Paul Grundy, Research entomologist, Qld DPI&F/ Cotton CRC explains some of the new and innovative approaches to combating insecticide resistance being trialled in Central Queensland.

Paul Grundy from DPIF and the Cotton CRC has been doing work novel options in resistance management for helicoverpa in Central Queensland (CQ). Paul, what have you been doing and why?

What we have been looking at is developing a more efficient Bollgard® resistance management strategy for CQ. In particular what we have been focusing on in this current season is looking at the whole trap cropping program and ways that we could improve this strategy by using products like Magnet®.

Why is there a need to improve on the current system?

Moth flush counts

Essentially the problem that we have which is unique to CQ is that because our crop finishes that little bit earlier, our conditions are warmer and the day lengths aren’t receding quite as quickly as they do down south, a large proportion of our heliothis would naturally escape those fields before there is a chance to do pupae busting operations.

The system that we have had in CQ to date is pigeon pea trap crops. The idea of that trap crop is that the emerging moths that are escaping Bollgard® II paddocks get attracted to the trap crops and we can then deal with them mechanically by pupae busting them under these crops.

The problem that we have had with trap crops in CQ though is that in some seasons our trap crops don’t necessarily match up with when the emergence of the last generation may occur. We have also had problems with the quality of trap crops that have been grown. Pigeon pea can be quite variable from season to season and with some of the water restrictions that we have had, perhaps some of the pigeon pea hasn’t been looked after quite as well as it could be.

Light trap catches of Spodoptera litura

The other problem we have found with trap crops is that they are an indirect way of targeting those resistant or potentially resistant moths in that we are capturing their progeny. What we thought with by looking at Magnet® is that it is perhaps more direct in that we are targeting; the moths themselves rather than targeting the eggs and larvae from those moths.

How did you go about measuring the effectiveness of the Magnet®?

What our question was for this season is to see whether we could use the Magnet® on an area wide scale. We went and picked our two areas in Theodore that were roughly about 800 hectares in size each and we aerially applied the Magnet® to one of those areas and then looked at doing moth flush counts as well as light trap counts to see whether we actually had an area wide impact on the moth numbers in the treated areas as opposed to our control area.

Can you tell us about those two methods of counting moths?

Flush counts are a fairly basic method of counting moths. What we do is walk into a crop, gather a bucket full of soil out of that crop and we walk transects through those crops where we throw the soil out in front of us and count the moths as they emerge out of the crop.

This allows you to put a measure on the moth numbers that are actually present and you can actually work that out on a per hectare basis. This method gives us an idea of the number of moths per hectare and we can get a relative difference between the two treatments.

Using flush counts you can’t get a specific idea of exactly what’s flying out in front of you so we use our light traps to get down to a species level and tell whether they are heliothis armigera, punctigera or some other species.

So looking at the two comparison areas, what did you find with your light trap measurements and your flush measurements?

Other pest species Spodoptera litura most prevalent and observed as late instars on BGII crops throughout the Dawson Valley season long

It was very interesting. When we put the treatment on, we went with an aerial application late in the afternoon and we found even by the following morning we had about an 87% reduction in moth numbers in the treated area. We went back on the second day and that reduction in numbers had increased to about 97%. So, within about a 48hour period judging from the flush counts we had quite considerable reductions. We calculated out over that 800 hectares that we killed somewhere around 400,000– 500,000 moths in that area over a week long period. So it was quite a substantial result.

Part of the implication of this work is resistance management for transgenic crops. Can you ‘crystal ball’ a bit and tell me how this could work?

What we are looking at is using Magnet as a technology to replace trap cropping, targeting that last heliothis generation that may be emerging from Bollgard®. If we can bust those moths before they escape or as they start escaping those fields and prevent them going off into the surrounding environment, hopefully they are not going to come back next year and cause us a problem. Really it’s about getting a break in resistance and that’s how we are hoping this product will fit a niche for our resistance management specific to CQ.

In Bollgard II® there is what we are calling secondary pests coming through, has this work showed up anything effective for any of the secondary pests?

One of the pests that we noticed within Bollgard® crops throughout the Dawson area this year in particular was Spodoptera (cluster caterpillar). There were low numbers of that pest throughout a lot of the Bollgard® II fields and when we came to look at the actual moth numbers that we were catching in our light traps we found that we had a significant impact on spedoptra as a species as well. I think that is a real fringe benefit with the approach of using Magnet® compared a pigeon pea trap crop which is really only specific to heliothis, so it’s a multiple approach affect.

Will this work continue next season?

This season we have answered the questions as to whether we can get area wide suppression with Magnet® over a regional scale. What we really want to focus on next season is replicating that result and coming up with a use pattern strategy for it. For example, this season we went with a 1 in 72 row application. To be economically viable we really need to start expanding that out to 1 row in 150 or 1 row in 200.

WHERE TO FROM HERE?
Experiments this season will focus on identifying a probable pattern that fits CQ scenario and building a statistically valid measure of impact.

Acknowledgements:
CRDC
Ag Biotech
Moura Aerial Agriculture

Further Information: 
Dr Stephen Allen, Robert Eveleigh, John Marshall,  Craig McDonald, David Kelly or James Quinn