Re-engineering the sterile insect technique

The mass release of sterile insects (the Sterile Insect Technique, SIT) is a highly effective area-wide method of pest control with a low environmental impact. SIT relies on the sterilization by irradiation of large numbers of insects. This has unavoidable costs in terms of the fitness of the irradiated insects and the financial requirements of constructing and operating the radiation facility. In many cases it is considered important to release only males, but large-scale sex-separation is also problematic. I have proposed that both of these difficulties can be overcome by using engineered strains of insects carrying a dominant, repressible, lethal gene or genetic system. As a proof of principle, my group and others have constructed strains of Drosophila melanogaster with the required genetic properties.     

Molecular technologies to improve the effectiveness of the sterile insect technique

The application of the Sterile Insect Technique (SIT) in area-wide integrated pest management (AW-IPM) programmes continues to increase. However, programme efficiency can still be considerably enhanced when certain components of the technology are improved, such as the development of improved strains for mass rearing and release. These include strains that (1) produce only male insects for sterilization and release and (2) carry easily identifiable markers to identify released sterile insects in the field. Using both classical and modern biotechnology techniques, key insect pests are targeted, where SIT programmes are being implemented. The pests include mosquitoes, the Mexican fruit fly, the codling moth, the oriental fruit fly and the pink bollworm. This special issue summarizes the results of research efforts aimed at the development and evaluation of new strains to a level where a decision can be made as to their suitability for use in large scale SIT programmes. Major beneficiaries will be operational AW-IPM programmes that apply the SIT against major insect pests.     

Developing transgenic Anopheles mosquitoes for the sterile insect technique

In the last 10 years the availability of the genome sequence of Anopheles gambiae and the development of a transgenic technology for several species of Anopheles mosquitoes have, in combination, helped in enabling us to gain several insights into the biology of these mosquitoes that is relevant to their capacity as vectors of the malaria parasite. While this information is anticipated to inform many novel vector control strategies, the technique most likely to benefit in the near future from the availability of a reliable transgenic technology is the sterile insect technique (SIT), which relies on releasing large numbers of sterile insects to compete for mates in the wild, leading to population suppression. Although SIT has been proven to work reliably for many insects, the construction of suitable strains, and induction of sterility, has until now been a laborious process, combining classical genetics with radiation-induced sterility. Using transgenesis to create strains of Anopheles suitable for SIT could potentially offer several advantages over current approaches, in that the basic design of transgenic constructs designed for other insects should be rapidly transferable to mosquitoes, and induction of sterility as a product of the transgenic modification could obviate the requirement for radiation and its associated deleterious effects. In this paper the progress of different transgenic approaches in constructing tools for SIT will be reviewed.     

转基因在苹果蠹蛾不育昆虫释放技术中的应用

使用不育昆虫释放技术是一项新兴的苹果蠹蛾Cydia pomonella(L.)防治方法,使用转基因得到不育雄蛾具有比传统辐射方法更多的优点。转基因技术通过使用基于piggyBac等转座子的质粒载体,并插入显性条件致死基因以培育遗传性别品系,同时插入荧光蛋白等标记基因来显示转基因的效果;在人工控制的发育条件,建立成熟的稳定苹果蠹蛾品系,用以最终的田间释放以达到防治的目的。     

苹果蠹蛾不育昆虫释放技术研究进展

不育昆虫释放技术(sterile insect technique,SIT)是一种环境友好、可作为大面积害虫综合治理(AW-IPM)的防治技术,是以压倒性比例释放不育昆虫来减少田间同种害虫繁殖量的害虫治理方法。苹果蠹蛾Cydia pomonella(L.)是世界重要的梨果类害虫,现已入侵世界5洲71国。本文综述了苹果蠹蛾大规模饲养技术、辐射不育技术、释放技术3个关键环节的研究与技术进展,主要包括:苹果蠹蛾人工饲料、实验种群建立、饲养设备与条件、收集和质量评估、长距离运输、辐射源与设备、辐射剂量与敏感性、释放方法、释放标记和释放量等,并介绍了各国采用SIT技术的应用效果。苹果蠹蛾在我国新疆、甘肃、宁夏、内蒙、黑龙江、吉林6个省区发现,对我国苹果产业安全生产构成严重威胁,我国很有必要引进并建立苹果蠹蛾SIT防治技术体系。     

Remating in Ceratitis capitata sterile males: Implications in sterile insect technique programmes

Sterile insect technique (SIT) is used, among other biological control tools, as a sustainable measure for the management of Ceratitis capitata Wiedemann (Diptera: Tephritidae) in many agricultural regions where this pest can trigger severe economic impacts. The tendency of wild females to remate multiple times has been deeply studied; it has been a common point of controversy when evaluating SIT programmes. Nevertheless, the remating potential of the released sterile males remains unknown. Here, under laboratory conditions, the remating capability of mass-reared sterile males was determined. Wild-type virgin females were offered to sterile males (Vienna-8 strain), which had the opportunity to mate up to four consecutive times. The remating assays were carried out at 24 hr, 48 hr, 4 days and 7 days after the first mating. At the end of each tested time period, males were divided according to their mating response, mated or unmated, and subsequently reused for the next round of mating assays. The frequency of successful remating in each tested time period was obtained. Insemination was confirmed by determining the sperm transfer in mated female spermathecae by quantitative real-time PCR. Our results demonstrate that 73% of the mass-reared sterile males were able to remate 24 hr after the first mating, 55% of which remated again the day after. Close to 25% of the V8 sterile males tended to copulate in all of the four mating opportunities. The qPCR analysis of the spermathecae contents verified an effective transfer of V8 sperm to wild females with every mating; 99% of copulations resulted in sperm transfer. These findings shed light on the remating potential of V8 sterile males, an aspect until now underestimated in many SIT programmes.     

Eradication of the screwworm from Libya using the sterile insect technique

The introduction in 1988 of the New World screwworm into Libya presented a serious threat to the livestock and wildlife sectors o f the African continent and the Mediterranean region. In this article, Moisés Vargas-Terán, Brian S. Hursey and Edward P. Cunningham describe the action taken to determine the extent of the problem, to prevent the spread of the infestation and to eradicate the fly from the region using the sterile insect technique.     

Control of the olive fruit fly using genetics-enhanced sterile insect technique

Ubiquitin signaling pathways rely on E3 ligases for effecting the final transfer of ubiquitin from E2 ubiquitin conjugating enzymes to a protein target. Here we re-evaluate the hybrid RING/HECT mechanism used by the E3 family RING-between-RINGs (RBRs) to transfer ubiquitin to substrates. We place RBRs into the context of current knowledge of HECT and RING E3s. Although not as abundant as the other types of E3s (there are only slightly more than a dozen RBR E3s in the human genome), RBRs are conserved in all eukaryotes and play important roles in biology. Re-evaluation of RBR ligases as RING/HECT E3s provokes new questions and challenges the field.     

Mathematical model to assess the control of Aedes aegypti mosquitoes by the sterile insect technique

We propose a mathematical model to assess the effects of irradiated (or transgenic) male insects introduction in a previously infested region. The release of sterile male insects aims to displace gradually the natural (wild) insect from the habitat. We discuss the suitability of this release technique when applied to peri-domestically adapted Aedes aegypti mosquitoes which are transmissors of Yellow Fever and Dengue disease.     

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.     

A genetic sexing system to improve the sterile insect technique against the Mediterranean fruit fly

The autosomal recessive allele v wing (v) in the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), produces flies that when reared at 30 degrees C have stubby wings. The mutant was used to construct a translocation-based genetic sexing system in an attempt to improve the efficiency and effectiveness of the sterile insect release method for field control.     

昆虫不育技术防治柑橘大实蝇研究概况

柑橘大实蝇Bactrocera minax(Enderlein)是柑橘果树上的重要害虫,我国在20世纪80、90年代曾经成功利用昆虫不育技术防治柑橘大实蝇的危害。本文从人工饲养、不育昆虫的获取以及野外释放等方面对利用昆虫不育技术防治柑橘大实蝇进行了综述,以期为我国柑橘大实蝇的可持续治理提供参考。     

Dispersion theory and the sterile insect technique: application to two species of fruit fly

Dispersion theory is applied to the distribution of two kinds of sterile insect, Mediterranean fruit fly (Medfly), Ceratitis capitata (Wiedemann), and Queensland fruit fly (Qfly), Bactrocera tryoni (Froggatt) (Diptera: Tephritidae). Dispersion theories are an essential basis of sampling theory and sampling plans, but this paper looks at them from another direction and uses data from arrays of sterile insect technique (SIT) monitoring traps to compare the utility of different measures such as coefficient of variation (CV), the exponent b of Taylor's power law, and exponent k of the negative binomial distribution and also derives predictions pertaining to the density (and hence release rate) of sterile insects that would be required to achieve effective coverage of the target area. This is far more useful than reliance on just the mean values of trap catches because such reliance takes no account of the fact that sterile flies distribute themselves unevenly with many patches inadequately covered despite the impression given by the mean. Data were used from recapture rates following either ‘roving releases’ of Medfly or releases from fixed points of Qfly. The relation of recapture rate to CV indicated that a doubling of release rate in order to double average recapture rate from 150 per trap per week to a value of 300 would have very little effect in terms of reducing CV and that there appears to be no practical prospect of reducing CV to below unity with the current methods of release without incurring a manifold increase in cost. Similarly, models derived from the negative binomial equation indicated that a law of diminishing returns applies in terms of the increase in the amount of adequate coverage (such as the percentage of traps catching >50 flies per week) that can be obtained by increasing release rates.     

椰子织蛾不育技术的生物学基础

【背景】椰子织蛾是新入侵我国海南岛的棕榈害虫,昆虫不育技术是控制该害虫的潜在措施。【方法】通过研究椰子织蛾生殖、发育、存活等特性,探讨椰子织蛾不育技术的生物学基础。【结果】在(28±2)℃、(70±10)%RH、以椰子老叶饲养的条件下,每雌产卵量约170粒,净增值率约55.4,倍增时间约9.6 d,表明椰子织蛾可在室内大量饲养,为辐射不育提供虫源。椰子织蛾雌雄比为1∶1.04,雄虫先熟,产卵前期短,产卵期集中,表明该害虫交配行为相对简单,有利于不育雄虫发挥效能。雌蛹显著重于雄蛹,有利于不育过程中雌雄虫的分离。发育起点温度11.5℃,有效积温996.9日度,在海南岛每年发生4~5代,这些数据可用来预测椰子织蛾种群动态,便于释放不育雄虫。【结论与意义】本研究从生物学角度表明椰子织蛾可用昆虫不育技术进行防控,为其进一步的不育技术研发提供相关信息。     

Aedes aegypti lines for combined sterile insect technique and incompatible insect technique applications: the importance of host genomic background

Aedes aegypti L. (Diptera: Culicidae), being the primary vector of pathogenic arboviruses, is a target for the development of novel genetic approaches to complement current conventional vector control strategies such as the combined sterile insect and incompatible insect technique (SIT/IIT). A transinfected line of Ae. aegypti carrying the wAlbB Wolbachia strain (WB2) was introgressed into two genomic backgrounds, Brazil and Mexico, producing two new Ae. aegypti strains (WB2-BRA and WB2-MEX). These strains were evaluated with respect to several life-history traits such as fecundity, fertility, longevity, pupa size, pupation curve, and male mating competitiveness, as well as their response to irradiation. Our results show that the impact of Wolbachia infection depends on the genomic background and that the Brazilian one had no significant effect, whereas the Mexican one negatively affected fertility, longevity, and pupal size. Interestingly, Wolbachia-infected Ae. aegypti lines required a lower irradiation dose to achieve complete female sterility than the uninfected ones. The present findings are discussed given the potential use of Wolbachia-infected Ae. aegypti lines in combined SIT/IIT population suppression programs.     

Impact of lek mating on the sterile insect technique: A modeling study

Modelling studies are presented which describe the effect of lek mating on the control of a wild population by sterile male release. The mixed leks are assumed to follow a Poisson-binomial distribution and the system includes three parts: territory defense, matings inside a lek and matings outside a lek. The effects of parameters on the hatchability are discussed. Among the parameters, sterile type effect (W_s), female choice (f_s) and mating competitiveness (C_m) are the most important. The application to determining the effects of sterile male release and on the proportion of sterile males required for eradication are also discussed.     

Modelling the effects of inherited sterility for the application of the sterile insect technique

1 The sterile insect technique (SIT) involves the release of large numbers of sterile or partially‐sterile insects into a wild pest population to dilute the number of successful wild matings, with the eventual aim of eradication or area‐wide suppression. General population models, encompassing a wide range of SIT types, were used to derive principles for optimizing the success of SIT, with particular emphasis on the application of partial sterility leading to inherited sterility in the F₁ population. 2 The models show that inherited sterility can only be guaranteed to be more effective than complete sterility if matings between irradiated‐lineage partners are unsuccessful. This is widely assumed but rarely examined experimentally. 3 The models allow the critical overflooding ratio, φ_c, to be calculated for a particular target species, suggesting the release rate required to prevent population increase. Successful eradication using SIT alone should aim for a substantially higher release rate than suggested by φ_c. 4 The models show that pest populations may continue to increase in the first few generations of SIT releases, regardless of release rate, as irradiated‐lineage individuals infiltrate the population. This does not necessarily imply that the SIT programme will be unsuccessful in the longer term. 5For pests with overlapping generations, the models suggest that frequent small releases may be more effective than less frequent large releases, particularly when the average release rate is close to the critical threshold for success.