Physiological Entomology最新文献

Galleria mellonella (Linnaeus, 1758) is a Lepidopteran pest insect infesting the honeycombs, and the last instar larva of the insect is also a valuable model organism for the evaluation of drug efficacy, pathogenicity of infectious agents and environmentally sound chemical insecticides. Levamisole is an anthelmintic drug that is used for the treatment of parasitic infections in animals. In this study, we investigated the oxidative and genotoxic effects of dietary levamisole on the haemolymph of G. mellonella last instars to evaluate levamisole as an alternative chemical for traditional insecticides. In this context, first instar larvae were reared up to the last instars on artificial diets containing levamisole (w/w) and a control diet without levamisole. Malondialdehyde (MDA) and protein carbonyl (PCO) contents, and the activity of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST) and glutathione peroxidase (GPx) were determined to evaluate oxidative stress in the haemolymph of G. mellonella last instars. Furthermore, a comet assay was performed on haemolymph for evaluating DNA damage levels. The dietary levamisole led to a significant decrease in MDA and PCO contents and antioxidant enzyme activities (SOD, CAT, GST and GPx) when compared to the control diet. However, dietary levamisole significantly increased tail moment, tail %DNA and tail length, which are strong indicators of DNA damage. We infer from these that levamisole induced DNA damage and crippled antioxidant enzymatic defence in correlation with gradually increasing dietary concentration. The study would also provide valuable insights into the multifunctional aspects of levamisole, including its use in pest management.

Defensive secretions produced by certain hemipterans are known to deter natural enemies and play a crucial role in reducing microbial infections. In this study, we investigated the protective mechanisms of the chinch bug Blissus pulchellus against entomopathogenic fungi and we explored the relationship between the major volatile compounds produced by B. pulchellus and their potential role in enhancing its resilience to disease. Both adults and nymphs exhibited low susceptibility to infection by various strains of Metarhizium anisopliae and Beauveria bassiana. The close and continuous contact of conidia with antimicrobial substances on the insect's integument significantly inhibited germination rates. Conidia washed from insects after 4 h of contact with their integument exhibited germination rates of less than 20% on culture media. Chemical analyses of body extracts from adults and nymphs revealed both qualitative and quantitative differences in their defensive compound profiles. Our findings suggest that the aldehydes are the primary compounds responsible for fungal inhibition, effectively protecting the insect from infection. Identifying fungal strains capable of overcoming the fungitoxic compounds produced by B. pulchellus is crucial for advancing mycopesticide development to manage chinch bug populations in pastures.

The present study assessed the feeding efficiency, macronutrient assimilation and larval development of the Parthenium beetle, Zygogramma bicolorata Pallister, a biocontrol agent for the invasive Parthenium weed, under varying temperature conditions. We hypothesized that deviations from the optimal temperature (~25°C) would impair larval feeding efficiency due to temperature-induced stress. Our results revealed that both larval consumption and growth rates declined at temperatures below (15°C, 20°C) and above (30°C) the optimal temperature (25°C). In contrast, food conversion efficiency improved as temperatures increased from 15 to 30°C. Protein assimilation by larvae decreased across the temperature range, while glucose assimilation increased. Triglyceride assimilation initially decreased from 15 to 20°C/25°C but increased from 20°C/25°C to 30°C. As temperatures increased from 15 to 30°C, both the body size and developmental durations of larvae decreased. These findings suggest that Z. bicolorata larvae adopt different survival strategies depending on temperature conditions. At suboptimal temperatures, larvae grow larger, assimilate more proteins and triglycerides, but consume and utilize food more slowly. Conversely, at supraoptimal temperatures, larvae exhibit reduced body size and food consumption rates, but their food utilization efficiency improves, leading to faster development. Therefore, both low and high temperatures could limit the biocontrol efficiency of Z. bicolorata larvae in the Indian subcontinent.

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.