Two-spotted spider mite

Description

Two-spotted spider mites suck the contents of plant cells, causing bleached, stippled or otherwise discolored foliage. They also make silken strands on plant parts, especially when populations are high. The mites have globular bodies that are 1⁄50 inch (0.5 mm) or less in diameter. Adults have two dark blotches on the body and overall coloration that varies from gray to green or yellowish. Overwintering females may turn pink to orange during fall to early spring.

Lifecyle

Spider mites develop through five life stages. Females lay round eggs that hatch into six-legged larvae. Larvae develop into eight-legged protonymphs, then deutonymphs and then adults. Spider mites have many generations per year, and their abundance can increase rapidly when temperatures are warm. Egg to adult development takes five to 20 days, depending on temperatures.

Host plants

Two-spotted spider mites can feed on more than 300 different species of plants. Greenhouse ornamental hosts include dracaena spikes, ivy geraniums, New Guinea impatiens, impatiens, hydrangea, sweet potato vine, marigolds, poinsettias, vinca, verbena and viola. Many herbaceous perennials including hollyhock, monarda, columbine, daylily, butterfly bush, primula, scabiosa, verbena and salvia are also prone to mites. Herbs such as lemon balm, lemon verbena, lemon grass, oregano and mints can also be favored hosts. Greenhouse vegetables including cucumbers, tomatoes and beans are susceptible to mites. Weeds such as chickweed, oxalis, pigweed and henbit found in and around greenhouses can be sources of continuing infestations.

Damage

Two-spotted mite feeding initially causes tiny, pale specks (stippling) on leaves. As feeding continues foliage can become pale green, yellowish, or whitish in large patches. Leaves may eventually turn brownish in large patches or overall and drop prematurely. Their pale cast skins and webbing may be visible on the underside of leaves where mites generally feed. This also reduces crop aesthetic quality. Plants may grow slowly or remain undersized if heavily infested. Plants that are severely infested when young may die.

Photos courtesy of Cornell University and USDA

Description

Adult broad mites are almost microscopic (less than 0.2 mm long). They are translucent and colorless to pale brown. There are four pairs of legs; the last pair in the female ends in a long hair; the last pair on the male ends in a strong claw. The egg is elliptical, translucent, colorless, about 0.08 mm long and is covered by 29 to 37 whitish bumps. Larvae have three pairs of legs and are whitish due to minute ridges on the skin. They are about 0.1 mm long.

Lifecycle

Female broad mites lay 30 to 76 eggs on the leaf surface over an 8- to 13-day oviposition period. Unmated females lay male eggs; mated females usually lay four female eggs for every male egg. The larvae hatch in two or three days and emerge from the egg to feed. Larvae are slow moving and do not disperse far. In two or three days, the larvae develop into a quiescent larval stage. Quiescent female larvae become attractive to the males which pick them up and carry them to the new foliage. Males and females are very active, but the males apparently account for much of the dispersal of a broad mite population in their frenzy to carry the quiescent female larvae to new leaves. When females emerge from the quiescent stage, males immediately mate with them. Males live five to nine days; females live eight to 13 days.

Host plants

Broad mites infest African violet, ageratum, azalea, begonia, dahlia, gerbera, gloxinia, ivy, jasmine, impatiens, lantana, marigold, peperomia, snapdragon, verbena and zinnia.

Damage

Leaves curl downward and turn copper or purplish. Internodes shorten and lateral buds break more than normal. This new growth may also be stunted or killed, which forces out additional shoots. Flowers are distorted and fail to open normally. Unless controlled, broad mites usually destroy the commercial value of infested ornamental crops.

Description

The adult female mite is yellowish brown, with hind legs reduced to slender threadlike structures. The male is approximately 75% the size of the female. On the adult males the fourth pair of legs is modified and used to transport the pupae or adult females.

The eggs are elliptical, opaque, smooth and nearly twice as long as wide. The larvae are opaque white with a peculiar triangular enlargement at the posterior end of the body. The pupae are non-motile.

They are sometimes confused with the broad mite but that pest is broader, smaller and moves much faster.

Lifecycle

One to three eggs are laid per day in clusters, with a total of 12 to 16 eggs per life span. The duration of the egg stage is three to seven days, one to four days for the larvae, two to seven days for resting pupae or one to three weeks per generation.

Host plants

Cyclamen, African violet, begonia, gerbera, ivy, chrysanthemum, geranium, fuchsia, larkspur, petunia, snapdragon and other greenhouse grown plants. 

Damage

Infested plants may have a streaked and/or blotched appearance, distorted leaves with small, distorted flowers, fewer flowers than normal, or complete abortion of flower buds. Also look for irregular folding of leaves, thickening of leaves or shortening of petioles.

Description

Lewis mites are approximately 0.3 mm in length at mature size and range from green to yellowish in color as immatures, but develop to a light orangish color as they mature. Unlike two-spotted spider mites, Lewis mites lack the (proportionally) large, dark-colored spots on their abdomen. Due to their size, magnification is necessary to scout for Lewis mites effectively.

Eggs start off clear in color but develop to a milky white color before they hatch.

Lifecycle

Lewis mites have one larval and two nymphal stages before they mature into adults. They can complete their life cycle in about 14 days at an average daily temperature of around 77° F. Adults lay 60 to 90 eggs per month. The comparatively slow life cycle of Lewis mites contributes to why populations often go undetected until crops are mature.

Host plants

Primarily poinsettia.

Damage

Lewis mites tend to congregate along leaf veins or edges as populations grow. Eggs are laid on the undersides of leaves. Stippling damage caused by Lewis mites is often faint in the early stages of an outbreak and mimics mild chlorosis in poinsettias. Since feeding is frequently concentrated along veins as populations grow, many growers mistake these symptoms for mineral nutrient deficiency symptoms. Once populations reach a critical mass, webbing is visible, and damage is severe, affected plants may be unsalable.

Photos courtesy of Cornell, University of California and Washington State University

Description

Bulb mites are 1⁄50 to 1⁄25 inch long with eight legs. They are shiny white to translucent with two brown spots on their body, with short reddish-orange legs. These extremely small, slow-moving mites are usually found in clusters underneath bulb scales or at the base of the bulb.

Lifecycle

Each female bulb mite lays up to 100 eggs during her lifespan. The life cycle takes up to 40 days to complete depending upon relative humidity, temperature and host plant. For example, at 77° F, the life cycle takes approximately 12 days. They do not undergo a resting stage or diapause.

Host plants

Amaryllis, crocus, freesia, gladiolus, hyacinth, lily, Dutch iris, narcissus and tulip, as well as garlic and onion bulbs.

Damage

Visible signs of damage are typically not apparent until bulb mite populations are extensive. Infested bulbs may rot with new growth stunted and distorted. Bulb mites are secondary pests commonly associated with bulbs already injured from fungus gnat larvae and/or root rot pathogens. They infest bulbs and corms by penetrating the basal plate or outer skin layers. Infested bulbs decay and turn rotten. Bulb mites may feed in Easter lily stems causing the stems to become brittle. Infested lilies are shorter with fewer stem roots. Look for stunting with low mite populations to failure of bulbs to produce new growth with heavy infestations. Leaves will be stunted, distorted and turn yellow. Flowers will not develop. Infested bulbs show reddish-brown discoloration and may rot after planting.

Sources: University of Florida, University of California Agriculture and Natural Resources, University of Minnesota, University of Connecticut, University of Kentucky, Ball Seed