Occurrence and Control Methods of the Sesame Capsule Borer

The sesame capsule borer is one of the major pests of sesame. It mainly damages sesame. It commonly occurs in China's major sesame-producing areas such as Henan, Hubei, Anhui and Jiangxi, generally reducing yields by 10%-20%, and by up to 30% in severe cases, significantly lowering sesame quality. In response to its occurrence, the patterns of occurrence were carefully studied, control agents were screened, and control methods were explored.

1. Patterns of occurrence

The sesame capsule borer has 4 generations per year in Henan, with overlapping generations, and overwinters as mature larvae. Adults appear from late July to late November, with the peak emergence period in early August. Adults are phototactic; during the day they mostly rest on the undersides of sesame leaves or in weed clumps, and at night they are active and lay eggs. Eggs are laid singly on sesame leaves, stems, flowers, capsules and tender shoots, with an egg period of 6-7 days. The larvae have a migratory habit, feed on leaf mesophyll, and readily bore into flower centers and capsules to cause damage. The larval period is about 15 days. Mature larvae spin grayish-white thin cocoons in rolled leaves, in capsules or in stem crevices and pupate there, with a pupal period of about 7 days. Completing one generation takes 37-38 days.

2. Damage symptoms

The larvae spin silk to bind flowers and leaves together, feed on leaf mesophyll, and also often bore into flower centers, tender stems and capsules to feed. They can eat all the seeds, causing the capsules to turn black and drop off and the plants to wither and yellow.

3. Morphological characteristics

The adult sesame capsule borer has a body length of 7-9 mm and is pale yellowish-brown, with 3 indistinct yellowish-brown spots near the anterior margin and two indistinct black spots on the hind wings. The egg is about 0.4 mm long, oblong, initially milky white, later turning pale yellow to pink. The larva has a body length of 16 mm, a blackish-brown head, and a body color of green, yellow-green, pale grayish-yellow or reddish-brown, etc. The pupa is about 10 mm long, pale grayish-green to dark greenish-brown, with the tips of the proboscis and antennae separated from the body. 4. Control methods

1. Agricultural control:

Clear weeds and fallen leaves and twigs from field edges, roadsides and fields. Use rational crop rotation, and carry out paddy-upland rotation where conditions permit. Plow and harrow thoroughly to reduce overwintering sources of the pest. Irrigate at the seedling and flowering stages to increase soil moisture.

2. Chemical control:

(1) Fumigation: In early August, during the peak emergence period of adults, mix 100-150 g of 80% dichlorvos with 4 kg of sawdust and wheat bran, place 40 piles per mu evenly under the sesame plants; the efficacy generally lasts 8-10 days.

(2) Spraying: 7-10 days after the peak emergence period of adults is the peak hatching period of larvae, when spraying gives the best control effect. Use 30-40 ml of 2.5% deltamethrin emulsifiable concentrate per mu; 20-30 ml of 20% fenvalerate emulsifiable concentrate; or 25-30 ml of 50% fenitrothion emulsifiable concentrate, mixed with 50 kg of water, diluted evenly and sprayed.

(3) Dusting: At the peak hatching period of larvae, use 1.5% dimethoate powder; 2.5% trichlorfon powder; or 2% fenitrothion powder, at 1.5-2 kg per mu, applied evenly with a duster.