How to control the rice whorl maggot, Hydrellia philippina

Scientific name Hydrellia philippina Ferino, belonging to the order Diptera, family Ephydridae. "Maoyan shuiying" is a collective term for the shore flies that damage rice; besides Hydrellia orientalis, it also includes Hydrellia griseola, the rice stem maggot (Ephydra macellaria Egger) and several other species. Five species have been found worldwide, all similar in appearance. It is distributed in rice-growing areas throughout the country.

Hosts Rice, wild rice stem (Zizania latifolia), wild rice, Leersia japonica and others.

Damage characteristics The larvae bore into and feed on the leaf sheath and leaf mesophyll; yellow-brown frass and debris accumulate in the tunnels in the leaf sheath, which later rots and causes the plant to lodge.

Morphological characteristics The adult is 1.7—2.3mm long with a wingspan of 4.6mm, grayish brown to blackish gray, with a lead-gray head. The compound eyes are densely covered with short black hairs. The frons is short. The abdomen is black but densely covered with fine hairs, giving it a greenish gray appearance, except that the dorsal surface of the abdomen is dark gray, with a gray band along the posterior margin of each segment. The male has a laterally flattened process at the tip of the abdomen, situated in the middle of the base of the lateral caudal lobes. The egg is 0.5-0.7mm long, elongate spindle-shaped, initially milky white, later turning grayish white. The mature larva is 6—8mm long, initially milky white, later turning pale yellow to yellow-green, elongate cylindrical, with 11 segments, a smooth body surface and bristles. The mouth hook is dark brown and forked at the posterior end. The prothoracic spiracles are protruding, and the tip of the abdomen has a pair of spiracles. The pupa is 5—9mm long and 2—3mm wide, with 12 body segments, cylindrical, initially yellow-brown, later turning yellow-brown or brown, with 2 clusters of black bristles at the front of the head. The tail has a pair of black spiracular processes.

Life habits In Xiangzhou, Guangxi, and in Taiwan, China, there are 8 generations a year; it overwinters as larvae on Leersia japonica in ditches, on ratoon seedlings of late rice and on wild rice stem, and the overwintering larvae begin activity in mid-March of the following year and move onto the rhizomes. The peak occurrence of the 2nd and 3rd generations is from mid-April to early June and from late May to mid-July; the 4th, 5th and 6th generations occur from early July to mid-August, from early August to mid-September, and from early September to mid-October. Each female can lay 10-40 eggs. The adult lives 4—8 days. The eggs are laid singly; the egg stage is 2—4 days, the larval stage 11—20 days, and the pupal stage 5—11 days. In addition, the habits of the rice stem whorl maggot are similar to those of this insect. It damages rice mainly from early May to mid-October, with the peak damage period from late July to early October, and the 3rd and 4th generations occur in large numbers throughout the year.

Control methods (1) By regularly dissecting plants to check pupation progress, predict the peak emergence period of adults and the peak hatching period of eggs, dissecting once every 5—10 days. (2) Before March each year, thoroughly remove the residual rice stubble and either bury it deep or burn it. (3) Focus on controlling the 1st and 2nd generations, check the 3rd and 4th generations, kill newly hatched larvae and also control adults. Spray 25% ikaruga emulsifiable concentrate at 1500 times dilution, or 2.5% deltamethrin emulsifiable concentrate at 2500 times dilution, 10% imidacloprid wettable powder at 2500 times dilution, 50% fly maggot powder or 35% quchulin emulsifiable concentrate at 2000 times dilution. (4) Implement quarantine; rice seedlings carrying shore flies must not be transported out.