Association between changes in reproductive activity and D-glucose metabolism in the tephritid fruit fly, Bactrocera dorsalis (Hendel)

Female semiochemicals stimulate male courtship but dampen female sexual receptivity

Chemical communication plays a vital role in mate attraction and discrimination among many insect species. Here, we document a unique example of semiochemical parsimony, where four chemicals act as both aphrodisiacs and anti-aphrodisiacs in different contexts in Bactrocera dorsalis. Specifically, we identified four female-specific semiochemicals, ethyl laurate, ethyl myristate, ethyl cis-9-hexadecenoate, and ethyl palmitate, which serve as aphrodisiacs to attract male flies and arouse male courtship. Interestingly, these semiochemicals, when sexually transferred to males during mating, can function as anti-aphrodisiacs, inhibiting the receptivity of subsequent female mates. We further showed that the expression of elongase11, a key enzyme involved in the biosynthesis of these semiochemicals, is under the control of doublesex, facilitating the exclusive biosynthesis of these four semiochemicals in females and guaranteeing effective chemical communication. The dual roles of these semiochemicals not only ensure the attractiveness of mature females but also provide a simple yet reliable mechanism for female mate discrimination. These findings provide insights into chemical communication in B. dorsalis and add elements for the design of pest control programs.

Differential responses of Ceratitis capitata to infection by the entomopathogenic fungus Purpureocillium lilacinum

The medfly Ceratitis capitata is one of the most damaging fruit pests with quarantine significance due to its extremely wide host range. The use of entomopathogenic fungi constitutes a promising approach with potential applications in integrated pest management. Furthermore, developing insect control methods can involve the use of fungal machinery to cause metabolic disruption, which may increase its effectiveness by impairing insect development. Insect species, including C. capitata, relies on reproduction potential, nutrient reserves, metabolic activities, and immune response for survival. Accordingly, the purpose of this study was to investigate the impacts of the entomopathogenic fungus Purpureocillium lilacinum on C. capitata pre-mortality. The medfly V8 strain was subjected to laboratory bioassays, which consisted on determining the virulence of P. lilacinum on the medfly. Purpureocillium lilacinum was applied on abdominal topical of 5-day-old males and females. Following the fungal inoculation, we have confirmed (i) a significant increase in tissue sugar content, (ii) a significant decrease in carbohydrase activities, digestive glycosyl hydrolase, and proteinase activities in whole midguts of treated flies, (iii) the antimicrobial peptides (AMPs) genes expression profile was significantly influenced by fly gender, fly status (virgin, mature, and mated), and time after infection, but infection itself had no discernible impact on the AMPs for the genes that were examined. This study provides the first insight into how P. lilacinum could affect C. capitata physiological mechanisms and provides the foundation for considering P. lilacinum as a novel, promising biocontrol agent.

Canopy distribution and microclimate preferences of sterile and wild Queensland fruit flies

Insects tend to live within well-defined habitats, and at smaller scales can have distinct microhabitat preferences. These preferences are important, but often overlooked, in applications of the sterile insect technique. Different microhabitat preferences of sterile and wild insects may reflect differences in environmental tolerance and may lead to spatial separation in the field, both of which may reduce the control program efficiency. In this study, we compared the diurnal microhabitat distributions of mass-reared (fertile and sterile) and wild Queensland fruit flies, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae). Flies were individually tagged and released into field cages containing citrus trees. We recorded their locations in the canopies (height from ground, distance from canopy center), behavior (resting, grooming, walking, feeding), and the abiotic conditions on occupied leaves (temperature, humidity, light intensity) throughout the day. Flies from all groups moved lower in the canopy when temperature and light intensity were high, and humidity was low; lower canopy regions provided shelter from these conditions. Fertile and sterile mass-reared flies of both sexes were generally lower in the canopies than wild flies. Flies generally fed from the top sides of leaves that were lower in the canopy, suggesting food sources in these locations. Our observations suggest that mass-reared and wild B. tryoni occupy different locations in tree canopies, which could indicate different tolerances to environmental extremes and may result in spatial separation of sterile and wild flies when assessed at a landscape scale.

Transcriptome analysis of Anastrepha fraterculus sp. 1 males, females, and embryos: insights into development, courtship, and reproduction

BACKGROUND

Anastrepha fraterculus sp. 1 is considered a quarantine pest in several American countries. Since chemical control applied in an integrated pest management program is the only strategy utilized against this pest, the development of pesticide-free methods, such as the Sterile Insect Technique, is being considered. The search for genes involved in sex-determination and differentiation, and in metabolic pathways associated with communication and mating behaviour, contributes with key information to the development of genetic control strategies. The aims of this work were to perform a comprehensive analysis of A. fraterculus sp. 1 transcriptome and to obtain an initial evaluation of genes associated with main metabolic pathways by the expression analysis of specific transcripts identified in embryos and adults.

RESULTS

Sexually mature adults of both sexes and 72 h embryos were considered for transcriptome analysis. The de novo transcriptome assembly was fairly complete (62.9% complete BUSCO orthologs detected) with a total of 86,925 transcripts assembled and 28,756 GO annotated sequences. Paired-comparisons between libraries showed 319 transcripts differently expressed between embryos and females, 1242 between embryos and males, and 464 between sexes. Using this information and genes searches based on published studies from other tephritid species, we evaluated a set of transcripts involved in development, courtship and metabolic pathways. The qPCR analysis evidenced that the early genes serendipity alpha and transformer-2 displayed similar expression levels in the analyzed stages, while heat shock protein 27 is over-expressed in embryos and females in comparison to males. The expression of genes associated with courtship (takeout-like, odorant-binding protein 50a1) differed between males and females, independently of their reproductive status (virgin vs mated individuals). Genes associated with metabolic pathways (maltase 2-like, androgen-induced gene 1) showed differential expression between embryos and adults. Furthermore, 14,262 microsatellite motifs were identified, with 11,208 transcripts containing at least one simple sequence repeat, including 48% of di/trinucleotide motifs.

CONCLUSION

Our results significantly expand the available gene space of A. fraterculus sp. 1, contributing with a fairly complete transcript database of embryos and adults. The expression analysis of the selected candidate genes, along with a set of microsatellite markers, provides a valuable resource for further genetic characterization of A. fraterculus sp. 1 and supports the development of specific genetic control strategies.

Adult diet does not compensate for impact of a poor larval diet on stress resistance in a tephritid fruit fly

Adult holometabolous insects may derive metabolic resources from either larval or adult feeding, but little is known of whether adult diets can compensate for deficiencies in the larval diet in terms of stress resistance. We investigated how stress resistance is affected and compensated for by diet across life stages in the marula fruit fly Ceratitis cosyra (Diptera: Tephritidae). Larvae were fed diets containing either 8% torula yeast, the standard diet used to rear this species, or 1% yeast (low protein content similar to known host fruit). At emergence, adults from each larval diet were tested for initial mass, water content, body composition, and desiccation and starvation resistance or they were allocated to one of two adult diet treatments: sucrose only, or sucrose and yeast hydrolysate. The same assays were then repeated after 10 days of adult feeding. Development on a low protein larval diet led to lower body mass and improved desiccation and starvation resistance in newly emerged adults, even though adults from the high protein larval diet had the highest water content. Adult feeding decreased desiccation or starvation resistance, regardless of the diet provided. Irrespective of larval diet history, newly emerged, unfed adults had significantly higher dehydration tolerance than those that were fed. Lipid reserves played a role in starvation resistance. There was no evidence for metabolic water from stored nutrients extending desiccation resistance. Our findings show the possibility of a nutrient-poor larval environment leading to correlated improvement in adult performance, at least in the short term.

Effect of sweeteners on the survival and behaviour of Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)

BACKGROUND

The oriental fruit fly Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) causes serious damage that affects fruit production. Chemical insecticides have been widely used for the prevention and control of this destructive pest. However, the resistance of B. dorsalis to these compounds has become a serious problem. This study tested six sweeteners for their toxicity to B. dorsalis.

RESULTS

B. dorsalis fed on erythritol, aspartame and saccharin exhibited significantly higher mortality than those fed on sucrose. Flies fed on erythritol died faster than did the control flies (water). However, no dose-dependent effects were observed at the concentrations tested. These three sweeteners decreased the climbing ability of B. dorsalis. Notably, adults fed on saccharin exhibited significantly decreased climbing ability after 12 h compared with those fed on sucrose. Additionally, these three sweeteners had a negative effect on the frequency and duration of the flies' behaviour patterns (flying, walking, grooming and inactivity). Saccharin not only induced a marked reduction in the frequency of flights and walks but also induced decreases in the time spent flying and walking and increases in inactivity compared with sucrose. Erythritol induced a reduction in movement and increased the time spent inactive compared with the control and other treatments.

CONCLUSION

Three sweeteners had significant negative effects on the survival of B. dorsalis. Erythritol was toxic to B. dorsalis. Aspartame and saccharin also decreased the survival and behaviour of adult flies and may be toxic to (or contribute to poor nutrition in) B. dorsalis. These sweeteners could therefore be developed as additive ingredients in baits.