J. E. Carpenter

Inherited Sterility in Insects

The unique genetic phenomena responsible for inherited sterility (IS) in Lepidoptera and some other arthropods, as compared with full sterility, provide advantages for pest control. Lepidopteran females are usually more sensitive to radiation than males of the same species. This allows the radiation dose to be adjusted to suit programme requirements. When partially sterile males mate with wild females, the radiation-induced deleterious effects are inherited by the F1 generation. As a result, egg hatch is reduced and the resulting offspring are both highly sterile and predominately male. Compared with the high radiation required to achieve full sterility in Lepidoptera, the lower dose of radiation used to induce F1 sterility increases the quality and competitiveness of the released insects as measured by improved dispersal after release, increased mating ability, and superior sperm competition. F1 sterile progeny produced in the field enhance the efficacy of released partially sterile males, and improve compatibility with other pest control strategies. In addition, F1 sterile progeny can be used to increase the production of natural enemies, and to study the potential host and geographical ranges of exotic lepidopteran pests.

Impact of Moth Suppression/Eradication Programmes Using the Sterile Insect Technique or Inherited Sterility

Numerous lepidopteran species have been investigated as candidates for control using the sterile insect technique (SIT) or inherited sterility (IS). However to date only two programmes are operational — the pink bollworm containment programme in the San Joaquin Valley, California, USA, and the codling moth suppression programme in British Columbia, Canada. Both of these programmes have been highly successful in controlling the pest populations, reducing insecticide use, and improving interactions between growers and the general public. However, other benefits, including the positive economic impacts of these programmes, have not been fully quantified. Methods to reduce the cost of lepidopteran programmes might include combining the SIT/IS with other pest control tactics such as mating disruption or the release of natural enemies, the development of genetic sexing strains, or the application of molecular technologies to develop genetic markers and genetic sterility. In future the greatest potential for impact of lepidopteran SIT/IS programmes may be in combating key invasive threats such as the eradication of an outbreak of the painted apple moth in New Zealand.

Inherited sterility in Cactoblastis cactorum (Lepidoptera: Pyralidae)

Newly emerged male and female adult cactus moths, Cactoblastis cactorum (Berg), were treated with increasing doses of gamma radiation, and the moths were outcrossed to fertile counterparts. Fecundity of the moth pairs was not affected by increasing doses of radiation. The minimum dose at which treated females were found to be 100% sterile when mated to untreated males was 200 Gy. Fertility of treated males declined with increasing doses of radiation to approach 0% near 500 Gy. Inherited effects resulting from irradiation of P males and females were expressed in the F1 generation as increased developmental time from oviposition to larval eclosion, increased egg mortality, and increased neonate to adult stage mortality. A shift in the F1 sex ratio in favor of males was not observed.

Developing a Sterile Insect Release Program for Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae): Effective Overflooding Ratios and Release-Recapture Field Studies

Abstract In an effort to continue the development of a sterile insect release program against the invasive cactus moth, Cactoblastis cactorum (Berg), we released partially sterile males alone or in combination with fully sterile females at a 5:1 or 10:1 (treated:fertile) overflooding ratio inside large field cages containing Opuntia stricta Haworth (Haworth) host plants. Insects were allowed to mate and lay eggs, and all eggsticks were collected daily. Percent egg hatch and reduction in F1 fertile larvae were used to ascertain the effectiveness of each release combination. In addition, limited field release-recapture experiments were conducted to examine the dispersal ability of untreated and treated cactus moth males. Results suggest that an overflooding ratio as low as 5:1 can effectively suppress C. cactorum in field cages and that releasing both genders together is more effective than releasing males only. In open field releases, the dispersal ability of C. cactorum was not significantly affected by treating the adults with gamma radiation.

Season-Long Releases of Partially Sterile Males for Control of Codling Moth (Lepidoptera: Tortricidae) in Washington Apples

Abstract Season-long field studies were conducted in Washington apple orchards that compared the following: (1) twice per week releases of partially sterile codling moths, Cydia pomonella (L.), treated with either 100 or 250 Gy, and (2) combinations of mating disruption plus the release of partially sterile (100 Gy) codling moths, to control wild codling moth populations. No significant differences in the level of fruit damage at either midseason or harvest were found between any of the treatments, or between the treatments and the inside controls. Damage in all plots was <0.1%. In both studies, trap data suggest that the movement of the 100 Gy-treated moths into the other treatments and the inside controls may have masked treatment effects. However, fruit damage was significantly lower in all treatment plots when compared with control plots located outside of the treatment areas. Results indicated that the release of partially sterile male (and fully sterile female) codling moths does not result in increased fruit injury and that the lower dose of radiation used to partially sterilize males results in insects that are more active, disperse greater distances and are generally more competitive.

Improved quality management to enhance the efficacy of the sterile insect technique for lepidopteran pests

Lepidoptera are among the most severe pests of food and fibre crops in the world and are mainly controlled using broad spectrum insecticides. This does not lead to environmentally sustainable control and farmers are demanding alternative control tools which are both effective and friendly to the environment. The sterile insect technique (SIT), within an area‐wide integrated pest management (AW‐IPM) approach, has proven to be a powerful control tactic for the creation of pest‐free areas or areas of low pest prevalence. Improving the quality of laboratory‐reared moths would increase the efficacy of released sterile moths applied in AW‐IPM programmes that integrate the (SIT). Factors that might affect the quality and field performance of released sterile moths are identified and characterized in this study. Some tools and methods to measure, predict and enhance moth quality are described such as tests for moth quality, female moth trapping systems, ‘smart’ traps, machine vision for recording behaviour, marking techniques, and release technologies. Methods of enhancing rearing systems are discussed with a view to selecting and preserving useful genetic traits that improve field performance.

Improvement of the sterile insect technique for codling moth Cydia pomonella (Linnaeus) (Lepidoptera Tortricidae) to facilitate expansion of field application

The codling moth Cydia pomonella (L.) (Lepidoptera Tortricidae) is a key pest of pome fruit (apple, pear and quince) and walnut orchards in most temperate regions of the world. Efforts to control the codling moth in the past mostly relied on the use of broad spectrum insecticide sprays, which has resulted in the development of insecticide resistance, and the disruption of the control of secondary pests. In addition, the frequent reliance and use of these insecticides are a constant threat to the environment and human health. Consequently, there have been increased demands from the growers for the development of codling moth control tactics that are not only effective but also friendly to the environment. In that respect, the sterile insect technique (SIT) and its derivative, inherited sterility (IS), are, together with mating disruption and granulosis virus, among the options that offer great potential as cost‐effective additions to available control tactics for integration in area‐wide integrated pest‐management approaches. In support of the further development of the SIT/IS for codling moth control, the Joint FAO/IAEA Programme of Nuclear Techniques in Food and Agriculture implemented a 5‐year Coordinated Research Project (CRP) entitled ‘Improvement of codling moth SIT to facilitate expansion of field application’. Research focussed on sterile codling moth quality and management (e.g. mobility and life‐history traits in relation to rearing strategy, dispersal, flight ability, radiosensitivity and mating compatibility) and a better understanding of the basic genetics of codling moth to assist the development of genetic sexing strains (e.g. cytogenetics, the development of dominant conditional lethal mutations, molecular characterization of the sex chromosomes, sex identification in embryos and cytogenetic markers). The results of the CRP are presented in this special issue.

Diel Flight Pattern and Flight Performance of Cactoblastis cactorum (Lepidoptera: Pyralidae) Measured on a Flight Mill: Influence of Age, Gender, Mating Status, and Body Size

Abstract Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae) is an invasive herbivore that poses a serious risk to Opuntia cacti in North America. Knowledge of the flight behavior of the cactus moth is crucial for a better understanding of natural dispersal, and for both monitoring and control. We used computer-linked flight mills to investigate diel flight activity and flight performance in relation to gender, age, mating status, and body size. Maximal flight activity for both mated and unmated moths occurred during twilight, whereas flight activity was low during photophase. The total distance flown and the number of initiated flights within a diel cycle were higher in both unmated and mated females than in males, but the longest single flight was similar in both genders. These findings suggest that pheromone trap captures of males likely indicate the simultaneous presence of females and that mated females might even be in areas where males are not detected yet. Flight performance heterogeneity was large, with a small portion of the population (both males and females) performing long unbroken flights, whereas the majority made short flights. Females had higher pupal and adult body size and shorter longevity than males. A few individuals, particularly young mated females, flying long distances may be important for active spread of a population and the colonization of new habitats. Implications of this study in the control of the cactus moth by using the sterile insect technique are discussed.

Mobility of Mass-Reared Diapaused and Nondiapaused Cydia pomonella (Lepidoptera: Tortricidae): Effect of Different Constant Temperatures and Lengths of Cold Storage

Desirable behavioral attributes in mass-reared insects should include the ability to perform favorably under the various environmental conditions they encounter upon release in the field. Insect quality also may be influenced by storage conditions and storage duration before field release. We studied the effects of three different constant ambient temperatures (15, 20, and 25 degrees C) and different lengths of adult cold storage (0, 24, 48, and 72 h at 2 degrees C) on the locomotor activity of adult Cydia pomonella (L.) mass reared through diapause or standard production protocols. Mobility was assessed in actographs housed in a climate controlled chamber; tests lasted 24 h. We found that adult mobility was significantly higher for both males and females at 25 and 20 degrees C than at 15 degrees C. There were no significant differences in mobility in moths reared through diapause or nondiapaused production protocols. In addition, temporal analysis of the data revealed a significant shift in the diel patterns of activity for both genders when adults were tested at the three different temperatures. Moths exposed to the lower temperature shifted their activity pattern from evening to mid-afternoon, which may be an adaptive behavior to take advantage of the expected warmest period of the day. Diapaused adults were significantly less mobile when stored in the cold (24, 48, or 72 h of storage at 2 degrees C) than were diapaused adults that did not experience cold storage (0 h). However, length of time in cold storage did not significantly influence the mobility of adult codling moths reared through standard production protocols.

Mobility of Mass-Reared Diapaused and Nondiapaused Cydia pomonella (Lepidoptera: Tortricidae): Effect of Mating Status and Treatment with Gamma Radiation

Mass-reared insects may differ in their behavioral traits depending on whether they have undergone diapause. We studied the mobility of mass-reared diapaused and nondiapaused Cydia pomonella (L.) with a focus on understanding the effect of mating status and treatment with gamma radiation as these insects are destined for use in an areawide program that uses the sterile insect technique (SIT). Actograph-measured mobility was assessed one gender at a time for 4 h during which the photoperiod transitioned from day to night. We tested 20-30 individuals per treatment. For experiments on the effect of mating status, we used 24-48-h-old adults (diapause [D]-virgin, D-mated, standard [N]-virgin, and N-mated), which is the typical age class that is released in the SIT program. Diapaused females were significantly more mobile than females reared through standard production, whereas no differences were detected in male mobility because of rearing strategy. Mated females were significantly more mobile than virgin females, whereas no difference in mobility because of mating status was detected for males. Mated females were significantly more mobile than mated males. In contrast, virgin females were significantly less mobile than virgin males. For experiments on the effect of treatment with gamma radiation, adults from all rearing strategies and treatments (D-0Gy, D-100Gy, D-250Gy, N-0Gy, N-100Gy, and N-250Gy), were tested simultaneously. Adult males were tested at two different constant temperatures (25 and 20 degrees C), whereas adult females were tested only at 25 degrees C. For standard-reared adults, we found a significant linear decrease in mobility as the radiation dose increased from 0 to 250 Gy. In contrast, the relationship between mobility and dose of radiation was quadratic for diapaused males and absent for diapaused females.