Evaluating irradiation dose for sterility induction and quality control of mass-produced fruit fly Bactrocera tryoni (Diptera: Tephritidae)

Real-time PCR-based Y-specific sperm quantification assay in Queensland fruit fly: Insights to patterns of sperm storage

Studies of reproductive biology in insects often require quantification of sperm production, transfer or storage. Here, we develop a quantitative real-time PCR-based assay using a Y-specific marker for quantification of sperm from spermathecae of female Queensland fruit fly ('Q-fly'), overcoming constraints typical of traditional sperm quantification methods. The assay enables accurate and reliable quantification of as few as 50 sperms and provides a means to analyse large numbers of samples with flexible timing. The real-time PCR method enables revised understanding of how many sperms are stored by female Q-flies, the distribution of storage between the two spermathecae and the relationship between copula duration and sperm storage. Real-time PCR assays based on Y-specific markers provide an effective solution for sperm quantification in tephritid flies, as well as in other insects and potentially other animals with sperm storage organs.

Impact of gamma radiation dose on sterility and quality parameters of Anastrepha fraterculus (Diptera: Tephritidae)

Anastrepha fraterculus (Wiedemann, 1830) (Diptera: Tephritidae) is a major fruit pest, which is basicaly controlled using insecticides, which represents a risk to beneficial arthropods, human health and food contamination. The sterile insect technique (SIT) is a potential alternative tool for the management of this pest, however, only conflicting data is found regarding the optimal dose to achieve sterility. Thus, this study evaluated the effect of gamma radiation doses (0, 40, 50, 60 and 70 Gy) on male and female reproductive sterility, gonads morphometry, emergence, flight ability, and longevity under nutritional stress of A. fraterculus. Full female sterility was achieved at 50 Gy, while full male sterility was achieved at 70 Gy. Both ovarian and testicular sizes were affected by irradiation, while no influence was observed on the quality parameters evaluated. Our results suggest that 70 Gy applied 48 h before adult emergence can be used to sterilize A. fraterculus in a SIT programme.

Insight into the evolutionary profile of radio-resistance among insects having intrinsically evolved defence against radiation toxicity

Ionizing radiation (IR) has wide-ranging applications in various fields. In agriculture, pest control is one of the important applications, because insect pests have become a threat to the global agriculture industry. IR are used routinely to prevent crop loss and to protect stored food commodities. Radio-sterilization and disinfestation treatments are commonly used procedures for insect pest control. From various studies on insect radio-sterilization and disinfestation, it has been established that compared to vertebrates' insects have high levels of radiation resistance. Therefore, to achieve adequate radio-sterilization/disinfestation; exposure to high doses of IR is necessary. However, studies over decades made a presumption that radiation resistance is general among insects. Recent studies have shown that some insect orders are having high IR resistance and some insect orders are sensitive to IR. These studies have clarified that radiation resistance is not uniform throughout insect class. The present review is an attempt to insight at the evolutionary profile of insect species studied for radio-sterilization and disinfestation treatment and are having the trait of radio-resistance. From various studies on insect radiation resistance and after phylogenetic analysis of insect species it appears that the evolutionary near species have drastically different levels of radio-resistance and trait of radiation resistance appears to be independent of insect evolution.

Does the Effect of Irradiation Dose Vary Between Flies Selected and Non-selected to Resist Desiccation? The Case of Anastrepha ludens (Diptera: Tephritidae)

The sterile insect technique (SIT), used to control different species of tephritid fruit flies (Diptera: Tephritidae), is an important element in sustainable agriculture because of its low negative impact on the environment. In SIT, flies are mass produced and sterilized in the laboratory and then released in a target area. However, once released, laboratory flies may confront harass environments that would reduce their performance and consequently SIT efficiency. Selecting flies that resist stressful conditions may help to improve the efficiency of the SIT by releasing males that resist desiccation, for example, ensuring, thus, their survival in environments with low relative humidity. However, the selection process may affect the resistance of flies to the stress of sterilization, since some life history traits are affected. Here, we studied the effect of irradiation on Anastrepha ludens (Loew) (Diptera: Tephritidae) desiccation resistant flies (DR) compared with nonselected flies (NS). We measured the effect of gamma irradiation dose (0, 20, 40, 60, and 80 Gy) on sterility (males and females) and quality parameters (emergence, flight ability, survival, and male sexual performance) in A. ludens adults of the DR and NS (control) strains. Our results indicate that irradiation affected equally the sterility of adults of both strains. None of the quality parameters differed between strains. The only difference was that DR flies survived longer than control flies. Thus, flies that are resistant to desiccation can be used in the SIT without altering the current process of irradiation and packing.

Genetic engineering of sex chromosomes for batch cultivation of non-transgenic, sex-sorted males

The field performance of Sterile Insect Technique (SIT) is improved by sex-sorting and releasing only sterile males. This can be accomplished by resource-intensive separation of males from females by morphology. Alternatively, sex-ratio biasing genetic constructs can be used to selectively remove one sex without the need for manual or automated sorting, but the resulting genetically engineered (GE) control agents would be subject to additional governmental regulation. Here we describe and demonstrate a genetic method for the batch production of non-GE males. This method could be applied to generate the heterogametic sex (XY, or WZ) in any organism with chromosomal sex determination. We observed up to 100% sex-selection with batch cultures of more than 103 individuals. Using a stringent transgene detection assay, we demonstrate the potential of mass production of transgene free males.

Caffeine as a promotor of sexual development in sterile Queensland fruit fly males

Sterile insect technique (SIT) is an environmentally benign pest management technique that involves releasing millions of sterile insects to suppress reproduction of pest populations. Many fruit flies, including Queensland fruit fly (Bactrocera tryoni Froggatt, ‘Q-fly’), have long adult maturation periods such that pre-maturation mortality can greatly reduce abundance of sexually active sterile males and impede SIT efficacy. Q-fly is the most difficult and costly challenge to market access for Australia’s horticulture industries, and has been targeted for intensive use of SIT program. We here demonstrate potential of pre-release caffeine supplements as a novel means to accelerate sexual maturation in male Q-fly. In mating trials, analytical caffeine was very effective at accelerating sexual maturation, while no positive effects of caffeine-containing instant coffee or guarana supplements were detected. In parallel, development of testes and ejaculatory apodemes was accelerated in males provided analytical caffeine but not instant coffee or guarana. High doses of guarana and instant coffee reduced longevity while even the highest doses of analytical caffeine did not affect longevity. Pre-release caffeine supplements promote sexual maturation in Q-flies, and similar benefits are expected in other fruit flies having long adult maturation periods.

Mass Rearing, Quality Parameters, and Bioconversion in Drosophila suzukii (Diptera: Drosophilidae) for Sterile Insect Technique Purposes

The spotted wing drosophila, Drosophila suzukii Matsumura, has emerged as a major invasive insect pest of small and stone fruits in both the Americas and Europe in the last decade. Females oviposit in ripening fruit, and significant economic losses can occur. Control measures are mainly associated with the use of pesticides, but the sterile insect technique (SIT), an ecologically friendly pest-specific method, could be used against this species. The objective of this study was to estimate the mass rearing, quality control parameters, and bioconversion using four artificial larval diets and their economic aspects oriented to the SIT application. Diets were based on the combination of coconut fiber, corncob powder, Brewer's and Torula yeast and were used as oviposition substrate and larval development. We found that a life cycle is completed in 10.19 ± 0.35 d and that adults live an average of 33.67 ± 0.76 d. The highest number of pupae per gram of diet and the maximum bioconversion (6%) were associated with flies developed in the coconut fiber + Brewer's yeast diet. Under our conditions, the establishment of D. suzukii required at least four generations. The use of 30 × 40 × 30 cm Plexiglas cages, each loaded with 5,000 adults and stocked with 500 g of coconut fiber and Brewer's yeast diet distributed in 15 × 5 × 10 cm plastic trays with a diet layer 3-cm thick, allows a minimum production of 84,000 pupae of D. suzukii per day.

Accelerated Sexual Maturation in Methoprene-Treated Sterile and Fertile Male Queensland Fruit Flies (Diptera: Tephritidae), and Mosquito Larvicide as an Economical and Effective Source of Methoprene

Queensland fruit flies Bactrocera tryoni ('Q-fly') have long adult prereproductive development periods, which can present challenges for sterile insect technique (SIT) programs. Holding the sterile flies in release facilities is expensive for control programs. Alternatively, releases of sexually immature males can lead to substantial mortality of sterile males before they mature. Recent studies have reported effectiveness of dietary supplementation with a mosquito larvicide (NOMOZ) that contains S-methoprene, a juvenile hormone analogue, for accelerating sexual development of fertile Q-fly males. However, it is not known whether effects on sterile flies are comparable to effects on fertile flies, or whether effects of methoprene-containing larvicide are comparable to effects of analytical standard methoprene such has been used in most studies. Here we address both knowledge gaps, investigating the effects of analytical standard methoprene and NOMOZ mixed with food and provided for 48 h following emergence on sexual development and longevity of fertile and sterile Q-flies. Compared with controls, fertile and sterile male Q-flies that were provided diets supplemented with methoprene from either source exhibited substantially accelerated sexual development by 2-3 d and longer mating duration. Unlike males, females did not respond to methoprene treatment. Although fertile and sterile flies were generally similar in sexual development and response to methoprene treatment, sterile flies of both sexes tended to have shorter copula duration than fertile flies. Neither methoprene supplements nor sterilization affected longevity of flies. The present study confirms effectiveness of dietary methoprene supplements in accelerating sexual development of both fertile and sterile male (but not female) Q-flies, and also confirms that low-cost mosquito larvicides that contain methoprene can achieve effects similar to those for high-cost analytical grade methoprene as prerelease supplements for Q-fly SIT.

Comparison of Gel Larval Diet With Traditional Lucerne Chaff and Carrot Solid Diets for Rearing of Queensland Fruit Fly (Diptera: Tephritidae)

Sterile insect technique (SIT) for Queensland fruit fly, Bactrocera tryoni Froggatt, Australia's most economically damaging fruit fly species, is currently undergoing a major renewal and expansion. SIT relies on efficient and economical mass-rearing procedures that produce high-quality flies. Two solid larval diets, carrot and lucerne chaff, have traditionally been used to rear Queensland fruit fly. Recently, a gel larval diet has been developed to eliminate biological bulking agents from the mass-rearing process, but to date, there has been no direct comparison of gel larval diet with traditional solid diets. In the present study, the performance of flies reared on gel larval diet was compared with the performance of flies reared on carrot and lucerne chaff diets. In addition, to investigate whether the performance of reared flies depends on ancestral diet as well as tested diet, we sourced eggs from a colony maintained on carrot diet and from a colony maintained on a lucerne chaff diet. Overall, the gel diet was as good or better than the solid diets in all quality control parameters, including, egg-larval duration, pupal number, pupal recovery, adult emergence, percentage of fliers, and rate of fliers. Of note, larvae developed faster and pupated more synchronously on the gel diet than on either of the solid diets. At the loading densities used, gel and carrot diets produced less waste than lucerne chaff diet. Gel diets offer a rearing solution for Queensland fruit fly that eliminates biological bulking agents and yields faster and more synchronous larval development without compromising productivity or quality.

Raspberry ketone accelerates sexual maturation and improves mating performance of sterile male Queensland fruit fly, Bactrocera tryoni (Froggatt)

BACKGROUND

Tephritid fruit flies are recognized as the most economically important insect pest group, causing significant losses to horticultural crops globally. The sterile insect technique (SIT) is used to suppress or eradicate pest fruit flies in many countries. The provisioning of adult dietary or olfactory supplementation pre-release is commonly used to improve the mating performance of sterile male flies in SIT. This study on a major pest species, Queensland fruit fly, Bactrocera tryoni (Froggatt), focused on improving mating performance by providing a semiochemical, raspberry ketone (RK), in the pre-release adult diet.

RESULTS

Survival was numerically higher for RK-supplemented males. Sexual maturity occurred 1 day earlier (from 7 to 6 days) in RK-supplemented sterile males. The mating latency period decreased with maturation age and was lower for RK-fed males. RK-supplemented sterile males increasingly mated with fertile females as they aged (10-19 days). The mating competitiveness of both RK-supplemented sterile males and RK-denied sterile males was greater than that of wild males.

CONCLUSION

The early sexual maturity and increased mating performance of RK-supplemented sterile males indicate that the effectiveness of SIT programmes can be increased through dietary supplementation with RK during the pre-release period. © 2018 Society of Chemical Industry.

Elucidation of molecular expression associated with abnormal development and sterility caused by electron beam irradiation in Spodoptera litura (F.) (Lepidoptera: Noctuidae)

PURPOSE

The objective of the present study was to elucidate the mode of indirect action of electron beam irradiation at the molecular level against a quarantine pest, Spodoptera litura (F.).

MATERIAL AND METHODS

Electron beam irradiation (50-200 Gy) was applied to S. litura eggs, larvae, pupae, and adults, after which the feeding area, body weight, deformity of pupae and adults, ovarian development, expression levels of vitellogenin (Vg) and vitellogenin receptor (VgR) genes, and protein levels were analyzed.

RESULTS

The amount of feeding by S. litura larvae and the synthesis level of 70 kDa storage protein significantly decreased as the electron beam dose increased. When larvae were treated with the electron beam, morphological deformities appeared in the pupae, and abnormal wing disc (AWD) expression significantly decreased. Ovarian development was completely inhibited in emerged adults that had undergone 200 Gy electron beam irradiation as pupae. Quantitative real-time PCR (qRT-PCR) assays showed significant downregulation of the Vg and VgR genes due to electron beam irradiation; whereas the synthesis level of Vg protein (190 kDa) did not decrease with time in eggs unlike in non-irradiated (control) S. litura eggs, exhibiting irradiation induced impairment of Vg functioning.

CONCLUSIONS

These findings of radiation-induced abnormal development and sterility in S. litura together with the correlated changes at the molecular level may facilitate the development of a phytosanitary strategy against this quarantine pest using electron beam irradiation.

RNA Interference-Mediated Knockdown of Male Fertility Genes in the Queensland Fruit Fly Bactrocera tryoni (Diptera: Tephritidae)

The Queensland fruit fly, Bactrocera tryoni, is Australia’s most important horticultural pest. The Sterile Insect Technique (SIT) has been used to control this species for decades, using radiation to sterilize males before field-release. This method of sterilization can potentially reduce the insects’ abilities to compete for mates. In this study, RNA interference (RNAi) techniques were examined for their potential to sterilize male B. tryoni without adversely affecting mating competitiveness. B. tryoni adults were injected or fed double-stranded RNAs (dsRNAs) targeting spermatogenesis genes (tssk1, topi and trxt); quantitative reverse-transcriptase PCR analyses confirmed that transcript levels were reduced 60–80% for all three genes following injections. Feeding produced a significant gene knockdown for tssk1 and trxt after three days, but interestingly, two genes (trxt and topi) produced an excess of transcripts after 10 days of feeding. Despite these fluctuations in transcript levels, all three dsRNAs impacted the fecundity of treated males, with tssk1- and topi-dsRNA-treated males producing 75% fewer viable offspring than the negative controls. Mating competition assays demonstrated that dsRNA-treated males can actively compete with untreated males. These findings suggest that RNAi technology could serve as an alternative to radiation as a means of sterilizing these insects in an SIT program.

Effects of Irradiation Dose on Sterility Induction and Quality Parameters of Drosophila suzukii (Diptera: Drosophilidae)

Drosophila suzukii (Matsumura, 1931) (Diptera: Drosophilidae) is a widely distributed pest of soft-skinned and stone fruits that is controlled mainly with pesticides. An alternative to the chemical control is the sterile insect technique (SIT), an ecologically friendly method of pest management that could be used against D. suzukii. The objective of the present study was to evaluate the effects of gamma radiation on reproductive sterility, ovarian morphometry, and quality parameters of D. suzukii. Full female sterility was achieved at 75 Gy, while an adequate level of male sterility (99.67%) was obtained at 200 Gy. The ovarian size showed an exponential decay in function of irradiation dose increase. There was no significant influence of irradiation dose on the quality parameters evaluated. Our data suggest that gamma radiation can be recommended to be used in an SIT program for D. suzukii.

Sexual Competitiveness, Field Survival, and Dispersal of Anastrepha obliqua (Diptera: Tephritidae) Fruit Flies Irradiated at Different Doses

The sterile insect technique (SIT) is used in area-wide pest management programs for establishing low pest prevalence and/or areas free of fruit flies (Diptera: Tephritidae). The aim of this technique is to induce high levels of sterility in the wild population, for this the released insects must have a high sexual competitiveness and field dispersal. However, radiation decreases these biological attributes that do not allow it to compete successfully with wild insects. In this study the sexual competitiveness, field survival and dispersal of Anastrepha obliqua (Macquart; Diptera: Tephritidae) irradiated at 0, 40, 50, 60, 70, and 80 Gy were evaluated in laboratory. A dose of 60 Gy produced 98% sterility, whereas doses of 70 and 80 Gy produced 99% sterility. Sexual competitiveness was assessed in field cages, comparing males irradiated at 0, 50, 60, 70, and 80 Gy against wild males for mating with wild fertile females. Males irradiated at 50 and 60 Gy achieved more matings than those irradiated at 70 and 80 Gy. Wild males were more competitive than mass-reared males, even when these were not irradiated (0 Gy). There was no effect of irradiation on mating latency, yet wild males showed significantly shorter mating latency than mass-reared males. Female remating did not differ among those that mated with wild males and those that mated with males irradiated with different doses. The relative sterility index (RSI) increased from 0.25 at 80 Gy to 0.37 at 60 Gy. The Fried competitiveness index was 0.69 for males irradiated at 70 Gy and 0.57 for those irradiated at 80 Gy, which indicates that a 10 Gy reduction in the irradiation dose produces greater induction of sterility in the wild population. There were no significant differences in field survival and dispersal between flies irradiated at 70 or 80 Gy. Reducing the irradiation dose to 60 or 70 Gy could improve the performance of sterile males and the effectiveness of the SIT. Our results also distinguish between the effects of irradiation and mass-rearing on the performance of sterile males.