Bisexual Attract-and-Kill: A Novel Component of Resistance Management for Transgenic Cotton in Australia.

In Australia, destruction of overwintering pupae of Helicoverpa armigera (Hübner) and Helicoverpa punctigera (Wallengren) (Lepidoptera: Noctuidae) has been a key component of mandatory resistance management schemes to constrain development of resistance to Bt toxins in transgenic cotton. This has been accomplished by tillage ('pupae busting'), but it is expensive and can interfere with farming operations. Bisexual attract-and-kill technology based on plant volatile formulations offers a potential alternative in some circumstances. We discuss strategies for using such products and describe two trials in which three applications of an attract-and-kill formulation substantially reduced the numbers of Helicoverpa spp. moths and the numbers of potentially overwintering eggs they laid. One trial tested a curative strategy in which the last generation of moths emerging from transgenic cotton was targeted. The other tested a preventive strategy which aimed to reduce the numbers of eggs in the last generation. The preventive strategy reduced egg numbers by about 90% and is now included as an optional alternative to pupae busting in resistance management strategies for Australian cotton. It is limited to fields which have not been defoliated prior to 31 March and was developed to be used primarily in southern New South Wales. In the 2020-2021 cotton season, it was adopted on approximately 60% of the eligible cotton area. We describe the process whereby the strategy was developed in collaboration with the transgenic technology provider, supported by the cotton industry, and approved by the regulatory authority.

Exposure of Helicoverpa punctigera pupae to extreme temperatures for extended periods negatively impacts on adult population dynamics and reproductive output.

Understanding the impact that heat stress has on critical life stages of an organism is essential when assessing population responses to extreme events. Heat stress may occur as repeated small-scale events or as a single prolonged event, which may cause different outcomes to the organism. Here, we subjected Helicoverpa punctigera (Wallengren) pupae to two temperatures (44.2 °C and 43 °C) and two exposure treatments - a single 3-h prolonged exposure prolonged and three repeated 1-h exposure period with 24 h recovery time between bouts - to assess the biological traits of individuals. The maximum temperatures were used as they were just below the critical thermal maximum (CTmax) 47.3 °C ± 0.3 °C of pupae for which they could survive exposure. Adults in the prolonged and repeated heat-stressed treatments had 1.70 and 3.34 more days to emergence and 1.57 and 3.30 days extended life span compared to those kept under a constant 25 °C temperature (control treatment). Both pre-oviposition and oviposition periods were extended in the heat-stressed groups. Fecundity in the prolonged and repeated heat-stressed females was reduced by 34.7% and 65.5% eggs in the 43 °C treatment group and by 94.3% and 93.6% eggs in the 44.2 °C treatment group compared to the control group. No eggs from females in either the prolonged and repeated heat-stress groups hatched. We establish that heat stress on pupae can influence the population dynamics of H. punctigera by reducing fecundity as well as extending the pre oviposition period, and affecting adult development. Also, as heat exposure on the parent generation resulted in no offspring production, it is critical to assess cross-generational responses to extreme heat stress.

Estimating the differences in critical thermal maximum and metabolic rate of Helicoverpa punctigera (Wallengren) (Lepidoptera: Noctuidae) across life stages.

Temperature is a crucial driver of insect activity and physiological processes throughout their life-history, and heat stress may impact life stages (larvae, pupae and adult) in different ways. Using thermolimit respirometry, we assessed the critical thermal maxima (CTmax-temperature at which an organism loses neuromuscular control), CO2 emission rate (V́CO2) and Q10 (a measure of V́CO2 temperature sensitivity) of three different life stages of Helicoverpa punctigera (Wallengren) by increasing their temperature exposure from 25 °C to 55 °C at a rate of 0.25 °C min-1 . We found that the CTmax of larvae (49.1 °C ± 0.3 °C) was higher than pupae (47.4 °C ± 0.2 °C) and adults (46.9 °C ± 0.2 °C). The mean mass-specific CO2 emission rate (ml V́CO2 h-1) of larvae (0.26 ± 0.03 ml V́CO2 h-1) was also higher than adults (0.24 ± 0.04 ml V́CO2 h-1) and pupae (0.06 ± 0.02 ml V́CO2 h-1). The Q10: 25-35 °C for adults (2.01 ± 0.22) was significantly higher compared to larvae (1.40 ± 0.06) and Q10: 35-45 °C for adults (3.42 ± 0.24) was significantly higher compared to larvae (1.95 ± 0.08) and pupae (1.42 ± 0.98) respectively. We have established the upper thermal tolerance of H. punctigera, which will lead to a better understanding of the thermal physiology of this species both in its native range, and as a pest species in agricultural systems.

Regional and seasonal activity predictions for fall armyworm in Australia.

Since 2016, the fall armyworm (FAW), Spodoptera frugiperda, has undergone a significant range expansion from its native range in the Americas, to continental Africa, Asia, and in February 2020, mainland Australia. The large dispersal potential of FAW adults, wide host range of immature feeding stages, and unique environmental conditions in its invasive range creates large uncertainties in the expected impact on Australian plant production industries. Here, using a spatial model of population growth and spread potential informed by existing biological and climatic data, we simulate seasonal population activity potential of FAW, with a focus on Australia's grain production regions. Our results show that, in Australia, the large spread potential of FAW will allow it to exploit temporarily favourable conditions for population growth across highly variable climatic conditions. It is estimated that FAW populations would be present in a wide range of grain growing regions at certain times of year, but importantly, the expected seasonal activity will vary markedly between regions and years depending on climatic conditions. The window of activity for FAW will be longer for growing regions further north, with some regions possessing conditions conducive to year-round population survival. Seasonal migrations from this permanent range into southern regions, where large areas of annual grain crops are grown annually, are predicted to commence from October, i.e. spring, with populations subsequently building up into summer. The early stage of the FAW incursion into Australia means our predictions of seasonal activity potential will need to be refined as more Australian-specific information is accumulated. This study has contributed to our early understanding of FAW movement and population dynamics in Australia. Importantly, the models established here provide a useful framework that will be available to other countries should FAW invade in the future. To increase the robustness of our model, field sampling to identify conditions under which population growth occurs, and the location of source populations for migration events is required. This will enable accurate forecasting and early warning to farmers, which should improve pest monitoring and control programs of FAW.

Advances in Attract-and-Kill for Agricultural Pests: Beyond Pheromones.

Attract-and-kill has considerable potential as a tactic in integrated management of pests of agricultural crops, but the use of sex pheromones as attractants is limited by male multiple mating and immigration of mated females into treated areas. Attractants for both sexes, and particularly females, would minimize these difficulties. Volatile compounds derived from plants or fermentation of plant products can attract females and have been used in traps for monitoring and control, and in sprayable attract-and-kill formulations or bait stations. Recent advances in fundamental understanding of insect responses to plant volatiles should contribute to the development of products that can help manage a wide range of pests with few impacts on nontarget organisms, but theory must be tempered with pragmatism in the selection of volatiles and toxicants and in defining their roles in formulations. Market requirements and regulatory factors must be considered in parallel with scientific constraints if successful products are to be developed.

Non-Target Impacts of an Attract-and-Kill Formulation Based on Plant Volatiles: Responses of some Generalist Predators.

Responses of non-target insects to a blend of plant volatiles used as components in an attract-and-kill formulation for Helicoverpa spp. (Lepidoptera: Noctuidae) were studied in an Australian cotton field. Two experiments, one involving suction sampling during the day and the other at night, were conducted. Rows that had been treated with the volatile blend, with no added insecticide, were sampled with a large suction sampler 18, 42, and 85 h (day experiment) and 6, 30, and 78 h (night experiment) after treatment. Rows located 5, 10, 20, and 300 m away from the treated row were similarly sampled. Of seven generalist predators, only one accumulated on the treated rows compared to the untreated rows. Of the other six, five were found in lower numbers on the treated rows, and for one no significant effects were detected. Compared to pre-spray baseline levels, numbers of several taxa increased across the whole field after spraying, suggesting area-wide attraction, but localized responses to the treated rows were weak, and apparent repellence was more common than attraction. We suggest that attract-and-kill with plant volatiles should have minimal effects on populations of these predators, and is likely to be compatible with integrated pest management.

Developing Bisexual Attract-and-Kill for Polyphagous Insects: Ecological Rationale versus Pragmatics.

We discuss the principles of bisexual attract-and-kill, in which females as well as males are targeted with an attractant, such as a blend of plant volatiles, combined with a toxicant. While the advantages of this strategy have been apparent for over a century, there are few products available to farmers for inclusion in integrated pest management schemes. We describe the development, registration, and commercialization of one such product, Magnet(®), which was targeted against Helicoverpa armigera and H. punctigera in Australian cotton. We advocate an empirical rather than theoretical approach to selecting and blending plant volatiles for such products, and emphasise the importance of field studies on ecologically realistic scales of time and space. The properties required of insecticide partners also are discussed. We describe the studies that were necessary to provide data for registration of the Magnet(®) product. These included evidence of efficacy, including local and area-wide impacts on the target pest, non-target impacts, and safety for consumers and applicators. In the decade required for commercial development, the target market for Magnet(®) has been greatly reduced by the widespread adoption of transgenic insect-resistant cotton in Australia. We discuss potential applications in resistance management for transgenic cotton, and for other pests in cotton and other crops.

Contradictions in host plant resistance to pests: spider mite (Tetranychus urticae Koch) behaviour undermines the potential resistance of smooth-leaved cotton (Gossypium hirsutum L.).

BACKGROUND: Two-spotted spider mites (Tetranychus urticae Koch) oviposit near leaf veins or in leaf folds on the undersides of cotton (Gossypium hirsutum L.) leaves where the humid boundary layer offers protection from desiccation. The authors predicted that the boundary layer of glabrous cotton leaves should be shallower than that of hairy leaves, providing some resistance to mites. The dynamics of mite populations, leaf damage, leaf gas exchange and crop yield on two leaf hair isolines (smooth versus hairy) in two genetic backgrounds was assessed. RESULTS: Mite colonies developed faster on the hairy leaf isolines, but leaf damage per mite was higher in smooth leaf isolines, indicating more intense damage. A 50% reduction in photosynthesis on the hairy isolines required 1.8 times more mites than smooth leaves. The yield of cotton was reduced in + mite treatments, but the magnitude of reduction was similar for hairy and smooth isolines. CONCLUSION: Paradoxically, the relative inhospitality of glabrous leaves may have induced mites to concentrate in protected leaf sections, causing more localised and more severe damage, negating the yield benefits from fewer mites. These results highlight interactions between leaf microenvironment, pest behaviour and plant productivity that may have implications for other instances of plant resistance.

Evaluation and treatment of hematospermia.

Hematospermia can be a distressing symptom for patients, but most cases are effectively managed by a primary care physician. Although the condition is usually benign, significant underlying pathology must be excluded by history, physical examination, laboratory evaluation, and, in select cases, other diagnostic modalities. In men younger than 40 years without risk factors (e.g., history of cancer, known urogenital malformation, bleeding disorders) and in men with no associated symptoms, hematospermia is often self-limited and requires no further evaluation or treatment other than patient reassurance. Many cases are attributable to sexually transmitted infections or other urogenital infections in men younger than 40 years who present with hematospermia associated with lower urinary tract symptoms. Workup in these patients can be limited to urinalysis and testing for sexually transmitted infections, with treatment as indicated. In men 40 years and older, iatrogenic hematospermia from urogenital instrumentation or prostate biopsy is the most common cause of blood in the semen. However, recurrent or persistent hematospermia or associated symptoms (e.g., fever, chills, weight loss, bone pain) should prompt further investigation, starting with a prostate examination and prostate-specific antigen testing to evaluate for prostate cancer. Other etiologies to consider in those 40 years and older include genitourinary infections, inflammations, vascular malformations, stones, tumors, and systemic disorders that increase bleeding risk.

Identifying hazards in complex ecological systems. Part 3: Hierarchical Holographic Model for herbicide tolerant oilseed rape.

This paper is the third in a series designed to demonstrate the application of rigorous, systematic hazard identification techniques to ecological systems. Here we use Hierarchical Holographic Modelling to identify the potential ecological hazards associated with the commercial release of herbicide tolerant oilseed rape. Hierarchical Holographic Models decompose complex systems into a series of sub-systems and consider interactions between the components and processes of these sub-systems in order to identify hazards. In this example we considered 1356 potential interactions between the biological, chemical and physical components and processes of the herbicide tolerant oilseed rape environment, and identified 152 potential hazards, grouped into 14 categories. The hazards were subsequently scored for degree of concern and plausibility, and then compared with an equivalent list of hazards generated independently by a checklist approach. The incidence of herbicide tolerant volunteers (and weeds) both on and off the farm had the highest average score of all the ecological hazard categories. The checklist based approach identified or implied 44% of the hazards identified in the Hierarchical Holographic Model, including nine of the ten hazards ranked most important. The checklist approach focussed almost exclusively on the phenotypic and genotypic hazards associated with herbicide tolerant oilseed rape and largely ignored the hazards associated with the circumstances surrounding its use. As a result the checklist identified only 6 out of the 79 potential hazards associated with changes to farming practice. The commercial release of herbicide tolerant oilseed rape will be associated with changes in tillage and the application of post-emergent herbicides. It may also lead to changes in spray schedules of insecticide and fungicide. Many of the environmental hazards identified with these changes are plausible and may warrant further investigation or targeted monitoring.