The geographical variation in elytral color polymorphism in Cheilomenes sexmaculata (Fabricius) was analyzed based on data from specimen surveys. In all, 1549 individuals collected from different latitudes throughout Indonesia to Japan were categorized into 20 morph types of elytra. Results show that the morph types have a geographical cline: dark types increased with latitude, although the light types showed higher relative frequency in lower latitudes, which suggests that the geographic variation in elytral color polymorphism in C. sexmaculata is a product of selection by climate. The darker morph types might be advantageously able to make fuller use of insolation at higher latitudes, whereas the lighter morph types were likely to reduce heat stress at lower latitudes. In most areas across Southeast and South Asia, all specimens were of the lightest type, which may imply either: (i) the saturation of genes expressing light morph types, which have less solar absorption, due to tropical climate; or (ii) an enhanced warning function of bright red against predators. On Miyako Island of Japan, a unique frequency of morph types was found compared to the adjacent areas.
Abstract. The ladybird beetle Cheilomenes sexmaculata (Fabricius) is widely distributed throughout the intermediate latitudinal and equatorial regions. It exhibits elytral colour polymorphism with a geographical cline showing increased prevalence of melanic morphs with increasing latitude. Over the past 100 years, this species has extended its distribution towards higher latitudes in Japan because of climatic warming. In this study, long-term changes in the frequency of different morphs and adult body size of this species during this range extension were analyzed based on a survey of specimens in collections. First, we examined specimens collected from areas that were colonized (34-36°N) during the period of range extension and when it ceased (1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005). Chronologically, both the proportions of melanic morphs increased and body size decreased significantly. Next, specimens were examined from newly colonized regions and the former range of distribution (32-34°N); these specimens were collected during period when range extension had ceased. In newly colonized regions, the frequency of melanic morphs was higher and the body size was smaller than in the former range of distribution. These two findings indicate that the smaller, melanic morphs may have undergone a positive-selection driven range extension to higher latitudes.
Abstract. Differences in the time of occurrence of both sexes of adult ladybirds, which refl ect differences in the longevity and reproductive strategies of the sexes, is important from the perspective of applied entomology, including biological control, as well as basic entomology. Nevertheless, there is little fi eld census data on this topic. We investigated the seasonal occurrence of both sexes of Cheilomenes sexmaculata (Fabricius) in Osaka City, central Japan, from 2003 to 2011. Female adults tended to appear earlier than males after hibernation or aestivation. That males never appeared earlier than females during the nine year period of this study indicate that protogyny occurs after hibernation and aestivation in this species.
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