Physiological Entomology最新文献

Dastarcus helophoroides (Fairmaire) serves as an ideal biological control agent for forest beetles. However, its survival ability at low temperatures is a critical factor for its use in colder regions. This study investigates the survival ability, supercooling point (SCP), impact of rapid cold hardening (RCH) and physiological changes of D. helophoroides under cold stress. SCPs of adults that underwent RCH were lower than those of adults cultured at room temperature, with SCPs of −25.1°C and −16.9°C, respectively. As the cold stress temperature decreased in the test, the survival ability of D. helophoroides adults also diminished, reaching the lowest survival rates at −20°C across all observation time points in the test. However, adults induced by RCH exhibited higher survival rates than those cultured at room temperature, suggesting that RCH enhances the cold resistance of D. helophoroides. The activities of superoxide dismutase (SOD) and catalase (CAT) in the adults increased as the stress temperature decreased. With prolonged cold stress, the activity of lactate dehydrogenase (LDH) initially decreased and then increased. Both fat and water content decreased with the lowering of stress temperature. These results provide insights into the cold resistance strategies of D. helophoroides.

Regulation of reproductive division of labour is generally modulated by the queen's chemical secretions, particularly the mandibular gland (MG) pheromone complex. Workers can activate their ovaries and lay unfertilised eggs with some dominant workers able to produce queen-like MG signals to become false queens. We examined the effect of social condition as a regulator of social behaviour, by investigating differential gene expression in the MG of two subspecies of African honey bees, with differing reproductive potentials and, at two ages. Sequencing of RNA from young and older Apis mellifera scutellata (low reproductive potential) and A. m. capensis (higher reproductive potential) workers was carried out. A total of 5646 transcripts were differentially expressed across four libraries, classified into 29 biological processes based on their gene ontology accessions. Further, 48 differentially expressed genes were found to be putatively associated with the biosynthesis of MG fatty acids. Of these, 25 were cytochrome P450s thought to participate in the caste-specific hydroxylation of stearic acid, a crucial regulatory point in the biosynthetic pathway. Multiple points of regulation were identified starting from in-situ biosynthesis and activation of stearic acid, caste-specific hydroxylation, transport between organelles, uncompleted β-oxidation and oxidation of 9-hydroxy-2-decenoic acid (9-HDA) to 9-oxo-2 (E)-decenoic acid (9-ODA). Our data shows that regardless of age, reproductively dominant individuals switch on a very specific set of genes as they transition from worker-like to queen-like MG signals. This study provides insight into the molecular-level changes that occur as workers switch from social cooperative behaviours to reproductive dominance.

Many insect species are migratory, but migration is energetically costly, leading to a trade-off between migration and subsequent reproduction. Of importance to the allocation of resources to migration and reproduction is the relative use of essential and nonessential fatty acids. How different ecological conditions experienced by individuals affect differential allocation of nutrients has not been well explored, especially in insects. Our goal was to evaluate how reproductive (summer) and migratory (fall) rearing conditions affect the source and allocation patterns of fatty acids used during experimental flights (0–6 h) in monarch butterflies (Danaus plexippus L.). We used larval and adult diets manipulated isotopically (δ¹³C) and chromatographic analyses to determine fatty acid composition and source in the fat body. C4 versus C3 carbohydrate feeding increased the δ¹³C value of lipids in monarchs (−31.2‰ vs. −22.1‰) and increased total fatty acid concentrations reflecting lipid synthesis during adult feeding. Fuel use during flight differed, with essential fatty acids being more conserved in fall versus summer conditions (21% vs. 32% loss, respectively), indicating that the environmental cues responsible for the onset of migration result in physiological changes that modify lipid use. Frequency of stopovers for nectar and nectar quality available during migration will influence the capacity of monarchs to conserve essential fatty acids up to and through the migration and overwintering period.

Cardiodactylus guttulus is a subtropical cricket endemic to the Ryukyu Islands. C. guttulus has a univoltine life cycle with an obligatory diapause in embryos during winter. An environmental time cue(s) is required to terminate diapause and synchronise the life cycle with the seasonal cycle. In several temperate crickets, chilling terminates embryonic diapause and induces prompt and synchronised hatching. In the present study, by observing the day of hatching after chilling, we investigated whether C. guttulus terminates embryonic diapause with reference to temperature as shown in temperate crickets. After chilling at 16°C, the hatching rates to day 120 after oviposition increased compared to the control maintained at 25°C without chilling. When the chilling treatment lasted more than 30 days, hatching occurred synchronously, showing that chilling at 16°C for 1 month is sufficient to terminate diapause and induce synchronised hatching in C. guttulus. In addition, longer exposure to 16°C was associated with shorter days of transfer from 16 to 25°C to hatching. This result suggests that embryogenesis post-diapause progressed slowly during chilling. These characteristics would be adaptive to warm winters in subtropical regions.

The boxwood moth, Cydalima perspectalis Walker (Lepidoptera: Crambidae), as invasive specialist species in Iran has caused considerable damage in endemic forest stands of Buxus hyrcana Pojark since 2016. Host plant species can alter herbivore–plant interactions through the quantitative and qualitative changes of hemocytes even within a specialist herbivore. To determine the hemocyte variations on different host plants across larval development, the third and sixth instar larvae of C. perspectalis fed on B. hyrcana (native boxwood) and B. microphylla Sieb. and Zucc. (introduced nonnative boxwood) were compared. Total (THC) and differential (DHC) hemocyte count were determined using light, phase-contrast, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Based on results, six types of hemocytes were recognized in hemolymph including prohemocytes (PRs), plasmatocytes (PLs), granulocytes (GRs), oenocytoides (OEs) and spherulocytes (SPs) as well as unknown elongated quadrangular cells (elongocytes [ELs], the term has been first employed here) with obvious and distinguishable nuclei which were observed by the SEM and TEM microscopy. The ELs were rectangular or trapezoidal in shape, and the largest cells in hemolymph—their length varied from 14.00 to 15.73 μm. Our results showed that the total number of hemocytes (THC) significantly increased across larval development. Moreover, host plant species significantly affected total hemocyte count where the THC of sixth instar larvae on B. microphylla (2561.00 ± 10.60 cell/mm³) was significantly higher than on B. hyrcana (2440.00 ± 51.50 cell/mm³). The differential hemocyte count (DHC) profile study showed that GRs along with PLs were the most abundant cells in the hemolymph irrespective of larval instar and host plant species. Furthermore, the GRs% and ELs% increased throughout the larval development on both host plants, while a significant reduction of PLs% was recorded from third instar to sixth instar during the larval stage on two Buxus species. Apart from larval instar, host plant species had a significant effect on DHC of C. perspectalis. Despite higher total hemocyte number when fed on B. microphylla, the PLs% and ELs% were significantly higher in sixth-instar larvae fed on B. hyrcana compared with B. microphylla. Oppositely, the percentage of GRs was 17% less in larvae reared on B. hyrcana than on B. microphylla. As hemocyte types are responsible for different immune functions, these findings on instar- and host plant-dependent variation in their relative abundance would be critical to understand the immune response of this specialist herbivore.

Evolution of increased immune defence is often limited by costs: correlated changes in other traits (viz. life-history traits) that otherwise reduce the fitness of the host organisms. Experimental evolution studies are useful for understanding the evolution of immune function and correlated changes in other traits. We experimentally evolved replicate Drosophila melanogaster populations to better survive infection challenges with an entomopathogenic bacteria, Enterococcus faecalis. Within 35 generations of directional selection, selected populations showed a marked increase in post-infection survival than ancestrally paired controls. We next measured various life-history traits of these populations. Our results show that the selected populations do not differ from control populations for larval development time and body weight at eclosion. No difference is also observed in case of fecundity and longevity (following the acute phase of infection), either when the flies were subjected to infection or when the flies were uninfected, although infected flies from all populations die much earlier than uninfected flies. Selected populations are either equally good or occasionally better as the control populations at surviving abiotic stressors (starvation and desiccation), although infected flies from all populations are more susceptible to stress than uninfected flies. Therefore, we conclude that (a) D. melanogaster populations can rapidly evolve to be more immune to infection with E. faecalis, (b) the evolution of increased defence against E. faecalis entails no life-history cost for the hosts and (c) evolving defence against a biotic threat (pathogen) does not make flies more susceptible to abiotic stressors.

Culex pipiens L. is a medically important mosquito due to its abundance and ability to transmit West Nile virus. Despite being the focus of many mosquito control strategies, very little is known about its mating behaviour. Several control strategies rely on knowing female mate preferences to ensure their efficacy. Therefore, the purpose of this study was to characterize mate selection based on mate quality. Because larger individuals should have more resources available to be used towards mating behaviour, it was hypothesized that larger mates (males or females) would be of higher value and preferentially mated with compared to smaller ones. By manipulating food availability, males and females were reared to be either large or small adults and were mated with either a large or small mate. Through a series of experiments, the effect of size on mate success and post-mating responses was assessed via insemination rates, blood feeding, egg laying, fertility and survival. Despite larger females living longer and being more fecund, males did not preferentially mate with larger females, nor did male size influence female survival or fecundity. Because larval rearing environment had an influence on adult morphology and fitness, it should be taken into consideration in mosquito control programmes.

Overwintering features of Drosophila parasitoids were studied in a temperate region of Japan, in an outdoor rearing experiment conducted from autumn to spring. Eight taxa, Asobara japonica, A. leveri, A. brevicauda, Leptolamina sp. TK1, Leptopilina tsushimaensis, Leptopilina japonica japonica, Ganaspis lupini and Trichopria drosophilae, were collected in this study. Among them, the first five emerged in spring, suggesting that they overwintered in diapause at the preimaginal stage. In the three Asobara species, however, a number of individuals emerged as adults in autumn and all of them died by mid-winter. We assessed whether the most abundant A. japonica emerging in autumn can leave offspring that survive the winter based on estimates of the lower developmental threshold and effective temperature for larval development, as well as local temperature conditions. The results suggest that the eggs laid after mid-October may not survive the winter and that the emergence of A. japonica after mid-October may not be adaptive. While it has been reported that Leptopilina japonica japonica also enters prepupal diapause, only one individual was collected, and therefore its overwintering features are not apparent in this study. As for the remaining species G. lupini and T. drosophilae, the outdoor rearing and experiment using laboratory strains suggest that they have limited overwintering capacity: the winter survivorship of adults was 14.3% and 4.1%, respectively; no G. lupini and only one individual of T. drosophilae emerged in spring; and both did not enter diapause at the preimaginal stage under short daylength in laboratory.

Leafcutter ants show a high degree of task division among the workers of different castes. For example, the smallest workers, the minims, care for the brood and the symbiotic fungus, whereas the larger mediae cut and transport plant material. This is reflected in the size and morphology of the mandibles, but also in their mechanical properties as mediae possess the hardest and stiffest cuticle and the minims—the softest and most flexible one. This is directly related to the content of the cross-linking transition metal zinc (Zn). The cuticle microstructure, which can be more or less anisotropic depending on the orientation of cuticle layers, is known to determine the resistance to loads and stresses and thus contributes to the biomechanical behaviour of the structure. To study how the mandible tasks are related to the cuticular organisation, we here documented the microstructure of the mandibles from the mediae and the minims by scanning electron microscopy. Afterwards, the mechanical properties (Youngs' modulus, E, and hardness, H) of the exo-, meso- and endocuticle were identified by nanoindentation. Tests were performed along the longitudinal and the circumferential axes of the mandibles. We found, that the minims possess mandibles, which are more isotropic, whereas the mandibles of the mediae are rather anisotropic. This difference was never determined within one species before and is probably linked to the task of the individual ant. To gain insight into the origins of these properties, we characterized the elemental composition of the different cuticle layers along the circumferential axis, revealing that only the exocuticle of the mandible cutting edge contains Zn. All other mechanical property gradients thus must be the result of the chitin fibre bundle architecture or the properties of the protein matrix, which awaits further investigation.