Abstract Polistes , primitively eusocial wasps, build paper nests using plant fibers and oral secretions produced by the wasps themselves. In general, a single larva is reared one per cell, spinning a completely closed cocoon upon pupation. By contrast, in the subgenus Gyrostoma of Polistes , the same cell is often simultaneously occupied by two successive broods. After cocoon spinning by the post‐feeding larvae in the central cells, an additional egg was laid on the silk cap inside the cell. Eggs grow and attain second‐instar larvae during the emergence of older occupants. In addition to the eggs laid on the silk cap, eggs are laid in newly constructed cells outside the combs. Although a recent study suggested that rearing two immatures in a single cell improved the cost of construction and maintenance of the nest, the disadvantages of rearing multiple immatures in a single cell have not yet been evaluated. We compared developmental time and mortality rates between immatures reared on silk caps in the central cells and those in the peripheral cells. In the central cells, the merit of shorter development for 1–2 days of the first‐instar larvae was shown; however, this was almost offset by the demerit of longer egg development. The survival rates of the eggs and first‐instar larvae did not differ between the two cell positions. We concluded that rearing two immatures in a single cell does not result in disadvantages during the early stages of development.
Abstract Synchronous hatching is widespread in insects and may confer adaptive advantages such as predator avoidance and aggregation of hatchlings. In Locusta migratoria , two mechanisms have been proposed to underlie hatching synchrony within egg pods: maternal phase effects and embryo–embryo interactions. This study examined whether maternal phase influences within‐pod hatching synchrony when embryo–embryo communication is experimentally manipulated. Eggs from solitarious and gregarious females were maintained either in contact (clumped) or individually separated and incubated at 30°C under continuous illumination. Mean hatching time, within‐batch variance in hatching time, and the duration from 10 to 90% hatching were analyzed. Gregarious eggs laid by crowd‐reared adults were slightly larger and hatched earlier on average than solitarious eggs laid by isolation‐reared adults under both egg conditions, confirming a phase‐dependent difference in embryonic developmental rate. In contrast, hatching synchrony was strongly influenced by egg condition: Most clumped eggs hatched within a few hours, whereas separated eggs hatched later and over a much broader time span. No significant phase‐dependent differences were detected in either the variance of hatching time or the 10–90% hatching period. These findings indicate that maternal phase primarily influences embryonic developmental rate, whereas physical contact among eggs is essential for the final synchronization of hatching within an egg pod. The results highlight the importance of distinguishing embryonic developmental timing from within‐pod hatching synchrony.
Abstract Sympetrum frequens , a common yet regionally declining dragonfly in Japan, is likely to use forests as seasonal habitats during the adult stage. After emerging from lowland wetlands in early summer, adults move to montane forests to avoid summer heat, and they return to the lowlands for reproduction in autumn, where they roost and forage in nearby forests. However, the spatial patterns of forest habitats remain unclear, probably because detecting individuals within forests is difficult. In contrast, after leaving forests, they become observable in foothills in late summer and in lowland paddy fields during autumn, where their distribution may retain the spatial legacies of recent forest use. This study analyzed the relationships between adult abundance observed during these periods and the surrounding forest landscapes across multiple spatial scales and elevation bands in central Japan to infer the forest habitats they previously occupied. In late summer, a significant positive effect of forest area at elevations of 400–600 m (average summer temperature range: 23.8–25.4°C) within 5 km best explained the number of adults at foothills. In autumn, adult abundance in the lowland paddy fields was best explained by a significant hump‐shaped relationship with forest area within 5 km, peaking at approximately 40% forest cover. These results suggest spatial and climatic structuring of their seasonal forest habitats, which may advance our ecological understanding and inform conservation planning for this species. Furthermore, this study underscores the value of landscape analysis that uses the outside‐forest abundance of multi‐habitat species to identify forest habitats.
Abstract Desiccation resistance is an important physiological trait in insects, but how seasonal cues jointly affect this trait remains poorly understood in gerrid water striders. This study examined how temperature and photoperiod from the nymphal stage through early adulthood influence desiccation resistance in Aquarius paludum amamiensis (Miyamoto). First‐instar nymphs were reared under four combinations of high or low temperature and long‐ or short‐day photoperiod. Desiccation resistance was evaluated 30 days after adult emergence by measuring survival time, water loss at death, water loss rate and initial body water content. Survival time was significantly affected by temperature, photoperiod and their interaction, with the shortest survival under high‐temperature–long‐day conditions. Water loss rate also showed a significant interaction and was higher under high‐temperature–long‐day than high‐temperature–short‐day conditions. Initial body water content was generally lower at high than low temperature. Reproductive activity was strongly affected by temperature: Nearly all females reared at high temperature oviposited, and total egg production was substantially greater than at low temperature. Including wing morph as an explanatory variable did not alter the principal interactions. These results indicate that the effect of photoperiod on desiccation resistance depends strongly on temperature, with long‐day conditions reducing survival primarily at high temperature. Because reproductive activity was affected mainly by temperature, the interaction in desiccation resistance may involve photoperiod‐dependent regulation of water balance beyond reproductive maturation alone.
Abstract Approximately 75% of lycaenid butterfly species in the world associate with ants during their larval stages to gain protection against natural enemies such as parasitoids. Despite intensive studies on lycaenid–ant interactions, parasitoids exploiting myrmecophilous hosts remain poorly understood, thereby limiting our understanding of the eco‐evolutionary dynamics of parasitoid–host interactions. Here, three sibling species of Cotesia Cameron (Hymenoptera: Braconidae) parasitising ant‐associated lycaenid larvae in Japan were identified, and their ecological differentiation within this parasitoid group was investigated. We propose the Cotesia inducta complex, comprising Cotesia inducta (Papp), Co . sp. aff. inducta and Co. suzukii sp. nov. Co. inducta is recorded from Japan (Honshu) for the first time, and Co. suzukii sp. nov. is described and illustrated from Japan (Honshu and Kyushu). Co. suzukii sp. nov. is a specialist parasitoid of Arhopala japonica (Murray) (Theclinae) on Quercus spp., whereas Co. inducta exhibits a broad host range across multiple lycaenid subfamilies (Curetinae, Polyommatinae and Theclinae) in Europe and Japan. Mitochondrial DNA analyses reveal the monophyly of the Co. inducta complex, as well as that of Co. inducta and Co. suzukii sp. nov. Both species are multivoltine; however, Co. inducta exploits different host species seasonally, whereas Co. suzukii sp. nov. consistently utilises Ar. japonica . Moreover, Co. inducta primarily parasitises flower‐feeding hosts, whereas Co. suzukii sp. nov. only uses leaf‐feeding hosts, indicating that host‐feeding habitat contributes to diversification within the Co. inducta complex. These findings provide fundamental ecological information on parasitoids associated with myrmecophilous butterflies.
