Biological Pest Control and Integrated Pest Management

Aphid Pests

Some Background

luster of yellow aphids on green leaf stages visible clearlylose-up of winged insect perched on textured white surfaceAphids, members of the order Hemiptera, are probably the most notorious pests in the world. With well over 4,000 aphid species in this huge order, there is an aphid for everyone, and nearly everyone in horticulture and agriculture may have to deal with an aphid infestation at some point in time.

They are often the first natural predators to appear — usually very early in the season. Some of the reasons for this are due to their aphid reproduction cycle but, perhaps, it is because they love tender plant growth. Aphids are called plant lice by some people, though based on our experiences, this is not typical for most aphids.

How They Become a Problem

green aphid adult on leaf with visible wings and detailsTrouble often starts in greenhouses when the operator cranks up the heat a little as the plant material he or she has sown begins to germinate and leaf out. Normally, aphids don’t attack the cotyledons but are keen on any new growth beyond that point.

They usually stay on the newest growth and follow it upward as the plant develops — through the budding and flowering stages.

The infestation process begins as winged adult aphids emerge from their winter hideaways (usually the craggy bark of nearby trees) during early spring when the weather is warm enough to allow their flight and migration. This can be very early in the season.

Of course, human introductions where aphids are brought into a structure by hitchhiking on purchased plants will be an exception to this rule. 

Remember: scout new plant material thoroughly before bringing it into your greenhouse. If infected plants are introduced, you might face an infestation quickly.

Exponential Growth

The winged adults light on plants ready to give birth, which, mostly in greenhouses, is done viviparously — in other words, they bear wingless living young, skipping the egg-laying stage entirely. This gives aphids a unique time-saving advantage. 

To further compound the speed in which aphids can multiply, the nymphal or immature stages are entirely female and then reproduce further parthenogenetically, which means they have no need to mate. 

Adding insult to the grower’s injury, the nymphal stages are born with the next brood within them already, a condition called paedogenesis. 

To aphids, the combination of these abilities spell exponential growth potential — to growers it means trouble if counteraction to naturally repel aphids or get parasitic wasps involved is not taken immediately.

A Serious Pest

various stages of aphid life cycle on green plant surfaceAn additional problem that may also affect the aesthetics of the plant include presence of cast skins — a by-product of aphids molting from one nymphal stage to the next (which is occasionally confused by novices as stationary whiteflies since they’re white).
Another aesthetics problem, if the population becomes large enough, is the formation of black-sooty mold growing on the sugary, ant-attracting excrement of these pests.
This excrement (a.k.a. poop) is known to attract sugar-feeding ants, which may, in an effort to manage their food source, herd or physically move aphids and protect them from biocontrols, natural and introduced. 

This last condition, if the aphid population grows large enough to support ants, can make organic control of woolly apple aphid or green peach aphid even more challenging.

close-up of multiple aphids in various sizes on surfaceWinged aphids start the ball rolling. From that point on the aphids no longer have wings and those forms will not be present. If you detect some winged aphids, your population is probably in its beginning stages, however like everything else in the complicated world of pests, there are exceptions. In this case the exception is if your aphid population is in full swing, a brood of winged aphids will be developed. 

The reason for this is simple: the host plant is becoming overloaded and may not be able to support further aphid population growth. The colony wants to spread. 

In other words, if you detect plants loaded with aphids and some winged forms, the problem is quickly going to affect nearby plants. There is no greater time to control aphids.

Some Advice to Control Aphids

green aphids feeding on a brown plant stem close-upIf it’s not yet clear, aphids can be disastrous. Their ability to damage crops, including fruits attacked by the rosy apple aphid or woolly apple aphid, requires vigilance from growers. Regular scouting is crucial early in the season. Predatory insects, like lady beetles, can help control them naturally by attacking young aphids on infested plants.

Aphids aren’t usually difficult to spot, though they go undetected by too many growers. Unfortunately, growers notice the ants or cast skins before seeing the pests themselves. 

This is unnecessary, though, as the first aphids should be easily noted with proper scouting. Early presence of aphid predators like beneficial insects or lady beetles can avert greater damage.

For the Scout

white flower and curled leaves in black and whiteAphids, at least the winged forms, may be inadvertently captured on sticky traps, but physical plant inspections are much more valuable to the scout. Many aphids are green in color, which can make detection more difficult, but several species are not well camouflaged and can be quite colorful. 

Since aphids tend to congregate on the growing tips and flower buds, they can be easier to spot, the scout should know where to look and not be stuck searching for tiny individuals. The color of these three to six mm pests can range from yellow to red, green and blue to gray, and even black to white and fuzzy-looking. 

Most species have two horn-like structures, called cornicles, on the posterior end of their abdomens, flanking a small caudal tail (they have a total of three things on their butt). 

Their antennae are rather long and are swept back toward their rear along the sides of their body. In combination, these features can aid in their identification and determine whether they are parasitized aphid forms.

Some Solutions for Aphid Control

black aphids on nasturtium stem with orange flower close-upThere are many biological pest control agents available to specifically address naturally killing aphids or aiding crops damaged by potato aphid, melon aphid, or rosy apple aphid. Some, like Aphidius spp., can be used preventively — which is highly recommended, especially when considering the awesome destructive potential of these pests. 

Chemical controls, such as insecticidal soaps, horticultural oil, or neem oil, can also be effective, but great care must be taken as improper use can kill beneficial insects.

In our opinion, if scouting is done right and if ladybug larvae or green lacewing larvae are used preventively, aphids can be a non-issue for growers. Effective aphid reproduction management ensures healthy crops.

Aphid control can be easily achieved, but only if aphids are understood and respected.