Packing and Postirradiation Handling of the Anastrepha ludens (Diptera: Tephritidae) Tapachula-7 Genetic Sexing Strain: Combined Effects of Hypoxia, Pupal Size, and Temperature on Adult Quality

Effect of Chilling on Quality Control Parameters of Sterile Queensland Fruit Fly (Diptera: Tephritidae)

Queensland fruit fly (Q-fly), Bactrocera tryoni (Froggatt), presents a major threat to Australian fruit production and trade. The sterile insect technique (SIT) is increasingly employed to manage Q-fly. Quality of sterile males released in SIT programs, and hence program efficacy, can be affected by pre- and post-production processes, such as mass rearing, packing, irradiation, transportation, and release. Given long distances from rear-out facilities to release sites, adult flies are usually chilled to reduce metabolism and stress during transportation. To guide SIT procedures, it is important to understand the impact of such practices on performance of sterile Q-fly. The present study assesses the effect of chilling temperature and exposure period on quality parameters of sterile Q-fly. We considered the effects of two temperature regimes (4 and 6°C) and six exposure periods (0, 1, 2, 4, 6, and 12 h) on chill-coma recovery time, flight ability, survival under nutritional stress, and longevity of both males and females. Flies chilled at 4°C took longer to recover than that those chilled at 6°C. Flight ability, survival under nutritional stress, and longevity all decreased as chilling period increased but did not differ between the two tested temperatures. We recommend that periods of chilling during transportation from rear-out facilities to release sites be minimized in order to retain quality of sterile Q-fly and that increased release rates be considered when longer chilling periods are required.

The Sterile Insect Technique: Success and Perspectives in the Neotropics

The sterile insect technique (SIT), an environmentally friendly means of control, is currently used against plant, animal, and human pests under the area-wide integrated pest management. It consists in the mass production, sterilization, and release of insects in an affected area where sterile males mate with wild females leading to no reproduction. Here, we review SIT in the Neotropics and focus on particular recent successful cases of eradication of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), as well as effective programs used against the Mexican fruit fly Anastrepha ludens (Loew), the New World screwworm fly Cochliomyia hominivorax (Coquerel)), and the Cactus moth Cactoblastis cactorum (Berg). We examine when SIT does not work and innovations that have made SIT more efficient and also highlight complimentary techniques that can be used in conjunction. We address potential candidate species that could be controlled through SIT, for example Philornis downsi Dodge & Aitken. Finally, we consider the impact of climate change in the context of the use of the SIT against these pests. Given the recent dramatic decline in insect biodiversity, investing in environmentally friendly means of pest control should be a priority. We conclude that SIT should be promoted in the region, and leadership and political will is needed for continued success of SIT in the Neotropics.

Determining the Sterilization Doses under Hypoxia for the Novel Black Pupae Genetic Sexing Strain of Anastrepha fraterculus (Diptera, Tephritidae)

A common strategy used to maintain sterile fly quality without sacrificing sterility is to irradiate the insects under an oxygen-reduced atmosphere. So far, sterilizing doses for the South American fruit fly Anastrepha fraterculus have only been determined under normoxia. Our study reports for the first time the dose-sterility response under hypoxia for two different A. fraterculus strains. The pupae were derived from a bisexual strain (a Brazilian-1 population) and a recently developed genetic sexing strain (GSS-89). Two hours prior to irradiation, pupae were transferred to sealed glass bottles and irradiated when oxygen concentration was below 3%. Four types of crosses with nonirradiated flies of the bisexual strain were set to assess sterility for each radiation dose. For males from both strains, Weibull dose-response curves between radiation doses and the proportion of egg hatch, egg-to-pupa recovery, and recovery of adults were determined. The GSS males revealed high sterility/mortality levels compared to males from the bisexual strain at doses < 40 Gy, but a dose of 74 Gy reduced egg hatch by 99% regardless of the male strain and was considered the sterilizing dose. The fertility of irradiated females was severely affected even at low doses under hypoxia.

Combined Effects of Methoprene and Metformin on Reproduction, Longevity, and Stress Resistance in Anastrepha ludens (Diptera: Tephritidae): Implications for the Sterile Insect Technique

Survival and mating success are traits of quality in mass-reared sterile males. Thus, studying the trade-offs between these traits may help to improve process in the sterile insect technique (SIT). Here, we tested the hypothesis that modifying individual metabolism, especially of energetic reserves, may reduce the negative impact of an early reproduction on the survival of Anastrepha ludens flies. Appling metformin (a drug used to treat type II diabetes) that improves insects' survival, through dietary restriction mimicry, and methoprene (a juvenile hormone analogue) that accelerates the age to reproduction in insects, we explore the dynamic of this trade-off. We fed A. ludens flies with metformin, methoprene, or a mixture of metformin-methoprene for five consecutive days. We determined the effect of these treatments on the fecundity and fertility (number of eggs and percentage of hatching) of females, on sexual maturation and mating success of males, and on the survival of both sexes. The results showed that the acceleration in sexual maturation by the action of methoprene significantly reduced survival in both sexes of two different fly strains. However, adding metformin to the diet buffered this negative effect, without reducing the mating propensity compared with the males treated only with methoprene. The response to metformin was sex-specific since females responded to high doses of the substance, whereas males responded better to low doses. These results suggest that trade-offs between survival and reproduction do not necessarily depend on energy reserves but they are intrinsically related to metabolic regulation and hormonal control.

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.

Behavioral Responses and Pupa Development Patterns After Hypoxia or Anoxia in a Desiccation-Resistant Anastrepha ludens Strain

The aim of this study was to experimentally test for adult cross-resistance to hypoxia or anoxia in a desiccation-resistant population of Anastrepha ludens Loew. We compared desiccation resistant flies with unselected (control) flies by measuring the effect of pre-emergence hypoxia on some fitness parameters (emergence, flight ability, copulation success, latency to copulation, copulation duration, ovary size). Anoxia effects were determined using eye color changes during pupa development and fly emergence after re-oxygenation. Both strains were negatively affected in all measured parameters when exposed to hypoxia for more than 48 h. However, after hypoxia, control flies showed, in general, shorter latency to mate and longer copula duration than desiccation-resistant flies. Anoxia-induced arrest of pupa development, whereas returning to normoxia conditions induced resumption of development. Anoxia period length (longer than 72 h) increased mortality to 100% in the control line, whereas the desiccation-resistant line survived even at 120 h of anoxia. Thus, pre-release hypoxia must not exceed 24 h in order to maintain insect quality independently of fly type.

Light Conditions After Emergence Affect Food Consumption and Survival of Ceratitis capitata (Diptera: Tephritidae) Sterile Males

To favor and standardize fruit fly production, many environmental factors are regulated in a mass-rearing facility. Specifically, in the holding rooms where sterile fruit flies are kept before releasing, they are exposed to constant darkness in order to reduce aggressive interactions and depletion of energy resources. However, such light conditions could negatively affect the quality traits and male mating performance. The objective of this study was to determine whether light conditions have an effect on quality traits in mass-reared 'Mediterranean fruit flies' Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). Under laboratory conditions and in two sequential experiments, we studied the effect of 1) different light intensities and 2) photoperiods, on adult food consumption, adult body weight, survival, and percent of flying and calling males. In the first experiment, sterile male flies were exposed to different light intensities during 3 d after emergence: 1000, 500, or 250 lux, with a 12:12 photoperiod. Complete darkness was used as a control. In the second experiment, adult flies were exposed to the following photoperiods (L(1000 lux)-D): 14-10, 12-12, 8-16, 4-20, and 0-24 as a control. Our results showed that flies under darkness ingested less food, were heavier, and exhibited higher survival than flies under any treatment of light intensity or photoperiod. Furthermore, the percentage of fliers and number of calling males did not differ among treatments. We conclude that holding males for 3 d under darkness do not affect their quality; indeed, emerging under this condition appears to favor them. The implications of these findings for SIT programs are discussed.