Natural cycle of garden-friendly insects can be beneficial

Published on Wednesday, 6 August 2014 21:31 - Written by KEITH HANSEN Keeping It Green

One of the plants that we like to have in the IDEA Demonstration Garden, located in the Tyler Rose Garden, is Asclepias — commonly known as butterfly weed. I don’t particularly like that common name because it really isn’t a weed, but a very attractive and important food plant for monarch butterflies.

Tropical butterfly weed, (Asclepias curassavica), which is also called blood flower, is currently blooming and is closely related to butterfly weed. If you look closely, you can see the new growth is covered with hundreds of bright yellow aphids. This happens every year, and is not a cause for alarm. As a matter of fact, it can be considered a good thing.

Even though the aphids (which some folks call plant lice) are feeding on the plants, they don’t ever seem to do serious harm to this particular plant or its ability to flower. But the abundant aphids also serve as a “nursery” for all kinds of beneficial insects that feed on the aphids as their food source. From the blood weed, the beneficials can spread out to feast on insect pests on other nearby plants.

A quick survey revealed several syrphid fly larvae munching on the aphids. Syrphid flies are small flies that are often seen hovering around flowers and are sometimes mistaken for bees. Like all flies, their larval stage is a legless maggot, and these babies have a very big appetite for aphids. One larva can eat hundreds of aphids before it completes its lifecycle.

Another beneficial insect I spotted on the blood flower was the larval stage of the delicate lacewing. Actually, I first noticed a large number of the lacewing’s distinctive eggs attached to leaves on several plants. You may have seen these eggs on plants, on a wall, window screen or other places around the home or garden. They are fine, white, hair-like filaments with a swollen end, which are the eggs.

Lacewing larvae are very voracious predators of aphids and other soft-bodies insects. They had just begun to hatch and feed on the yellow aphids.

These are just two of the more common beneficial insects you can find in nearly every flower and vegetable garden. They are both predators, which means they actively seek out their prey. One of the most iconic insect predators is the praying mantis. They typically wait for their prey to come to them, grabbing them with their spiny front legs. Unfortunately, they are not very efficient at reducing our garden pest population, and also feed indiscriminately on both pests and beneficial insects, so they are not a reliable option for biological control. Still, they are cool to observe.

The other iconic and much more efficient predator of pests is the lady beetle. There are many species of lady beetles, and they control a wide number of garden pests, including aphids, scales and mealybugs, among others. Both the adult and larval stages feed on pests, and you should become familiar with what lady beetle larvae and pupa look like so you do not mistake them for plant pests. The larvae are dark purple with orange spots, and the pupal stage, which is usually found stuck to the bottom of a leaf, is swollen orange with dark spots.

Another general group of beneficial insects that feed on plant pests are called parasitoids. They are easy to overlook, but one of the coolest aphid enemies. These are very tiny wasps that lay an egg inside an aphid. The wasp larva hatches and eats the aphid from the inside out, killing the aphid in the process and leaving it a lifeless, puffy, brown shell. These shells are called mummies. The wasp larva then transforms into its adult stage and cuts a hole in the top of the aphid, emerging to continue the process.

“If there were an aphid version of the movie “Alien,” this would be it,” Extension Horticulture agent Skip Richter said.

So, look for aphid mummies with little holes in them. If you find them, let nature do the work for you instead of spraying with an insecticide that would not only kill the aphids, but also the good guys working for you. If you use an insecticide that kills the beneficials in the garden, the aphid population will rebound much faster than the good guys because aphids are born pregnant, reproducing faster than rabbits.

Learn to identify beneficial insects in all stages of their life cycles. Also, learn what parasitized aphids and caterpillars look like.

The Galveston County Master Gardeners have a helpful website that features photos of many different types of beneficial insects. If you find parasitized insects in your garden, that tells you that natural controls are working. If pests start to win the battle, causing major damage where more serious action is required, use the least toxic and pest-specific controls to conserve the abundant beneficials that inhabit every garden.

 

Keith Hansen is Smith County horticulturist with the Texas A&M AgriLife Extension Service. His web page is http://EastTexasGarden ing.tamu.edu. His blog is http://agri life.org/etg.