The research into aphid bio-control in cotton has documented the agents attacking cotton aphid in southern and central Queensland, and provided an indication of their relative importance.
When aphids are invading cotton crops in the summer, a complex of predators (particularly adult ladybirds) can prevent or severely restrict aphid establishment in the crops. Predators can also restrict aphid population increase within the crop.
When aphid populations reach high numbers in cotton crops, parasitic wasps can completely wipe out these populations within a few weeks.
Many weed species are hosts of the cotton aphid, but only a few are used by the aphid to maintain its survival over the winter months, when cotton plants are unavailable. These weeds should be controlled to reduce over-winter survival. However some weeds, which harbour other aphids, which do not attack cotton, play an important role in maintaining bio-control agents of cotton aphid over the winter months.
Barley crops also often harbour enormous numbers of bio-control agents and is a reservoir of bio-control agents in the late-winter and spring period.
Adoption of these findings by cotton growers will allow them to make a more objective and rational evaluation of the usefulness of the natural enemies they find in their crops. This information can be used to guide decisions about spraying for aphid control, particularly under the low spray regimes in Bollgard cotton.
