Pupae busting
- chemical free heliothis control

By Julie Ferguson, DPI Agency for Food and Fibre Sciences (Farming Systems), Pittsworth

There has been a lot of talk about 'pupae busting' in the past few years, but still some confusion about its value .

In winter, heliothis pupae go into a hibernation phase, or over-wintering, in the soil. They remain in a state of suspended development until soil temperatures begin to rise the following spring. There is nothing special about pupae busting, it is simply cultivating late summer crops to destroy over-wintering heliothis pupae. However, it is an opportunity to have a major impact on numbers of heliothis without the use of expensive insecticides,. The heliothis pupae that overwinter are all Helicoverpa armigera, the species that has developed resistance to a range of commonly used insecticides. Pupae busting is an important tool in reducing the proportion of the heliothis population carrying insecticide resistance from one season to the next.

It is important to identify crops that may be carrying over-wintering heliothis. The easiest way to do this is work out which crops had heliothis larvae in them when over-wintering began. Typically, diapause initiation starts in the second week of March. However, diapause initiation is triggered by falling temperatures and shortening days, so the precise timing of diapause intitiation will vary between years (Figure 1). From the time of diapause intitiation onwards, late summer crops that have large larvae have a high likelihood of carrying over-wintering pupae.

'Pupae bust' as soon as possible after harvest, particularly in irrigated crops where conservation of soil moisture isn't as critical. A rainfall event after pupae busting will break down the soil surface sealing any remaining live pupae in the soil. If you are concerned about the adverse effects on soil moisture due to working the soil and filling in cracks, consider pupae busting later. The latest date for pupae busting is the end of August, prior to emergence of moths in the spring.

Predators and parasites can reduce the survivorship of over-wintering pupae. Parasitic wasps and flies are frequently found in a range of crops, but their abundance varies from crop to crop. For example an unsprayed sorghum crop, or Gemstar® sprayed sorghum crop, is likely to have higher parasitism levels than a heavily sprayed cotton crop. There are predators such as true wireworm larvae, earwigs, spiders, birds and mice all of which eat pupae, but their effectiveness hasn't been quantified, so pupae busting is still the only reliable way to reduce over-wintering pupae survival.

Further information:

Julie Ferguson, Agency for Food and Fibre Sciences, DPI, Pittsworth
Phone: 07 4693 2486.

To access DPI's information and services

• Current national information on agricultural chemicals registered for use on various pests is available on the Infopest CD-ROM. Write to GPO Box 46, Brisbane, Qld. 4001, or email infopest@dpi.qld.gov.au for further information. Always refer to product labels before application.

• DPI's Internet site: www.dpi.qld.gov.au

Acknowledgment

The contents of this DPI Note were first published in the DPI Newsletter "Heliothis Stateline" No. 5, May 2001.
Editor: Julie Ferguson, DPI AFFS Farming Systems Institute Extension Officer,
PO Box 160, Pittsworth Q 4356
Ph: (07) 4693 2486; Fax: (07) 4693 1847.
Used by permission.

Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.