Journal of insect physiology最新文献

Beetle elytra act as natural protective covers and effectively shield their flexible abdomens and fragile hindwings from damage. The existing studies have attributed this contribution of the elytra to its honeycomb structures. In this combined experimental and theoretical study, we used the seven-spotted ladybird beetle to demonstrate that both biological morphology and the hollow structure of the dome-like elytra combined to reduce damage during falling. The falling ladybird beetles had a high probability (59.52%) of hitting the ground with the costal edge of the elytra. This strategy could assist with converting the translational energy into rotational kinetic energy, resulting in the reduction of the impulse during falling. In addition, the hollow structures on the elytra could further absorb the residual impact energy. In the future, this biological paradigm could be used as a basis for the development of falling/landing techniques for advanced robots.

Workers of social hymenopterans (ants, bees and wasps) display specific tasks depending on whether they are younger or older. The relative importance of behavior and age in modulating immune function has seldom been addressed. We compared the strength of encapsulation-melanization immune response (hereafter melanotic encapsulation) in paper wasps displaying age polyethism or experimentally prevented from behavioral specialization. Foragers of Polybia paulista had higher melanotic encapsulation than guards, regardless of their age. Nevertheless, melanotic encapsulation decreased with age when wasps were prevented from behavioral specialization. Thus, in this species, worker melanotic encapsulation seems more sensitive to task than age. Foraging is considered one of the riskier behaviors in terms of pathogen exposure, so upregulating melanotic encapsulation in foragers can possibly improve both individual and colony-level resistance against infections.

Herbivorous insects can identify their host plants by sensing plant secondary metabolites as chemical cues. We previously reported the two-factor host acceptance system of the silkworm Bombyx mori larvae. The chemosensory neurons in the maxillary palp (MP) of the larvae detect mulberry secondary metabolites, chlorogenic acid (CGA), and isoquercetin (ISQ), with ultrahigh sensitivity, for host plant recognition and feeding initiation. Nevertheless, the molecular basis for the ultrasensitive sensing of these compounds remains unknown. In this study, we demonstrated that two gustatory receptors (Grs), BmGr6 and BmGr9, are responsible for sensing the mulberry compounds with attomolar sensitivity for host plant recognition by silkworm larvae. Calcium imaging assay using cultured cells expressing the silkworm putative sugar receptors (BmGr4-10) revealed that BmGr6 and BmGr9 serve as receptors for CGA and ISQ with attomolar sensitivity in human embryonic kidney 293T cells. CRISPR/Cas9-mediated knockout (KO) of BmGr6 and BmGr9 resulted in a low probability of making a test bite of the mulberry leaves, suggesting that they lost the ability to recognize host leaves. Electrophysiological recordings showed that the loss of host recognition ability in the Gr-KO strains was due to a drastic decrease in MP sensitivity toward ISQ in BmGr6-KO larvae and toward CGA and ISQ in BmGr9-KO larvae. Our findings have revealed that the two Grs, previously considered to be sugar receptors, are molecules responsible for detecting plant phenolics in host plant recognition.

Farnesol, a sesquiterpene found in all eukaryotes, precursor of juvenile hormone (JH) in insects, is involved in signalling, communication, and antimicrobial defence. Farnesol is a compound of floral volatiles, suggesting its importance in pollination and foraging behaviour. Farnesol is found in the resin of Baccharis dracunculifolia, from which honeybees elaborate the most worldwide marketable propolis. Bees use propolis to seal cracks in the walls, reinforce the wax combs, and as protection against bacteria and fungi. The introduction within a honeybee hive of a compound with potential hormonal activity can be a challenge to the colony survival, mainly because the transition from within-hive to outside activities of workers is controlled by JH. Here, we tested the hypothesis that exogenous farnesol alters the pacing of developing workers. The first assays showed that low doses of the JH precursor (0.1 and 0.01 µg) accelerate pharate-adult development, with high doses being toxic. The second assay was conducted in adult workers and demonstrated bees that received 0.2 µg farnesol showed more agitated behaviour than the control bees. If farnesol was used by corpora allata (CA) cells as a precursor of JH and this hormone was responsible for the observed behavioural alterations, these glands were expected to be larger after the treatment. Our results on CA measurements after 72 h of treatment showed bees that received farnesol had glands doubled in size compared to the control bees (p < 0.05). Additionally, we expected the expression of JH synthesis, JH degradation, and JH-response genes would be upregulated in the treated bees. Our results showed that indeed, the mean transcript levels of these genes were higher in the treated bees (significant for methyl farnesoate epoxidase and juvenile hormone esterase, p < 0.05). These results suggest farnesol is used in honeybees as a precursor of JH, leading to increasing JH titres, and thus modulating the pacing of workers development. This finding has behavioural and ecological implications, since alterations in the dynamics of the physiological changes associated to aging in young honeybees may significantly impact colony balance in nature.

In nectivorous pollinators, timing and pattern of allocation of consumed nectar affects fitness traits and foraging behavior. Differences in male and female behaviors can influence these allocation strategies. These physiological patterns are not well studied in Lepidoptera, despite them being important pollinators. In this study we investigate crop-emptying rate and nectar allocation in Manduca sexta (Sphingidae), and how sex and flight influence these physiological patterns. After a single feeding event, moths were dissected at fixed time intervals to measure crop volume and analyze sugar allocation to flight muscle and fat body. Then we compared sedentary and flown moths to test how activity may alter these patterns. Sedentary males and females emptied their crops six hours after a feeding event. Both males and females preferentially allocated these consumed sugars to fat body over flight muscle. Moths began to allocate to the fat body during crop-emptying and retained these nutrients long-term (four and a half days after a feeding event). Males allocated consumed sugar to flight muscles sooner and retained these allocated nutrients in the flight muscle longer than did females. Flight initiated increased crop-emptying in females, but had no effect on males. Flight did not significantly affect allocation to flight muscle or fat body in either sex. This study showed that there are inherent differences in male and female nectar sugar allocation strategies, but that male and female differences in crop-emptying rate are context dependent on flight activity. These differences in physiology may be linked to distinct ways males and females maximize their own fitness.

Extreme temperatures threaten species under climate change and can limit range expansions. Many species cope with changing environments through plastic changes. This study tested phenotypic changes in heat and cold tolerance under hardening and acclimation in the melon thrips, Thrips palmi Karny (Thysanoptera: Thripidae), an agricultural pest of many vegetables. We first measured the critical thermal maximum (CT_max) of the species by the knockdown time under static temperatures and found support for an injury accumulation model of heat stress. The inferred knockdown time at 39 °C was 82.22 min. Rapid heat hardening for 1 h at 35 °C slightly increased CT_max by 1.04 min but decreased it following exposure to 31 °C by 3.46 min and 39 °C by 6.78 min. Heat acclimation for 2 and 4 days significantly increased CT_max at 35 °C by 1.83, and 6.83 min, respectively. Rapid cold hardening at 0 °C and 4 °C for 2 h, and cold acclimation at 10 °C for 3 days also significantly increased cold tolerance by 6.09, 5.82, and 2.00 min, respectively, while cold hardening at 8 °C for 2 h and acclimation at 4 °C and 10 °C for 5 days did not change cold stress tolerance. Mortality at 4 °C for 3 and 5 days reached 24.07 % and 43.22 % respectively. Our study showed plasticity for heat and cold stress tolerance in T. palmi, but the thermal and temporal space for heat stress induction is narrower than for cold stress induction.

With increasing soil depth, the amplitude and phase of the daily temperature cycle decreases and is delayed, respectively. The onion fly, Delia antiqua, which pupates at a soil depth of 2–20 cm, advances the eclosion phase of its circadian clock as the temperature amplitude decreases. This “temperature-amplitude response” compensates for the depth-dependent phase delay of the temperature change and ensures eclosion in the early morning. To clarify the physiological mechanisms that induce a temperature-amplitude response, we performed phase-resetting experiments using a 12-h high- or low-temperature pulse with an amplitude of 1 °C or 4 °C. Based on the results obtained, four phase transition curves and four phase response curves were constructed. These curves show that the phase of the eclosion clock shifted more as the magnitude of the temperature change increased. The 24-h temperature cycle delayed, rather than advanced, the phase of the D. antiqua circadian eclosion rhythm. Therefore, we propose that a small phase delay is caused by a small temperature amplitude at a deep site in the soil and a large phase delay is caused by a large temperature amplitude at a shallow site, leading to the temperature-amplitude response exhibited by D. antiqua.

The environment is changing faster than anticipated due to climate change, making species more vulnerable to its impacts. The level of vulnerability of species is influenced by factors such as the degree and duration of exposure, as well as the physiological sensitivity of organisms to changes in their environments, which has been shown to vary among species, populations, and individuals. Here, we compared physiological changes in fecundity, critical thermal maximum (CT_max), respiratory quotient (RQ), and DNA damage in ovaries in response to temperature stress in two species of fruit fly, Drosophila melanogaster (25 vs. 29.5 °C) and Drosophila pseudoobscura (20.5 vs. 25 °C). The fecundity of D. melanogaster was more affected by high temperatures when exposed during egg through adult development, while D. pseudoobscura was most significantly affected when exposed to high temperatures exclusively during egg through pupal development. Additionally, D. melanogaster males exhibited a decrease of CT_max under high temperatures, while females showed an increase of CT_max when exposed to high temperatures during egg through adult development. while D. pseudoobscura females and males showed an increased CT_max only when reared at high temperatures during egg through pupae development. Moreover, both species showed an acceleration in oogenesis and an increase in apoptosis due to heat stress. These changes can likely be attributed to key differences in the geographic range, thermal range, development time, and other different factors between these two systems. Through this comparison of variation in physiology and developmental response to thermal stress, we found important differences between species and sexes that suggest future work needs to account for these factors separately in understanding the effects of constant increased temperatures.

Parasitoids have utilized a variety of strategies to counteract host defense. They are in different taxonomic status and exhibit phenotypic and genetic diversity, and thus are thought to evolve distinct anti-defense mechanisms. In this study, we investigated the performance of two closely related parasitoids, Exorista japonica and Exorista sorbillans (Diptera: Tachinidae) that are biological control agents in agriculture and major insect pests in sericulture, on the host Bombyx mori. We show that the host is more susceptible to E. sorbillans infection while relatively resistant to E. japonica infection. Moreover, the expression levels of host antimicrobial peptides (AMPs) genes are repressed at early infection and induced at late infection of E. japonica, while AMPs are over-expressed at early infection and return to normal levels at late infection of E. sorbillans. In parallel, Toll and IMD pathway genes are generally induced at late infection of E. japonica, whereas these genes are up-regulated at early infection and down-regulated at late infection of E. sorbillans. Activating of host Toll/IMD pathways and AMPs expression by lipopolysaccharide (LPS) represses the larval growth of E. sorbillans. Conversely, inhibiting host Toll/IMD pathways by RNA interference significantly promotes E. japonica development. Therefore, the Toll/IMD pathways are required in the host for defense against infection of dipteran parasitoids. Overall, our study provides the new insight into the diversified host-parasitoid interactions, and offers a theoretical basis for further studies of the adaptive mechanism of dipteran parasitoids.

Many insects living in seasonal environments sense seasonal changes from photoperiod and appropriately regulate their development and physiological activities. Genetic researches have indicated the importance of a circadian clock system in photoperiodic time-measurement for photoperiodic regulations. However, most previous studies have focused on the effects on a single photoperiodic phenotype, without elucidating whether the circadian clock is involved in the core photoperiodic mechanism or only in the production of one target phenotype, such as diapause. Here, we focused on two different phenotypes in a bivoltine Kosetsu strain of the silkworm Bombyx mori, namely, embryonic diapause and larval development, and examined their photoperiodic responses and relationship to the circadian clock gene period. Photoperiod during the larval stage clearly influenced the induction of embryonic diapause and duration of larval development in the Kosetsu strain; short-day exposure leaded to the production of diapause eggs and shortened the larval duration. Genetic knockout of period inhibited the short-day-induced embryonic diapause. Conversely, in the period-knockout silkworms, the larval duration was shortened, but the photoperiodic difference was maintained. In conclusion, our results indicate that the period gene is not causally involved in the photoperiodic response of larval development, while that is essential for the short-day-induced embryonic diapause.