What are the control methods for the jujube gall midge, a pest of jujube trees?

Jujube gall midge (Contarinia sp.)

(1) Aliases and taxonomic status: jujube bud maggot, leaf-rolling maggot, jujube maggot, belonging to Diptera, Cecidomyiidae.

(2) Distribution: This insect is distributed in all jujube-growing areas across the country, with the five major jujube areas of Shandong, Shanxi, Henan, Hebei and Shaanxi suffering the most severe damage; it is one of the main pests of jujube leaves.

(3) Damage characteristics: The larvae suck the sap of young jujube leaves to cause damage. The female adult of the jujube gall midge lays eggs in the gaps of unexpanded young leaves; after the larvae hatch, they suck the sap of the young leaves, and after the leaves are stimulated, both sides roll lengthwise, with the larvae hiding inside to cause damage. After being damaged, the leaves become tube-shaped, and the young tender leaves turn purplish red in color, hard and brittle in texture, and soon turn black and wither. Generally, seedlings in nursery land and young trees suffer heavier damage.

(4) Morphological characteristics

Adult: The adult body resembles a mosquito, orange-red or grayish brown, with black, kidney-shaped compound eyes, a grayish brown head and thorax, and grayish black, moniliform antennae, with a black raised back. The abdomen and back of the thorax have 3

dark brown patches, the forewings are semi-transparent, oval, the hindwings are degenerated into halteres, and there are 3 pairs of legs. The female has a large abdomen, with the ventral surface yellow-white or orange-yellow, 8 segments in total, and the dorsum of segments 1-5 has reddish brown bands. The male is smaller in body, grayish yellow, with narrow and long abdominal segments, 9 segments in total. The antennae are well developed, longer than half the body, and the external genitalia are gray. They are formed by the basal segment and the terminal segment of the gonopods, nearly ring-shaped, and the end of the aedeagus is shaped like the character "shan" (mountain).

Egg: Nearly long conical, semi-transparent, glossy, slightly narrow at one end; newly laid eggs are white, later turning red.

Larva: Milky white, maggot-shaped, legless, with distinct body segments.

Pupa: A naked pupa, spindle-shaped, initially milky white, later turning yellow-brown. In the female pupa, the legs are shorter than the abdominal segments. In the male pupa, the legs reach the end of the abdomen.

Cocoon: Long oval, grayish white, with soil particles attached outside.

(5) Occurrence habits: In the jujube areas of North China, this insect has 5-7 generations a year, overwintering as mature larvae in cocoons in shallow soil. In April of the following year, adults emerge and lay eggs on newly sprouting jujube buds. Early May is the peak damage period. The peak occurrence periods of the 1st-4th generation larvae are respectively: early June, late June, mid-to-late July, and early-to-mid August. In mid-August, the 5th generation larvae begin to appear. Apart from the overwintering larvae, the average larval stage and pupal stage are 10 days. The depth at which overwintering larval cocoons enter the soil varies with soil type: in loess soil, mostly 2-3 cm below the ground surface, while in sandy soil, 3-5 cm. The most suitable development temperature is 23-27°C. In addition, in May, if there is drought and little rain, the occurrence of this insect is relatively late.

(6) Forecasting and prediction: The method of predicting the emergence of overwintering larvae from the soil can be used. Bury a certain number of jujube gall midge cocoons in the soil layer 2-3 cm deep under the tree canopy, cover them with a cage, and from early April onward, check the number of emerged larvae daily. When emerged larvae reach 50%, this is the control period for this insect, and from this period the peak occurrence period of the first generation larvae can be calculated.

(7) Control methods

① Agricultural control measures: In combination with winter management of jujube trees, dig around the tree base to eliminate overwintering cocoons.

② Chemical control: Before the overwintering adults emerge or before mature larvae enter the soil, carry out ground sealing, and spray 50% phoxim at 300 times under the tree canopy; after spraying, shallow rake to kill emerged larvae or mature larvae. For canopy spraying control, during the peak damage period of larvae, spray 50% omethoate at 1500 times + pyrethroid pesticides at 2000-3000 times, etc., all of which can achieve good control effects.