Control methods for damage caused by bean blister beetles on potatoes

Bean blister beetles have currently been found causing damage on plastic-mulched potatoes in Longhu District, Shizuishan City, over an area of about 30 mu, with leaves in some fields severely damaged, affecting the normal growth of potatoes.

There are three species of blister beetles, namely the white-striped bean blister beetle (Epicauta gorhami Marseul), the yellow-black flower blister beetle (Mylabris cichorii Linne), and the large yellow-black flower blister beetle (Mylabris phalerata Pallas), which are widely distributed across the country. They mainly damage beans, peanuts and peppers, and can also damage crops such as tomatoes, potatoes, eggplants, sugar beets, water spinach and amaranth. Damage is caused by the adults, which mainly feed on leaves and petals, eating bean leaves into notches with only the veins remaining, and also feed on bean pods, causing notches that affect yield and quality.

I. Morphological characteristics

Bean blister beetles all belong to the order Coleoptera, family Meloidae. The adult white-striped bean blister beetle is 15-18 mm long and dark brown. The head is slightly triangular and reddish brown. The center of the pronotum and each of the two elytra bear a longitudinal yellowish-white stripe. The eggs are elongated oval, yellowish white, and the egg masses are arranged in a chrysanthemum shape. The first-instar larva is a dark brown triungulin, active in movement; the 2nd to 4th and 6th instars are scarabaeiform; the 5th instar is a legless pseudopupa. The naked pupa is about 15 mm long, yellowish white, with 9 relatively long spines on each of the lateral and posterior margins of the pronotum. The adult yellow-black flower blister beetle is about 15 mm long, with a prominent longitudinal suture on the pronotum; the elytra are yellow except for 3 wavy black transverse bands, so the elytra appear yellow and black in alternation. The large yellow-black flower blister beetle has an adult similar in shape to the yellow-black flower blister beetle, with the elytra also yellow and black in alternation, but it is larger, 20-28 mm long, and the longitudinal suture on the pronotum is not prominent.

II. Life habits

Bean blister beetles have one generation per year in Northeast and North China, and two generations per year in the Yangtze River basin and the provinces south of the Yangtze River basin. They overwinter in the soil as 5th-instar larvae (pseudopupae). In one-generation regions, the overwintering larvae pupate in mid-June, and adults emerge to cause damage from late June to mid-August, with August being the period of severe damage. In two-generation regions, the overwintering-generation adults occur from May to June, concentrating their damage on early-sown soybeans and then moving to vegetables. The first-generation adults cause the heaviest damage to soybeans, after which their numbers gradually decline and they move to vegetables to cause damage. The adults are active during the day, gathering in groups on the branches and leaves of bean plants to cause damage, and are lively and good at crawling. When disturbed, the adults quickly scatter or drop to the ground, and can secrete a yellow liquid containing cantharidin from the ends of the femora; if it touches human skin, it can cause redness, swelling and blistering. The adults lay eggs in the soil at a depth of about 5 cm, with about 70-150 eggs per hole.

III. Integrated control methods

(1) Deep plowing of the soil in winter can expose the overwintering pseudopupae on the soil surface to be killed by freezing or eaten by natural enemies, reducing the base number of insect sources the following year.

(2) Manual capture and killing: taking advantage of the adults' habit of gathering in groups to cause damage, use nets to capture and kill them, but care should be taken not to touch the skin.

(3) Repelling adults: at the initial stage of adult occurrence, after manually capturing some adults, string several of them on iron wire and hang them around bean crops in the field, which can repel adults from flying in to cause damage.

(4) Chemical control: during the adult occurrence period, spray with 90% trichlorfon crystal at 1000 times dilution.