Seasonal changes in cuticular hydrocarbons in response to polyphenism in the host-alternating aphid Prociphilus oriens

In most terrestrial arthropods, cuticular hydrocarbons (CHCs) function to assist in desiccation tolerance and chemical communications. However, few studies have clarified whether CHC profiles change among developmental stages or among different morphs in non-social insects. In the present study, we evaluated how CHC profiles change in accordance with polyphenism in the host-alternating aphid Prociphilus oriens, which exhibits a complex life cycle and five distinct morphs. These morphs are sexual or asexual and adapt to different host plants. We found that all generations of P. oriens shared high proportions of n-alkanes, but its composition varied among morphs. Three morphs that are attended by ants were characterized by relatively high proportions of n-C25 to n-C27, whereas two morphs that are not attended by ants had higher proportions of longer-chain n-alkanes, such as n-C27 and n-C29. The CHC profiles of sexual females were largely different from those of males. Considering that sexual females of Prociphilus spp. lack organs that secrete sex pheromones (scent plaques), the CHCs of sexual females are likely to function as a sex attractant. High proportions of methyl-branched alkanes were detected in the long and flocculent waxy substances of autumnal migrants. These methyl-branched alkanes are considered a cue to recognize conspecifics. We concluded that the functions and components of CHCs differ among morphs, and that those of sexual females differ from those of males and asexual generations because of their function in sexual communication.     

Isolation and characterization of microsatellite loci from the woolly apple aphid Eriosoma lanigerum (Hemiptera: Aphididae: Eriosomatinae)

Eight novel microsatellite primer pairs are presented for Eriosoma lanigerum, representing the first microsatellite markers available for this genus. Loci were characterized for 27 individuals from one single orchard in Central Chile. All loci were polymorphic within E. lanigerum (three to 11 alleles per locus; observed heterozygosity ranging from 0.41 to 0.93), and are therefore useful for population genetic studies within the species.     

Frequency‐dependent selection acting on the widely fluctuating sex ratio of the aphid Prociphilus oriens

Frequency‐dependent selection is a fundamental principle of adaptive sex ratio evolution in all sex ratio theories but has rarely been detected in the wild. Through long‐term censuses, we confirmed large fluctuations in the population sex ratio of the aphid Prociphilus oriens and detected frequency‐dependent selection acting on these fluctuations. Fluctuations in the population sex ratio were partly attributable to climatic factors during the growing season. Climatic factors likely affected the growth conditions of host plants, which in turn led to yearly fluctuations in maternal conditions and sex ratios. In the process of frequency‐dependent selection, female proportion higher or lower than ca. 60% was associated with a reduction or increase in female proportion, respectively, the next year. The rearing of aphid clones in the laboratory indicated that mothers of each clone produced an increasing number of females as maternal size increased. However, the mean male number was not related to maternal size, but varied largely among clones. Given genetic variance in the ability to produce males among clones, selection should favour clones that can produce more numerous males in years with a high female proportion. Population‐level sex allocation to females was on average 71%–73% for three localities and more female‐biased when maternal conditions were better. This tendency was accounted for by the hypothesis of competition among foundresses rather than the hypothesis of local mate competition. We conclude that despite consistent operation of frequency‐dependent selection, the sex ratio continues to fluctuate because environmental conditions always push it away from equilibrium.     

中国绵蚜亚科三新种二新亚种记述(同翅目：蚜总科：瘿绵蚜科)

本文记述了中国绵蚜亚科Eriosomatinae种新和2新亚种,即：北扣绵蚜新种Colophina arc tica Zhang et Qiao,sp.nov.,多室四脉绵蚜新种了Tetraneura olychorema Zhang,sp.nov.,食榆四脉 绵蚜新种T.Ulmicema Zhang,sp.nov.,白卡绵蚜东台新亚种Kaltenbachiella pallida dongtaiensis Zhang ssp.Nov.和钉四脉绵蚜冰草新亚种Tetraneura capitatatusagropyricena Zhang,ssp.Nov.模式标本保存在中国科学院动物研究所。     

Spatiotemporal fluctuations in natural selection acting on the gall‐parasitic aphid Tetraneura sorini

The measurement of the selection gradient is crucial for understanding the magnitude of selection acting directly on a trait and predicting the evolutionary trajectory of that trait. This study evaluated the selection gradient acting on the morphology of the gall‐parasitic aphid Tetraneura sorini during the galling process and compared the strength among populations. Gall formers (first instars) frequently fight with conspecifics or heterospecifics for usurping incipient galls using their well‐developed hind legs. First instars that successfully acquired galls were found within galls, whereas those that failed were found dead on leaf surfaces. Selection gradients were estimated using logistic stepwise regression and partial least square (PLS) regression. Calculated selection differentials indicated that first instars that secured galls were larger in body size than failed individuals through all populations. However, selection gradients on weapon traits varied largely among populations or among years in the same population. We confirmed microevolutionary changes in the relationship between traits, which accorded with the expectation from changes in the selection gradients. When gall formers were transferred onto developing buds individually, individuals that successfully induced galls had smaller body size than failed individuals. Available evidence suggests that the selection gradient on body size becomes higher with an increasing proportion of T. sorini in the Tetraneura species community. Thus, we concluded that more intense fighting with conspecifics leads to stronger selective pressure on body size, but that selective pressure for each trait is variable depending on differences in the tactics and species composition among populations.     

Female-biased sex allocation in wild populations of the eriosomatine aphid Prociphilus oriens: local mate competition or transgenerational effects of maternal investment?

Several aphid species exhibit female-biased sex allocation. Local mate competition (LMC) has been postulated to be the evolutionary factor of the female-biased sex allocation. We estimated individual sex allocation in the eriosomatine aphid Prociphilus oriens and explained the observed pattern of sex allocation based on a hypothesis other than LMC. On the basis of the relationship between maternal body size and brood size, we estimated the cost of producing a female to be 1.85 times the cost of producing a male. The population-wide allocation to males was 22–24 %. Winged mothers exhibited a large variation in the number of male and female embryos they had, including 23–30 % of winged mothers producing only female embryos. There was polymorphism in the sex-ratio expression. Thus, the constant male hypothesis assuming LMC was not supported. Winged mothers that produced an all-female brood contained larger female embryos than did mothers that produced a bisexual brood. Previous studies have indicated that a large sexual female produces a single large egg, which hatches into a first-instar larva containing a larger amount of gonads. Thus, in eriosomatine aphids, maternal investment in daughters directly affects the potential fecundity of granddaughters, whereas investment in sons does not. We propose a hypothesis that higher fitness returns from maternal investment in daughters than in sons may have primarily led to the evolution of highly female-biased sex allocation in P. oriens.