Physiological Entomology最新文献

Global climate change is projected to increase the incidence of heat waves, their magnitude and duration resulting in insects experiencing increasing environmental stress in both natural and managed ecosystems. While studies on insect thermal tolerance are rapidly increasing, variation across developmental or juvenile stress cross-stage effects within and across generations remain largely unexplored. Yet in holometabolous insects, heat stress at an early developmental stage may influence performance and survival during later stages. Here, we investigated the effects of pupal mild heat stress on the performance of laboratory-reared adult Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) measured as longevity, critical thermal maximum (CT_max), critical thermal minima (CT_min), heat knockdown time (HKDT) and chill coma recovery time (CCRT). Pupal heat stress significantly influenced performance of B. dorsalis adults resulting in impaired longevity and heat tolerance (CT_max and HKDT) in both sexes with improved and compromised cold tolerance (CT_min and CCRT) in females and males, respectively. These findings highlight the role of juvenile stages in mediating stress responses at adult stages. For B. dorsalis, pupal heat stress largely compromised thermal tolerance implying that the species has limited potential to shift its geographic range in heat prone areas. Significant benefits in cold tolerance in females following heat stress may help in improving survival in the cold in the short-term despite restricted activity to the same traits in males. This study suggests that basal heat tolerance and not short-term compensatory thermal plasticity following heat stress may have aided the recent invasion of B. dorsalis in African landscapes.

In this study, we explored the potential contribution of the gut microbiome to reproductive isolation in tunnelling dung beetles, using Onthophagus taurus (Schreber, 1759) and its sister species O. illyricus (Scopoli, 1763) as a model system (Coleoptera: Scarabaeidae: Scarabaeinae: Onthophagini). Gut microbiota play critical roles in normative development of these beetles, and are vertically inherited via a maternally derived faecal pellet called the pedestal. We first compared the developmental outcomes of individuals reared with pedestals derived from either the same or the sister species (Self and Cross inoculation treatments, respectively). We then crossed the resulting adult O. taurus in three combinations (Self female X Self male; Self female X Cross male; Cross female X Self male). We predicted that if the vertically transmitted gut microbiome plays a role in reproductive isolation by facilitating species recognition, the Self X Self line would have improved reproductive outcomes compared to the lines in which partners had mismatched gut microbiomes. Instead, we found that between-partner concordance of maternally transmitted gut microbiota resulted in fewer offspring, and that this reduction was due to partial pre-copulatory isolation as evidenced by reduced sperm transfer in the Self X Self line. This pattern is consistent either with microbiome-mediated familiarity/kin recognition, or with absence of mate choice in crosses with mismatched microbiomes. We discuss our results in the light of recent research on the influence of extracellular microbial symbionts over insects' mating preferences.

Pesticides are an essential part of agricultural practices that ward off pathogens and diseases from the agricultural crop. However, apart from target organisms, these chemicals also have adverse effects on non-target organisms. Dimethoate is an insecticide used extensively in agriculture and horticulture practices worldwide. We used the silkworm Bombyx mori as a model organism to study the effect of commercial formulation of dimethoate (Dimethoate-30% EC) on the gut, silk gland, and fat body tissues. LD₅₀ of dimethoate-30% EC on silkworm (B. mori) was 997 ppm, as reported in a previous study. We used concentrations of 25, 50, and 100 ppm in our experiments. Our results showed that sub-lethal doses of dimethoate caused weight loss and induced damage at the histological level to the mid-gut, silk gland, and fat body of B. mori. It also caused a decrease in the level of antioxidants like CAT, SOD, GPx, GSH, and GST, indicating that dimethoate has produced a shift of ROS balance towards free radical generation and therefore resulted in overall damage to this organism. Sub-lethal doses of this pesticide also caused lipid peroxidation in the silk gland, gut, and fat body of B. mori, damaging these tissues. The disruption was also seen in the mid-gut and middle silk gland at the DNA level, where it caused single-strand breaks, as was revealed by single cell gel electrophoresis studies. Damage at histological, biochemical, and molecular levels was most extreme at a concentration of 100 ppm, the highest sub-lethal concentration given to B. mori.

Plants are equipped with various defensive attributes against herbivores, including volatile and nonvolatile compounds. In maize plants, benzoxazinoids mediate resistance against some herbivores, with the most abundant being (2R)-2-β-D-glucopyranosyloxy-4-hydroxy-7-methoxy-2H-1,4-benzoxazin−3(4H)-one (DIMBOA-Glc), and its corresponding aglucone 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA). Both compounds have been shown to interfere in the larval development of generalist herbivores but are less effective on specialist, that is, grass-feeding, herbivores. Using a Brazilian population of Spodoptera frugiperda, we investigated (i) the level of constitutive benzoxazinoids in Neotropical maize genotypes, that is, Zapalote Chico, Mirt 2A, Sintético Spodoptera, L3, BRS 4103 and BRS 1040 (ii) the effect of S. frugiperda herbivory on benzoxazinoid levels in these genotypes and (iii) the impact of the genotypes on the development of S. frugiperda larvae. The results showed that the six maize genotypes produce different levels of benzoxazinoids, with Mirt 2A and BRS 1040 producing constitutively higher levels of HDMBOA-Glc and DIMBOA-Glc respectively compared to the other genotypes. When feeding on BRS 1040 and Mirt 2A, S. frugiperda larvae took an additional week to pupate, but this effect does not affect larval survival, what was the same and high on all the genotypes (>70%). Furthermore, production of DIMBOA-Glc and HDMBOA-Glc in these genotypes was suppressed, suggesting that S. frugiperda larvae can alter maize defence plant responses. In summary, our results demonstrate that Neotropical maize genotypes produce varying levels of benzoxazinoids, genotypes respond differently to S. frugiperda herbivory and S. frugiperda is able to cope with secondary metabolite-based defence in Neotropical maize.

The side effects of insecticides on non-target species are important to secure the intended effectiveness of pest management programmes. The cotton aphid Aphis gossypii is a frequent problem in industrial greenhouse cultivation, and insecticide and parasitoids are often used for crop protection. Among insecticides, mixtures are playing increasing roles in pest management in the greenhouse production system, as well as parasitoid use. The insecticide mixture thiacloprid + deltamethrin and the parasitoid wasp Aphidius colemani are the main agents used against the cotton aphid and are the focus of this study. Here, we report the effects of the thiacloprid + deltamethrin on A. gossypii and Ap. colemani. The low concentrations 2.79 g a.i/L (LC₁₀) and 7.28 g a.i/L (LC₃₀) compromised the life parameters of the aphid progeny and increased the development time at all juvenile stages. In addition, fecundity, longevity and other parameters (r, R₀ and T) were significantly impaired by thiacloprid + deltamethrin at both concentrations. The median lethal time estimate (LT₅₀) for Ap. colemani was 18.73 h; the parasitoid mortality was significant up to 24 h after application but decreased afterward. Regardless, the parasitoid life table parameters were also compromised by insecticide exposure, similarly to the parasitoid population growth and parasitism efficacy. These results demonstrate the effect of the insecticide mixture against A. gossypii, and the increased risk of its adverse impacts on the parasitoid Ap. colemani, which signals against their simultaneous application to control this pest species.

Intermittent food scarcity is commonly encountered in all organisms including insects. Although the forkhead box O (FOXO) transcription factor is a well-known component of signalling cascades related to starvation stress, the detailed regulatory mechanisms during long-term starvation remain poorly understood in insects. In the present study, using the red flour beetle, Tribolium castaneum, as a model organism, we showed that starvation treatment increased the expression of FOXO at both mRNA and protein levels and promoted its nuclear translocation to activate its transcriptional activity. Knockdown of FOXO leads to a significant reduction in the lifespan of T. castaneum accompanying reduced glycogen and triglyceride depletion as well as decreased glucose and trehalose accumulation under starvation conditions. Consistently, expression patterns of genes involved in gluconeogenesis, glycogenolysis and trehalose metabolism under starvation conditions were significantly affected in dsFOXO-injected beetles. These results provided evidence that FOXO played an important role in the tolerance to prolonged starvation by regulating metabolic and transcriptional responses.

Tuta absoluta (Lepidoptera: Gelechiidae) is a worldwide invasive insect species, considered a major pest of tomato. It has recently established in Burkina Faso, where chemical control remains the only affordable option to limit damages. Nesidiocoris tenuis (Hemiptera: Miridae) is commercialized as a biological agent to control this pest in other parts of the world. But very limited information exists on this predator in Burkina Faso. In this study, we first performed an insect survey in all agricultural regions areas of the country, and we found N. tenuis to be widely observed in all of them. Then, we performed two laboratory bioassays and demonstrated that all instars preyed on T. absoluta eggs, whether they were fed ad libitum or they had to actively forage for their prey. Because insecticide tolerant populations of T. absoluta were recently identified, we finally aimed at identifying agrochemicals that do not harm N. tenuis. We evaluated the toxicity of two synthetic insecticides, three bio-bacterial insecticides and eight plant extracts, all being active ingredients available on the local market. Most of them (i.e., abamectin, emamectin benzoate, spinosad, spinetoram) were highly toxic for both T. absoluta and N. tenuis. In contrast, Bacillus thuringiensis var. Kurstaki, neem oil, Cleome viscosa (Asian spiderflower), Ocimum basilicum (Basil) and Cassia occidentalis (Coffee senna) were compatible with N. tenuis while still controlling T. absoluta. Based on our results, we recommend the application of Bacillus thuringiensis to both control T. absoluta and which does not compromise the maintenance of N. tenuis populations.

For insects living in an environment where food supplies constantly change, the ability to learn and to memorize the association of a specific cue with food is indispensable. The advantages of using insects for studies on learning and memory have been of great help to uncover a reliable capability of associative learning in various insect species. However, regarding neuronal and molecular mechanisms underlying learning and memory, reports are largely confined to a few insect species: the fruit fly, honey bee, and field cricket. In this review, I will introduce summarized results obtained from our studies on learning and memory in crickets. First, associative conditioning paradigms, which have been our main experimental procedures, will be described. Second, I will introduce the roles of octopamine and dopamine in conveying signals about appetitive stimuli and aversive stimuli, respectively, in learning and in memory retrieval. Third, short-term memory and long-term memory, two distinct memory phases of associative memory in crickets, will be introduced with details of signalling pathways involved in long-term memory formation. Fourth, the high capability of learning and memory and characteristics of complex memory will be described. Lastly, I will summarize the results of studies on age-related memory impairment in crickets. Crickets have the potential to be suitable model insects for studying neuromolecular mechanisms underlying learning and memory, following fruit flies and honey bees. Extensive studies on learning and memory in crickets will contribute to the elucidation of diversities in the neuromolecular mechanisms of learning and memory acquired through evolution in insects.

The larvae of Zophobas atratus F. (Coleoptera: Tenebrionidae) are a promising source of dietary protein for animal feed. However, there has been no detailed investigation on macronutrient selection and requirement in Z. atratus larvae. Here, we used the geometric framework to explore the behavioural and physiological regulation of protein and carbohydrate in Z. atratus larvae. When provided with pairs of nutritionally imbalanced but complementary foods (choice experiment), Z. atratus larvae self-composed a diet with a protein-to-carbohydrate (P:C) ratio of 1.47:1 or 1.19:1 throughout the experimental period. Across different choice combinations, the intake of carbohydrate was more tightly regulated than that of protein. When confined to one of six foods imbalanced with respect to P:C ratio (no-choice experiment), Z. atratus larvae regulated their protein–carbohydrate intake to form linear intake arrays across nutrient space in a manner similar to those previously described for other nutritional generalists. The negative slope of the linear intake arrays was shallow (−0.67 to −0.54), suggesting that protein was over-consumed by Z. atratus larvae to a greater extent than carbohydrates. The nutritional landscapes fitted for larval performance traits exhibited that the performance of Z. atratus larvae was maximized at the P:C ratio of 2:1 and fell rapidly as the P:C ratio decreased below 1:1. There was evidence for post-ingestive regulation for body nutrient growth through adjusting the utilization efficiencies of ingested protein and carbohydrate. Our results represent the most comprehensive analysis of macronutrient regulation in Z. atratus and have implications for designing an optimal diet for this beneficial insect.