Key takeaways
- 4,000+ aphid species in the order Hemiptera — at least one applies to nearly any horticultural or agricultural crop.
- Aphids reproduce viviparously, parthenogenetically and with paedogenesis — exponential growth in days, not weeks.
- The honeydew aphids produce attracts black sooty mold and sugar-feeding ants — aesthetics damage plus disruption of biocontrol agents.
- Winged aphids signal one of two things: the infestation is just starting, or a heavy colony is about to spread to nearby plants.
- Preventive go-to controls: Aphidius spp., ladybug larvae, and green lacewing larvae. Insecticidal soaps and horticultural oils work too — with care for beneficials.
Aphids, members of the order Hemiptera, are probably the most notorious pests in the world. With well over 4,000 species, there is an aphid for every crop — and nearly every grower in horticulture and agriculture will deal with an aphid infestation sooner or later.
Background
Aphids are often the first natural predators to appear in the season — usually very early. Some of this is due to their reproductive cycle, but mostly it’s because they love tender plant growth. Aphids are called “plant lice” by some, though based on most growers’ experience, this isn’t typical for most aphids.
How They Become a Problem
Trouble often starts in greenhouses when the operator cranks up the heat a little as plant material begins to germinate and leaf out. Normally aphids don’t attack the cotyledons, but they’re 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 flight and migration. This can be very early in the season.
Of course, human introductions are the big exception — aphids brought into a structure by hitchhiking on purchased plants don’t need spring weather to find your crop.
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 — in greenhouses, that’s 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, the nymphal (immature) stages are entirely female and then reproduce parthenogenetically — they have no need to mate.
Adding insult to the grower’s injury: the nymphal stages are born with the next brood already inside them, a condition called paedogenesis.
For aphids, the combination of these abilities spells exponential growth potential. For growers it means trouble — unless you act immediately to repel aphids or get parasitic wasps involved.
A Serious Pest
An additional problem that affects the aesthetics of the plant is the presence of cast skins — a by-product of aphids molting from one nymphal stage to the next (occasionally confused by novices as stationary whiteflies since they’re white).
Another aesthetics problem is the formation of black sooty mold growing on the sugary, ant-attracting excrement (a.k.a. honeydew) these pests produce. This excrement 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 or introduced.
This 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.
What Winged Aphids Tell You
Winged aphids start the ball rolling. From that point on, aphids no longer have wings — those forms won’t be present. If you detect winged aphids, your population is probably in its beginning stages. However, like everything in the complicated world of pests, there’s an exception: if your aphid population is in full swing, a brood of winged aphids will develop.
The reason is simple: the host plant is becoming overloaded and may not be able to support further population growth. The colony wants to spread. If you detect plants loaded with aphids AND some winged forms, the problem is quickly going to affect nearby plants. There’s no greater time to control aphids.
Some Advice to Control Aphids
If 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 — with proper scouting, the first aphids should be easily noted. Early presence of aphid predators like beneficial insects or lady beetles can avert greater damage.
For the Scout
Aphids — at least the winged forms — may be inadvertently captured on sticky traps, but physical plant inspections are much more valuable. 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 3–6 mm pests can range from yellow to red, green and blue to gray, and even black to white and fuzzy-looking.
Anatomical Identification Markers
Most species have two horn-like structures called cornicles on the posterior end of their abdomens, flanking a small caudal tail (so 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 identification — and help you determine whether they are parasitized aphid forms (the result of Aphidius mummification).
Some Solutions for Aphid Control
There 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 given the 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 — improper use can kill beneficial insects.
Aphid control can be easily achieved, but only if aphids are understood and respected.
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.
For over 30 years, Green Methods has been a leader in the production and application of beneficial organisms used in biological pest control and integrated pest management programs.