Stephanie Bloem

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.

Applications of F1 sterility for research and management of Cactoblastis cactorum (Lepidoptera: Pyralidae)

The unintentional arrival of the cactus moth, Cactoblastis cactorum (Berg), in Florida has raised concerns for the safety of native and rare Opuntia species in the Florida Keys and the potential spread of C. cactorum to the Opuntia-rich areas of the western United States and Mexico. In addition to threatening the biodiversity of these native ecosystems, such non-target effects would generate negative publicity that could heighten public concern over the use of exotic natural enemies and jeopardize future biological control programs against weeds. In this paper we discuss the use of inherited (F1) sterility in Lepidoptera to study, predict, and manage the expanding populations of C. cactorum. Research areas in which the use of F1 sterility would be most applicable include (1) elucidation of the host range of C. cactorum for key native Opuntia species from across the U.S., (2) prediction of the geographic range of C. cactorum in the U.S. and Mexico, and (3) delineation of the impact of native natural enemies on the spread of C. cactorum. The use of F1 sterility for control of C. cactorum would be most appropriate for (1) eradication of C. cactorum from areas of new introductions, or from isolated and/or environmentally sensitive areas such as the Florida Keys, (2) establishment of a barrier by means of release of irradiated moths along the leading edge of the C. cactorum geographical range, and (3) provisioning sterile C. cactorum in the field as hosts for released natural enemies to increase their initial survival and establishment.

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.

Area-Wide Control Tactics for the False Codling Moth Thaumatotibia leucotreta in South Africa: a Potential Invasive Species

The false codling moth Thaumatotibia leucotreta (Meyrick) is a key pest of citrus, stone fruit, and other crops in many countries throughout continental Africa, including South Africa. There is a growing awareness that this damaging pest could soon be introduced into other countries including the USA as a direct result of increased international trade and daily direct flights fromAfrican countries. South Africa currently employs a combination of cultural, chemical, microbial and augmentative biological control to suppress false codling moth. Augmentative biological control makes use of the egg parasitoid Trichogrammatoidea cryptophlebiae Nagaraja. However, this integrated programme is not adequate for effective false codling moth control. The sterile insect technique (SIT) is now being developed as an additional method for false codling moth suppression in South Africa, but also as a tactic that could be rapidly integrated in an area-wide integrated pest management strategy if false codling moth were to be introduced or become established as an exotic invasive pest in other countries such as the USA. The SIT is regarded as a host-specific and environment-friendly pest control tactic that is compatible with the application of augmentative biological control. However, fully successful integration of the SIT and parasitoid releases into an effective pest management approach can occur only if the parasitoids do not negatively impact irradiated insects and their progeny more severely than they affect the wild pest population, and if the release of irradiated insects does not negatively impact the efficacy of the parasitoids. Therefore, knowledge of the compatibility of T. cryptophlebiae and the release of irradiated false codling moth is crucial to the evaluation of the combined use of these tactics. The development and combination of these offshore integrated pest management strategies in South Africa will develop and/or enhance scientific expertise and infrastructure in that country, reduce wild populations of false codling moth and lower the risk of its introduction into countries currently free of this pest. In addition, the development of these control tactics and the improved infrastructure (e.g. rearing/irradiation facilities in South Africa) will provide resources, technology, and strategies for eradicating invasive populations of the false codling moth should this pest be introduced into new geographical areas.

Influence of Radiation Dose on the Level of F1 Sterility in the Cactus Moth, Cactoblastis cactorum (Lepidoptera: Pyralidae)

Abstract We examined inherited sterility effects on the F1 and F2 generations of the cactus moth, Cactoblastis cactorum (Berg) after gamma sterilization. Our objectives were to identify the dose of gamma radiation that would fully sterilize F1-generation moths and result in no viable offspring when F1 males were inbred- or out-crossed to fertile females, and that would allow maximum production of F1 sterile C. cactorum adults by irradiated males. Newly emerged adults of C. cactorum were exposed to increasing doses of gamma radiation and inbred or out-crossed to fertile counterparts. Inherited effects resulting from irradiation of males and females were expressed in the F1 generation as reduced egg hatch, increased developmental time for the F1 egg, and increased F1 larval to adult mortality. These effects were most pronounced when parental adults were irradiated at 200 Gy. Survival of F1-generation offspring originating from irradiated male × fertile female crosses was greatest at 200 Gy. In addition, inbred- and out-crosses of surviving F1 adults, with 1 parent irradiated at 200 Gy, resulted in no F2 adults. Maximum production of sterile F1 adults at 200 Gy suggests this dose is the most appropriate dose for implementing the sterile insect technique (SIT)-F1 sterility for control of C. cactorum in North America and for testing host suitability and potential geographical range in the field.

CACTOBLASTIS CACTORUM (Lepidoptera: pyralidae): Observations of Courtship and Mating Behaviors at Two Locations on the Gulf Coast of Florida

Abstract Cactoblastis cactorum (Berg) has become an invasive pest of Opuntia spp. along the coastal areas of southeastern United States from the panhandle of Florida to South Carolina. Spread of this insect into cactus dominated natural areas of the United States and Mexico and into agricultural opuntia fields of Mexico is raising concerns within international governments and conservation organizations. Interest is growing in using the Sterile Insect Technique (SIT) to manage C. cactorum populations. Information on courtship and mating behaviors of this insect is important in the development and application of SIT. We conducted mating table studies and determined that this moth exhibits simple rather than elaborate mating behaviors and that courtship and mating take place briefly during morning twilight. Typically, females initiate calling, males respond to females, and copulation are complete before sunrise. Successfully mated females attract males within a short period (mean of 5.2 min), while unsuccessful females continue calling for about 40 minutes. Mating pairs remain in copula for a mean of 31.8 min. Generally, mated females are busy ovipositing the first few nights after mating, not exhibiting additional mating behaviors. A release of marked males revealed that males stay near the release site and can be recovered and identified for subsequent population estimate studies. This study on courtship/mating behavior is helpful to the ongoing C. cactorum research to develop a successful SIT program, identify the female calling pheromone, improve monitoring traps, and develop a technique to estimate adult moth population abundance.

Effect of radiation on fecundity and fertility of codling moth Cydia pomonella (Linnaeus) (Lepidoptera: Tortricidae) from South Africa

Codling moth Cydia pomonella (Linnaeus) (Lepidoptera: Tortricidae) is the key pest of pome fruit in South Africa, and it’s control in apple and pear orchards relies on the application of insecticides and pheromone‐mediated mating disruption. Development of resistance to insecticides and placement of restrictions on the use of certain insecticides has made control of codling moth in South Africa increasingly problematic. The use of the sterile insect technique (SIT) as a control tactic for codling moth is under investigation as a potential addition to the current control strategy. We investigated the radiosensitivity of a laboratory strain of codling moth that was established from moths collected from commercial and organic orchards in the Western Cape, South Africa. Fecundity and fertility of this strain following radiation were consistent with values for the codling moth strain in the Canadian rearing facility in British Columbia. For both strains, the female codling moth was considerably more radiosensitive than the male. At a radiation dose of 100 Gy or higher, treated females were 100% sterile. The fertility of the South African strain was higher (86.3%) than for the Canadian strain (71.9%). This difference in fertility between the two strains was maintained when the dose of radiation was 100 Gy. However, the level of fertility was very similar between the two strains for doses ≥150 Gy. Therefore, based upon previously published work and the data from this study, an operational dose of 150 Gy is recommended for future codling moth SIT programmes in South Africa.

DEVELOPMENT OF THE MOST EFFECTIVE TRAP TO MONITOR THE PRESENCE OF THE CACTUS MOTH CACTOBLASTIS CACTORUM (LEPIDOPTERA: PYRALIDAE)

Abstract Various trap specifications were evaluated to identify the most effective trap for capturing wild male Cactoblastis cactorum (Berg). All traps were baited with virgin female C. cactorum and, except for the first comparison of trap type, a standard wing trap was used in all experiments. Although wing traps captured more males than did the other trap types (delta or bucket), the differences were not significant. However, significantly higher numbers of males were captured in wing traps placed 2 m above ground than traps at 1 m or 0.5 m, and wing traps baited with four virgin females caught significantly more males than wing traps baited with a single female. Differences in number of males captured by young and old females were not significant, but more than twice as many males were captured in traps baited with one-day-old females than traps baited with four day old females. In addition, there were no significant differences in number of males caught in unpainted, white, wing traps and wing traps painted one of eight different colors (flat white, black, dark green, fluorescent green, yellow, fluorescent yellow, orange, or blue), although, more males were captured in the unpainted wing traps. The results presented here suggest that the best trap currently available to monitor C. cactorum is a standard (unpainted) wing trap, placed at a height of 2.0 m aboveground, and baited with four newly emerged females.