Alternative, biologically-based approaches for pest management are sorely needed and one approach is to use genetically engineered insects. Herein we describe a series of integrated field, laboratory and modeling studies with the diamondback moth, Plutella xylostella, a serious global pest of crucifers. A "self-limiting" strain of Plutella xylostella (OX4319L), genetically engineered to allow the production of male-only cohorts of moths for field releases, was developed as a novel approach to protect crucifer crops. Wild-type females that mate with these self-limiting males will not produce viable female progeny. Our previous greenhouse studies demonstrated that releases of OX4319L males lead to suppression of the target pest population and dilution of insecticide-resistance genes. We report results of the first open-field release of a non-irradiated, genetically engineered self-limiting strain of an agricultural pest insect. In a series of mark-release-recapture field studies with co-releases of adult OX4319L males and wild-type counterparts, the dispersal, persistence and field survival of each strain were measured in a 2.83 ha cabbage field. In most cases, no differences were detected in these parameters. Overall, 97.8% of the wild-type males and 95.4% of the OX4319L males recaptured dispersed <35 m from the release point. The predicted persistence did not differ between strains regardless of release rate. With 95% confidence, 75% of OX4319L males released at a rate of 1,500 could be expected to live between 3.5 and 5.4 days and 95% of these males could be expected to be detected within 25.8-34.9 m from the release point. Moth strain had no effect on field survival but release rate did. Collectively, these results suggest similar field behavior of OX4319L males compared to its wild-type counterpart. Laboratory studies revealed no differences in mating competitiveness or intrinsic growth rates between the strains and small differences in longevity. Using results from these studies, mathematical models were developed that indicate release of OX4319L males should offer efficacious pest management of P. xylostella. Further field studies are recommended to demonstrate the potential for this self-limiting P. xylostella to provide pest suppression and resistance management benefits, as was previously demonstrated in greenhouse studies.
The fall armyworm, Spodoptera frugiperda, is a significant and widespread pest of maize, sorghum, rice, and other economically important crops. Successful management of this caterpillar pest has historically relied upon application of synthetic insecticides and through cultivation of genetically engineered crops expressing insecticidal proteins (Bt crops). Fall armyworm has, however, developed resistance to both synthetic insecticides and Bt crops, which risks undermining the benefits delivered by these important crop protection tools. Previous modelling and empirical studies have demonstrated that releases of insecticide- or Bt-susceptible insects genetically modified to express conditional female mortality can both dilute insecticide resistance and suppress pest populations.Here, we describe the first germline transformation of the fall armyworm and the development of a genetically engineered male-selecting self-limiting strain, OX5382G, which exhibits complete female mortality in the absence of an additive in the larval diet. Laboratory experiments showed that males of this strain are competitive against wild-type males for copulations with wild-type females, and that the OX5382G self-limiting transgene declines rapidly to extinction in closed populations following the cessation of OX5382G male releases. Population models simulating the release of OX5382G males in tandem with Bt crops and non-Bt 'refuge' crops show that OX5382G releases can suppress fall armyworm populations and delay the spread of resistance to insecticidal proteins.This article describes the development of self-limiting fall armyworm designed to control this pest by suppressing pest populations, and population models that demonstrate its potential as a highly effective method of managing resistance to Bt crops in pest fall armyworm populations. Our results provide early promise for a potentially valuable future addition to integrated pest management strategies for fall armyworm and other pests for which resistance to existing crop protection measures results in damage to crops and impedes sustainable agriculture.
Abstract The mass release of transgenic insects carrying female lethal self‐limiting genes can reduce pest insect populations. Substantial releases are also a novel resistance management tool, since wild type alleles conferring susceptibility to pesticides can dilute resistance alleles in target populations. However, a potential barrier is the need for large‐scale area‐wide releases. Here, we address whether localized releases of transgenic insects could provide an alternative means of population suppression and resistance management, without serious loss of efficacy. We used experimental mesocosms constituting insect metapopulations to explore the evolution of resistance to the Bacillus thuringiensis toxin Cry1Ac in a high‐dose/refugia landscape in the insect Plutella xylostella . We ran two selection experiments, the first compared the efficacy of “everywhere” releases and negative controls to a spatially density‐dependent or “whack‐a‐mole” strategy that concentrated release of transgenic insects in subpopulations with elevated resistance. The second experiment tested the relative efficacy of whack‐a‐mole and everywhere releases under spatially homogenous and heterogeneous selection pressure. The whack‐a‐mole releases were less effective than everywhere releases in terms of slowing the evolution of resistance, which, in the first experiment, largely prevented the evolution of resistance. In contrast to predictions, heterogeneous whack‐a‐mole releases were no more effective under heterogeneous selection pressure. Heterogeneous selection pressure did, however, reduce total insect population sizes. Whack‐a‐mole releases provided early population suppression, indistinguishable from homogeneous everywhere releases. However, insect population densities tracked the evolution of resistance in this system, as phenotypic resistance provides access to additional diet containing the toxin Cry1Ac. Thus, as resistance levels diverged between treatments, carrying capacities and population sizes increased under the whack‐a‐mole approach. Synthesis and applications . Spatially density‐dependent releases of transgenic insects, particularly those targeting source populations at a landscape level, could suppress pest populations in the absence of blanket area‐wide releases. The benefits of self‐limiting transgenic insects were reduced in spatially localized releases, suggesting that they are not ideal for “spot” treatment of resistance problems. Nevertheless, spatially homogeneous or heterogeneous releases could be used to support other resistance management interventions.
The sterile insect technique (SIT) is a pest control strategy involving the mass release of radiation-sterilized insects, which reduce the target population through nonviable matings. In Lepidoptera, SIT could be more broadly applicable if the deleterious effects of sterilization by irradiation could be avoided. Moreover, male-only release can improve the efficacy of SIT. Adequate methods of male-only production in Lepidoptera are currently lacking, in contrast to some Diptera. We describe a synthetic genetic system that allows male-only moth production for SIT and also replaces radiation sterilization with inherited female-specific lethality. We sequenced and characterized the doublesex (dsx) gene from the pink bollworm (Pectinophora gossypiella). Sex-alternate splicing from dsx was used to develop a conditional lethal genetic sexing system in two pest moths: the diamondback moth (Plutella xylostella) and pink bollworm. This system shows promise for enhancing existing pink bollworm SIT, as well as broadening SIT-type control to diamondback moth and other Lepidoptera.
Striated Darters (Etheostoma striatulum) are small, uncommon darters endemic to the Middle-to-Upper regions of the Duck River, Tennessee. Since their description, they have become increasingly rare within their range. Historically, Striated Darters occupied 16 tributaries of the Duck River; as of 2011, their known distribution has declined to nine tributaries. Due to this documented decline, Striated Darters are currently under review for federal listing under the Endangered Species Act. Effective management and conservation of this species will also require information about their distribution. This study aims to delineate the present-day distribution of the Striated Darter through a species-specific environmental DNA (eDNA) assay. Aquatic species discard DNA fragments in many ways (e.g., urination and reproduction) into the water column which can then be identified using well-established molecular techniques. Due to the Striated Darter's reclusive and cryptic behavior, conventional techniques are ineffective for detection, requiring the use of much more efficient and sensitive eDNA monitoring techniques. At 30 historical sites in the Duck River, three water samples will be taken and then filtered for molecular analyses. A qPCR assay will be designed to detect Striated Darters across all sites and conclusions will be run through a hierarchical occupancy model to test for the probability of detection at the qPCR replicate, sample replicate, and site levels. Another project investigating the population status of the Striated Darter will be running similar occupancy models using conventional techniques, which will allow for comparison between traditional and molecular approaches.
Abstract The diamondback moth, Plutella xylostella , is one of the most economically important agricultural pests. The larvae of this moth cause damage by feeding on the foliage of cruciferous vegetables such as cabbage, broccoli, cauliflower and rapeseed. Control generally comprises chemical treatment; however, the diamondback moth is renowned for rapid development of resistance to pesticides. Other methods, such as biological control, have not been able to provide adequate protection. Germline transformation of pest insects has become available in recent years as an enabling technology for new genetics‐based control methods, such as the Release of Insects carrying a Dominant Lethal (RIDL ® ). In the present study, we report the first transformation of the diamondback moth, using the piggyBac transposable element, by embryo microinjection. In generating transgenic strains using four different constructs, the function of three regulatory sequences in this moth was demonstrated in driving expression of fluorescent proteins. The transformation rates achieved, 0.48–0.68%, are relatively low compared with those described in other Lepidoptera, but not prohibitive, and are likely to increase with experience. We anticipate that germline transformation of the diamondback moth will permit the development of RIDL strains for use against this pest and facilitate the wider use of this species as a model organism for basic studies.
Summary Spawning migration by freshwater eels to their marine spawning grounds is widely considered to be direct and rapid; however, emerging evidence suggests that eel migratory behaviour is more complex than previously thought, with potential implications for eel conservation and management. Over a 5‐year period, we tagged 97 yellow‐phase short‐finned eels Anguilla australis with acoustic transmitters in the freshwater reaches of a south‐eastern Australian river to: (i) examine environmental correlates associated with seaward migration; (ii) test the hypothesis that migration is rapid and direct once initiated and (iii) assess individual variation in behaviour associated with seaward migration. Twenty‐three of the tagged eels migrated from fresh water into the estuary, whilst the remainder stayed within fresh water. Movement was detected primarily at night and eels entered the estuary throughout the year, with an increase in frequency over summer and following high river flows. Time in the estuary ranged from 1 to 305 days (median: 77 days). Movement into the sea was influenced primarily by the lunar phase, and to a lesser degree by water temperature, and occurred from late summer to early autumn. The extended residence and complex movements of migrating eels in the estuary suggest that they are considerably more vulnerable to exploitation than would be predicted by the generalised eel migration model of direct movement out to sea.
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