3-8-2008
In planning for mite releases this year, I started wondering about the pesticide resistant strains, and whether the resistance may come at a cost in regards to their hardiness in other ways. Are there any thoughts about releasing mites in organic fields, and if it may be better to use more of a "wild-type" strain, since the pesticide resistance won't be necessary?
Steve Matthiasson
3-17
I’m a little rusty on pred mite pesticide resistant strains, but the sulfur resistance/tolerance would clearly be important. Also, if pyrethrin or some of the earlier generation pyrethroids are in your toolbox, that might be a worthwhile resistance to look for in your released mites as well since those pyreths can flare regular mites.
Laura Breyer
3-18
I called around to see if there were some good studies on pesticide resistant predatory mites. Looks like I’ve got a hit on some old research papers. They’re being mailed to me and I’ll try and put something informative on the server after my review.
The summary of what I was told is female predatory mites, such as Galendromus occidentalis, become lay egging adults within 4-5 days, in 90F degree weather, after hatching. This means you can have three generations, or more, within 12 days. In a sprayed environment, the surviving predatory mites become “resistant” because of natural selection in a hostel environment. When the predatory mite populations’ crash, it is likely due to repeated sprays, within 12 to 14 days, with a product, or products, the predatory mites haven’t adjusted too. It could also be due to rotating products too quickly.
We’ve seen this with Vine Mealybug sprays. Blocks with one Danitol was ok, blocks with one or two Lannate applications were ok, but blocks with Danitol followed by Lannate had late season mite flares… however I’ve already found some predatory mites in these areas this year. The populations are low so I’ll be adding more to try and balance what the sprays have disrupted. One release of 2500 predatory mites per acre with a follow-up release as needed is what I’m recommending for the disrupted blocks. If my predatory mite populations don’t keep up with the injurious populations, a control application will be advised.
The goal is balancing the ratios while maintaining cost and control. A release of 2500 occidentalis per acre will cost approximately $20 per acre, after release. If we release in cool weather, a blend of 50% californicus (better in 70F weather) and 50% occidentalis (best in 90F weather) will run approximately $18 per acre (NOTE – use 100% occidentalis in warm weather).
If I’ve interpreted my phone conversations correctly, after the residue of the applied product(s) dissipate the surviving offspring will revert back to their normal state of being “non-resistant”. Again, this is because of the fast generation turn over.
I’ve seen some insectary ads advertising “resistant” predatory mites. Even though this claim seem to be true, if they are using this as justification for price increases don’t be fooled. Interview the insectaries and find out how much they know about egg production. In all reality, you are purchasing the predatory mite for their ability to lay eggs not just eat. In order to maintain balance, the predatory mites need to increase populations quickly.
Don Thomas