Every year I get questions about products that increase the Brix content (sugar levels) of plants and that high sugar levels in plants will eliminate insect problems. People want to know if these products are snake oils or real…
I don’t have any data to support either side of the argument, but I reviewed information about insect nutrition to see if I could find any information to support the claims. I came across a couple of things that are worthy of mentioning.
First what do we know about insect feeding and why an insect feeds on a particular plant?
Just like we want to have a “balanced diet”, insects must have certain nutrients at a given level to have normal development. Mother Nature has taken care of this by having insects co-evolve with the plants on which they feed that give them the necessary mounts of, carbohydrates (sugars), proteins (amino acids) and fats. When you look at chewing insects that feed on plants, they generally need equal amounts of amino acids and carbohydrates. Sucking insects that feed on phloem, like aphids, tend to have higher requirements and/or tolerance for sugars.
Plants are immune to feeding by most insects. By that I mean, most insects are specialists
and have a limited number of plants that it can feed on. Of course, there are always exceptions (true generalists, like the corn earworm/bollworm/soybean podworm) but for the most part, there is some cue in the plant that will cause an insect to feed on the plant. The cue that triggers feeding in one insect, may deter feeding of other insects – just like Goldilocks, each insect prefers ‘just right’.
So what happens if an insect feeds on a plant that doesn’t have the right balance of nutrients? 1) an insect can eat more to get the minimal requirement of the nutrient that
is low in the plant; 2) it can move to another plant, if one is nearby (this is harder for a wingless insect, like a worm since they have limited mobility); or 3) the insect has to change the way it metabolizes nutrients to maximize the resources consumed more efficient in utilizing nutrients. I also came across something that said that if their tasters noticed high sugar content, they may leave before doing much feeding. And of course, insect death would also be an option if it do one of the three adaptations listed above. Additionally, just like us, the insect that eats an improper diet may be more prone to disease.
So when we look at plants that have had their Brix level increased due to an application of one of these products and possible insect effects:
- Option 1, the sugar is high which would mean that an insect would have to eat more to get the necessary amount of amino acids. (MORE DAMAGE)
- Option 2, the insect meets its need for sugar so it moves to another plant for necessary amino acids. (SOME DAMAGE, BUT THEN LEAVES)
- Option 3, the insect changes its internal biochemistry to absorb more of the nutrient that is low in the plant. (PROBABLY THE SAME AS A NON-TREATED PLANT)
- Option 4, their sensors taste too much sugar and find another plant (LESS DAMAGE)
- Option 5, they die from an improper diet (MORE OR LESS – DEPENDS ON HOW MUCH THEY FEED BEFORE DYING)
There are data that suggest that these products increase yields. I know of a couple of farmers that swear by it. These yield increase may be real, but I am not confident that yield increases are the result of the removal of insects from the system. Given that insects have shaped plant defenses and plants have shaped insect feeding in a ‘survival of the fittest’ over the ages, changing the plant may change insect feeding.
So where does that leave us with the original question: is the claim that these products get
rid of all insects valid? Probably not. There is a possibility that the products reduce insect feeding for some species, but it is also likely that some insects will increase feeding for others. There are simply not enough data out there to provide a definitive answer.