You Grow Girl™

Guest post by Arzeena Hamir

Predatory Mite

The predatory mite, Phytoseiulus persimilis, is a welcome insect in the garden and greenhouse. It is a fast moving insect with an orange teardrop-shaped body. The species is a specialized predator of the two-spotted spider mite and feeds on all stages of its prey, from egg to adult. The adult P. persimilis is a voracious eater, eating between 5 and 20 prey per day. It uses its sense of smell to find plants infected by spider mites. As soon as it comes into contact with spider mite webbing, it will intensify its search.

P. persimilis can be purchased from many biological control companies. It is often shipped in a glass vial or on trays of bean leaves. The easiest methodof application is to sprinkle about 20 adults on each plant. These predatory mites prefer to work their way up a plant, searching for food, so try to introduce them as low down as possible. In addition, if many plants are infected, keep them close together with their leaves touching so that these predators will be able to easily move from one plant to another.

Unlike the spider mite, P. persimilis prefers humid conditions. Misting will not only help it multiply, but will keep the spider mite population down as well. A relative humidity of 70 per cent is ideal for P. persimilis. Once its food supply is exhausted, the numbers of P. persimilis will decline as well.

Two-Spotted Spider Mite

Spider mites, also known as two-spotted mites, become a particular problem for the gardener through the winter. Normally, they hibernate in ground litter or under the bark of trees or shrubs. However, if they stowaway onto a plant being brought indoors, the artificial lights, and warm, dry, conditions of most heated homes will allow them to keep infecting plants.

The spider mite, Tetranychus urticae, is a tiny, 8-legged pest related to the spider & tick. Adults are normally green or yellow but turn red when day lengths shorten in the autumn. They attack plants by stabbing the underside of the leaves and sucking out the sap. This damage causes a distinctive stippling effect due to the loss of chlorophyll. As their numbers increase, the number of white speckles on the leaf increases and the leaf eventually dies. Once the spider mites begin reproduction, a distinctive `webbing’ forms, usually under the leaf and then at the growing tip of the plant.

What makes this pest truly difficult to control is its rate of reproduction. Each female will lay up to 12 eggs per day. Mating is not required for egg production. At 21°C, these eggs will hatch in as few as three days and will develop into adults in only 14 days. If left unchecked, 10 spider mites in May will become 100,000 by July!

Spider mites have been found in greenhouses across North America and Europe and are known to attack over 200 species of plants including azalea, camellia, citrus, evergreens, hollies, ligustrum, pittosporum, pyracantha, rose, and viburnum; fruit crops such as blackberries, blueberries and strawberries; vegetables including tomatoes, squash, eggplant, cucumber; and trees such as maple, elm, ash, black locust, and poplar.

Misting plants at least twice a day will keep spider mite numbers down. Populations can also be reduced by spraying the underside of the leaves with a jet of water to break up the webs and wash the mites off. Soap sprays are also very effective at controlling spider mites. The active ingredient, potassium or sodium salts of fatty acids, is not toxic and can safely be used indoors. A homemade spray can also be prepared using ordinary dishwashing detergent. Mix 5 tablespoons of detergent in 1 gallon of water and spray the plants, especially the underside of the leaves.

Resources
Cornell University Biological Control A guide to P. persimilis, the predatory mite

Illustrations by Davin Risk

Round 1: Lady Bugs

Known by many names, ladybird, ladybug or lady beetle, ladybugs are most welcome in the garden. They are recognized as one of the most beneficial garden insects.

Aphids are one of the major foods of all four thousand species of this metamorphosing insect. Ladybugs eat aphids whole as adults, and one ladybug may eat as many as five thousand in a lifetime. As youngsters they stab aphids with their mandibles (biting jaws) and suck out their juices, not unlike the way the aphid sucks sap from leaves. Ladybugs are often named after the number of spots on their wing covers. There is ten-spot ladybug, the six-spot ladybug etc. Their wing covers are most often red or orange with black spots, but variations include black with yellow or orange spots, yellow with black, orange with white or even orange yellow and black all in one. In times of danger, ladybugs are able to roll over and play dead. Their enemies don’t like to eat them because the joints in their bodies give off a fluid that tastes bad. Their bright colouring is said to warn birds of their awful taste.

Round 2: Aphids

Known by many names, aphid, green fly, and plant lice, this insect is probably the most despised of all garden pests. Most people recognize this insect and the damage it does well before they know what it is.

The aphididae family or aphid, is an insect that sucks the sap from the young leaves and buds of plants. There are many different species of aphid. Some only invade one type of plant, while others are less discerning. Either way, very few plants are impervious to some species of aphid. They can be identified as tiny, soft-bodied, pear shaped insects, which come in a rainbow of colours, green, yellow, black, grey, red, purple and brown. This variation in colour can be confusing to someone who is not familiar with them. Some have wings, while others are wingless. Most aphids have a pair of tube-like structures protruding from their abdomen called cornicles and a third projection from the tip of the abdomen called a cauda.

Differences between aphids are not just a result of variation among species, but are a result of the aphid’s peculiar lifecycle. In the Spring all of the aphids that hatch from over-wintered eggs are wingless females. These females are all born with the ability to reproduce live miniature offspring called nymphs, without the need to mate. As a result, they will rapidly reproduce all summer long. This is why it can sometimes appear that an infestation has taken place overnight. In the Fall, both males and females are produced which subsequently mate to create eggs for over-wintering. Some of these females have wings, while all of the males do.

Round 3: Ladybugs

That schoolyard myth that ladybugs have a spot for every year they’ve lived is untrue. Ladybugs metamorphose, and those that are long lived hibernate over one winter. Seeking shelter in protected spaces, such as under a layer of leaves in the woods, their body temperature lowers and they become inactive until spring. Post-hibernation, ladybugs mate and then females lay eggs in clusters. Over about four weeks, they will metamorphose and become adults. The tiny oval shaped yellow eggs hatch. The ladybugs emerge as larvae, feed for two or three weeks, then, attaching themselves to a leaf or stem, pupate (the structure of the larval body rearranging itself completely). A week later, they split open, shedding their exoskeletons, the familiar looking adult emerging and leaving the pupal shell behind. At first, their wing shells are yellow and soft: like butterflies, they must wait for their wings to dry. As they dry, they change colour. As larvae, they don’t yet need wings: aphids are in good supply because the momma ladybug has laid her eggs in strategic locations where aphids are plentiful. The larvae look like tiny, six-legged alligator-like crawlers, usually dark brown or black. Juvenile ladybug larvae are often crushed by well meaning gardeners: their bad looks get them mistaken for pests.

Ladybugs ‘mass’ together in huge groups for hibernation: sightings of colonies of hundreds of thousands have been reported. Scientific factsheets on this insect also tell of gathering places ladybugs return to year after year.

There are problems with purchasing and dispersing ladybugs though. Depending on when they are collected they may have less appetite and reproduce less, or they may disperse very quickly. Some gardeners even advocate glueing their lovely wings shut with a mixture of pop and water so they won’t leave the garden. It may be that species native to a place are better aphid-eaters than imports. Ladybugs can be attracted with flowers such as angelica and dill, and weeds like yarrow and dandelion (see aphids for more ladybug attracting plants).

Among others, these insects are also threatened by the use of pesticides. There aren’t always enough ladybugs around to control aphids, and if insecticides are used instead, the ‘good’ bugs are killed along with the ‘bad’. That means even fewer ladybugs the next year.

Historically speaking, there used to be a lot more home gardens. Maybe that’s why the ladybug is a symbol of good luck to many people. Because they have such an appetite for aphids, there presence is a good sign to gardeners.

Ladybugs have recently been involved in research on the effect of transgenic crops on beneficial insects. A Scottish study found that ladybugs that fed on aphids in turn fed on transgenic potatoes lived half as long and ate half as much.
Check it out if you like at “Pest Management at the Crossroads”

Round 4: Aphids

Aphids generally appear in clusters or groups on the stems and young leaves of plants. Sometimes large colonies will develop on the underside of leaves. The damage they do to plants includes mutations and stunted growth in the new foliage that often appear as curling in the leaves, and poor blooms on flowering plants. When aphids suck sap from plants they can’t metabolize all the sugar they ingest and secrete a sticky honeydew substance as a result. Black fungus called “sooty mould” grows on the honeydew secretions causing further damage to the plant leaves. Aphids also transmit virus diseases from plant to plant as a result of sucking sap from one plant and then moving to another plant, much as mosquitoes transmit diseases amongst humans.

The old adage that an ounce of prevention is worth a pound of cure applies well to organic gardening. One of the best environmentally sound ways to prevent aphids is to attract insects to your garden that like to eat them. There are several insects that will earn their keep, devouring aphids and keeping their populations in check. The most well known of these is the lady bug [see column to the right]. The lady bug larvae, as well as the adult insect are voracious aphid munchers, devouring thousands within their short lives. You can attract them to your garden by planting Queen Anne’s Lace, butterfly weed, tansy, and goldenrod. Many of these plants will attract other beneficial insects as well. Green lacewings, lacewing larvae (often called aphid lions), hover fly larvae, or parasitic wasps are all insects that specifically seek out aphids as prey. You can even purchase lady bugs if you would prefer a faster method of increasing the population of beneficial insects in your garden.

But what do you do if a colony is already invading your plants and you need to get rid of them now? The first and oldest method for removing aphids organically is by squishing them. It’s messy but it gets the job done if there are only a few insects present. The second manual method of removal is spraying them with a strong burst of water. This washes them off the plant and kills quite a few of them without any damage or harm to the plant. If you have a large colony developing, it might be a good idea to try something stronger. Insecticidal soap, is a foliar spray that can be purchased from Health food or environmental stores. The soap comes in concentrated form and can be added to a spray bottle with lots of water. Since the ratio of soap to water is small, the concentrate lasts a long time and is relatively economical. Insecticidal soap is relatively mild on your plants but you should still exercise caution when using it. Read the directions that come with the product before using. You can also make your own spray using water and citrus peel. The citrus harms the soft bodies of the aphids but won’t do any damage to your plants. Just steep some citrus peel (any kind) in hot water and pour the resulting “tea” into a spray bottle for use.

Hopefully with some of these suggestions, you will not only be able to identify this nasty critter when you see it, but have a successful plan of attack that you can put to good use.

Ladybug rounds written by Beate Schwirtlich
Aphid rounds written by Gayla Trail
Title illustration by Lorraine High
Insect illustrations by Davin Risk