Aphids

Aphids are a common garden pest on Pohnpei related to whiteflies. They prey on cucumbers, squash, and other vegetable crops. Though they are said to like tomatoes, too, I have never had aphids on my tomato plants even when there were other heavily-infested plants nearby. The tiny creatures are larger than whiteflies and have a greenish, brownish coloration. Unlike whiteflies, they have no wings. They congregate in huge numbers all over a plant, but particularly on the undersides of the leaves, where they suck the plant's sap. Like whiteflies, aphids produce a clear, sticky substance called honeydew that coats the leaves and stems where they are feasting. The presence of the honeydew tends to result in mold growth on the plants leaves. Aphids will not kill a plant as quickly as whiteflies, but if there are enough of them, you'll start to get leaf die-off. The stress of the attack will also cause other problems with many vegetable crops, such as cucumbers (which get bitter when under stress).

THE ANT-APHID RELATIONSHIP

Though it may sound strange, ants farm aphids. Yes, that's right. They treat them like livestock, the way we keep cows for milk. The presence of a large number of ants on a plant is usually a strong sign that there are aphids there as well. Ants will protect aphids from predators so that they can milk them for their honeydew. Ants even herd the aphids and take them back to their nests live, so they can be kept and milked in captivity. Weird, eh? Normally, getting rid of the ants would be one step in the process of erradicating the aphids, because the aphids would then be more susceptible to attacks by predators. But since there are no natural aphid predators on Pohnpei, killing the ants won't help.

FIGHTING THEM

I haven't found any good, practical methods to eliminating aphids on my Pohnpei plants, other than using toxic chemicals.

INSECTICIDAL SOAP SPRAY

Special soap sprays are available in the garden section of the hardware store that are said to kill aphids and whiteflies, but you have to spray every part of the plant carefully every few days to make an impact. I did not have success with this at all when trying to fight whiteflies. The problem is that the soap causes cellular damage of the plant's leaves, killing or weakening some of them. It also just doesn't kill off the whole population of bugs.

MANUAL REMOVAL

Spraying off all surfaces of the plant with a high-pressure hose can remove many of the pests, but the effect is temporary. Most of the aphids will merely return to the plant. Removing heavily infested leaves just causes the buggies to move to some other part. Plants that are out in Pohnpei's rain seem to fair better than those that are protected. Perhaps the regular downpours hamper the growth of aphid populations.


BIOLOGICAL CONTROL

Ladybugs (ladybirds), green lacewings, and types of wasps prey on aphids. Unfortunately none of the right species are found on Pohnpei. In 2012, 50,000 Encarsia formsa wasps were released on Pohnpei to attack the whitefly population, but this species is not known to affect aphids.