Organic Insect Control – A Case Study

We have a new community garden, created from a vacant lot, and bordered by a condo complex on one side, a retirement community on a second side (and both come complete with chemical/pesticide maintenance), and an avocado orchard on the third side.

We swore to avoid toxic compounds around our food and use Integrated Pest Management instead. I.P.M. uses natural insect control mechanisms instead of poisons, and targets specific garden pests, rather than trying to kill everything that loves.

IPM allows us to keep our organic garden free from toxins and naturally control pests. The alternative – chemical dependency – as practiced by commercial agriculture and many home owners, has a number of flaws.

A horrible example non-organic pest control was the Med-fly spraying. The entire valley was coated repeatedly with bait that did kill the few Med-flies, but also killed all the other insects to such an extent that the birds left.

Without the birds and the insect predators to harass them, the surviving whiteflies, aphids and soft-bodied scale populations exploded. They destroyed everything in their path. No amount of Malathion could keep them in check.

The thing that finally stopped them was the return of the birds and predators, and abandonment of toxins.

Med-flies were a special circumstance – Is it still hold true today for our garden pests?

A month ago, our garden suffered an invasion of aphids. They attacked our broccoli, cauliflower and other cabbage-family plants. Because the garden is new and an organic island amid commercially managed properties, and without resident predator populations, the aphids moved in and became established.

Some of the gardeners were ready to pull out pesticides and/or insecticidal soaps to eliminate the pests. However, I implored the gardeners to try the most benign solution first. The first step is simply water jetting the offending insects from the plants. Aphids legs become atrophied and immobile when they have settled in place. Once they are washed off a plant, they cannot climb back up.

The reason we used a simple water solution instead of toxic or soapy sprays is this: water will physically remove most of the pests and it does not harm the predatory insects that may be hunting the pests.

Had we let the gardeners use insecticidal soaps, they would have killed some, but not all, of the pests. Aphids have a waxy coating, and many water-based sprays or mists will simply roll off their backs. Spraying would not have destroyed the pests, but would more than likely destroyed all the predatory insects, which lack the waxy-protection, in the process.

Yesterday, when talking with the children and their parents, we checked on the aphids that were left in the garden. There were still some aphids after jetting the plants. What was also evident was predation by tiny wasps and aphids dying from both predation and fungal diseases.

I took some photos, but all I had was a video cam that doesn’t do extreme close-ups. I pulled the still (above) from one of the videos. There were large areas thick with aphids, primarily within the curled leaves. We also saw dead aphids and aphid ‘mummies’, indicating that predation was happening. The big tip-off was when we saw wasps actively working the aphids.

What is most interesting is that no one had released wasp in the garden, and they probably do not come from the over-maintained condo complexes surrounding the garden.

The wasp found us, and they have come to the rescue…

I went back this morning, about 14 hours later, to re-take the photos with a macro lens. What I found this morning was very different from what I saw just a half day before. The splits in the leaf on the top-left side of the photo are the same places I broke taking the top photo.

The aphids had been reduced by 75% to 80% – literally over night. In place of an army of aphids was a battlefield, littered with skeletal remains of aphids sucked dry (possibly by roving ladybug larva) and ‘mummies’, aphids that have been parasitized from within. You all saw the movie, “Alien”, right? Same thing…

The picture above shows the same leaf shown in the first photo.  Instead of fields of aphids, there are a few survivors, and the tiny wasps are at work, laying eggs in them for the next generation.

To find a large enough infestation to photgraph, I had to search way down through the garden, but I did find another area being hunted.

This picture reminds me of the dinner-table scene in “Alien” – it shows a wasp (just barely visible), which has pupated in the body of an aphid, beginning to emerge from the body of the aphid.
In the following photo, an adult wasp (almost transparent) is caught in the act of laying an egg for the next generation of predators that will protect our garden. The wasp is facing to the right, and her body is curled under her while she lays an egg in another victim.

Here is a closer view, enhanced to make the wasps more visible. Many of the aphids show the dark spot on their rear ends indicating they have been parasitized.

Our aphid problem is not at an end – we will continue to get these and other pest into the garden. However, if we refrain from whipping out toxins, we can help nature take its chosen course and have a productive, toxin and pest free garden.

The take-away here is that IPM is nature’s own way of managing pests and that it works. Spraying with insecticides would have only made the problem worse. This is another example showing that Nature’s way of managing pests works best. It is in our own interests to learn how to work within her system.

To learn more about the “Alien vs. Preadtor” world of IPM, visit the University of California’s I.P.M. page.

To follow the progress of the garden where these photos were taken, visit Camarillo Community Gardens.