Physiological Entomology最新文献

Cryptic colouration is a primary anti-predation strategy in herbivorous insects. Achieving crypsis often requires acquiring dietary carotenoids—tetraterpene pigments vital for plant colouration and photoprotection. Silicon (Si) accumulation in plants makes tissues tougher and less digestible for insects, but its effect on plant pigment levels remains unclear. It is also unknown whether feeding on silicified plants impairs insects' ability to sequester carotenoids and achieve crypsis. Using the model grass Brachypodium distachyon, we demonstrate that the cotton bollworm (Helicoverpa armigera) larvae exhibited stunted growth and reduced carotenoid sequestration, particularly lutein, into their haemolymph when feeding on Si-supplemented (+Si) plants. This reduction led to distinct body-colour morphs: larvae feeding on +Si plants developed brown colouration, contrasting sharply with the green leaves, whereas larvae feeding on Si-free (−Si) plants exhibited green cryptic colouration that blended seamlessly with the foliage. Plant leaves contained various carotenoids (neoxanthin, violaxanthin, β-carotene and lutein) and chlorophylls (a and b), but larvae only sequestered β-carotene and lutein into their haemolymph while excreting substantial amounts of pigments, regardless of plant Si status. Under insect-free conditions, +Si plants had lower carotenoid and chlorophyll contents than −Si plants. However, following insect herbivory, pigment levels in −Si and +Si plants equalised. Insect herbivory also increased Si accumulation in +Si plants. Our findings provide novel evidence that plant Si defences can disrupt cryptic colouration in insect herbivores by restricting carotenoid sequestration from host plant tissues. This disruption could increase insect visibility to predators, potentially elevating their risk of predation.

Circadian rhythms are essential for predicting environmental changes; however, little is known about factors regulating their ontogeny. Honey bee workers emerge from the pupae with no behavioural circadian rhythms but show strong rhythms later in their lives. Although a previous study showed that temperature in a colony plays a role in accelerating the ontogeny of circadian rhythms in young bees, it is still unknown whether there is an optimal temperature for the acceleration of rhythm ontogeny. In the present study, we examined the influence of four different temperatures (25, 29, 34 and 38°C) for 48 h and found that as the temperature increased, more bees exhibited circadian activity rhythms for a 5 days observation period. We also examined the influence of temperature and other factors in a colony by exposing bees to air inside the hive at 34°C (a temperature nearly identical to brood nest temperature) or 29°C. We found that regardless of whether bees were exposed to colony air, they maintained their temperature at 34°C during their first 48 h and were more likely to exhibit circadian activity rhythms during the 5-day observation period compared with bees maintained at 29°C. These results suggest that the temperature in a colony is the main factor influencing the ontogeny of circadian rhythms in young bees. We also demonstrate the presence of a critical period during which this temperature effect significantly accelerates rhythm ontogeny.

Many insect species produce nutritive ejaculates, which represent the male's contribution to female reproductive fitness. Studies on the quantification of male contribution are assessed via indirect observations and direct assessment through the post-copulation effect on female reproductive performance, such as longevity and fecundity. Few studies directly address the nutritive content transferred by males via spermatophores. In species with multiple copulations, males produce ejaculates whose proportion of allocated substances varies according to the adult diet. We hypothesized that the spermatophores of C. montrouzieri show significant variations in nutrient composition when dietary modifications occur and whether this affects female fecundity and fertility. To test this hypothesis, we analysed the macronutrients proteins, lipids, sugars and glycogen using colorimetric methods. We tested for quantitative changes in these macronutrients in adult males well fed with Planococcus citri mealybugs, under limited amounts of P. citri (food scarcity), and with honey. The macronutrient profile of a spermatophore from a well-fed C. montrouzieri is composed of approximately 49.62 μg/mL lipids, 5.18 μg/mL glycogen, 3.25 μg/mL sugar and 0.27 μg/mL proteins. When compared with the spermatophores produced by males subjected to food scarcity or honey, no significant difference was found in the macronutrients. Fecundity was not affected, but there was a significant reduction in fertility in females that mated with males fed with honey.

It is imperative to determine the expression patterns and functions of genes essential for reproduction in mosquito vectors, such as Culex pipiens, to optimize vector control strategies, such as the sterile insect technique (SIT). The reproductive organs of mosquitoes are responsible for various processes, including spermatogenesis, seminal fluid secretion and female insemination during mating. Using Illumina RNA-seq and quantitative real-time PCR (qRT-PCR) validation, this study aimed to identify and categorize genes associated with the male accessory glands, as well as potentially other reproductive structures, of Cx. pipiens. Analysis of young and old male accessory gland tissues revealed 345 and 26 upregulated transcripts, respectively. Further qRT-PCR analysis showed that six genes were highly upregulated in old male accessory gland (MAG) tissue, including dual specificity mitogen-activated protein kinase hemipterous, atrial natriuretic peptide receptor and zinc-binding dehydrogenase. Additionally, 17 genes were found to be highly upregulated in young MAG tissue, with some of them speculated to have reproductive functions; among the notably upregulated genes were those encoding heterogeneous nuclear ribonucleoprotein, protein cluster segregational and two cytosol aminopeptidases. The function of cytosol aminopeptidase (CPIJ003539) has been validated in male Cx. pipiens through in-cage insemination and fertility assays, revealing that females mated with dsi-aminopeptidase knockdown males had impaired sperm storage and egg production abilities. These findings provide promising prospects for the development of targeted vector control strategies for Culex mosquitoes to achieve more successful outcomes concerning the efficient reduction of pest populations.

Sleep serves an essential function, and as such sleep deprivation has numerous negative effects on a wide range of organisms, including Drosophila. The link between sleep and cellular/humoral immunity is well studied, but behavioural immunity has been neglected for the most part. Here, we investigate the role of sleep deprivation on Drosophila nigrospiracula susceptibility to parasitism by the ectoparasitic mite, Macrocheles subbadius. We tested the hypothesis that sleep deprivation reduces behavioural resistance against mites, resulting in higher rates of infection among sleep-deprived (SD) flies compared to non-sleep-deprived flies, and that this is mediated by lower endurance (in negative geotaxis assays) among SD flies. We tested the impact of sleep deprivation on two age groups, flies 14 and 21 days post-eclosion. The prevalence of infection was 15% higher and mite abundance nearly 3x higher in older flies compared to younger flies. Moreover, older sleep-deprived flies experienced increased susceptibility to infection and lower climbing endurance compared to control flies. 21-day-old SD flies were 11% more likely to be infected and accumulated nearly double the number of mites as control flies. As such, we performed endurance assays on 21-day-old flies; control flies were 1.7x more likely to initiate climbing and climbed 6x longer in duration than SD flies. Taken together, our results show that increased susceptibility to parasitism among sleep-deprived flies is mediated by a concomitant decline in endurance. These findings contribute to our understanding of the importance of sleep and consequently the adverse effects of sleep deprivation on animals, particularly with regard to behavioural immunity.

Selection acts on reproductive timing and egg number to maximize reproductive success based on available resources. Species often vary in these life history traits due to differences in trait variation and local selection pressures, especially when species are adapted to different environments. Yet, species may share similar life history traits given common correlations, such as a positive relationship between body size and fecundity. In this study, we tested whether species adapted to different environments differ in their reproductive timing and egg load using two species of Tephritid fruit flies: Rhagoletis pomonella adapted to downy hawthorn and Rhagoletis suavis adapted to black walnut. In both species, older females were more likely to produce eggs and have more eggs. However, reproductive timing differed between species; hawthorn flies produced eggs earlier than walnut flies. In contrast to the common association of larger body size with earlier reproduction and higher egg counts, we did not find that adult female body size predicted reproductive timing in either species. In hawthorn flies with earlier reproductive maturity, body size did not affect egg number. For walnut flies with later reproductive maturity, larger females produced more eggs. Our findings suggest that while the time to accumulate resources and develop eggs is a common constraint, reproductive strategies are likely shaped by adaptation to specific host plants. Our study highlights the complex interaction between selection pressures and trait correlations in shaping life history traits across species.

Understanding the role of nutrients in microbial population dynamics relies on a sound appreciation of their nutritional environment and how this may vary in different habitats. For microbial pathogens and commensals, this can be especially challenging because the microbe may share nutritional resources with its host. Here we design a series of 20 synthetic cell-free haemolymphs (nutribloods) that mimic haemolymph nutrient profiles of caterpillars fed on one of 20 chemically defined diets that vary in their protein: carbohydrate (P:C) ratio and caloric density. Using these, we are able to simulate the range of nutritional conditions that insect blood pathogens might face, providing a model system for understanding the role of nutrition in microbial growth. We tested this using the entomopathogen, Xenorhabdus nematophila, a Gram-negative extracellular bacterium of insect hosts. This revealed that whilst bacterial fitness peaked in nutriblood nutrient space that was high in carbohydrates and low in proteins, levels of amino acids in the nutribloods also appear to be an important driving force for bacterial growth. Using synthetic haemolymphs that had average levels of all nutrients other than carbohydrate, protein or amino acids, we also established that bacterial growth is generally enhanced by carbohydrates and amino acids but reduced by proteins. Here, we have established a tractable model system for examining the role that nutrition plays in the growth of an entomopathogenic bacterium. In future work, this model host–pathogen system can be used to test a range of nutritionally driven processes, including competition during co-infection and interactions with the host microbiome, as well as comparative studies of other entomopathogens.

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.