What’s the problem with insects?
Cotton has a long growing season as well as extended periods of flowering and fruit development. This means cotton is susceptible to insect damage over a much longer time than other crops. From the time the seedlings first appear to defoliation just before harvest, cotton plants can suffer damage that affects yield or quality.
Cotton growers have previously relied heavily on applications of broad spectrum pesticides to control insect pests. In the past few years they have moved much more toward integrated pest management where predatory or ‘beneficial’ insects are encouraged onto the farm to provide a level of natural control of the pest species.
Additional crop areas called trap crops or refuge crops are planted to move pest insects away from the cotton and to increase the number of beneficial insects in the area.
Less harmful, more selective chemical pesticides are used if necessary and researchers continue to focus on the management techniques offered by transgenic cotton crops.
Australia's worst cotton pest is Helicoverpa armigera, a type of cotton bollworm.
The adult of this pest is a moth that lays its eggs on cotton plants. When the caterpillar (larvae) hatches, it starts eating the food around it – the cotton plant. The caterpillar then burrows into the cotton seedpod (boll) to find more food, and in the process damages the cotton. Because of this it is called the cotton bollworm or cotton boll weevil.
When the larvae have grown, they crawl down the stem of the plant into the soil. Here they turn into pupae, inside a hard case. The pupae metamorphose (change) into the adult moth stage in the soil. Four or five generations of these moths can be produced each year.
Cotton is also attacked by several hundred other species of insects apart from the bollworm. The cotton leafworm, cotton fleahopper, cotton aphid, rapid plant bug, cochineal bugs, southern green stinkbug, spider mites, grasshoppers, thrips, and tarnished plant bugs all feed on various parts of cotton plants. Because of the large number of insect cotton pests, repeated spraying of insecticides are needed throughout the growing season.
A problem with insects - work sheet [PDF 47kb | 2 pages]