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Many species show rhythmicity in activity, from the timing of flowering in plants to that of foraging behavior in animals. The free-running periods and amplitude (sometimes called strength or power) of circadian rhythms are often used as indicators of biological clocks. Many reports have shown that these traits are highly geographically variable, and interestingly, they often show latitudinal or longitudinal clines. In many cases, the higher the latitude is, the longer the free-running circadian period (i.e., period of rhythm) in insects and plants. However, reports of positive correlations between latitude or longitude and circadian rhythm traits, including free-running periods, the power of the rhythm and locomotor activity, are limited to certain taxonomic groups. Therefore, we collected a cosmopolitan stored-product pest species, the red flour beetle Tribolium castaneum, in various parts of Japan and examined its rhythm traits, including the power and period of the rhythm, which were calculated from locomotor activity. The analysis revealed that the power was significantly lower for beetles collected in northern areas than southern areas in Japan. However, it is worth noting that the period of circadian rhythm did not show any clines; specifically, it did not vary among the sampling sites, despite the very large sample size (n = 1585). We discuss why these cline trends were observed in T. castaneum. [ABSTRACT FROM AUTHOR]

Many parasitoid wasps exhibit 'oviposition learning,' whereby females associate host-related cues with oviposition and use them in subsequent searches for hosts. This is affected by various factors that have yet to be fully elucidated. We examined the effects of host developmental stage on oviposition learning in parasitoid wasps that utilize both larval and pupal hosts using Heterospilus prosopidis Viereck ( Hymenoptera: Braconidae), an ectoparasitoid of Bruchinae beetles ( Coleoptera: Chrysomelidae), as a model. First, we examined whether the induction of host species preference differs between oviposition on larval and pupal hosts. Oviposition choice experiments were performed for both larval and pupal hosts using two equally preferred host species - Callosobruchus chinensis (L.) and Callosobruchus maculatus ( Fabricius) - and wasps that were conditioned by an oviposition experience on either of the two host species. We found an induction of host species preference in wasps conditioned with pupal hosts but not in wasps conditioned with larval hosts. Next, we examined whether the induced preference was host-stage-specific. Oviposition experiments with pupal-host-conditioned wasps and larval hosts as choice hosts indicated that learned cues were not used when searching for larval hosts. Similar results were obtained for larval-host-conditioned wasps. We compared oviposition behavior on larval and pupal hosts but found no behavioral differences that could contribute to the observed difference in host preference induction. Our results indicate that larval and pupal hosts have different effects on host preference following an oviposition experience in H. prosopidis, although the detailed mechanisms remain unclear. These findings are notable because in parasitoid wasps that utilize both larval and pupal hosts, host developmental stages have attracted little attention as factors affecting oviposition learning. [ABSTRACT FROM AUTHOR]