by Jorge Hendrichs and To Kill a Pest Alan Robinson The use of radiation is improving the biological control of insect pests. he IAEA’s support to Member States in What is Biological Control? the field of insect pest control has mainly Despite centuries of technological development, Tfocused on the Sterile Insect Technique (SIT), insect pests continue to exact a very high toll on which is a type of insect birth control, where mass agricultural production and human health. A well- reared and systematically released sterile males established, successful approach to this problem is of the target pest insect mate with wild females the use of natural enemies, called biological control in the field, thereby interfering in an environment- agents, to manage pest populations. The biological friendly way with the reproduction of the pest control agent can be a predator, a parasitoid, a bac- A giant ichneumon wasp population. This approach effectively reduces terium, a fungus or a virus. In this article we will con- adult boring the surface the use of insecticides and has been successfully centrate on predators, which eat the pest (prey), and of fir trunk infested with used to manage, and in some cases eradicate, parasitoids, which parasitize the pest (host) by sting- wood wasp larvae. populations of major pest insects. Nevertheless, ing and thereby laying eggs into it. (Photo: Boris Hrasovec, there are other areas where Member States can Faculty of Forestry, benefit from radiation in the field of entomology. When insects escape their native natural enemies, Bugwood.org) One of these is biological control. either because they invade new countries leaving 34 | IAEA Bulletin 51-1 | September 2009 Animal Kingdom | To Kill a Pest behind their biological control agents or as a result of the disturbance of these natural enemies, they Biological Control of the become pests. As shown in Box 1, if appropriately applied, biological control offers one of the most Cassava Mealybug promising, environmentally-sound, and sustaina- ble tools for control of such insect pests. However, his insect became a devastating pest of cas- there are many constraints to the expansion of bio- Tsava in Sub-Saharan Africa following its intro- logical control programmes, related to the produc- duction into Congo from South America in the tion, shipment and release of biological control 1970s and its rapid spread to the rest of the sub- agents. The commercial and public biological con- continent. Cassava is the prime source of carbo- trol industry is growing but still represents less than hydrates, proteins and vitamins for 200 million 3% of pest control sales. Regulatory, technical and Africans. A natural parasitoid (insert image) of the other constraints have kept the market share rela- cassava mealybug was identified in Paraguay, the tively small. The challenges include the high cost origin of the pest in South America, and trans- of production, adequate quality control and assur- ferred to the International Institute for Tropical ance, trade barriers and regulations that complicate Agriculture, in Ibadan, Nigeria where it was mass shipping. reared. It was released from over 150 sites in the region, became established and brought the There are several ways in which nuclear techniques pest under control in 95% of all fields. can address these constraints and the Joint FAO/ IAEA Programme of Nuclear Techniques in Food and Agriculture has now completed a Coordinated Research Project on this topic with the participation Screening Exotic of 18 research teams from 15 countries. Biological Control Agents to Safeguard Biodiversity Regulating Biological Control ♦ In the USA the field evaluation of an exotic Agents herbivore in sterilized form, for the eventual biological control of the Brazilian pepper tree, Lack of international harmonization among coun- a major weed that has been accidentally intro- tries and availability of enabling regulations is duced. probably the most important barrier to the wider implementation of biological control, ‘gatekeeper’ ♦ Also assessment of irradiated cactus moths, regulations place barriers in the way of efficient a pest of different native cactus plant in some introduction and application of biological control locations, and a biological control agent of intro- agents. However, the Secretariat of the International duced cactus weeds in others, to confirm under Plant Protection Convention, of the Food and natural conditions oviposition preferences to Agriculture Organization of the United Nations predict the host range, the ability of larvae to sur- (FAO) has published a revised International Standard vive and cause damage on related native plants, for Phytosanitary Measures (ISPM) on ‘Guidelines for as well as to study possible interactions with nat- the export, shipment, import, and release of biolog- ural enemies. ical control agents and other beneficial organisms’, which should help to solve some of these prob- lems and increase trans-boundary trade in biolog- diversity or even attack beneficial species or com- ical control agents. mercial crops? There are numerous examples where introduced biological control agents have ‘jumped species’. Since such mistakes are permanent in time Safeguarding Biodiversity and space, the feasibility of such introductions need therefore to be carefully assessed before the intro- At times, the biological control agent chosen to duction of any biological control agent is under- be released is an exotic species to the environ- taken. One of the best-known of these mistakes is ment. One of the key concerns in this approach is the cane toad in Australia, which was introduced to the question of specificity of the biological con- control pest insects in sugar cane, however, it very trol agent in its new ecosystem, i.e. will the intro- quickly began to feed on other species and multi- duced biological control agent remain associated plied in numbers until it became a pest itself. Once with the pest or will it expand its range to impact biological control agents are released, they cannot on other species in the ecosystem and so affect bio- be recalled and, as they are fertile, they have the IAEA Bulletin 51-1 | September 2009 | 35 Animal Kingdom | To Kill a Pest Improved Mass Production of Biological Control Agents ♦ In Bulgaria, an irradiated factitious host used to rear the wasp that parasitizes moth pests in mills and grain warehouses. ♦ In Pakistan, irradiated moth eggs utilized as a prey substitute to feed a predator for area- wide control of cotton and sugarcane pests. ♦ In Poland, radiation used to successfully extend the shelf-life of parasitoids to control stored grain moths causing damage in grain warehouses. ♦ In Turkey, an irradiated factitious host used to mass rear a parasitoid of the olive fly for use in an area-wide pilot project in an olive pro- duction area. have to be reared in order to produce the biological control agent for release, in other words it is a two component biological system. This is in contrast to the SIT where only one species needs to be reared. This increased complexity makes the mass rearing of biological control agents logistically demanding and more expensive. Top: Mucidifurax raptor opportunity to reproduce and increase in numbers. Often the natural prey or host species are them- wasp on a fly puparium. This is fine if they remain “locked onto” the pest spe- selves difficult or expensive to rear in large numbers Once the female chooses cies but can be disastrous if they find new non-pest and the use of more readily available substitutes a suitable puparium host, hosts in the new ecosystem. would be an advantage – the so called factitious she lays a single egg in it. species. However, these types of species are not The egg hatches, and the Radiation can play an important role in the safe always as acceptable as the natural prey or host; this wasp larva feeds on the evaluation of the potential host range of a biologi- is especially the case for biological control agents fly pupa. cal control agent in a new ecosystem. It provides a which lay eggs in living hosts which are then sub- way to sterilize and release biological control agents ject to its immune response. Radiation can be used (Photo: USDA ARS Photo Unit, USDA Agricultural in the field without establishing them permanently to suppress the immune response of the host mak- Research Service, and without affecting their behaviour, and to assess ing it more suitable for parasitism. Bugwood.org) what they eat and do not eat, what hosts they para- sitize, and where they go. Repeated releases of steri- A host is often suitable for parasitism only within lized biological control agents will provide without a very small window of time during development Bottom: Braconid wasps: risk critical information under natural conditions in and radiation can be used to enlarge this window parasitoids on sphinx or order to improve decision making relating to even- by reducing the speed of development of the host. hawk moths. tual fertile release. The limited shelf life of hosts and prey also restricts (Photo: David Cappaert, their use during mass-production and for certain Michigan State University, USA. Bugwood.org) species radiation can be used to arrest develop- Improving Mass Production ment and thus allow for storage and stockpiling of hosts or prey to be used when required by the cus- As a biological control agent preys on or parasitizes tomers (farmers, greenhouses, grain mills, poultry another insect species, it follows that both species houses, etc.). 36 | IAEA Bulletin 51-1 | September 2009 Animal Kingdom | To Kill a Pest There is also the use of the controversial phenom- enon known as ‘radiation hormesis’, i.e. the use of Supplementing Biological very low doses of radiation to stimulate biological Control Agents in the Field processes. There is some preliminary evidence that this process can increase parasitisation rates and ♦ In China, irradiated moths released into field reproduction.