Potato ladybird also known as the big twenty-eight star ladybird, belongs to the Coleoptera family, and the nightshade twenty-eight star ladybird are plant-feeding ladybirds, the two are often mixed, not only similar in morphological habits, feeding hosts, pest symptoms are also more similar, are adults and larvae as pests solanaceae, gourd family, legume, cruciferous family, Asteraceae, lily family and other plants, of which potatoes, eggplant, pepper and other nightshade crops or weeds such as dragon sunflower, mandala are the most seriously affected.
In China, potato ladybirds are affected in the northeast, north China and northwest of the Yangtze River Basin. According to records, there is a distribution of potato ladybirds in Hubei Province, but the insect has not been found in the Wuhan area for many years, and all the eggs seen in the field are eggplant 28 star ladybirds.
In the spring of 2021, potato ladybird hazards were found on winter-sown potatoes, vegetable goji berries and weed dragon flowers in Huangpi District and Jiangxia Districts of Wuhan City, and showed a large incidence. Today, we will introduce the pest characteristics, morphological characteristics and living habits of potato ladybirds, and help vegetable farmers to control them in a targeted manner.
The larvae and adults of the potato ladybird mainly nibble on the epidermis and flesh of the host leaves, forming a regular arrangement of black-brown lattice translucent concave lines, and in severe cases, the affected leaves become brown and wither until the leaves and plants all dry up and die. At the same time, it also nibbles on the fruit, and the place where it is eaten is cracked and concave, and the flesh tissue changes color, stiffens, and roughens, losing its commodity value.
▲Potato plants are harmed by potato ladybugs
▲Goji leaves are harmed by potato ladybirds
Adult potato ladybirds are 6 to 8 mm long and 5.0 to 6.5 mm wide, scoop-shaped, with a nearly ovoid periphery, dorsal hemispherical arch, russet brown, and densely covered with fine yellow-gray hairs.
The head is rectangular , with an arc-shaped protrusion at the leading edge , and the sides are flanked by dark brown compound eyes. The anterior margin of the dorsal plate of the anterior thorax is concave, the anterior margin angle is prominent, and there is a large black longitudinal sword-like stripe in the center, with 2 large black spots on each side, or even or divided.
▲ Potato ladybird adult thorax back plate
Adult insects are bright yellow in the early stage of feathering, elytra have no spots, and late feathering black spots appear rapidly; there are a total of 28 black spots in the two elytra wings, and the black spots are not neatly arranged.
▲Potato ladybird adults first feather
▲ Potato ladybird forewings have black spots on their forewings
The egg is approximately 1.4 mm long, warhead-shaped and upright. The eggs are laid in chunks, but the egg masses are loosely arranged and have significant gaps.
▲ Potato ladybird egg pieces
The larvae are 4 years old, and the mature larvae are 9 to 10 mm long, pale yellowish brown, spindle-shaped, with a bulge on the back and dense branches on the dorsal surface. The pupa is 6 to 8 mm long, oval, slightly flattened at the front, and pale yellow.
▲ Potato ladybird larvae
▲ Potato ladybird pupae
Adults overwinter in leeward sunward caves, tree holes, earth caves, stone crevices, wall crevices, bark crevices, window sills, hedges, and in the soil surface of slopes. Adults emerge in north China in mid-to-late May of the following year, and in northern Shaanxi in late April. It first roosted on nearby weeds before it began to migrate to nearby potatoes, eggplants, and legumes to breed.
The Wuhan area is at its peak from mid-April to mid-May, with the first generation of adults entering the peak period in late May, and the population in the field after mid-June as the temperature rises and potato harvest begins to decrease.
Adults are active during the day, feeding, mating, laying eggs, have suspended death, and are often suspended to death when disturbed. Adults have a long lifespan, with the first generation about 45 days and the overwintering generation reaching 250 days.
The spawning period is long, with eggs mostly on the back of the leaves, and each female can lay about 300 eggs. The larvae are 4 years old, and the hatching larvae are mostly concentrated and have the habit of feeding on eggs; after 2 years, they begin to disperse, mostly feeding on the back of the leaves; and the mature larvae pupate on the back of the host leaf, stem or nearby weeds.
Warm and humid climatic conditions favor the occurrence of potato ladybirds, but the larval development rate decreases above 28 °C, and the high temperature inhibits the development of various insect states. The suitable relative humidity of egg hatching is 90%, and the relative humidity below 50% cannot hatch; the suitable relative humidity of larval development is 50% to 75%, and the humidity required by young to advanced larvae in this range is gradually reduced. There is a predisposition to feeding, and adults feed potatoes more than eggplants.
Agricultural control: potatoes and other crops are harvested in time to level the land, remove weeds and residual plants, destroy the wintering site of potato ladybirds, and reduce the source base of overwintering insects.
Physical control: Using the pseudo-death nature of potato ladybirds, knocking on the plants makes the adults fall into the basin to kill. Take advantage of the recognizability of the eggs to manually remove the egg masses.
Biological control: In the early stage of egg hatching, spray control was carried out with 1000-2000 times of coccidioides containing 40 billion/g of spores, 1000-2000 times of beetle green zombie liquid of 10 billion/g of beetles containing spores, and 16000 IU/mg of Thuringiensis 1000-2000 times liquid, and 2.5% neone emulsion 1000 times liquid could also be selected for spray control.
Chemical control: at the peak of egg hatching, 50% octathion emulsion 1000 times liquid, or 2.5% cypermethrin emulsion 2000 times liquid, or 4.5% high performance cypermethrin emulsion 2000 times liquid, or 10% bifenthrin emulsion 1500 times liquid, or 2.5% cypermethrin emulsion 2000 times liquid, or 20% chloranthropanthrine paralyticamide suspension 2000 to 3000 times liquid, or 10% bromo cypermamide dispersible oil suspension 2000 to 3000 times liquid, or 3% cypermethrin emulsion 2000 times liquid, or 3% cypermethrin suspension liquid Acetamidine microemulsion 1000 times liquid for spray control. Special attention should be paid to the uniformity of the medicine on the back of the leaf, and the second spray control should be carried out according to the insect situation after 10 days.
Note: This article is excerpted from the article "Potato Ladybird Outbreak in Wuhan City in spring 2021" of China Vegetables, No. 11, 2021, authors: Wang Pan, Yang Fan, Zhou Lilin, Luo Haibo, Wang Yong, Si Shengyun. Unit: Vegetable Research Institute, Wuhan Academy of Agricultural Sciences. The picture is taken by Si Shengyun, all rights reserved and may not be reproduced.