Preventing Procreation: The IAEA's Research for Mosquito Control
Mosquitoes are one of the world's most dangerous pests. These carriers of diseases such as dengue and malaria wreak havoc over large parts of the world, causing sickness and death. In the future they could be tackled through the use of a nuclear technique.
At the FAO/IAEA Insect Pest Control Laboratory in Seibersdorf (IPLC), Austria, a project is underway to adapt a method known as the sterile insect technique (SIT) to control mosquitoes. The SIT has been used for over 50 years to suppress or eradicate many pests and the IPLC supports SIT projects in around 75 countries.
This technique suppresses or even eradicates insect populations by using radiation to sterilize male insects that are mass-produced in special rearing facilities. One pest that is successfully controlled with the SIT is the fruit fly. It lays its eggs in fruit and when the larvae develop they eat the pulp, damaging the crop and the livelihoods of farmers and exporters.
SIT is also being used to control tsetse flies, the carriers of parasites that cause sleeping sickness in humans and the wasting disease nagana in domestic animals. With this technique, large numbers of sterile males are released on a regular basis into a target area where they mate with wild females. Mating produces no offspring, and the wild insect population <a href="/newscenter/news/iaea-impact-senegal-nears-first-victory-eradicating-tsetse-flies">progressively declines</a>.
At the laboratory in Seibersdorf, the whole life cycle of the mosquito (adults-eggs-larvae-pupae) is constantly repeated. Entomologists have already developed a mass-rearing system for the pests and currently up to 125,000 adult male and female mosquitoes live and mate in specially-built cages.
Pig's blood, collected from local abattoirs, is used to feed the female insects. It is heated first to body temperature. Around two litres of blood are used each day.
In the wild, the female mosquitoes bite humans to get the blood meal they need for egg development. If the person bit is infected with a disease, the mosquito picks it up as it feeds. The disease does not harm the pest but it can transmit it further when it bites again.
Eggs are collected from the holding cages on a daily basis and poured into filter paper. For the SIT to work, millions of sterile insects need to be released over a target area, so mass rearing of pests is the first step in any SIT programme.
As part of the mass-rearing system, the FAO/IAEA scientists have developed trays where the mosquito eggs can be placed into water, which is part of their natural habitat. Here they develop into larvae and feed on the special meal that has also been developed at the laboratory and consists of tuna meal and bovine liver powder.
Once full, the trays can be stacked in a space-saving system where the eggs are left to hatch. This usually takes around 48 hours, after which they develop into larvae. These live in water but swim to the surface to breathe.
The larval stage in the life cycle of a mosquito, which lasts from four to nine days, is followed by pupation. In the pupae stage the insect undergoes a complete transformation. This phase takes up to two days.
The pupae need to be collected to prepare them for irradiation. Currently the pupae and larvae are separated by hand, but the entomologists are developing methods for the automatic separation of pupae and larvae, which is less time-consuming.
Irradiation of pupae takes place in a device that contains a radioactive source. This process sterilizes them — rendering them infertile — but does not make them radioactive. After irradiation the pupae are placed in the holding cages and the adult flies emerge.
Work in the labs also focuses on research into various irradiation methods and the effects of mass-rearing, handling and sterilization on the fertility and competitiveness of male mosquitoes. When released into the wild, the sterile males still need to be able to locate females and mate with them.
At the laboratory the interaction between fertile and sterile males competing for females is closely observed and assessed. This takes place in a greenhouse that was designed to mimic the natural habitat of these tropical pests.
