the High and Low Latitudinal Populations in the Asian Corn Borer.

Individual insects often exhibit two alternative pathways of non-diapausing and diapausing developments. Yet, most studies have focused on the latitudinal variation in life-history traits for non-diapausing individuals. No study has examined the differences in life history traits between non-diapausing and diapausing individuals along a latitudinal gradient. We used six different geographical populations of Ostrinia furnacalis to examine the latitudinal variation in life-history traits between non-diapausing and diapausing individuals in terms of their sex ratio, larval and pupal developmental times, pupal weight, growth rate, adult weight and weight loss, and sexual size dimorphism. The results showed that latitudinal variation in life-history traits for both non-diapausing and diapausing individuals exhibited a sawtooth pattern, but the life-history pattern of the two alternative developmental pathways was significantly different between the high and low latitudes. For the non-diapausing pathway, the high-latitudinal populations showed a significantly shorter larval developmental time, higher growth rate and greater body weight than the low-latitudinal populations, suggesting countergradient variation. Conversely, in the diapausing pathway, the high-latitudinal populations had longer larval developmental times, lower growth rates and relatively smaller body weights than the low-latitudinal populations, suggesting cogradient variation. We also found that in the high-latitudinal populations, larvae in the non-diapausing pathway had shorter developmental time and higher body weight, whereas larval developmental time of the low-latitudinal populations was longer and the body weight was smaller. The relationship between larval developmental time and pupal weight was also different between the two developmental pathways. These results provide new insights into the evolution of life-history traits in this moth.

A multi-year dormancy strategy in a cabbage beetle population in southeastern China.

The life cycle of the cabbage beetle Colaphellus bowringi in southeastern China is complex due to four options for adult development: summer diapause, winter diapause, prolonged diapsuse, and nondiapause. However, detailed information on the multi-year emergence patterns of diapausing individuals in this beetle has not been documented. In this study, we monitored the adult emergence patterns of diapausing individuals and estimated the influence of the diapause-inducing temperature and photoperiod on the incidence of prolonged diapause under seminatural conditions for several years. The duration of diapause for adults collected from the vegetable fields in different years varied from several months to 5 years. Approximately 25.9%-29.2% of individuals showed prolonged diapause (emergence more than 1 year after entering diapause) over the 5 years of observation. Furthermore, regardless of insect age, the emergence of diapausing adults from the soil always occurred between mid-February and March in spring and between late August and mid-October in autumn, when the host plants were available. The influence of diapause-inducing temperatures (22, 25, and 28°C) combined with different photoperiods (L:D 12:12 h and L:D 14:10 h) on diapause duration was tested under seminatural conditions. Pairwise comparisons of diapause duration performed by the log-rank test revealed that the low temperature of 22°C combined with the long photoperiod of L:D 14:10 h induced the longest diapause duration, whereas the low temperature of 22°C combined with the short photoperiod of L:D 12:12 h induced the highest proportion of prolonged diapause. This study indicates that C. bowringi adopts a multi-year dormancy strategy to survive local environmental conditions and unpredictable risks.

Effects of temperature on life-history traits of the newly invasive fall armyworm, Spodoptera frugiperda in Southeast China.

In mid-May, 2019, the fall armyworm (FAW) Spodoptera frugiperda invaded Jiangxi Province, China, and caused extensive damage to corn crops. However, little attention has been given to the life-history traits of the FAW. In the present study, we systematically investigated the life-history traits of the newly invasive FAW on corn leaves at 19, 22, 25, 28, and 31°C under a photoperiod of LD 15:9 hr. The FAW thrived on the corn leaves with short developmental periods, high survival rates of larvae and pupae, very high mating success rates, and high fecundity. The pupal developmental stage was significantly longer in males than females at all temperatures, thus resulting in a protogyny phenomenon. The pupal weight was heaviest after a relatively shorter larval development stage at a higher temperature (25°C); thus, the FAW did not follow the temperature-size rule. Females were smaller than males, indicating sexual size dimorphism. A small proportion of females delayed their pre-oviposition period and began to lay eggs on the 7th to 9th day after adult emergence. There were positive relationships between pupal weight and larval developmental time and between adult weight and fecundity. There was a negative relationship between fecundity and longevity. These findings can help us to predict the population dynamics of the FAW on corn and to develop a suitable and practical management strategy.

Inheritance of key life-history traits in crosses between northern and southern populations of the cabbage beetle Colaphellus bowringi (Coleoptera: Chrysomelidae).

A southern population (S) from Xiushui County (29°1'N, 114°4'E) and a northern population (N) from Shenyang city (41°48'N, 123°23'E) of the cabbage beetle, Colaphellus bowringi vary greatly in their life-history traits, and may serve as an excellent model with which to study the inheritance of life-history traits. In the present study, we performed intraspecific hybridization using the two populations, comparing the key life-history traits (fecundity, development time, body weight, growth rate, and sexual size dimorphism (SDD)) between the two populations (S♀ × S♂ and N♀ × N♂) and their two hybrid populations (S♀ × N♂ and N♀ × S♂ populations) at 19, 22, 25, and 28°C. Our results showed that there were significant differences in life-history traits between the two parental populations, with the S population having a significantly higher fecundity, shorter larval development time, larger body weight, higher growth rate, and greater weight loss during metamorphosis than the N population at almost all temperatures. However, these life-history traits in the two hybrid populations were intermediate between those of their parents. The life-history traits in the S × N and N × S populations more closely resembled those of the maternal S population and N population, respectively, showing maternal effects. Weight loss for both sexes was highest in the S population, followed by the S × N, N × S, and N populations at all temperatures, suggesting that larger pupae lost more weight during metamorphosis. The changes in SSD with temperature were similar between the S and the S × N populations and between the N and the N × S populations, also suggesting a maternal effect. Overall, our results showed no drastic effect of hybridization on C. bowringi, being neither negative (hybrid inferiority) nor positive (heterosis). Rather, the phenotypes of hybrids were intermediate between the phenotypes of their parents.

Expression of alternative developmental pathways in the cabbage butterfly, Pieris melete and their differences in life history traits.

The seasonal life cycle of the cabbage butterfly, Pieris melete is complicated because there are three options for pupal development: summer diapause, winter diapause, and nondiapause. In the present study, we tested the influence of temperature, day length, and seasonality on the expression of alternative developmental pathways and compared the differences in life history traits between diapausing and directly developing individuals under laboratory and field conditions. The expression of developmental pathway strongly depended on temperature, day length, and seasonality. Low temperatures induced almost all individuals to enter diapause regardless of day length; relatively high temperatures combined with intermediate and longer day lengths resulted in most individuals developing without diapause in the laboratory. The field data revealed that the degree of phenotypic plasticity in relation to developmental pathway was much higher in autumn than in spring. Directly developing individuals showed shorter development times and higher growth rates than did diapausing individuals. The pupal and adult weights for both diapausing and directly developing individuals gradually decreased as rearing temperature increased, with the diapausing individuals being slightly heavier than the directly developing individuals at each temperature. Female body weight was slightly lower than male body weight. The proportional weight losses from pupa to adult were almost the same in diapausing individuals and in directly developing individuals, suggesting that diapause did not affect weight loss at metamorphosis. Our results highlight the importance of the expression of alternative developmental pathways, which not only synchronizes this butterfly's development and reproduction with the growth seasons of the host plants but also exhibits the bet-hedging tactic against unpredictable risks due to a dynamic environment.

Effect of rearing conditions on the correlation between larval development time and pupal weight of the rice stem borer, Chilo suppressalis.

A strong positive correlation between development time and body size is commonly assumed. However, the evidence is increasing that the correlation between the two traits can be positive, zero or negative, depending on whether the two traits are under antagonistic or synergistic selection. In the present study, we examined the relation between larval development time and pupal weight of the rice stem borer Chilo suppressalis under laboratory and field conditions. For individuals reared at constant temperatures (22, 25, 28 and 31°C), a longer larval period tended to result in larger pupae, showing a positive correlation between larval development time and pupal weight; whereas for those reared under field conditions, a longer larval period tended to result in smaller pupae at 23.5 and 29.8°C, showing a negative correlation between the two traits. There was no correlation between the two traits at the mean daily temperature of 31°C. At constant temperatures, larval development time shortened significantly as rearing temperature increased, whereas pupae tended to become larger at higher temperatures, although no significant difference was detected among temperatures for pupal weight. Under field conditions, larval development time decreased significantly as the mean daily temperature increased, whereas pupal weight of females increased significantly with the increase in the mean daily temperature, which is an example of the reverse temperature-size rule. Feeding method significantly affected larval development time and pupal weight. For individuals fed on live rice plants, larval development time shortened significantly and pupal weight increased significantly compared with those reared on fresh rice stems.

Chilling effect on termination of reproductive diapause in Listronotus maculicollis (Coleoptera: Curculionidae).

Diapausing adults of the annual bluegrass weevil, Listronotus maculicollis, were collected from their hibernating sites at different times in autumn and winter, and subjected to different conditions to observe diapause termination by dissecting and measuring the reproductive organs. When diapausing weevils were maintained under laboratory cold conditions (10 h light at 6 °C:14 h dark at 4 °C) from early December to late March, the sizes of reproductive organs of both sexes increased or fluctuated slightly, and very few females had developing oocytes, suggesting that most adults did not resume development during the chilling period. When diapausing weevils (chilled for 40-83 days) were transferred to warm conditions (LD 14:10 and 21 °C) for different lengths of time, reproductive organ sizes in both sexes increased as chilling period prolonged, implying that chilling played an important role in diapause termination. Under field conditions, an apparent peak of reproductive development was observed on January 07 when 80% of males and 53% of females had resumed growth of reproductive organs. Diapausing weevils collected in September without chilling did not develop successfully despite exposure to warm conditions. In contrast, 87% of males and 93% of females collected from the field on January 21 had initiated reproductive development after 5 days of exposure to warm conditions, indicating the necessity of chilling for diapause termination. Male and female reproductive organ sizes increased faster and to a greater final size the longer the preceding chilling period was. The prolonged chilling period in the field resulted in more synchronized and advanced development in L. maculicollis when exposed to warm conditions.

Latitudinal cogradient variation of development time and growth rate and a negative latitudinal body weight cline in a widely distributed cabbage beetle.

The evolutionary and phenotypic responses to environmental gradients are often assumed to be the same, a phenomenon known as "cogradient variation". However, only a few insect species display cogradient variation in physiological traits along a latitudinal gradient. We found evidence for such a response in the examination of the life history traits of the cabbage beetle Colaphellus bowringi from 6 different geographical populations at 16, 19, 22, 24, 26 and 28°C. Our results showed that larval and pupal development times significantly decreased as rearing temperature increased, and that growth rates were positively correlated with temperature. Body weight tended to decrease with increasing temperature, consistent with the general pattern in ectothermic animals. Larval development time was positively correlated with latitude, whereas the growth rate decreased as latitude increased, showing an example of latitudinal cogradient variation. Body weight significantly decreased with increasing latitude in a stepwise manner, showing a negative latitudinal body weight cline. Females were significantly larger than males, consistent with the female biased sex dimorphism in insects. Body weight tended to decrease with increasing rearing temperature, whereas the differences in sexual size dimorphism (SSD) tended to decrease with increasing body weight, which biased our results toward acceptance of Rensch's rule. We found that weight loss was an important regulator of SSD, and because male pupae lost significantly more weight at metamorphosis than female pupae, SSD was greater in adults than in pupae. Overall, our data provide a new example that a latitudinal cogradient variation in physiological traits is associated with a negative latitudinal body weight cline.

Life-history responses of the rice stem borer Chilo suppressalis to temperature change: Breaking the temperature-size rule.

Temperature is a key environmental factor for ectotherms and affects a large number of life history traits. In the present study, development time from hatching to pupation and adult eclosion, pupal and adult weights of the rice stem borer, Chilo suppressalis were examined at 22, 25, 28 and 31°C under L18:D 6. Larval and pupal times were significantly decreased with increasing rearing temperature and growth rate was positively correlated with temperature. Larval and pupal developmental times were not significantly different between females and males. The relationship between body weight and rearing temperature in C. suppressalis did not follow the temperature-size rule (TSR), both males and females gained the highest body weight at 31°C. Females were significantly larger than males at all temperatures, showing a female biased sex size dimorphism (SSD). Contrary to Rensch's rule, SSD and body weight in C. suppressalis tended to increase with rising temperature. Male pupae lost significantly more weight at metamorphosis compared to females. We discuss the adaptive significance of the reverse-TSR in the moth's life history.

Variation of life-history traits of the Asian corn borer, Ostrinia furnacalis in relation to temperature and geographical latitude.

Life-history traits from four geographical populations (tropical Ledong population [LD], subtropical Guangzhou [GZ] and Yongxiu populations, and temperate Langfang population [LF]) of the Asian corn borer, Ostrinia furnacalis were investigated at a wide range of temperatures (20-32°C). The larval and pupal times were significantly decreased with increasing rearing temperature, and growth rate was positively correlated with temperature. The relationship between body weight and rearing temperature in O. furnacalis did not follow the temperature-size rule (TSR); all populations exhibited the highest pupal and adult weights at high temperatures or intermediate temperatures. However, development time, growth rate, and body weight did not show a constant latitudinal gradient. Across all populations at each temperature, female were significantly bigger than males, showing a female-biased sexual size dimorphism (SSD). Contrary to Rensch's rule, the SSD tended to increase with rising temperature. The subtropical GZ population exhibited the largest degree of dimorphism while the temperate LF exhibited the smallest. Male pupae lose significantly more weight at metamorphosis compared to females. The proportionate weight losses of different populations were significantly different. Adult longevity was significantly decreased with increasing temperature. Between sexes, all populations exhibit a rather female-biased adult longevity. Finally, we discuss the adaptive significance of higher temperature-inducing high body weight in the moth's life history and why the moth exhibits the reverse TSR.

Inheritance of diapause in crosses between the northernmost and the southernmost strains of the Asian corn borer Ostrinia furnacalis.

The northernmost Harbin strain (N strain) of the Asian corn borer, Ostrinia furnacalis enters facultative diapause as fully grown larvae in response to short daylengths; whereas the southernmost Ledong strain (S strain) exhibits almost no diapause under the same light conditions. In the present study, we examined the inheritance of diapause induction and termination by crossing the two strains under a range of environmental conditions. The N strain showed a typical long-day response with a critical daylength of approximately15.88 h at 22°C, 15.72 h at 25°C and 15.14 h at 28°C, whereas the S strain showed a weak photoperiodic response at 22°C. The F1 progeny also showed a long-day response at 22, 25 and 28°C. However, the critical daylengths in S ♀ × N ♂ crosses were significantly longer than those in N ♀ × S ♂ crosses, indicating a sex linkage in the inheritance of diapause induction, with the male parent having more influence on the following F1 progeny. The incidence of diapause in S ♀ × N ♂ crosses was the same as in the N strain under short daylengths of 11-13 h, indicating that diapause trait is completely dominant over the non-diapause trait. The critical daylength in backcross to N was significantly longer than it was in backcross to S, showing a grandfather gene effect. Whether the inheritance of diapause fits an additive hypothesis or not was dependent on the rearing photoperiod, and the capacity for diapause was transmitted genetically in the manner of incomplete dominance. The duration of diapause for the reciprocal crosses under different diapause-terminating conditions showed different patterns of inheritance. The results in this study reveal that genetic and genetic-environmental interactions are involved in diapause induction and termination in O. furnacalis.

Photoperiod and temperature effects on the adult eclosion and mating rhythms in Pseudopidorus fasciata (Lepidoptera: Zygaenidae).

Daily distributions of eclosion and mating activities of Pseudopidorus fasciata Walker (Lepidoptera: Zygaenidae) were recorded under natural and various laboratory conditions. Eclosion of this insect exhibited circadian gating in constant darkness (DD) but not in constant light (LL) at 28°C. Under natural conditions, the majority of adults emerged in midmorning with an eclosion peak around 1000 hours. The eclosion distribution was significantly affected by ambient temperature but not by photoperiod under laboratory conditions. Eclosion was more spread out at 22°C than at higher temperatures, and peak eclosion times were advanced at higher temperatures up to 30°C. Under natural and laboratory diurnal cycles, adults of P. fasciata preferred to mate at dusk, within a few hours before the start of the scotophase. Photoperiod and ambient temperature interacted in regulating the mating distribution in P. fasciata. Mating rhythmicity disappeared under DD and LL, under which the insect either mated arrhythmically (DD) or barely mated (LL). Overall, eclosion rhythm in this insect was predominantly regulated by temperature rather than photoperiod, whereas photoperiod appeared to be more influential than temperature in rhythmic gate of mating patterns.

A comparison of the life-history traits between diapause and direct development individuals in the cotton bollworm, Helicoverpa armigera.

In order to understand the differences of life-history traits between diapause and direct development individuals in the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), the development time, body size, growth rate, and adult longevity were investigated between the two populations, which were induced under 12:12 L:D and 16:8 L:D photoperiods, respectively, at 20, 22, and 25°C. The results indicated that the larval development time, pupal weight, adult weight, and growth rate were significantly different between diapause and direct developing individuals. The diapause developing individuals had a significantly higher pupal and adult weight and a longer larval time compared with direct developing individuals. However, the growth rate in diapause developing individuals was lower than that in the direct developing individuals. Analysis by GLM showed that larval time, pupal and adult weight, and growth rate were significantly influenced by both temperature and developmental pathway. The pupal and adult weights were greater in males than females in both developmental pathways, exhibiting sexual size dimorphism. The dimorphism in adult weight was more pronounced than in pupal weight because female pupae lost more weight at metamorphosis compared to male pupae. Protogyny was observed in both developmental pathways. However, the protogyny phenomenon was more pronounced at lower temperatures in direct developing individuals, whereas it was more pronounced in diapause developing individuals when they experienced higher temperatures in their larval stage and partial pupal period. The adult longevity of diapause developing individuals was significantly longer than that of direct developing individuals. The results reveal that the life-history strategy was different between diapause and direct developing individuals.

Diapause induction and termination in the small brown planthopper, Laodelphax striatellus (Hemiptera: Delphacidae).

The small brown planthopper, Laodelphax striatellus (Fallén) enters the photoperiodic induction of diapause as 3rd or 4th instar nymphs. The photoperiodic response curves in this planthopper showed a typical long-day response type with a critical daylength of approximately 11 h at 25 °C, 12 h at 22 and 20 °C and 12.5 h at 18 °C, and diapause induction was almost abrogated at 28 °C. The third stage was the most sensitive stage to photoperiod. The photoperiodic response curve at 20 °C showed a gradual decline in diapause incidence in ultra-long nights, and continuous darkness resulted in 100% development. The required number of days for a 50% response was distinctly different between the short- and long-night cycles, showing that the effect of one short night was equivalent to the effect of three long nights at 18 °C. The rearing day length of 12 h evoked a weaker intensity of diapause than did 10 and 11 h. The duration of diapause was significantly longer under the short daylength of 11 h than it was under the long daylength of 15 h. The optimal temperature for diapause termination was 26 and 28 °C. Chilling at 5 °C for different times did not shorten the duration of diapause but significantly lengthened it when chilling period was included. In autumn, 50% of the nymphs that hatched from late September to mid-October entered diapause in response to temperatures below 20 °C. The critical daylength in the field was between 12 h 10 min and 12 h 32 min (including twilight), which was nearly identical to the critical daylength of 12.5 h at 18 °C. In spring, overwintering nymphs began to emerge in early March-late March when the mean daily temperature rose to 10 °C or higher.

Diapause induction and termination in Hyphantria cunea (Drury) (Lepidoptera: Arctiinae).

The fall webworm, Hyphantria cunea (Drury), enters facultative diapause as a pupa in response to short-day conditions during autumn. Photoperiodic response curves showed that the critical day length for diapause induction was 14 h 30 min, 14 h 25 min and 13 h 30 min at 22, 25 and 28°C, respectively. The photoperiodic responses under non-24 h light-dark cycles demonstrated that night length played an essential role in the determination of diapause. Experiments using a short day length interrupted by a 1-h light pulse exhibited two troughs of diapause inhibition and the effect of diapause inhibition was greater in the early scotophase than in the late scotophase. The diapause-inducing short day lengths of 8, 10 and 12 h evoked greater intensities of diapause than did 13 and 14 h. Diapause can be terminated without exposure to chilling, but chilling at 5°C for 90 and 120 d significantly accelerated diapause development, reduced mortality, and synchronized adult emergence. Additionally, the potential for H. cunea from the temperate region (Qingdao) to emerge and overwinter under field conditions in subtropical regions (Nanchang) of China was evaluated. Pupae that were transferred to Nanchang in early July showed a 60% survival rate and extremely dispersed pupal period (from 12 to 82 days), suggesting that some pupae may undergo summer diapause. Diapausing temperate region pupae that were moved out-of-doors in Nanchang during October showed approximately 20% overwintering survival; moreover, those pupae that overwintered successfully emerged the next spring during a period when their host plants would be available. The results indicate that this moth has the potential to expand its range into subtropical regions of China.

Evidence for inbreeding depression and pre-copulatory, but not post copulatory inbreeding avoidance in the cabbage beetle Colaphellus bowringi.

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.

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 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.

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.