With the advent of Bt cotton, mirids have become more of a pest in cotton and are attracting a number of insecticide applications. This has the potential to disrupt IPM in cotton and increase the risk of mite, aphid or whitefly outbreaks.

The aim of this project was to identify factors which could influence mirid damage to cotton. In particular, the project looked at current mirid management methods, tested the effectiveness of potential predators and identified other interspecific interactions which could reduce mirid damage to cotton.

We found that pest managers that only sprayed for mirids once the numbers had exceeded the recommended threshold suffered no yield loss, and if anything it was beneficial to the profitability of the field. Nevertheless, we did find that pest managers were less likely to use the beatsheet threshold than the visual survey threshold, indicating that more extension work is needed in this area.

The project was able to identify a number of predators that could reduce mirid numbers and affect mirid feeding behaviour. In particular the plain brown lynx spider, which is very common in cotton, was a very efficient predator of mirids. More work is needed to confirm their effectiveness under field conditions.

The project also showed that mirids may not attack cotton if alternative foods, such as Helicoverpa eggs, are available. Thus a Helicoverpa egg lay in a Bt crop could be advantageous if the field has a heavy mirid infestation because it could reduce the likelihood that the mirids present will attack the cotton. This finding needs to be confirmed under field conditions.

The reproductive status of the mirid had little effect on mirid damage, but damage caused by mites and aphids overrode any damage caused by mirids. This indicates that if pest managers have to choose between mirid and mite control, they should be more concerned about controlling the mites.

The results of this project indicate that insecticide applications to control mirids can be kept to a minimum; 54% of the sprays in the mirid survey were applied to mirid numbers below threshold. If these sprays were irradiated, there would be a huge saving in insecticides, no cost in yield, and a large advantage in terms of the development of IPM in cotton. The results of this project indicate that this should be the goal of mirid management in cotton.