Linda Edwards
[Editor’s note: As of 2024, Organic BC is more than three decades in the making, and younger sister the BC Organic Grower is on it’s 27th volume! What better time to look back on some original content from the early days of this magazine? Read on for an early-2000’s series on predator insects by Linda Edwards.]
Fly Away Home: Lady Bug Beetles (Coccinellidae)
First published in Summer 2001 (Vol 4, no 3)
Lady bug beetles are probably the best known and most appreciated, if not loved, of all insects. The adults come in many sizes and colours—pink, red, yellow, and orange. Some have no spots and others have as many as 19. These adults over winter in groups under rocks, fallen trees, and in hollows in hillsides and mountainsides. Their bright yellow, spindle-shaped eggs are laid end up on leaves, in clusters of 10 to 30.
The egg clusters are similar to those of their much less popular cousins, the Colorado potato beetle. However, you will find potato beetle eggs only on potato and nightshade plants and rarely are aphid populations high enough on these plants to attract lady bugs to stay long enough to lay eggs. In other words, you are safe to destroy egg clusters you may find on these plants.
In about five days, tiny, bristly black, alligator-shaped larvae hatch out. After they moult, they are grey to blue-grey with purple and orange markings. They feed for about a month and then enter a pupal or resting stage where they become adults in about 10 days. The pupae are immobile, orange-red bumps with black markings that you find attached to everything from bark and leaves to fence posts.
Both the adults and larvae live mainly on aphids. However, they are not very effective at keeping aphid populations from becoming a problem in the first place. Unlike some other predators and parasites, lady bug adults have no special ability to locate their prey. They have to actually bump into something to find it. They also have a short attention span; careful observations (an entomologist’s idea of fun) have shown that if they do not locate prey in 2.5 minutes on a plant they leave, so that low populations tend to escape their notice and therefore control. When there are high populations of aphids, lady bugs do accumulate and are effective in cleaning up infestations. Unfortunately, damage has often already occurred.
One should never use the word “stupid” to describe insect behaviour—though it is tempting when contemplating lady bug larvae. They can be observed wandering aimlessly on the top of a leaf where there are no aphids and never checking underneath where there may be many. Needless to say, survival rate is very low. This, plus the fact that this insect has only one to two generations a year, means the numbers of lady bugs available for biological control is relatively low.
Don’t bother buying ladybugs for control of aphids in a specific situation. The insectaries that sell them, collect them as hibernating adults (usually in Colorado) and keep them cool and dormant until they ship them to you. When you open the container in your garden or orchard, the beetles fly out with only one genetically implanted aim in mind: to fly as far as they can as quickly as they can to get off that mountaintop where they entered hibernation. Flight distances are usually at least half a kilometre and not infrequently much further. Years of research have clearly shown that the only way to keep them where you want them is to put a cage over the plants to be protected.
As you know, damaging outbreaks of aphids in organic production tend to be infrequent. If lady bugs aren’t effective in preventing this from happening, what is? It is the many other less conspicuous predators and parasites. Next issue, I will tell you about one of my favourites—Aphidoletes aphidimyza—the serial killer of the predator world.
The Serial Killer of the Predator World: Aphid Midges (Aphidoletes aphidimyza)
First published in Fall 2001 (Vol 4, no 4)
Most predators kill and feed until satisfied and then rest until they get hungry again. Not Aphidolotes! While a larva can get through a life cycle on as few as six aphids (the only food they eat), if there are more in the vicinity, it will just keep on killing! This ability to survive at low numbers but respond to high numbers is very useful. This means they don’t have to leave an area when numbers drop and can therefore keep resurgences of pests (as can occur with predators like lady beetles) from occurring. It also means because of this tendency to kill as many as possible not just as many as necessary, they can bring high populations of aphids under control more quickly than most of the other predators.
Aphidoletes kill aphids by piercing their victim’s leg tissues and injecting a toxin. This paralyzes the aphid, stopping it from feeding and therefore killing it. Every once in a while, the midge larvae stop and suck out the contents of their prey, leaving behind a black shrivelled body.
This is an indigenous and wide-spread species. The adults are seldom seen, however. They are very tiny, mosquito-like, dark brown, and only fly at night. They feed on honeydew generated by the aphids. Unlike predators like lady beetles, they have wonderful searching ability. An Aphidoletes adult released at the edge of an acre-sized field of plants, with just one plant in the middle with aphids, will find that plant and lay eggs on it. This kind of knowledge is another example of how entomologists like to spend their time!
The eggs—always laid near aphids—look like flecks of paprika. These hatch in two to four days. The larvae, which grow to a maximum of 0.3 millimetres, are bright to pale orange. They are cylindrical and smooth. They too are not easily seen because they are usually under an aphid, killing it. After feeding and growing for one to two weeks (faster in hot weather, slower when it is cool), the larvae drop to the ground and pupate for one to three weeks—again temperature dependent. The adults emerge, lay up to 200 eggs, and the cycle starts over again. There are three to five generations per season, which can result in very high populations. Short days in the fall triggers hibernation. They overwinter as pupae in the soil and leaf litter. It has been documented that there are at least 65 kinds of aphids that this predator will eat. Imagine if you will, years of entomologists searching out aphids and feeding them to Aphidolotes larvae. Yep! They eat that one too!
Such a wonderful predator! So why are there ever outbreaks of aphids anywhere? Their weakness from a growers point of view is that they don’t like cool weather. Their emergence from hibernation is triggered by long day length. They do not start to emerge until around the first week in June. Unfortunately, in many cases, by that time aphid populations may already be high (a good deal if you are an Aphidoletes and possibly why they have selected for late emergence) and be causing damage to crops. The Aphidolotes will become in many cases the most important predator in bringing them under control—but the higher the populations, the longer it will take.
Aphidoletes can be purchased for release. They are the main predator used against aphids in greenhouses so every insectary rears them. You receive pupae in containers. Put them in a warm place out of direct sunlight. Check about every 12 hours. When you see a number of adult “flies” under the lid, take them out and release them into the area where aphids are a problem. Do releases in the evening or very early in the morning before the sun comes up. The adults can dehydrate and die in direct sunlight. After at least most of the adults have flown, put the lid back on, and take it back inside until more adults emerge. Repeat until there are no more. It is okay to tap the side of the container to activate them.
The number you release depends on how much you want to spend, which tends to depend on how bad the situation is. Releases can be very effective especially in places where native populations of Aphidoletes may be low i.e. annual crops or a tree nursery. However, they will not be effective under cool conditions so early spring releases—before naturally occurring ones would emerge—are not recommended. Average daytime temperatures should be above 18 degrees Celsius. There have also been some successes with mid-summer releases, which reduced chronic aphid populations so much that there were very few that were left to over winter and consequently populations were much lower the following year. There have also been releases that made no difference at all. This insect also does not do well under very dry conditions. It is thought that the pupae tend to dry out.
Fair Weather Friends: Green Lace Wings (Chrysoperla cernea and Chrysoperla nigricornis)
First published in Winter 2002 (Vol 5, no 1)
Green lacewings are very good predators, but don’t rely on them to be effective until early summer. There are two main species in BC. Adults of both feed on aphid honeydew and plant fluids. C. nigricornis adults and the immature larvae of both are also predaceous. Aphids are preferred but they will also eat psylla, mites, leafhoppers, thrips, and small caterpillars.
The adults are one of the most beautiful insects—large membranous wings, green bodies, red or gold iridescent eyes, and long fine antennae. They are nocturnal and are often attracted to lights at night. The oval eggs on slender stalks are laid mainly on leaves. They are white at first but turn grey just before hatching. The larvae are mottled yellow, grey, or brown and look like little alligators. They are very active and voracious predators. The larvae form green pupae inside a spherical white cocoon in foliage when they complete their cycle. Egg to adult takes about 30 to 40 days and there are two generations a year.
They overwinter either in the pupae form or as adults in litter, buildings, or under bark. There are relatively few early in the spring so they are not very effective then. The overwintering adults are present but the females do not start laying until night temperatures are warm—usually mid- to late-June.
Lacewings can be purchased from insectaries. However, research has shown that this almost never increases local population. Most of the time, the lacewings arrive as eggs (without their stalks) glued to cardboard. This is the most inexpensive method. However, research and careful observations have shown that the first larva to hatch eats most or all of the other eggs on the cardboard. There are better survival rates from eggs mixed with materials like vermiculite, although at least a third are crushed during the mixing and handling. Larva in individual holders can also be purchased but they are very expensive. Adults are unsuitable because like ladybugs, they tend to fly up to four kilometers as soon as they are released.
Linda Edwards was one of the most influential members of the organic community in BC, and has been greatly missed since her passing in 2020. Linda was a scientist, researcher, and expert in organic fruit trees, and committed organic advocate through her work on the boards of many associations. She also, clearly, loved talking bugs!
Featured image: Lady Bug Beetle. Credit: (CC) Gorupka.
