Parasitoids vs chemicals

When the leaf miner first hit South Africa, the results were nothing short of devastating. Farmers spent thousands of rands per hectare on chemicals, but gained only a semblance of control over the pest. The reason was that this particular species, the pea leaf miner (Liriomyza huidobrensis), had already been exposed to pesticides in other countries, and this, combined with its rapid life cycle, meant it had developed resistance to most chemicals by the time it arrived in South Africa.

- Bill Kerr

The adult stage of L. huidobrensis is a very small fly, comparable in size with the familiar vinegar flies (Drosophila spp) attracted to overripe fruit. L. huidobrensis lays its eggs in the leaves of the host plant, lettuce being much favoured. It also causes lesions in the leaves to feed on the sap, and these are seen as small, white spots.

The hatched larvae make unsightly serpentine tunnels through the leaves, making the lettuce unmarketable.

RANGE OF PARASITOIDS

The chemical abamectin was found to reduce leaf miners to manageable levels, while having a minimal effect on beneficial insects. I started using this product on my cucurbits, beans and beet, and found that while it helped a great deal, it did not eliminate the pest.