Methods for controlling thrips pests and diseases in mango cultivation
Classification: Thysanoptera, family Thripidae.
I. Tea yellow thrips Scirtothrips dorsalis Hood
1. Damage
Adults and nymphs damage mango leaves, causing them to appear scalded by hot water and eventually wilt; they damage fruit, causing brown rough spots on the surface. This insect also damages tea plants, bananas and other crops.
2. Morphological characteristics
The adult body is about 1.0 mm long, yellow, with narrow, long, grayish-transparent wings bearing many fine hairs along the margins; the head width is about 1.8 times its length; the compound eyes are grayish-black and slightly protruding; there are 3 bright red ocelli; the antennae have 8 segments and are about 3 times the head length; the pronotum width is 1.5 times its length, with 1 pair of thick short spines at the posterior angles.
The egg is pale yellow and kidney-shaped.
The newly hatched nymph is milky white, later turning pale yellow, and resembles the adult in form.
3. Life habits
The number of generations per year is unknown. When temperatures are high, 1 generation can be completed in just over 10 days. Both adults and nymphs can damage leaves and fruit; damaged leaves become lighter in color, appearing scalded by hot water, with up to 19 insects on a single leaf; damaged fruit shows brown linear streaks or mottling on the surface, making the fruit surface rough and reducing its commercial value. This insect begins damaging mango fruit when the fruit is the size of a soybean; normally the insect hides under the sepals. In severe cases, it can cause small fruit to dry up, and the surface of damaged small fruit shows brown lines (spots); as the small fruit grows, these lines (spots) also grow longer and thicker, and by the time the fruit matures the surface becomes rough.
4. Control methods
When this insect is found causing damage, spray 80% dichlorvos or 40% dimethoate at 2000 times dilution, or 20% fenvalerate or 2.5% deltamethrin at 4000 times dilution. In severe cases, spray once every 7 days for 3 consecutive sprays.
II. Red-banded thrips Selenothrips rubrocinctus (Giard)
1. Damage
Adults and nymphs damage the leaves of young mango seedlings, causing numerous dirty black spots, blackened leaf tips, curled leaf margins, and eventually complete defoliation and death of the whole plant; this insect also excretes a red liquid onto the leaves, which after drying appears as rust-brown or shiny black spots, affecting photosynthesis. This insect also damages rubber, coffee, cashew, lychee, longan, citrus and other crops.
2. Morphological characteristics
The adult is elongated, dark brown, with a body length of 1.0-1.5 mm; the wing margins have dense fringe hairs and are grayish-black.
The egg is kidney-shaped, yellowish-white, about 0.25 mm long.
The nymph is elongated, yellow, with a band of bright red at the base of the abdomen; when fully grown, the body length is about 1.0 mm.
The pupa is elongated, about 1.0 mm long, similar in form to the nymph but with fully developed wing pads.
3. Life habits
About 10 generations occur per year. The female adult reproduces by parthenogenesis, laying eggs singly on the lower leaf surface, each with a drop of feces-like material; the egg stage lasts 1-3 days, and the pupal stage 6 days. Adults and nymphs mostly live in depressions near the main vein or in small grooves, often with the tip of the abdomen raised and bearing a spherical droplet at the end.
4. Control methods
When an outbreak occurs, spray 40% dimethoate or 50% fenitrothion or 80% dichlorvos at 1500 times dilution for control.