如何利用辐射防治害虫

解读“核”

害虫会传播疾病。例如,蚊虫是传播疟疾的罪魁祸首。仅在2021年就有2.47亿人感染疟疾,60多万人因此丧生。

害虫会传播疾病。例如,蚊虫是传播疟疾的罪魁祸首。仅在2021年就有2.47亿人感染疟疾,60多万人因此丧生。寄生害虫,如寄生蝇,可能威胁整个生态系统,并危及动物和生物多样性的长期保护。其他害虫,如果蝇、飞蛾、采采蝇和螺旋虫,会毁害农作物和家畜,并威胁农民的生计、损害国际贸易和破坏全球粮食安全。据官方估计,2021年,害虫毁害了高达40%的全球作物,造成了2200亿美元的损失。

利用辐射可以帮助控制或管理害虫—即虫害防治,有效地防止害虫危及人类和动物健康、生态系统和粮食安全(包括作物和畜牧生产)。利用辐射防治害虫的方法包括昆虫不育技术、遗传不育和生物防治。

什么是昆虫不育技术?

昆虫不育技术是一种利用电离辐射对实验室饲养的大量昆虫进行绝育的方法,这些不育昆虫随后被释放到害虫孳生区域,与野生害虫种群交配。由于这些不育昆虫不能产生任何后代,昆虫种群数量随着时间的推移不断降少。

尽管对于许多种类的昆虫,既可以释放不育雄虫,也可以释放不育雌虫,但在大多数情况下,作为昆虫不育技术的一部分只释放雄虫更具成本效益。这样做有几个关键原因。首先,不育雄虫在阻碍野生种群繁殖方面要有效得多,因为它们会主动寻找野生雌虫交配,并能与多个雌虫交配。因此,只释放雄虫可以加速诱导不育,因为不育雄虫只与野生雌虫交配,而不会被不育雌虫干扰。此外,在绝育过程失效这种不大可能发生的情况下,只释放雄虫也消除了将可育雌虫引入环境的风险。其次,对于只释放雄虫的昆虫种类而言,与既释放雄虫又释放雌虫相比,包装和释放不育昆虫的成本减少一半。第三,只释放雄虫要安全得多,因为在一些情况下,释放雌虫会产生负面影响——例如,只有雌性蚊虫会叮人吸血,以获取蛋白质,同时可能传播致命的疾病

昆虫不育技术是目前最安全和最环保的昆虫节育方法之一,通过减少使用杀虫剂来保护环境。此外,由于不育昆虫无法自我复制,因此这种方法不会带来将非本地物种引入生态系统的风险,而是创造了一个解决害虫问题的长期方案。

自20世纪50年代以来,昆虫不育技术已在全球成功地用于防治一些影响人类和家畜健康的害虫,如新世界螺旋虫、采采蝇和传播疾病的蚊虫,以及破坏作物和影响贸易的害虫,如果蝇和飞蛾。

(信息图表:Adriana Vargas/原子能机构)

什么是遗传不育?

遗传不育是另一种昆虫不育技术,与传统方法非常相似,因为这种方法也涉及饲养、辐照和向目标区域释放半不育雄虫,以减少可育雄虫的交配。然而,使用这种技术后,被饲养和释放的雄虫仍具有一定程度的生育能力,但它们的所有后代都是天生不育。

这种技术在只有使用非常高的辐射剂量方能使特定种类的雄虫(如飞蛾)完全不育时才会使用。然而,高剂量可能弱化雄蛾,使其没有能力与野生飞蛾竞争繁殖。因此,这种技术涉及使用低得多且较弱的剂量,不妨碍飞蛾的繁殖机会,但会诱发飞蛾后代遗传不育。

这种技术有很多优点。它使科学家们能够针对那些需要非常高辐射剂量才能不育的物种。然而,雌蛾往往对辐射更敏感,在辐照后会完全不育。而辐照雄蛾只是一定程度上不育,并生出完全不育的后代。释放一定程度上遗传不育的雄蛾,往往有助于将野生种群数量抑制到比常规昆虫不育技术中释放的同等数量完全不育雄蛾所能达到的更大程度,因为这些雄蛾能够在下一代产生多个完全不育的后代。

可以对蛾类害虫进行绝育,但是它们需要较高的辐射剂量,这往往会弱化受辐照雄蛾与野生雄蛾竞争的能力。相反,可利用较弱的半不育剂量诱发飞蛾后代完全不育。这就是所谓的遗传不育(信息图表:Adriana Vargas/原子能机构)。

什么是生物防治?

生物防治是一种通过大量繁殖和释放害虫天敌从而杀死害虫的方法,这些天敌如以害虫的卵和幼虫为食的捕食性昆虫,或将卵产到宿主害虫体内的寄生虫(也称为拟寄生物)。

与基于利用核技术的昆虫不育技术和遗传不育方法不同,在生物防治中,核技术只用于特定目的。辐射可以用来提高饲养、运输和部署这些害虫天敌的适用性、成本效益和安全。辐射还可以提升生物防治方法的效果,并减少与生物防治相关的许多限制。例如,辐射可用于降低生物防治物的生产成本。例如,针对拟寄生物,辐射可以降低宿主昆虫的自然防御能力(即免疫反应),以提高拟寄生物的生产力和存活率。此外,辐射有助于阻碍宿主昆虫发育,保证从蛹中只生出拟寄生物。如果一些宿主昆虫存活下来,使用辐射能确保它们不育,从而消除生出可育宿主昆虫而在新环境中成为害虫的风险(见下方的信息图表)。在适当的情况下,低剂量的辐射也可以促进一些捕食性昆虫繁殖,在这些捕食性昆虫不威胁非靶标昆虫种群的环境中,可用来提高生物防治的有效性。

一只瓢虫在芦笋植物上取食飞蛾卵 (信息图表:Adriana Vargas/原子能机构)。

同样地,辐照可以帮助运输捕食性昆虫和拟寄生物,即通常所称的生物防治物。例如,拟寄生物可能需要宿主昆虫才能在运输中存活下来,而捕食性昆虫可能需要以其他昆虫为食。因此,生物防治物通常与它们的“猎物昆虫”及其卵一起运输,作为运输期间的食物来源。然而,并非所有用作拟寄生物宿主的昆虫都会受到拟寄生物的影响,因此,如果这些宿主昆虫在运输过程中存活下来并被释入环境,它们将成为害虫。  在运输前对宿主昆虫进行辐照,将确保不会有新的害虫被意外地引入到生物防治区域。

生物防治有助于防治害虫,同时通过辐照生物防治物的宿主,就不会意外地将新的害虫引入环境。(信息图表:Adriana Vargas/原子能机构)。

原子能机构的作用是什么?

What is the Sterile Insect Technique (SIT)?

The sterile insect technique is a method that uses ionizing radiation to sterilize large numbers of insects reared in a laboratory, which are then released over infested areas to mate with the wild pest population. As these sterilized insects are incapable of producing any offspring, the insect population declines over time.

Although both sterile males and females can be released in the cases of many insect species, for most, releasing only the males as part of SIT is more cost-effective. There are few key reasons for this. Firstly, sterile males are much more effective at hindering the reproduction of wild populations, because they actively search for wild females to mate with and can mate with multiple females. Therefore, releasing males only, speeds up the induction of sterility since the sterile males mate with the wild females only, without being distracted by the sterile females. Moreover, in the unlikely event of a fault in the sterilization process, this removes the risk of introducing fertile females into the environment. Secondly, In the case of insect species for which only males are released, the costs of packing and releasing the sterile insects are cut by half when compared against releasing both males and females. Thirdly, it is a lot safer, since in some cases, releasing female insects can have a negative impact — for instance, only the female mosquitoes bite humans in search for blood as a source of protein, and can spread deadly diseases.

The SIT is one of the safest and most eco-friendly insect birth control methods available, which ensures environmental protection through a reduced use of insecticides. In addition, since sterile insects cannot self-replicate, this creates a long-term solution for the pest problem without running the risk of introducing non-native species into the ecosystem.

Since the 1950s, SIT has been successfully used in the global control of some insects affecting the health of people and livestock, such as the new world screwworm, the tsetse fly and disease transmitting mosquitoes, as well as in the control of insect pests that destroy crops and affect trade, such as the fruit flies and moths.

(Infographic: Adriana Vargas/IAEA)

What is Inherited Sterility?

Inherited sterility, also known as F1 sterility, is another type of SIT, very similar to the traditional method, as it involves rearing, irradiation and release of semi-sterile male insects into a target area to reduce the mating of their fertile counterparts. In this technique, however, the reared and released male insects have a certain degree of fertility, but all their offspring is born sterile.

This technique is used when males of particular types of pests, such as moths, cannot be fully sterilized unless very high doses of radiation are used. A high dose, however, may weaken the insect and hinder its ability to compete with wild moths for reproduction. Therefore, this technique involves using much lower and less debilitating doses, which do not hinder the insects’ opportunities to reproduce, but which induce inherited sterility in the moths' offspring.

This technique has a number of advantages. It enables the scientists to target species that require very high doses of irradiation to become sterile. However, the females are fully sterile after irradiation, since female moths tend to be more sensitive to radiation. The irradiated males are only partially sterile and give birth to fully sterile offspring. The release of partially sterile males with inherited sterility, often helps to suppress wild populations to a greater extent than an equal number of fully sterile males released in conventional SIT, since the males can produce multiple fully sterile copies in the next generation.

Moth pests can be rendered sterile, however, they require higher doses of radiation, which tend to weaken the insect’s ability to compete with wild males. Instead, less debilitating semi-sterilizing doses are used to induce full sterility in the moths' offspring. This is known as inherited sterility (Infographic: Adriana Vargas/IAEA).

What is Biological Control?

Biological control is a method that uses mass-production and release of the pest’s natural enemies, such as predatory insects who feed off the pest’s eggs and larvae, or parasites (known as parasitoids) that lay eggs into their host insect, killing the insect.

Unlike the SIT and inherited sterility methods, which are based on the use of nuclear techniques, in biological control nuclear techniques are only used for particular purposes. Radiation can be used to increase the applicability, cost-effectiveness and safety of rearing, shipping and deploying these natural pest enemies. It can also improve the results of the method and alleviate a number of constraints associated with it. For example, radiation can be used to reduce the cost of production of biological control agents. In case of parasitoids, for example, radiation can lower the host insect’s natural defences (i.e. immune response) to increase the productivity and survival rate of parasitoids. Moreover, radiation helps to prevent development of the host insects, assuring that only parasitoids emerge from the pupae. In cases where some host insects do survive, the use of radiation ensures they are sterile in order to eliminate the risk of releasing fertile host insects, which can become pests in the new environment (see infographic below). In appropriate contexts, low doses of radiation can also stimulate the reproduction of some predators, which could be used to improve the effectiveness of biological control in environments where these predators do not threaten non-target insect populations.

A ladybug feeding off moth eggs on an asparagus plant (Infographic: Adriana Vargas/IAEA).

Similarly, irradiation can help in the transport of predatory insects and parasitoids, often referred to as biological control agents. Parasitoids, for example, may require host insects in order to survive transportation, and predatory insects may need to feed off other insects. For this reason, they are often transported together with their “prey insects” or their eggs, which serve as a source of food during transportation. However, not all the insects being used as hosts of the parasitoid are affected by the parasitoid, therefore, in case these hosts manage to survive transportation and are released into the environment they will become pests.  Irradiation of the host before transportation, will ensure that no new pests can be accidentally introduced to the area undergoing biological control.

Biological control helps to control insect pests, while by irradiating the host of the biological control agent no new pests are accidentally introduced into the environment. (Infographic: Adriana Vargas/IAEA).

What is the role of the IAEA?

  • Through the Joint FAO/IAEA Centre of Nuclear Techniques in Food and Agriculture, the IAEA assists countries in developing and applying radiation-based technologies, such as the SIT, inherited sterility and biological control to optimise insect pest management practices to improve food production, human health and preservation of natural resources.
  • The IAEA conducts research and develops new methods at its laboratories at Seibersdorf, Austria, to build knowledge and further improve the techniques, associated with mass-rearing, sterilization and quality control of major insect pests. Research findings, new procedures and methodologies are transferred to member states to improve their pest control practices.
  • The IAEA technical cooperation department, with assistance from the Joint FAO/IAEA Centre, is supporting the transfer of technology to manage pest species and to protect the indigenous fauna and ecosystems.
  • The IAEA also offers practical assistance including guidance and expert support, as well as the provision of biological materials to the member-states through its coordinated research projects and field projects. Through resource sharing, the IAEA plays a crucial role in the application of area-wide integrated pest management programmes. Click here for more information on the IAEA’s work in pest control.