The effect of dietary restriction on longevity, fecundity, and antioxidant responses in the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)

Ionotropic Receptor 8a (Ir8a) Plays an Important Role in Acetic Acid Perception in the Oriental Fruit Fly, Bactrocera dorsalis

Bactrocera dorsalis is one of the major invasive pests worldwide. The acetic acid-enriched sweet bait trapping is an important method for monitoring and controlling this fly. Several studies showed that acetic acid is perceived by ionotropic receptors (IRs). Thus, we annotated 65 IR genes in the B. dorsalis genome. We also investigated the IRs involved in acetic acid perception in this fly by behavioral, electrophysiological, and molecular methods. As the results indicated, the antennae are the main olfactory organs to sense acetic acid. Among the antennal IRs showed acetic acid-induced expression profiles, IR8a was proven to perceive acetic acid by CRISPR/Cas9-mediated mutagenesis. Additionally, calcium imaging showed that IR64a and IR75a are potential acetic acid receptors respectively co-expressed with IR76b and IR8a. This study represents the first comprehensive characterization of IRs in B. dorsalis at the whole-genome level, revealing the significant role of IRs in acetic acid perception.

High-Sucrose Diet Exposure on Larvae Contributes to Adult Fecundity and Insecticide Tolerance in the Oriental Fruit Fly, Bactrocera dorsalis (Hendel)

Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) is one of the broad host ranges and economically-important insect pests in tropical and subtropical areas. A wide range of hosts means they have strong adaptation ability to changes in dietary macronutrients (e.g., sucrose and protein). However, the effects of dietary conditions on the phenotypes and genotypes of B. dorsalis are still unclear. In this study, we aimed to investigate the effects of larval dietary sucrose on the life history traits and stress tolerance of B. dorsalis, and its defense response at the molecular level. The results showed that low-sucrose (LS) induced decreased body size, shortened developmental duration, and enhanced sensitivity to beta-cypermethrin. Otherwise, high-sucrose (HS) diet increased developmental duration, adult fecundity, and tolerance to malathion. Based on transcriptome data, 258 and 904 differentially expressed genes (DEGs) were identified in the NS (control) versus LS groups, and NS versus HS groups, respectively. These yielded DEGs were relevant to multiple specific metabolisms, hormone synthesis and signaling, and immune-related pathways. Our study will provide biological and molecular perspective to understand phenotypic adjustments to diets and the strong host adaptability in oriental fruit flies.

Weathering of 3-component synthetic food cones: effects on residual amount, release rate, and field capture of 3 pest species of fruit flies (Diptera: Tephritidae)

Food-based baits are an important component of trapping networks designed to detect invasive tephritid fruit flies (Diptera: Tephritidae). An aqueous solution of torula yeast plus borax (TYB) is widely used, but synthetic food lures have been developed to facilitate field procedures, ensure standard composition, and lengthen the interval of bait attractiveness. Cone-shaped dispensers, containing ammonium acetate, putrescine, and trimethylamine (so-called 3C food cones), are currently being used in some large-scale trapping systems (e.g., Florida). Prior work in Hawaii showed that traps baited with 3C food cones capture similar numbers of Mediterranean fruit flies (medflies), Ceratitis capitata (Wiedemann), as TYB-baited traps after 1-2 wk of weathering but capture fewer medflies thereafter. In addition, 3C food cones attract fewer oriental fruit flies, Bactrocera dorsalis (Hendel), and melon flies, Zeugodacuscucurbitae (Coquillett) than TYB even when the food cones are freshly deployed. The current study describes an additional trapping experiment that expands upon earlier work by (i) presenting 3C food cones either unbagged (as done previously) or in nonporous or breathable bags to possibly reduce volatilization and lengthen bait effectiveness and (ii) measuring the content of the 3 components over time to potentially associate fruit fly captures with the loss of these food cone constituents. Implications of these findings for fruit fly surveillance programs are discussed.

Effects of Midazolam on Antioxidant Levels, Biochemical and Metabolic Parameters in Eurygaster integriceps Puton (Hemiptera: Scutelleridae) Eggs Parasitized by Trissolcus semistriatus Nees (Hymenoptera: Scelionidae)

Eurygaster integriceps Puton (Hemiptera: Scutelleridae) is among the most important insect pests of wheat (Triticum sativum L.) and barley (Hordeum vulgare L.) grown in the Middle East. Biological and chemical methods are insufficient to control E. integriceps populations below economic thresholds. In this study, we investigated the effects of midazolam, a clinical drug, on selected metabolic enzyme activity, antioxidant levels, and biochemical parameters in E. integriceps eggs parasitized by Trissolcus semistriatus Nees (Hymenoptera: Scelionidae). Increasing concentrations of midazolam caused cell damage in the parasitized eggs due to its oxidative effects. Transferase enzymes, such as, aspartate transferase, alanine transferase, and gamma glutamyl transferase activities were altered following exposure. Metabolic enzymes, such as, creatine kinase, alkaline phosphatase, amylase, and lactate dehydrogenase also were adversely affected. Levels of the non-enzymatic antioxidants uric acid, bilirubin, and albumin also were altered.

Insect Models in Nutrition Research

Insects are the most diverse organisms on earth, accounting for ~80% of all animals. They are valuable as model organisms, particularly in the context of genetics, development, behavior, neurobiology and evolutionary biology. Compared to other laboratory animals, insects are advantageous because they are inexpensive to house and breed in large numbers, making them suitable for high-throughput testing. They also have a short life cycle, facilitating the analysis of generational effects, and they fulfil the 3R principle (replacement, reduction and refinement). Many insect genomes have now been sequenced, highlighting their genetic and physiological similarities with humans. These factors also make insects favorable as whole-animal high-throughput models in nutritional research. In this review, we discuss the impact of insect models in nutritional science, focusing on studies investigating the role of nutrition in metabolic diseases and aging/longevity. We also consider food toxicology and the use of insects to study the gut microbiome. The benefits of insects as models to study the relationship between nutrition and biological markers of fitness and longevity can be exploited to improve human health.

miR-275/305 cluster is essential for maintaining energy metabolic homeostasis by the insulin signaling pathway in Bactrocera dorsalis

Increasing evidence indicates that miRNAs play crucial regulatory roles in various physiological processes of insects, including systemic metabolism. However, the molecular mechanisms of how specific miRNAs regulate energy metabolic homeostasis remain largely unknown. In the present study, we found that an evolutionarily conserved miR-275/305 cluster was essential for maintaining energy metabolic homeostasis in response to dietary yeast stimulation in Bactrocera dorsalis. Depletion of miR-275 and miR-305 by the CRISPR/Cas9 system significantly reduced triglyceride and glycogen contents, elevated total sugar levels, and impaired flight capacity. Combined in vivo and in vitro experiments, we demonstrated that miR-275 and miR-305 can bind to the 3'UTR regions of SLC2A1 and GLIS2 to repress their expression, respectively. RNAi-mediated knockdown of these two genes partially rescued metabolic phenotypes caused by inhibiting miR-275 and miR-305. Furthermore, we further illustrated that the miR-275/305 cluster acting as a regulator of the metabolic axis was controlled by the insulin signaling pathway. In conclusion, our work combined genetic and physiological approaches to clarify the molecular mechanism of metabolic homeostasis in response to different dietary stimulations and provided a reference for deciphering the potential targets of physiologically important miRNAs in a non-model organism.

Oxidative Damage Is Influenced by Diet But Unaffected by Selection for Early Age of Oviposition in the Marula Fly, Ceratitis cosyra (Diptera: Tephritidae)

The expression of life-history traits, such as lifespan or reproductive effort, is tightly correlated with the amount and blend of macronutrients that individuals consume. In a range of herbivorous insects, consuming high protein to carbohydrate ratios (P:C) decreases lifespan but increases female fecundity. In other words, females face a resource-based trade-off between lifespan and fecundity. Redox metabolism may help mediate this trade-off, if oxidative damage is elevated by reproductive investment and if this damage, in turn, reduces lifespan. Here, we test how diets varying in P:C ratio affect oxidative damage and antioxidant protection in female and male of the marula fly, Ceratitis cosyra (Diptera: Tephritidae). We use replicated lines that have been subjected to experimental evolution and differ in their lifespan and reproductive scheduling. We predicted that high fecundity would be associated with high oxidative damage and reduced antioxidant defences, while longer lived flies would show reduced damage and elevated antioxidant defences. However, higher levels of oxidative damage were observed in long-lived control lines than selection lines, but only when fed the diet promoting lifespan. Flies fed diets promoting female fecundity (1:4 and 1:2 P:C) suffered greater oxidative damage to lipids than flies fed the best diet (0:1 P:C) for lifespan. Total antioxidant capacity was not affected by the selection regime or nutrition. Our results reiterate the importance of nutrition in affecting life-history traits, but suggest that in C. cosyra, reactive oxygen species play a minimal role in mediating dietary trade-offs between lifespan and reproduction.

Effects of Different Nitrogen Sources and Ratios to Carbon on Larval Development and Bioconversion Efficiency in Food Waste Treatment by Black Soldier Fly Larvae (Hermetia illucens)

Simple Summary

Black soldier fly larvae (BSFL) have received global research interest and industrial application due to their high performance on the organic waste treatment. However, the substrate C/N property, which may affect larvae development and the waste bioconversion process greatly, is significantly less studied. The current study focused on the food waste treatment by BSFL, compared the nitrogen supplying effects of 9 nitrogen species (i.e., NH₄Cl, NaNO₃, urea, uric acid, Gly, L-Glu, L-Glu:L-Asp (1:1, w/w), soybean flour, and fish meal), and further examined the C/N effects on the larval development and bioconversion process. We found that NH₄Cl and NaNO₃ led to poor larval growth and survival, while 7 organic nitrogen species exerted no harm to the larvae. Urea was further chosen to adjust the C/Ns. Results showed that lowering the C/N from the initial 21:1 to 18:1–14:1 improved the waste reduction and larvae production performance, and C/N of 18:1–16:1 was further beneficial for the larval protein and lipid bioconversion, whereas C/N of 12:1–10:1 resulted in a significant performance decline. Therefore, the C/N range of 18:1–16:1 is likely the optimal condition for food waste treatment by BSFL and adjusting food waste C/N with urea could be a practical method for the performance improvement.

Abstract

Biowaste treatment by black soldier fly larvae (BSFL, Hermetia illucens) has received global research interest and growing industrial application. Larvae farming conditions, such as temperature, pH, and moisture, have been critically examined. However, the substrate carbon to nitrogen ratio (C/N), one of the key parameters that may affect larval survival and bioconversion efficiency, is significantly less studied. The current study aimed to compare the nitrogen supplying effects of 9 nitrogen species (i.e., NH₄Cl, NaNO₃, urea, uric acid, Gly, L-Glu, L-Glu:L-Asp (1:1, w/w), soybean flour, and fish meal) during food waste larval treatment, and further examine the C/N effects on the larval development and bioconversion process, using the C/N adjustment with urea from the initial 21:1 to 18:1, 16:1, 14:1, 12:1, and 10:1, respectively. The food wastes were supplied with the same amount of nitrogen element (1 g N/100 g dry wt) in the nitrogen source trial and different amount of urea in the C/N adjustment trial following larvae treatment. The results showed that NH₄Cl and NaNO₃ caused significant harmful impacts on the larval survival and bioconversion process, while the 7 organic nitrogen species resulted in no significant negative effect. Further adjustment of C/N with urea showed that the C/N range between 18:1 and 14:1 was optimal for a high waste reduction performance (73.5–84.8%, p < 0.001) and a high larvae yield (25.3–26.6%, p = 0.015), while the C/N range of 18:1 to 16:1 was further optimal for an efficient larval protein yield (10.1–11.1%, p = 0.003) and lipid yield (7.6–8.1%, p = 0.002). The adjustment of C/N influenced the activity of antioxidant enzymes, such as superoxide dismutase (SOD, p = 0.015), whereas exerted no obvious impact on the larval amino acid composition. Altogether, organic nitrogen is more suitable than NH₄Cl and NaNO₃ as the nitrogen amendment during larval food waste treatment, addition of small amounts of urea, targeting C/N of 18:1–14:1, would improve the waste reduction performance, and application of C/N at 18:1–16:1 would facilitate the larval protein and lipid bioconversion process.

Molecular Identification and Immunity Functional Characterization of Lmserpin1 in Locusta migratoria manilensis

Simple Summary

Insect serpins play a vital role in the defense mechanism of insects, especially in the Toll pathway and PPO (prophenoloxidase) cascade. In this study, we provided an answer to the open question of whether serpin1 was involved in the humoral immune responses of Locusta migratoria manilensis. We identified a new Lmserpin1 gene from L. migratoria manilensis and investigated its expression profiles in all examined stages and tissues. Meanwhile, by interfering with Lmserpin1 gene, we examined the mortality of L. migratoria manilensis under Metarhizium anisopliae infection, as well as the activities of protective enzymes and detoxifying enzymes and the expression level of three immune-related genes (PPAE (prophenoloxidase-activating enzyme), PPO, and defensin). The results indicated that Lmserpin1 gene up-regulated the immune responses of L. migratoria manilensis and inhibited the infection of M. anisopliae. Our results are of great importance for better understanding of the mechanism characterization of Lmserpin1 in L. migratoria manilensis.

Abstract

Serine protease inhibitors (Serpins) are a broadly distributed superfamily of proteins that exist in organisms with the role of immune responses. Lmserpin1 gene was cloned firstly from Locusta migratoria manilensis and then was detected in all tested stages from eggs to adults and six different tissues through qRT-PCR analysis. The expression was significantly higher in the 3rd instars and within integument. After RNAi treatment, the expression of Lmserpin1 was significantly down-regulated at four different time points. Moreover, it dropped significantly in the fat body and hemolymph at 24 h after treatment. The bioassay results indicated that the mortality of L. migratoria manilensis treated with dsSerpin1 + Metarhizium was significantly higher than the other three treatments. Furthermore, the immune-related genes (PPAE, PPO, and defensin) treated by dsSerpin1 + Metarhizium were significantly down-regulated compared with the Metarhizium treatment, but the activities of phenoloxidase (PO), peroxidase (POD), superoxide dismutase (SOD), glutathione S-transferase (GST), and multifunctional oxidase (MFO) were fluctuating. Our results suggest that Lmserpin1 plays a crucial role in the innate immunity of L. migratoria manilensis. Lmserpin1 probably took part in regulation of melanization and promoted the synthesis of antimicrobial peptides (AMPs).

Selection on age of female reproduction in the marula fruit fly, Ceratitis cosyra (Walker) (Diptera: Tephritidae), decreases total antioxidant capacity and lipid peroxidation

The oxidative damage caused to cells by Reactive Oxygen Species (ROS) is one of several factors implicated in causing ageing. Oxidative damage may also be a proximate cost of reproductive effort that mediates the trade-off often observed between reproduction and survival. However, how the balance between oxidative damage and antioxidant protection affects life-history strategies is not fully understood. To improve our understanding, we selected on female reproductive age in the marula fruit fly, Ceratitis cosyra, and quantified the impact of selection on female and male mortality risk, female fecundity, male sperm transfer, calling and mating. Against expectations, upward-selected lines lived shorter lives and experienced some reductions in reproductive performance. Selection affected oxidative damage to lipids and total antioxidant protection, but not in the direction predicted; longer lives were associated with elevated oxidative damage, arguing against the idea that accumulated oxidative damage reduces lifespan. Greater reproductive effort was also associated with elevated oxidative damage, suggesting that oxidative damage may be a cost of reproduction, although one that did not affect survival. Our results add to a body of data showing that the relationship between lifespan, reproduction and oxidative damage is more complex than predicted by existing theories.

Thermal effect on the fecundity and longevity of Bactrocera dorsalis adults and their improved oviposition model

The oriental fruit fly, Bactrocera dorsalis, is a destructive polyphagous pest that causes damage to various fruit crops, and their distribution is currently expanding worldwide. Temperature is an important abiotic factor that influences insect population dynamics and distribution by affecting their survival, development, and reproduction. We examined the fecundity, pre-oviposition and oviposition periods, and longevity of adult B. dorsalis at various constant temperatures ranging from13°C to 35°C. The longevity of female B. dorsalis ranged from 116.8 days (18.8°C) to 22.4 days (34.9°C), and the maximum fecundity per female was 1,684 eggs at 28.1°C. Females were only able to lay eggs at 16.7°C to 34.9°C, and both the pre-oviposition and oviposition periods were different depending on the temperature. We modeled female reproduction in two oviposition models (OMs): 1) the current model developed by Kim and Lee, an OM composed of a fecundity model, age-specific survival model, and age-specific cumulative oviposition rate model, and 2) a two-phase OM modified the logic structure of the current model by separating pre-oviposition, so that oviposition was estimated with the female in oviposition phase who had complete pre-oviposition phase. The results of the two-phase OM provided more realistic outputs at lower and higher temperatures than those of the current model. We discussed the usefulness of the two-phase OM for the reproduction of insects with long pre-oviposition periods.

Exploring the role of host specialisation and oxidative stress in interspecific lifespan variation in subtropical tephritid flies

In herbivorous insects, the degree of host specialisation may be one ecological factor that shapes lifespan. Because host specialists can only exploit a limited number of plants, their lifecycle should be synchronised with host phenology to allow reproduction when suitable hosts are available. For species not undergoing diapause or dormancy, one strategy to achieve this could be evolving long lifespans. From a physiological perspective, oxidative stress could explain how lifespan is related to degree of host specialisation. Oxidative stress caused by Reactive Oxygen Species (ROS) might help underpin ageing (the Free Radical Theory of Aging (FRTA)) and mediate differences in lifespan. Here, we investigated how lifespan is shaped by the degree of host specialisation, phylogeny, oxidative damage accumulation and antioxidant protection in eight species of true fruit flies (Diptera: Tephritidae). We found that lifespan was not constrained by species relatedness or oxidative damage (arguing against the FRTA); nevertheless, average lifespan was positively associated with antioxidant protection. There was no lifespan difference between generalist and specialist species, but most of the tephritids studied had long lifespans in comparison with other dipterans. Long lifespan may be a trait under selection in fruit-feeding insects that do not use diapause.

Mutation of Bdpaired induces embryo lethality in the oriental fruit fly, Bactrocera dorsalis

BACKGROUND

Pair-rule genes were identified and named for their role in segmentation in animal embryos. Paired, a homolog of mammalian PAX3, acts as one of several pair-rule genes and is key in defining the boundaries of future parasegments and segments during insect embryogenesis.

RESULTS

We cloned the paired gene from the oriental fruit fly, Bactrocera dorsalis, and then applied CRISPR/Cas9-mediated genome editing to investigate its physiological function in the embryonic stage of this pest. We identified one transcript for a paired homolog in B. dorsalis, which encodes a protein containing a Paired Box domain and a Homeobox domain. Phylogenetic analysis confirmed that the paired gene is highly conserved and the gene was highly expressed at the 12-14 h-old embryonic stage. Knock-out of Bdpaired led to lack of segment boundaries, cuticular deficiency, and embryonic lethality. Sequence analysis of the CRISPR/Cas9 mutants exhibited different insertion and deletions in the Bdpaired locus. In addition, the relative expression of Wingless (Wg) and Abdominal A (Abd-A) genes were significantly down-regulated in the Bdpaired mutant embryos.

CONCLUSION

These results indicate that Bdpaired gene is critical for the embryonic development of B. dorsalis, and could be a novel molecular target for genetic-based pest management practices to combat this serious invasive pest. © 2019 Society of Chemical Industry.

Assessment of Bactrocera dorsalis (Diptera: Tephritidae) Diets on Adult Fecundity and Larval Development: Insights Into Employing the Sterile Insect Technique

Bactrocera dorsalis (Hendel) is a notorious insect pest that attacks diverse vegetables and fruits worldwide. The sterile insect technique has been developed as an environmentally friendly and effective control method that depends on the mass production of target flies. Because dietary yeast (protein) and sucrose (carbohydrate) are important in adult diets, yeast:sucrose (Y:S) mixtures are crucial for the mass-rearing of B. dorsalis. In this study, we found adult diets with different ratios of yeast to sucrose-influenced fecundity, and an extremely high or low Y:S ratios significantly decreased egg production of B. dorsalis. Additionally, the maximum oviposition efficiency was realized at dietary yeast to sucrose ratios of 1:1 and 1:3, suggesting their potential use to produce more eggs for the mass production of B. dorsalis. Here, new gel diets having different yeast concentrations (g/L water) were also assessed for rearing B. dorsalis larvae. Gel diets containing 20 g/L yeast led to a higher pupation, pupal weight and adult eclosion rate, and a shorter developmental time than other yeast concentrations. Moreover, the present gel diet also resulted in greater pupal production and adult emergence rates than previously used liquid and solid artificial diets, revealing that it is suitable for rearing B. dorsalis larvae. This research provides a useful reference on artificial diets mixtures for mass rearing B. dorsalis, which is critical for employing the sterile insect technique.

Oxidative Effects of Gemifloxacin on Some Biological Traits of Drosophila melanogaster (Diptera: Drosophilidae)

In recent times, several studies have been undertaken on the artificial mass-rearing of insects in which clinical antibacterial antibiotics, including gemifloxacin, which is a DNA gyrase and topoisomerases inhibitor, are amended into the diet to control microbial contamination and preserve diet. The findings of these studies have suggested the possibility that these antibiotics influence the biological traits of insects in relation to their oxidative effects. This study investigated the effects of gemifloxacin on Drosophila melanogaster (Meigen) survival rates, development times, and male-female adult longevity. And we also determined the effects of gemifloxacin on lipid peroxidation product, malondialdehyde, protein carbonyl levels, and glutathione S-transferase activity of fruit fly eggs. First instars were fed on artificial diets containing 150, 300, 600, and 900 mg/liter concentrations of gemifloxacin until adult emergence. Our results indicate that sublethal effects of gemifloxacin are likely to significantly impair adult fitness and life-history parameters in D. melanogaster, probably because of its oxidative effects.

Influence of Metarhizium anisopliae (IMI330189) and Mad1 protein on enzymatic activities and Toll-related genes of migratory locust

Efficacy of Metarhizium anisopliae strain (IMI330189) and Mad1 protein alone or in combination by feeding method to overcome immune-related enzymes and Toll-like pathway genes was investigated in migratory locust. M. anisopliae (IMI330189) is a potent and entomopathogenic fungal strain could be effectively used against insect pests. Similarly, Mad1 protein adheres to insect cuticle, causing virulence to insects. We confirmed maximum 55% of mortality when M. anisopliae (IMI330189) and Mad1 was applied in combination. Similarly, increased PO activity was observed in locust with combined dose of Mad1 + IMI330189 whereas PO, POD, and SOD activities reduced using Mad1 independently. Four Toll-like signaling pathway genes (MyD88, Cactus, Pelle, and CaN) were investigated from midgut and body of the migratory locust after 72 h of treatments. Subsequently, the expression of MyD88 in the midgut and body significantly decreased with the application of Mad1 and Mad1 + IMI330189. Performance of these treatments was absolutely non-consistent in both parts of insects. Meanwhile, IMI330189 significantly raised the expression of Cactus in both midgut and body. However, the combined treatment (Mad1 + IMI330189) significantly reduced the Cactus expression in both body parts. Pelle expression was significantly increased in the midgut with the application of independent treatment of Mad1 and IMI330189 whereas the combined treatment (Mad1 + IMI330189) suppressed the Pelle expression in midgut. Its expression level was absolutely higher in body with the application of IMI330189 and Mad1 + IMI330189 only. On the other hand, Mad1 significantly increased the expression of CaN in midgut. However, all three treatments significantly affected and suppressed the expression of CaN gene in body of locust. This shows that the applications of M. anisopliae and Mad1 protein significantly affected Toll signaling pathway genes, which ultimately increased level of susceptibility of locust. However, their effect was significantly different in both parts of locust which recommends that the Toll-related genes are conserved in midgut instead of locust body.

Corazonin Signaling Is Required in the Male for Sperm Transfer in the Oriental Fruit Fly Bactrocera dorsalis

Corazonin (Crz) is a widely distributed neuropeptide (or neurohormone) in insects with diverse physiological functions. The present study aimed to reveal the functions of Crz and its receptor (CrzR) in the regulation of sexual behavior and fertility in male Bactrocera dorsalis. Tissue-specific expression analyses showed that the BdCrz transcript was most abundant in the central nervous system (CNS), and the BdCrzR transcript was most abundant in both the fat body and CNS. Immunochemical localization confirmed that three pairs of Crz-immunoreactive neurons are located in the dorsolateral protocerebrum region of male adult brain. Importantly, RNAi-mediated Crz knockdown lengthened mating duration in males, and knockdown of Crz or CrzR strongly decreased male fertility in the following 3 days, while the courtship behavior and mating efficiency were not affected. The reduced number of sperm in the reproductive organs of mated females indicated that Crz knockdown in males reduced sperm transfer. The findings of this study indicate that Crz contributes to the reproductive physiology of the oriental fruit fly B. dorsalis by regulating sperm transfer in male adults.

Adipokinetic hormone receptor gene identification and its role in triacylglycerol mobilization and sexual behavior in the oriental fruit fly (Bactrocera dorsalis)

Energy homeostasis requires continuous compensation for fluctuations in energy expenditure and availability of food resources. In insects, energy mobilization is under control of the adipokinetic hormone (AKH) where it is regulating the nutritional status by supporting the mobilization of lipids. In this study, we characterized the gene coding for the AKH receptor (AKHR) and investigated its function in the oriental fruit fly (Bactrocera dorsalis) that is economically one of the most important pest insects of tropical and subtropical fruit. Bacdo-AKHR is a typical G protein-coupled receptor (GPCR) and phylogenetic analysis confirmed that Bacdo-AKHR is closely related to insect AKHRs from other species. When expressed in Chinese hamster ovary (CHO) cells, Bacdo-AKHR exhibited a high sensitivity and selectivity for AKH peptide (EC₅₀ = 19.3 nM). Using qPCR, the developmental stage and tissue-specific expression profiles demonstrated that Bacdo-AKHR was highly expressed in both the larval and adult stages, and also specifically in the fat body and midgut of the adult with no difference in sex. To investigate the role of AKHR in B. dorsalis, RNAi assays were performed with dsRNA against Bacdo-AKHR in adult flies of both sexes and under starvation and feeding condition. As major results, the knockdown of this gene resulted in triacylglycerol (TAG) accumulation. With RNAi-males, we observed a severe decrease in their sexual courtship activity when starved, but there was a partial rescue in copulation when refed. Also in RNAi-males, the tethered-flight duration declined compared with the control group when starved, which is confirming the dependency on energy metabolism. In RNAi-females, the sexual behavior was not affected, but their fecundity was decreased. Our findings indicate an interesting role of AKHR in the sexual behavior of males specifically. The effects are associated with TAG accumulation, and we also reported that the conserved role of AKH-mediated system in B. dorsalis is nutritional state-dependent. Hence, we provided further understanding on the multiple functions of AKH/AKHR in B. dorsalis.

Effects of macronutrient intake on the lifespan and fecundity of the marula fruit fly, Ceratitis cosyra (Tephritidae): Extreme lifespan in a host specialist

In insects, lifespan and reproduction are strongly associated with nutrition. The ratio and amount of nutrients individuals consume affect their life expectancy and reproductive investment. The geometric framework (GF) enables us to explore how animals regulate their intake of multiple nutrients simultaneously and determine how these nutrients interact to affect life-history traits of interest. Studies using the GF on host-generalist tephritid flies have highlighted trade-offs between longevity and reproductive effort in females, mediated by the protein-to-carbohydrate (P:C) ratio that individuals consume. Here, we tested how P and C intake affect lifespan (LS) in both sexes, and female lifetime (LEP), and daily (DEP) egg production, in Ceratitis cosyra, a host-specialist tephritid fly. We then determined the P:C ratio that C. cosyra defends when offered a choice of foods. Female LS was optimized at a 0:1 P:C ratio, whereas to maximize their fecundity, females needed to consume a higher P:C ratio (LEP = 1:6 P:C; DEP = 1:2.5 P:C). In males, LS was also optimized at a low P:C ratio of 1:10. However, when given the opportunity to regulate their intake, both sexes actively defended a 1:3 P:C ratio, which is closer to the target for DEP than either LS or LEP. Our results show that female C. cosyra experienced a moderate trade-off between LS and fecundity. Moreover, the diets that maximized expression of LEP and DEP were of lower P:C ratio than those required for optimal expression of these traits in host-generalist tephritids or other generalist insects.

Phenotypic plasticity, trade-offs and gene expression changes accompanying dietary restriction and switches in Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)

In this study, we investigated the effects of dietary restriction (DR) and variable diets on phenotypes and gene expression in oriental fruit fly, Bactrocera dorsalis (Hendel), one of the most economically important pests in the family Tephritidae around the world. As expected, we found that DR altered the B. dorsalis phenotypes by significantly increasing stress resistance and lifespan, but reduced egg production when compared with the control diet. The results suggested a trade-off between reproduction versus somatic maintenance (stress resistance) and lifespan in B. dorsalis. Diet also had a significant effect on hatchability, and DR could increase the egg hatching success of B. dorsalis. Furthermore, DR up-regulated metabolic pathways involved in energy homeostasis and down-regulated pathways in egg production, which might mediate trade-offs between somatic maintenance and reproduction under DR regimes. The gene expression profiles in response to the acute dietary switches indicated that the digestive and metabolic pathways maybe involved in the adaptability of flies to variable dietary resources. In summary, the research facilitates a better understanding of the molecular mechanisms responsible for the B. dorsalis’ phenotypic adjustments to the different qualities of the available diets.

A Role of Corazonin Receptor in Larval-Pupal Transition and Pupariation in the Oriental Fruit Fly Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)

Corazonin (Crz) is a neuropeptide hormone, but also a neuropeptide modulator that is internally released within the CNS, and it has a widespread distribution in insects with diverse physiological functions. Here, we identified and cloned the cDNAs of Bactrocera dorsalis that encode Crz and its receptor CrzR. Mature BdCrz has 11 residues with a unique Ser11 substitution (instead of the typical Asn) and a His in the evolutionary variable position 7. The BdCrzR cDNA encodes a putative protein of 608 amino acids with 7 putative transmembrane domains, typical for the structure of G-protein-coupled receptors. When expressed in Chinese hamster ovary (CHO) cells, the BdCrzR exhibited a high sensitivity and selectivity for Crz (EC50 ≈ 52.5 nM). With qPCR, the developmental stage and tissue-specific expression profiles in B. dorsalis demonstrated that both BdCrz and BdCrzR were highly expressed in the larval stage, and BdCrzR peaked in 2-day-old 3rd-instar larvae, suggesting that the BdCrzR may play an important role in the larval-pupal transition behavior. Immunochemical localization confirmed the production of Crz in the central nervous system (CNS), specifically by a group of three neurons in the dorso-lateral protocerebrum and eight pairs of lateral neurons in the ventral nerve cord. qPCR analysis located the BdCrzR in both the CNS and epitracheal gland, containing the Inka cells. Importantly, dsRNA-BdCrzR-mediated gene-silencing caused a delay in larval-pupal transition and pupariation, and this phenomenon agreed with a delayed expression of tyrosine hydroxylase and dopa-decarboxylase genes. We speculate that CrzR-silencing blocked dopamine synthesis, resulting in the inhibition of pupariation and cuticular melanization. Finally, injection of Crz in head-ligated larvae could rescue the effects. These findings provide a new insight into the roles of Crz signaling pathway components in B. dorsalis and support an important role of CrzR in larval-pupal transition and pupariation behavior.

Life history trade-offs imposed by dragline use in two money spiders

Trade-offs among life history traits are central to understanding the limits of adaptations to stress. In animals, virtually all decisions taken during life are expected to have downstream consequences. To what degree rare, but energy-demanding, decisions carry over to individual performance is rarely studied in arthropods. We used spiders as a model system to test how single investments in silk use - for dispersal or predator escape - affect individual performance. Silk produced for safe lines and as threads for ballooning is of the strongest kind and is energetically costly, especially when resources are limited. We induced dragline spinning in two species of money spider at similar quantities to that under natural conditions and tested trade-offs with lifespan and egg sac production under unlimited prey availability and a dietary restriction treatment. We demonstrate strong trade-offs between dragline spinning and survival and fecundity. Survival trade-offs were additive to those imposed by the dietary treatment, but a reduction in eggs produced after silk use was only prevalent under conditions where food was restricted during the spider's life. Because draglines are not recycled after their use for dispersal or predator escape, their spinning incurs substantial fitness costs in dispersal, especially in environments with prey limitation. Rare but energetically costly decisions related to dispersal or predator escape may thus carry over to adult performance and explain phenotypic heterogeneity in natural populations.

Effects of thermal stress on lipid peroxidation and antioxidant enzyme activities of the predatory mite, Neoseiulus cucumeris (Acari: Phytoseiidae)

Changes in temperature are known to cause a variety of physiological stress responses in insects and mites. Thermal stress responses are usually associated with the increased generation of reactive oxygen species (ROS), resulting in oxidative damage. In this study, we examined the time-related effect (durations for 1, 2, 3, and 5 h) of thermal stress conditions-i.e., relatively low (0, 5, 10, and 15 °C) or high (35, 38, 41, and 44 °C) temperatures-on the activities of antioxidant enzymes including catalase (CAT), superoxide dismutase (SOD), peroxidase (POX), glutathione S-transferases (GSTs), and total antioxidant capacity (T-AOC) of the predatory mite Neoseiulus cucumeris. Also the lipid peroxidation (LPO) levels of the predatory mite were measured under thermal stress conditions. The results confirmed that thermal stress results in a condition of so-called oxidative stress and the four antioxidant enzymes play an important role in combating the accumulation of ROS in N. cucumeris. CAT and POX activity changed significantly when the mites were exposed to cold and heat shock, respectively. The elevated levels of SOD and GSTs activity, expressed in a time-dependent manner, may have an important role in the process of antioxidant response to thermal stress. However, the levels of LPO in N. cucumeris were high, serving as an important signal that these antioxidant enzyme-based defense mechanisms were not always adequate to counteract the surplus ROS. Thus, we hypothesize that thermal stress, especially extreme temperatures, may contribute much to the generation of ROS in N. cucumeris, and eventually to its death.