(Heteroptera: Miridae)

Two species of plant bugs are common pasta in Manitoba: i.e., the alfalfa plant bug, Adelphocoris lineolatus, and the tarnished plant bug, Lygus lineolaris. The tarnished plant bug is representative of a group of plant bugs, called lygus bugs. There are several species in Manitoba, including Lygus borealis and Lygus desertinus. This IPM profile only discusses the first 2 species but much of what is given is also applicable to other lygus bugs.

Adult lygus are about 5 mm long and 2.5 mm wide. They vary in color from pale green to reddish-brown and have a distinct triangle or "V" mark about one-third of the distance down the back, just in front of the wings. Legs and antennae are relatively long. Eggs are slightly curved and approximately 1mm long. Young nymphs are blue-green in color, and look like aphids but are more active. Color in the older nymphs becomes more variable and is similar to that of the adults. Nymphs develop prominent black dots on the top of the thorax and abdomen. There are five nymphal instars.

Like other hemipterans, the alfalfa plant bug is soft-bodied, has a half-membranous forewing and sucking mouthparts. A cuneus is present and 1 or 2 cells are present at the base of the membrane. It has a 4-segmented beak, 3-segmented tarsi and no ocelli.

Adelphocoris lineolatus adults are 7-9 mm long and 2.5-3 mm wide (Lygus bugs are only about half this length). Pale greenish-yellow in color, they are tinged with brown. The bases of the antennae are yellowish-brown whereas the apical portions are reddish-brown. The legs are yellowish-brown to dusky-brown and covered with black spots.

The nymphs are pale green to light brown, dotted with short, black hairs. Although they resemble the adults, they have wing pads rather than complete wings.

Tarnished plant bugs are common pests of fruits and vegetables, feeding on the foliage, shoots and fruits of host plants. It is the most important lygus bug on the Canadian prairies.

The adult tarnished plant bug, Lygus lineolaris, is a small, ovoid bug, about 6 mm in length. It is straw-green to dark brown in color, mottled with yellow, reddish-brown and black, A small, triangular, black dot is present at the tip of the cuneus.

The newly-hatched nymphs are small (about 1 mm long) and yellowish-green in color. They are distinguished from similar species by the presence of 3 black dots (2 on the thorax and 1 on the first abdominal segment).

1. Geographical Distribution:

Introduced from Europe, the alfalfa plant bug was found in Nova Scotia in 1917 and in the U.S.A. in

1929. It now occurs throughout the alfalfa-growing areas of North America. This species now, occurs across southern Canada (except British Columbia) and throughout the U.S.A. It is the main post of alfalfa seed crops.

The tarnished plant bug is found across southern Canada and throughout the U.S.A.

These insects are usually associated with alfalfa fields where they feed on their hosts.

The life stages of these bugs are found in or near their host plants.

General feeders, plant bugs may be found on most herbaceous plants. Host plants include weeds (e.g.,flixweed, kochia, lamb's quarters, mustard, Russian knapweed, and Russian thistle), flowers, forage crops (e.g., alfalfa, red clover), oil seed crops (e.g., canola, mustard), vegetables and various fruits (e.g.,strawberries), trees and shrubs.

The alfalfa plant bug has been reported to feed on weeds (e.g., ), alfalfa, red clover and sweet clover. Like the tarnished plant bug, the alfalfa plant bug is a pest of cotton in the southern U.S.A.

Tarnished plant bugs feed on weeds (e.g., chickweed, dandelion, red clover, red root pigweed, lambs quarters, plantain, golden rod, asters), flowers (e.g., dahlias, asters, chrysanthemums, daisies, gladioli, marigolds, poppies, zinnia), forage crops (e.g., red clover, alfalfa), oil seed crops (e.g., canola, mustard, sunflower), vegetables (e.g., asparagus, beans, beets, cabbage, cauliflower, celery, chard, cucumbers, peppers, potatoes, tobacco, tomatoes, turnips) and fruits (e.g., strawberries, apples, apricots, peaches, pears).

In the U.S.A., the tarnished plant bug is a post of cotton, among other crops.

Plant bugs overwinter in plant debris in such protected locations as fence-lines, roadside ditches, hedgerows and wooded areas. The adults resume their activities in the spring, feeding on early-developing plants. They mate and disperse into crops where they lay their eggs and continue feeding (from mid-May to mid-June, depending upon weather and location).

Eggs are slightly curved and about 1 mm long. Each egg is inserted individually into the hollow stems and leaf midribs or petioles of host plants. Egg-laying may continue into early July. Hatching usually occurs from late-May through mid-July.

Development from egg to adult usually takes about 45 days. There are 5 nymphal moults. There are 2 generations per year in the southern prairies. Late in the summer, the adults move out of the fields into their overwintering sites.

Alfalfa plant bugs overwinter as eggs that have been deposited in alfalfa stems. The yellow eggs are slightly curved with a cap sticking out of the stem. In the spring, the eggs hatch. They start to hatch about the end of May and are usually all hatched by the middle of June when alfalfa is coming into flower bud. The nymphs feed during June and July, moulting 5 times and maturing in 16-30 days. The resulting adults feed, mate and lay eggs in the hollow stems of growing alfalfa during the rest of the summer.

The adults overwinter, hidden in protective hedgerows, fallen leaves and other plant debris. Emerging in the spring (mid-April to late-May), they feed on host weeds. The eggs are laid on the stems and petioles of host weeds. About 10 days later, the eggs hatch and the nymphs feed. The nymphs moult 5 times before becoming adults.

The 1st-generation adults appear in mid-June to mid-July. They leave the host weeds, dispersing into adjacent crops. The second generation nymphs feed on the host plants, causing economic damage. The adults produced by this generation emerge in late-August and September. A smaller 3rd generation emerges in September and these adults overwinter.

In the U.S.A., tarnished plant bugs have 3 generations in the north and 5 generations in the south.

1. Seasonal Abundance:

There is usually 1 generation per year in the prairies. How, nymphs of a second generation may sometimes be found in late-August or September. Some eggs lay before mid-July may hatch and yield nymphs.

Hot, dry weather tends to cause a build-up in their population, increasing the likelihood of early-growth damage to the host crop.

Hot dry weather favors build-up of lygus populations and increases the possibility of damage to early growth.

Nothing was found in the available literature on the effects of weather on this species.

When weed growth conditions are good in June and July, fewer adults leave the weed hosts, reducing damage to adjacent crops. When drought conditions occur, these bugs readily leave the weed hosts and move on to crops.

Lygus bugs have piercing-sucking mouth parts and physically damage the plants by puncturing the tissue and sucking, plant juices. The plants also react to the toxic saliva that the insects inject when they feed.

In alfalfa, these bugs cause short stem internodes, excessive branching and small, distorted leaves. Feeding on the buds and blossoms cause these to drop. Feeding on the seeds in the pods causes the seeds to shrivel and turn brown.

In Manitoba, where there are about 8500 ha of alfalfa grow for seed and about 3.5 million kg of seed produced, damage due to plant bugs is very important.

Similar damage is seen in canola crops. Adult plant bugs may invade the fields during the early bud stage. The nymphs may appear at the flowering stage. Nymphs and adults may feed on the buds, flowers and seeds of canola plants. Puncture marks in the pods are visible and sometimes a small drop of plant juice exudes from the wound. Often, damage in canola fields is not noticed until swathing. Seed production may be reduced by about 10-15% in heavily-infested fields.

This species is the main insect past of alfalfa seed crops. Like other mirids, the alfalfa plant bug feeds by inserting its needle-like mouth-parts into the plant tissue and sucking up the plant juice. Feeding damage ultimately results in lowered seed production and quality. Alfalfa plant bugs attack alfalfa blossom buds, causing the buds to shrivel, turn greyish-white and die (lygus bugs usually attack later, feeding on blossoms and young seeds).

The second generation adults, emerging in June and July, cause most of the damage. They feed by sucking plant sap. As they feed, a toxic saliva is introduced into the plant, causing distortion, drop of terminal buds, wilting, stunting and die-back.

First generation injury may occur to crops when nymphs feed on buds after pollination or when adults feed on fast-growing terminal shoots and developing fruit during June and July. Damage is often highest on the edges of crops.

Damage to tree fruit crops may be intensified when weather conditions are unfavourable for weed hosts during June and July. The situation is further aggravated because fruit thinning has already been done, lowering the threshold for injury. These pests cause pitting or scabbing of apples and pears and "catfacing" of peaches and apricots.

Fruit crop losses vary from location to location and species o species. Peach fruit damage may reach 75%; asparagus damage may reach 22%.Heavily-infested alfalfa fields blossom normally but drop their flowers prematurely and developing seeds shrivel and fail to mature.

Natural enemies include damsel bugs, bigeyed bugs, ladybird beetles, lace wings, minute pirate bugs and spiders.

Tarnished plant bugs, like other species of Lygus, are attacked by damsel bugs, bigeyed bugs, and ants. Eggs may be parasitized by scelionid and mymarid wasps (Sohati et al., 1989).

Early monitoring of fields is important if damage is to be minimized. It is easily done using a standard, insect sweep net, being sure to sample throughout the field on a regular basis, starting at the bud stage.

Symptoms of damage by the alfalfa plant bug include the following: i.e.,

• poor blooming.

• blasted, whitish and dry flower buds.

• dropping of flowers before they are fully open.
• poor seed set and shrivelled seed at harvest.
• yellowing of the plant.

• excessive branch stemming.

• smaller, more numerous and distorted leaves.

Cultural controls include burning alfalfa stubble and straw in the spring before regrowth begins to destroy overwintering eggs. Weed control may help to reduce local populations.

Crop management is the most important method of control. Reducing adjacent weedy areas that serve as overwintering sites for the adults and weeds in crops that serve as early season hosts will lower local populations.

Burning alfalfa stubble and debris in the spring before any growth begins will control all plant bug

species that overwinter as eggs but not the lygus bug or the tarnished plant bug which overwinter as adults outside alfalfa fields.

Tarnished plant bugs can be controlled in ornamental plantings by removal of weeds and keeping lawns or grassy areas mowed to eliminate breeding sites.

Because plant bugs have 2 generations throughout most of their range in the southern prairies, 2 chemical treatments may be necessary.

Spraying should be done in the very early flower bud stage. In pedigreed alfalfa fields, spraying has to be done before alfalfa leaf cutter bees (i.e., Megachile rotunda) are placed in the field in most cases. Even when insecticides are used that are relatively harmless to the leaf cutter bees, spraying must still be done in the evening or early morning to minimize any possible bee kill.

In burned fields, insecticides are applied as the crop is coming into bloom to control other pests (e.g., lygus bugs); in unburned fields, insecticides are applied as the crop is coming into bud.

Insecticides registered for the control of the alfalfa plant bug include the following (the residue hazards, in days, to bees is given in brackets): i.e.,

• Dimethoate (Cygon).
• Trichlorfon (Dylox).

• Methidathion (Supracide).

• Deltamethrin (Decis).

Peripheral insecticide treatments are all that are usually required for the control of this insect pest. The field or orchard margins will usually contain the majority of these bugs. Various insecticides are registered for the control of the tarnished plant bug on different agricultural crops.

In alfalfa grown for forage, trichlorfon (e.g., Dylox 420 L [1.1- 1/acre]) is applied after planting, between the first and third cutting, to control the tarnished plant bull (and other plant and stink bugs). There is a 14-day pre-harvest interval.

In alfalfa grown for seed, dimethoate (e.g., Cygon 480 EC) is usually applied when the alfalfa is just beginning to produce flower buds or just before bloom. It must be applied at least 7 days before putting bees in the field.

In canola, spraying is best done at 'post-petal fall' to minimize the effects of the insecticide on pollinators. However, Dylox is the only insecticide registered specifically for lygus bugs on canola. Dylox 420 L may be applied only in the evening or early morning to crops in bloom.

Insecticides commonly used for the control of tarnished plant bugs on canola are given below: i.e.,

Deltamethrin.... 10 -

Dimethoate...... 560 28

Methidathion.... 280-560 10

Trichlorfon ..... 1155 14

In burned fields for control of lygus bugs, apply dimethoate, methidathion or deltamethrin just before the alfalfa begins to bloom. Wait 7 days after applying dimethoate or methidathion and wait 1 full day after applying deltamethrin, before putting or replacing leaf cutter bees on the crop.

In unburned fields for control of all plant bugs, apply dimethoate or methidathion when flower-buds are beginning to form.

If the alfalfa is in bloom and bees are in the crop, apply trichlorfon in late evening, when bees are not foraging.

In potato crops, permethrin (i.e., Ambush [ 0.06-0.08 1/acre), Pounce [0.075-0.11 1/acre]) can be used to control tarnished plant bugs, using air or ground equipment. There is a 1-day pre-harvest interval. Observe a 30 m setback distance for ground and 100 m setback distance by air near water bodies or other sensitive areas. Permethrin has a low acute mammalian toxicity. Very toxic to bees and fish. Do not contaminate ponds, lakes or streams during sprayer filling or while spraying. Avoid spraying when bees are foraging.

Chlorpyrifos (e.g., Lorsban 4E [0.405 1/acre]) is also registered for the control of tarnished plant bugs on potatoes. There is a 7-day pre-harvest interval.

Cypermethrin (e.g., Cymbush [0.08 1/acre] and Ripcord (0.025-0.05 1/acre]) is also registered for the control of tarnished plant bugs on potatoes. There is a 7-day pre-harvest interval.