Occurrence Patterns and Control Methods of the Azalea Lace Bug
The azalea lace bug (Stephanitis scotti) belongs to the order Hemiptera, family Tingidae. It is extremely widely distributed and is a major pest of azalea flowers. Its host plants are azaleas (Rhododendron spp.) and pieris (Pieris spp.), and it seriously affects the growth, reproduction and ornamental value of flowers in both genera.
1. Damage symptoms
The azalea lace bug mainly damages the leaves of host plants as nymphs and adults, sucking sap and excreting feces, causing the undersides of the leaves to appear rust-yellow and the upper surfaces to show needle-point-like white spots; in severe cases the entire leaf loses its green color and turns pale, affecting photosynthesis, causing the plant to grow slowly and drop its leaves early, and reducing its ornamental value.
2. Morphological characteristics
The adult is small and flat, about 3.4 mm long and about 2.0 mm wide, with a small, brown head and large, protruding compound eyes; the antennae have 4 segments, with the 3rd segment the longest; the pronotum is well developed, with reticulated markings, extending forward to cover the head and backward to cover the scutellum, with thin, rounded lateral carinae extending from both sides; the wings are membranous and transparent, with dark brown veins, and the forewings are covered with reticulated patterns, the two forewings joining in the middle to form a distinct "X" pattern; the female's abdomen is rounded and spindle-shaped; the male's abdomen is slender and elongate-oval. The egg is milky white, about 0.52 mm long and about 0.18 mm wide, banana-shaped, with a pouch-like opening at the top and a slightly curved end. The nymph has 5 instars; the mature nymph is flat, about 1.96 mm long and about 0.95 mm wide, with a well-developed pronotum, distinct wing pads, a dark brown body and well-developed red compound eyes. The head, thorax and abdomen all bear spine-like projections: 3 on the top of the head arranged in an isosceles triangle; 1 beside each compound eye; 2 pairs on the thoracic dorsum; and 1 each on the dorsum of abdominal segments 2, 4, 5 and 7.
3. Occurrence patterns
It has 7 to 10 generations per year, overwintering as adults and nymphs in dead branches and fallen leaves, weeds or the surface soil around the roots. If the climate is warm, overwintering is not obvious and its damage can be seen almost year-round. Each year in late March the overwintering adults and nymphs begin activity, and by mid-April the 1st-generation nymphs appear; the population is largest and the damage most severe from June to September. The egg stage lasts 7 to 15 days, the nymph stage 16 to 23 days, and one generation lasts an average of 28 to 30 days, with severe overlapping of generations. Newly hatched and newly molted nymphs are entirely snow-white, and the body color then gradually darkens. The nymphs are strongly gregarious and often cluster near the midrib and lateral veins on the undersides of leaves to feed. Newly emerged adults are pinkish-white and gradually turn dark brown after 2 hours; they are not good fliers, and can mate and lay eggs 2 days after emergence. Eggs are mostly laid in the leaf tissue beside the midrib on the underside of the host leaf, with a few laid on the marginal veins and midrib, and are covered on the outside with a brown gelatinous substance. Hot, dry weather is most favorable for the occurrence of this insect.
4. Control methods
4.1 Manual capture and killing
Because it is gregarious and is not toxic to humans, when only a small number of pests occur on potted azaleas they can be crushed by hand.
4.2 Horticultural measures
Dead branches, fallen leaves and weeds in the nursery are all places where it lurks and overwinters. Clearing fallen leaves in late autumn and timely cultivating and weeding can eliminate a large number of overwintering sources; choosing pest-free seedlings for planting can also reduce the occurrence of the pest.
4.3 Chemical control
When the pest occurs severely, chemical control is a fast and effective method. Spray with 10% cypermethrin emulsifiable concentrate at 1000 times dilution, or 40% omethoate emulsifiable concentrate or 50% fenitrothion emulsifiable concentrate at 2000 times dilution, 2.5% cyhalothrin emulsifiable concentrate at 2500 to 3000 times dilution, or 10% imidacloprid wettable powder at 1500 times dilution; the various chemicals should be used alternately, with good control results.
4.4 Protect and utilize natural enemies
The natural enemies of the azalea lace bug include green lacewings, spiders and ants, among which the green lacewing is the dominant species. With 4 to 5 green lacewings on a single potted azalea, the pest population density can be reduced and no control is needed. Therefore, when the pest occurs, attention should be paid to surveying the species and number of natural enemies; if predatory natural enemies such as green lacewings are found, pesticides should be used sparingly or not at all, so as to protect the natural enemies and keep the pest outbreak under control.