Identification and Control Methods for Cotton Aphid Infestation in Orchids

Cotton aphid Aphis gossypii Glover, also called melon aphid, belongs to Homoptera, Aphididae, commonly known as honey aphid, oil insect, oil sweat, etc. The cotton aphid is a worldwide pest and is also distributed throughout China, with the degree of damage varying by region. In the north, outbreaks are generally more severe, followed by the Yangtze River basin, and in the south, damage is also very serious in dry years. It has many host species, and on flowers it damages hibiscus, roselle, rose of Sharon,orchids, pomegranate, redbud, plum and plum, etc. Cotton aphid adults and nymphs cluster densely on tender shoots, flower buds and leaf undersides, sucking sap, causing the leaf undersides to shrivel and affecting flowering. Morphological characteristics: Wingless parthenogenetic female aphid: body length 1.5-1.8 mm, yellow-green in summer, dark green to blue-black in spring, with markings on the back, the whole body covered with wax powder, antennae with 6 segments, only the tip of the fifth segment having one sensorium, cornicles short, cylindrical, broader at the base, cauda nipple-shaped. Winged parthenogenetic female aphid: body length 1.2-1.7 mm, body yellow in summer, or green to dark green, blue-black in autumn, with 3-4 pairs of black spots on both sides of the back, antennae with 6 segments, longer than the body, the third segment with 4-10 sensoria, generally 6-7, almost arranged in a row, the fourth segment with 0-2 sensoria, near the tip of the fifth segment with one sensorium, cornicles cylindrical, black, with tile-like striations on the surface. Winged parthenogenetic male aphid: body length about 1.4 mm, head grayish-black, compound eyes reddish-brown, antennae with 6 segments, sensoria born on the 3rd, 4th and 5th segments. Egg: oval, length 0.5-0.6 mm, orange-yellow when newly laid, later turning dark brown, and pitch-black after 6 days. Occurrence pattern: more than 20 generations occur per year, overwintering as eggs on branches of hibiscus, rose of Sharon, pomegranate, etc., hatching at 11°C, first damaging the overwintering hosts, and after 3-4 generations producing winged migrant aphids, beginning to damage flowers in March-April, and in September and October producing winged migrant aphids that fly to overwintering hosts such as rose of Sharon to continue reproducing and damaging, and when the weather turns cold in November, producing winged male aphids and wingless female aphids, which mate and lay eggs. Cotton aphids are generally viviparous, and only produce egg-laying female aphids before overwintering. In addition to migration by winged aphids, aphids also have strong crawling ability. The optimum temperature for cotton aphid reproduction is 16-22°C; when the temperature is above 25-27°C and the relative humidity is above 75%, the population often declines significantly. When the climate is suitable, one generation can be reproduced in 4-5 days, and the reproductive capacity is large, with each female aphid producing an average of 5 young aphids. When the weather is cold, it takes 19 days to reproduce one generation, and continuous heavy rain can often cause a marked decline in the cotton aphid population. Control methods: 1. Protect and utilize natural enemies; natural enemies such as ladybugs and lacewings can already be mass-reared artificially and then released. 2. Clear overwintering hosts around orchid gardens such as chrysanthemums to eliminate overwintering eggs. 3. 3% pyrethrin, 2.5% derris extract, 800-1200 times dilution, 20% fenvalerate emulsifiable concentrate 3000 times dilution, 2.5% fenpropathrin emulsifiable concentrate 2000-3000 times dilution. 40% dimethoate emulsifiable concentrate 1000 times dilution spray. Liu Zhongjian