Which kinds of aphids are harmful to pear trees?

The main aphids harming pear trees are pear bifurcation aphid, pear yellow powder aphid and pear original tail aphid. These three kinds of aphids only harm pear trees, the occurrence of two aphids and yellow powder aphids are common and serious, and the original tail aphids rarely occur and the damage is mild. The morphological differences are as follows: (1) pear aphid: ① wingless female aphid is 2 mm long, green or dark green, covered with white wax powder. The compound eyes are reddish brown; the ends of antennae, tail, ventral canal, feet and legs, tibia and accessory segments are all black; there is a dark green longitudinal band in the center of the back. The length of ② winged female aphid is 1.5ml 1.7mm, and the wingspan is about 5mm. The head, chest, antennae and abdominal canal are light black; the abdomen is light brown or yellowish brown with brown markings. The midrib of the forewing is divided into two forks, hence the name of the aphid. The nymph of ③ is small, green and wingless, similar to the wingless female aphid. ④ eggs are about 0.7mm long, oval, black and glossy. (2) Pear yellow powder aphid: ① pear yellow powder aphid is a polymorphic aphid, which can be divided into four types: dry mother, common type, sexual mother and sexual type. The dry mother, common type and sexual mother are all female. Body length 0.7-0.8 mm, wingless, bright yellow, glossy, long oval. No ventral tube, no tail. ② overwintering eggs (hatched as dry mothers), about 0.33mm long, yellowish. The egg that produces the common type and sexual mother, with a body length of 0.26-0.3 mm, is initially yellowish and gradually changes to yellowish green. Produce sexual eggs, 0.36-0.42 mm in length, yellowish green. The ③ nymph is yellowish and resembles an adult, but it is small. (3) the original tail aphid of pear; the winged female aphid has black head and chest, green or yellowish green abdomen, short abdominal tube and short and round tail. Wingless viviparous female aphid, green or light brown, with a short ventral tube and a short round tail.