Nuclear techniques for peaceful development

Insects,isotopesand radiationWider use of nuclear techniquesis expectedin controlling harmful insects

by Donald A. Lindquist

Over 1 million species of insects inhabit the world,more than the total number of species of all otheranimals and plants combined. Fortunately for mankind,the vast majority of these insects are either beneficial orharmless. The relatively few species (15 000 or less)that are detrimental result in losses of 15-20% of theworld's agricultural (plant and animal) production.These losses are from direct damage to plants andanimals, as well as from diseases of plants and animalstransmitted by insects. Very significant additional lossesare caused by insects during storage of agriculturalproducts. Other losses occur from human diseases, suchas malaria, yellow fever, dengue, and onchocerciasis,that are transmitted by insects.

When there were few people in the world, the loss offood caused by insects was less important than todaybecause the amount of available food was adequate forthe. population. Factors other than insects, of course,limited food availability. However, insects becamemuch more important as the human population increasedand plants and animals were domesticated to feed thisincreased human population. When animals or plants areproduced in concentrated areas (monocultures) they pro-vide a culinary feast for insects and result in a greatincrease in insect pest numbers. Food must be producedin this manner to feed the number of people in the world;thus agricultural products, both during production andstorage, must be protected from insect attack (along withother pests, such as diseases, weeds, nematodes, rats,and birds). The total land in agricultural production usedtoday to feed the world's approximately 5 billion peopleis considerably less than 1 hectare per person.

Modern insecticides were rapidly developed afterWorld War II and provided plant and animal producerswith an extremely powerful tool for use against insects.Insecticides provide the primary method of insect

Mr Lindquist is head of the Insect and Pest Control Section in the JointFAO/IAEA Division of Isotope and Radiation Applications of AtomicEnergy for Food and Agricultural Development.

Setting up tsetse traps in Nigeria. The project to control the tsetsefly in Nigeria, known as BICOT, has shown encouraging results.(Credit: E. Offori)

control; however, they are not completely satisfactory.Thus, alternative methods of insect control are required;these include host resistance, insect attractants, traps,inundative release of parasites and predators, biologicalinsecticides, and the sterile insect technique, which willbe discussed later.

Integrated pest management

Integrated pest management (IPM) involving morethan one control tactic has been developed andimplemented in many parts of the world to more effec-tively utilize various insect control methods in anintegrated fashion and to reduce over-dependence oninsecticides. Utilizing natural control agents as much aspossible, IPM depends to a large extent on observationsof the number of damaging insects present; insect con-trol (almost always insecticides) is only applied whenthese numbers reach a critical level (the economicthreshold). IPM usually is applied on an individual fieldor farm basis, a procedure that frequently reduces theamount of insecticides used and the rate at which insectsbecome resistant to them.

Area-wide control

While IPM emphasizes insect control on anindividual field or farm basis, insects can be controlledover large areas, regardless of land ownership or

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Nuclear techniques for peaceful development

whether crops are produced. The objective of "area-wide insect control" under most situations is preventa-tive control, in that the pest insects are controlled at theirsource before they move into farmers' fields. Certaininsects, such as locusts, tsetse flies, mosquitoes, andsome pest Lepidoptera (which attack many food grains)are more amenable to area-wide control at less cost thanfield-by-field control. In some cases, the insect pests arepresent in a very small area and frequently on wild hostplants before they move to farmers' fields. Applyingcontrol technologies when insects are concentrated insmall areas is very effective in reducing control costslater in the season. Unfortunately, preventative insectcontrol has not received the attention that it should have.

Eradication of an insect species from a defined areais always approached from an area-wide basis. Whileeradication is applicable in relatively few situations, itseconomics are very favourable. The sterile insect tech-nique (SIT), which uses radiation to sexually sterilizeinsects and prevent reproduction, is particularly effec-tive in eradication programmes.

Research scientists are developing a number of newor alternative methods of insect control. Most of theseare applicable only on an area-wide basis. These includethe SIT; the use of insect pheromones (sex attractants)to prevent mating by confusing insects so that males andfemales cannot get together; other types of chemicalattractants; traps; and inundative release of parasites andpredators. Host plant resistance is also most effectivewhen applied on an area-wide basis.

Farmers or producers with very small holdings havemuch more difficulty in controlling insects than thosewith large holdings. The small producer frequently lacksresources for insect control and is also to a great extentat the mercy of insect control measures taken by neigh-bours. If they do not use effective ones, the smallproducer will suffer a serious insect problem.

Isotopes and radiation

The Joint Division of the IAEA and Food andAgriculture Organization (FAO) has been involved inthe use of isotopes and radiation in insect control since1964. Isotopes are used as tags or markers, for instance,of chemical molecules, insects, or plants. For example,with these tags one can follow the fate of insecticideswithin insects and the environment; the incorporation ofnutrients into the insect; and the movements of insectsunder field conditions. They also can mark plants onwhich insects feed so that the quantity of consumed foodcan be measured and directly correlated with plantresistance. They can be used as well to follow parasitesand predators of insects — for example, their move-ments, numbers, and ability to help control insect pests.

In a SIT operation, radiation is used to sexuallysterilize insects. The SIT is the largest part of theprogramme of the Insect and Pest Control Section of theJoint FAO/IAEA Division. Radiation is also used in

insect studies including genetics, genetic engineering,microbial control, quarantine treatments of agriculturalcommodities, and induction of mutants in plants to breedresistant varieties.

The sterile insect technique

The discovery that X-rays or gamma radiation couldcause sufficient genetic damage to insect reproductivesystems to induce sterility resulted from work conductedby H.J. Muller starting in the 1920s. Muller won aNobel Prize for his work on the genetic effects of irradi-ation in insects. The sterilizing effect of radiation wasnoted by scientists of the US Department of Agriculturewho had been seeking a method to sterilize insects formany years. These scientists had theorized that if largenumbers of the target insect species were reared, steri-lized, and released into the field, the sterile insectswould mate with the wild insects. These matings wouldresult in no offspring and thus a decline in the populationwould be obtained. They calculated that if sufficientnumbers of sterile insects were released, the reproduc-tive rate for the wild population would rapidly declineand reach zero. In simple language, birth control ofinsects. Radiation sterilization was the answer.

The first demonstration of this technology was theeradication of the screwworm from the Dutch island ofCuracao in 1954. The programme was conducted byscientists of the US Department of Agriculture in co-operation with the Dutch Government. Thus, the initialSIT project was international, and to a large extent,operational SIT projects since then have remained inter-national in scope.

At the present time, there are approximately 10 spe-cies of insect pests being attacked by the SIT. Researchand development is being conducted on other insect spe-cies and it is anticipated that the technology will be morewidely used in the future. It is applicable for area-wideinsect eradication, quarantine, and, in some cases, con-trol. It is not applicable on an individual field or farm

FAO/IAEA Symposium, November 1987

In November 1987, the IAEA and FAO are jointlysponsoring a major scientific gathering — the Interna-tional Symposium on Modern Insect Control: NuclearTechniques and Biotechnology. It is anticipated that par-ticipants will present data on emerging new insect con-trol technologies, as well as important information aboutchanging insect problems in developing countries. Theexchange of views and scientific information is expectedto help identify new problems, potential solutions, andopportunities for technology transfer — all towards thegoal of less expensive, sustainable agriculturalproduction.

The symposium is being held in Vienna, Austria, from16-20 November. Further information may be obtainedfrom IAEA Conference Services, or by writing the Insectand Pest Control Section of the Joint FAO/IAEA Division,A-1400 Vienna, Austria.

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basis. Therefore, SIT programmes tend to be large and,as a result, are considered expensive when viewed fromthe programme's total cost. However, when appliedagainst very damaging and widely dispersed insects thecost per unit area of land or production area is frequentlyless than the cost of each individual field being treatedseparately by other technologies. Further, economicsfavour eradication in many situations.

Since the SIT is species specific, the selection of theinsect pest or group of pests on which to work is ofprimary importance. It must be very destructive and itscontrol or eradication (of the single species or group ofspecies) must put money into the farmer's pocket. Whenmore than one species is attacked at the same time, theyare usually closely related and the mass-rearing proce-dures are quite similar.

More use of the SIT will result from increasedefficacy and improvement in economics. This continuesto show that when applied against an appropriate insector insects, the technique is more cost efficient than othertechnologies. Additional factors favouring its useinclude the growing problem of insect populations thatbecome resistant to insecticides, and concerns aboutenvironmental damage caused by continuous annual useof insecticides to control the same insect species.

The Joint FAO/IAEA insect pest programme

The selection of the species (the problem) for apply-ing the SIT is of primary importance. This selectionprocess, and subsequent actions by the IAEA and FAO,are based on the many tools available within the agenciesto assist Member States. A technical section is the onlyorganizational unit where all the tools can be broughttogether and co-ordinated for the purpose of technologytransfer to solve a specific problem in a Member State.In addition to the technical expertise available within asection, the tools range from advisory bodies to trainingsupport programmes to research contracts.*

The Joint FAO/IAEA Division also has access tosome tools from FAO, including its associate profes-sional officer programme and technical co-operationprojects. In addition, access to expertise in, andco-operation with, FAO technical divisions is veryvaluable.

Very few of all these tools are under the direct controlof a technical section. Consequently, the section mustplan several years in advance and keep many peopleinformed about progress, needs, and problems ofindividual projects. In the case of the Joint Division, thisplanning and information flow involves both the IAEAand FAO.

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* A detailed list of available tools in this case would include individualconsultants; consultant groups; advisory groups; sabbatical leave per-sonnel; training (fellowships for individual specialized training); train-ing courses; study tours; scientific visits; research contracts; researchagreements; technical contracts; research co-ordination meetings;symposia; seminars; technical co-operation projects (expert services;consultants; equipment); cost-free experts; and support by theAgency's Laboratory at Seibersdorf, Austria.

The IAEA's entomology laboratory at Seibersdorf is supportingresearch and development of the sterile insect technique for theeradication of insect pests. Here, a visiting scientist from Zambiachecks on tsetse flies used in experiments.

Project in Nigeria

A co-operative project betweent the IAEA, FAO, andNigeria — known as BICOT — seeks to develop the SITfor use against Glossina palpalis palpalis, one of thetsetse fly vectors of animal trypanosomiasis. Nagana, oranimal trypanosomiasis, is a major deterrent to agricul-tural development in much of Africa. Tsetse eradicationis an excellent method of controlling the disease.Through this large-scale research and developmenteffort, the target species has been eradicated from the1500 square kilometres that constitute the project area innorth-central Nigeria.

All the tools referred to earlier, including those madeavailable by FAO, have been utilized in developing andimplementing BICOT. Training has played a major rolein the project. At least partially because of this training,and the confidence that the Government of Nigeria hasin trained Nigerian personnel associated with theproject, the Nigerian Government has requested that theproject be expanded to include all of the agriculturaldevelopment and livestock grazing project in PlateauState, a total of 12 000 square kilometres. This expan-sion, BICOT-II, again will require the use of tools avail-able from the Agency and FAO for successfulimplementation. ;

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Support of IAEA's Seibersdorf Laboratory

The entomology unit of the Agency's SeibersdorfLaboratory provides invaluable research and develop-ment support for field projects and co-ordinated researchprogrammes. In addition, essential training, which can-not be obtained at other locations, is continuouslyprovided by this unit, through facilities made availableby the IAEA and FAO to support SIT projects and iso-tope applications in entomology.

In the case of BICOT, seven Nigerians have receivedtraining at Seibersdorf and several others were trainedelsewhere. Specialized equipment has been developedand fabricated at Seibersdorf and sent to Nigeria.Greatly improved tsetse rearing methods that were deve-loped at Seibersdorf and transferred to Nigeria have sig-nificantly reduced the cost of tsetse rearing. A biologicalevaluation system to measure the progress of eradicationalso has been developed at Seibersdorf and is currentlybeing used in BICOT and other field projects. A back-upcolony of tsetse flies has been maintained at Seibersdorfand several hundred thousand surplus insects have beensent to Nigeria as an adjunct to the locally producedtsetse flies.

The entomology unit also actively supports SIT fieldprogrammes for eradication of the Mediterranean fruitfly (medfly). Action programmes require the mass-rearing of this insect in huge numbers. A mass-rearingfactory at Tapachula, Mexico, produces 500 million ormore medflies per week. About half of these are males.The SIT was used to eradicate the medfly from Mexico,and now sterile flies are being released in Guatemala toeradicate the pest from that country. Rearing costs (dietingredients, materials, salaries) are about US $100 permillion flies.

At Seibersdorf, major emphasis is placed on develop-ing a genetically altered medfly strain in which thefemales can be selectively killed in the egg or very earlylarval stage. Medfly females add little or nothing to theefficacy of the SIT. With the genetic sexing strain,500 million males could be reared at Tapachula forabout the same cost as the 250 million males presentlybeing reared. Thus, a significant savings (about 40%) inmedfly mass-rearing can be achieved with a geneticsexing strain. In addition, the release of only sterilemales, instead of both sexes as is now done, willincrease the efficacy of the technology. Reduced costs ofaerial release of sterile flies also will be achieved.

Development research for additional savings involvesre-using the medfly larval rearing diet (which appearspossible without loss of quantity or quality of the reared

insects). The cost of the larval diet to rear medflies atTapachula is approximately US $25 per million. Re-using the larval diet once would save about 40% of this,or US $260 000 per year.

When the SIT is used for medfly eradication, reduc-ing the wild medfly population before the release of thesterile flies is frequently required for economic reasons.The current method is one or two aerial applications ofan insecticide bait spray. Although the insecticide,malathion, is very safe, it does have mild transitoryenvironmental effects. When very large areas aresprayed, it causes some concern which, on occasion,results in serious problems in programme operation. Aproject at Seibersdorf is to determine whether a strain ofthe biocontrol agent, Bacillus thuringiensis (B.t.), canreplace malathion in bait sprays. Laboratory data arevery positive. There is a reasonable chance that an effec-tive B. t. strain can be developed to replace malathion inbait sprays against the medfly before release of sterileinsects.

Results and challenges

Efforts by the IAEA and FAO to transfer the SITtechnology to developing countries have been reason-ably successful. The technical results have been excel-lent. One major benefit of projects such as BICOT is theincreased capability of local organizations and staff tohandle area-wide insect control programmes. This capa-bility is becoming much more important, not only forinsect control within a country but also for quarantineproblems relating to export of agricultural commodities.Insects frequently prevent export because of quarantinesagainst them in receiving countries. The elimination ofnewly introduced insect pests is becoming much moreimportant as agricultural trade increases. Theexperience gained by local organizations in SIT projectsis directly applicable to solving this problem.

One area needing significant improvement in thisprocess of technology transfer is management.Experience and training opportunities in management ofthe type required for SIT programmes is scarce ornonexistent in developing countries. Yet management isas important as technical expertise in operation of SITprojects.

Another area which needs improvement is refreshercourses for some individuals who have already receivedAgency training. Training should be viewed as a con-tinuous process. The cost may appear high, but the costof not subscribing to refresher training is higher.

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