Pest insects

by M. Arjoca,

Caterpillar on sunflower leavesThe insects are one of the most diverse animal groups, living in almost every environment. There are over a million species described and there are many more unknown. They feed themselves with pollen, nectar, leaves, stalks, flowers, roots and with other insects.

Many of them are beneficial insects because they help in garden and don’t cause damages or the damages are too insignificant. Plus, some insects can be pests just in the larva stage but in the adult stage are very helpful. For example, the larvae of tomato fruitworm (Helicoverpa zea) make real damages on crops but the adults are important pollinators. The caterpillars which chop our plants transform themselves in butterflies which pollinate flowers in the adult stage.

The idea is not to get totally rid of the bad insects but to maintain a balance between them and the good ones. Many gardeners try to attract beneficial insects in their garden growing certain flowers or companion plants.

The insects become pests when they attack the plants, eat them or just make them weak to diseases, fungi and other pests.

Frequent pests are: the aphids, whiteflies, mealybugs, spider mites, thrips, fungus gnats, cabbage worms, squash bugs, carrot flies, tomato hornworm, tomato fruitworm etc.

Aphids on a stalkAphids (Aphidoidea) – are small insects which live in colonies and attack the plants sucking their sap. The leaves and stalks become wrinkled, deformed and they wilt in time. The growth stops or is very slowly, the plants yellow and the crop is small. The aphids often transmit viruses which can kill the plants.

Many aphids are green, but they also can be black, brown, yellow, red, pink or gray. They multiply very fast in large number and being small and light can be carried on long distances by wind. Because the aphids excrete honeydew, a sticky and sweet liquid, some species of ants have aphid farms on different plants and they protect them from predators. The honeydew facilitates the spread of fungi on plants.

The aphids have many predators: ladybugs, hoverflies, parasitic wasp, spiders, lacewings etc. Besides these they can be infested with bacteria and fungi. The excessive heat, the frost and the rain are another enemies.

What can you do when your plants are infested with aphids:

Whiteflies effects on fuchsia plantWhiteflies (Aleyrodidae) – are like very small white butterflies. They live also in colonies and stay on the underside of leaves. They make serious damages to plants not only sucking the sap but also spreading viruses and diseases. Like the aphids the whiteflies excrete a liquid which facilitates fungi infestation. The leaves become yellow, they wilt and fall down, the flowers start to have spots and become twisted. The whiteflies are a very serious problem for farming because they have the capacity to adapt to the newest and strongest chemical insecticides. So the farmers try to control this pest combining different methods.

Their natural predators are: green lacewings, ladybugs, minute pirate bugs, big eyed bugs, damsel bugs and other bugs.

What can you do when the plants are infested:

Thrips (Thysanoptera) – are small insects, many species feeding themselves with flowers and vegetables which become wilted and deformed. Small white-grayish spots appear on leaves and the growth stops. Like the aphids and whiteflies, the thrips can propagate different plant viruses. They multiply fast and they like the warmth and moisture.

What can you do when the plants are infested with thrips:

Spider mites (Tetranychidae) – are barely visible insects which weave webs on leaves and feed themselves with the sap of plants. Usually they stay on the underside of leaves and they like the warmth and the dryness. On the upper side of  leaves appear yellow dots which become transparent and then the leaves fall down. The spider mites are very resistant to chemical insecticides, but they have natural predators: some ladybugs, minute pirate bugs, big-eyed bugs, predatory thrips and some other mites.

What can you do when the plants are infested with spider mites:

Leaf miners on nasturtium leafLeaf miners – the larvae of different insects (some moths, flies, bugs, wasps) live inside the leaves being this way protected from predators. They destroy the leaf tissue making tunnels through it. Living inside the leaves makes their control very difficult using insecticides.

What can you do when the plants are infested with leaf miners:

The world of insects which feed on plants is very large. Here is an insects database.