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close this bookSPORE Bulletin of the CTA No. 20 (CTA Spore, 1989, 16 p.)
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View the documentPheromones for cotton and rice pests
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Pheromones for cotton and rice pests

Simple, low cost and non-polluting techniques have been developed for protecting cotton against three species of bollworm, and for protecting rice against stem-borer. Plastic strips, impregnated with highly specific sex-attractant pheromones are distributed within crops. The chemicals, which mimic the pheromones released by female insects, are slowly released and so saturate the atmosphere within the crops that males become confused and fail to locate and mate with the females.

In trials with cotton in Pakistan, plastic twist-ties were used to release pheromones . Twist-ties consist of a thin wire embedded in plastic: they are used widely to fasten plastic rubbish bags and are cheap to produce. For pest control, the plastic is impregnated with the chemical - in this case, three pheromones specific to pink, spiny and spotted bollworm.

The special twist-ties are attached to the cotton plants before the pests become established; they provide protection for the critical period of fruit formation. Immediately before the trial, infestation was so severe that farmers had to apply pyrethroid every 12 days during fruit formation but with the use of twist-ties the number of insecticide sprays could be reduced to two

The twist-tie used in cotton was developed by the Shin-Etsu Chemical Company of Japan. A similar approach has been developed by a British company, Biological Control Systems, for ricestem borer. BCS produce squares of black plastic polymer 2 x 2 cm and 1 mm thick, also impregnated with pheromone. These are placed in split canes, which are distributed in rice fields. Trials in Spain showed that treatment with pheromones released in this way protected crops for more than 100 days and gave results comparable to rice fields treated with conventional pesticide.

The advantage of CTOp protection with pheromones is that they are not toxic to living organisms and their effect is specific to target species, leaving Beneficial insects unharmed. However, one problem is that the intense ultra-violet light in tropical sunshine can inactivate pheromones. Many insect pheromones occur as isomers, only one of which is active, and uftraviolet light can induce molecules to <flip> between the two isomeric forms.

For more details, contact:

Shin Etsu Chemical Company Fine Chemicals Dept.
6-1 Ohtemachi 2 Chome Chiyoda-ku Tokyo JAPAN or
Biological Control Systems -Treforest Industrial Estate
Pontypridd -Mid Glamorgan CF37 5SU UK

All male Tilapia

Scientists at the University of Wales, Swansea, UK have developed a way to produce all male Tilapia fish biologically. Until now, this could be achieved only by treating Tilapia fingerlings with hormones, which can present problems.

All male Tilapia are necessary for maximum production. If females are present in a pond males become sexually mature very quickly and are not worth eating because they are so small. But if it is possible to inhibit this maturation' the males will put their energy into growth. They are then ready for the market in a few months

The key to the new technique is gymogenesis, which is the deveIopment of eggs without fertilization, and which then carry only those genes derived from the mother. The technique causes male fish, which carry those genetic factors for producing males, to be converted into females. By gynogenesis these fish give birth to, and carry only those genes coming from the mother, which means they will all be male.

The technique that requires a hatchery with the necessary equipments but such a hatchery could then supply all-male fingerlings to local fish forms. And this is what scientists from Swansea are now doing in the Philippines. Trials are now under way with the Bureau of Fisheries and Aquatic Resources to find a suitable hatchery which will undertake some trials. Local fish farmers who will join in the trials will then be sought.

For more details, contact:

School of Biological Sciences
University of Wales
Swansea SA2 8PP