Beneficials and biologicals: Two is better than one!

Above is biological insecticide – Beauveria bassiana on thrip adult.
Below is beneficial nematode – Steinernema feltiae attacking thrip larva.

Does it pay to use a biological insecticide and apply a beneficial insect at the same time? Will they compete with each other, or will they actually help each other? I recently was sent a study published in 2021 by a USDA researcher who has done some great work with both biologicals and beneficial insects. Dr. David Shapiro-Ilan is with the USDA Fruit and Tree Laboratory in Byron, Georgia. He has done some good work on biological insect control in pecan orchards and so seeing his name on this study got my attention.

The title is: Combined Effect of Entomopathogens against Thrips tabaci: Laboratory, Greenhouse and Field Trials. In this study Dr. Shapiro-Ilan and other researchers looked at the use of two different biological insecticides, Beauveria bassiana (BoteGHA ES, SPE-120, MycoTrol, Botanigard, etc.) and Metarhizium anisopliae (Novozymes was producing Met 52 EC but hard to find now). These two biological insecticides are effective, to a degree, and used for many insect species.

The researchers also looked at two beneficial nematode species for control of thrips, Heterorhabditis bacteriophora and Steinernema feltiae. These two nematodes can infect the soil dwelling stage for thrips or pre-pupae and pupae stages.

Then the researchers also looked at the additive or synergistic effects of adding a biological insecticide and a beneficial nematode together. This is where it got interesting, singularly, none of the treatments alone did as well as they did working together – a biological combined with a beneficial. In fact, the effect was dramatic and statistically significant.

The best treatment was a combination of the biological Beauveria bassiana with the Heterorhabditis bacteriophora nematode. Almost as good was the biological Metarhizium anisopliae with the Steinernema feltiae nematode. The interesting thing was that the combination of Beauveria bassiana and Heterorhabditis bacteriophora nematode had a synergistic effect on each other. They worked well together, much better than the addition of each individual’s % control! The other combinations also worked well together but the effect was additive and not synergistic, meaning that the combination was the addition of the % control of one, added to the % control of the other. Also, the combinations can be tank mixed for field applications and result in much better thrips control than either biocontrol alone. As a reminder, always apply beneficials late in the evening as temperatures are moderating.

What is the downside? The cost biocontrol can be expensive! The research trial used upwards of 1 billion nematodes per acre which would cost about $500 per acre. Most beneficial companies recommend 50 million nematodes per acre which is around $70 per acre – this is somewhat affordable. The cost of the either biological insecticide is around $75 per acre, so that the cost of both together is somewhere close to $150 per acre for thrips control in onions. Is that going to work? Depends on the cost of the onions! What this research does show is that biocontrol works and works well. Affording it is up to you!

Author: Bob Whitney, Regents Fellow & Extension Organic Specialist

Agriculturalist, extension educator and researcher, organic agriculture enthusiast and promoter, international program developer, Christian, husband, father and friend.

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