Occurrence and Control of the Jujube Tree Pests Giant Mealybug and Jujube Bud Mite

Occurrence and Control of the Jujube Tree Pests Giant Mealybug and Jujube Bud Mite

1 Giant Mealybug

Belongs to the order Homoptera, family Margarodidae, and is a pest of jujube trees, also known as tree louse and straw-sandal insect. It is widely distributed in China, found in Hebei, Shanxi, Shandong, Shaanxi, Henan and other provinces (regions). In early spring the nymphs gather on young shoots and buds to suck sap, causing bud death, tree decline, and heavy flower and fruit drop.

1.1 Morphological characteristics. The egg is oval, light yellow when first laid, later turning brown. The nymph resembles the female adult, but is smaller and darker in color. The male pupa is cylindrical, brownish red, about 5 mm long, covered with a white cotton-like substance. The female is wingless, flat-oval, about 10 mm long, resembling a straw sandal, reddish brown, covered with white waxy powder. The antennae are filiform and black. The legs are black. The mouthparts are dark brown, situated between the front legs. The male is purplish red, 5-6 mm long, with a wingspan of 10 mm. It has 1 pair of wings, pale black, and spherical compound eyes, black.

1.2 Ecological habits. This insect overwinters as eggs in the soil. In early spring of the following year, as the temperature rises, the eggs hatch into nymphs. At first the nymphs remain inside the egg capsule; when the sap begins to flow, the nymphs break out of the capsule, emerge from the soil and climb up the trees. March is the peak period of emergence. The nymphs are mostly active around midday when the temperature is high, climbing up the trees to suck sap. After the nymphs' first molt in early April, the body enlarges and secretes waxy powder. After the nymphs' third molt in April-May, the male nymphs pupate in bark crevices and tree holes; the male adults emerge about 10 d later, and the female nymphs reach sexual maturity after three molts. After mating, the male adults die. In May-June the females descend the trees and burrow into the soil at a depth of 5-7 cm, where they secrete a white cottony egg capsule and lay eggs inside it, spending the summer and winter there.

1.3 Control methods. First, manual control. Carry out good field land preparation and dig out the egg capsules to destroy the insects. At the same time, in combination with tending and management, remove withered grass and fallen leaves and burn them in a centralized manner, so as to reduce the pest population density, reduce the sources of infestation, and lessen the damage caused by this insect. Second, biological control. Protect natural enemies such as the red-ringed ladybird to reduce the pest population density. Third, chemical control. Apply pesticides at the peak hatching period of the nymphs: spray No. 30 machine oil emulsion at 30-40 times dilution, spray 25% carbaryl wettable powder at 400-500 times dilution, or 20% fenvalerate at 6,000 times dilution plus 40% omethoate at 1,500 times dilution.

2 Jujube Bud Mite

Belongs to the order Acarina, family Eriophyidae, and is a pest of jujube trees, also known as jujube rust mite and jujube wall louse. It is distributed in Henan, Gansu, Ningxia, Anhui, Zhejiang and other provinces (regions). After jujube trees are damaged, the leaves curl, the leaf color turns gray, and flower drop, fruit drop and leaf drop are severe; rust spots appear on the fruit surface, causing reduced fruit yield and declining quality.

2.1 Morphological characteristics. The egg is spherical, milky white, smooth and transparent. The nymph is carrot-shaped, smaller than the adult mite, milky white or light yellow, with 2 pairs of tarsi, a smooth abdomen with faint transverse striations, and a slightly pointed tail. The adult mite is carrot-shaped, 0.15 mm long. It is initially milky white, later light yellow, semi-transparent and glossy, with 2 pairs of appendages on the cephalothorax, of which 1 pair are the chelicerae (feather claws), short and stout; the cheliceral claws are relatively small, with bluntly rounded tips, and there is 1 brown spot on the anterior lateral side of the coxa. The rostrum is needle-like, located behind and between the chelicerae beneath the head. The thoracic dorsal plate is broadly nearly circular, and the abdomen has many transverse striations.

2.2 Ecological habits. This insect overwinters as adult and nymph mites in the scales of jujube spurs or in the bark crevices of jujube branches. This insect reproduces quickly, has strong stress resistance, spreads rapidly, is widely distributed, and is difficult to prevent and control. When jujube buds sprout in spring, the overwintering mites begin to move and feed. When the density is low, they mostly concentrate on the underside of jujube leaves along both sides of the three main veins, with a very small activity radius, but they have the habit of migrating with the wind, and spread and cause damage quickly. The peak damage period is reached in June. They can damage both sides of the leaves, but mainly the underside. Damaged leaf surfaces curl upward longitudinally, the leaf color changes from green to gray, and the leaf texture becomes brittle. When the temperature is high and atmospheric humidity is relatively low, it is unfavorable for the development of this insect. During the high-temperature weather of July-August, the mites move from the leaves to the scale buds to spend the summer, and the number of these mites on the leaves decreases. In September the reproduction rate of these mites declines, and the population density becomes smaller. After the end of September, these mites enter dormancy to overwinter.

2.3 Control measures. First, carry out good nursery stock quarantine work to prevent the spread and damage of this insect. Second, carry out good management and care work such as watering, weeding and fertilizing to strengthen tree vigor, so as to improve the insect resistance of the nursery stock. At the same time, in combination with winter pruning, remove diseased and pest-infested branches, scrape off old cracked bark, and burn them in a centralized manner to eliminate overwintering sources of the insect. Third, before jujube trees sprout, spray 1 time with 3-5 degrees Baumé lime sulfur mixture to kill overwintering adult mites and old nymph mites. In early to mid-May, promptly spray 20% clofentezine at 2,000 times dilution, 2% abamectin at 4,000 times dilution, 50% menazon at 1,000 times dilution, or 20% pyridaben at 3,000 times dilution. Fourth, protect and utilize natural enemies, such as ladybirds and minute pirate bugs, to lessen the damage caused by this insect.