The scientific name *Hydrellia philippina* Ferino belongs to the order Diptera, commonly known as true flies. This species is often grouped under the general term "rice waterflies," which refers to a group of pests that damage rice crops. In addition to the Oriental-eyed waterfly, there are several related species such as the gray-horned waterfly and the rice fly (*Ephydra macellaria* Egger). Five species have been identified globally, all sharing similar physical characteristics. These pests are widely distributed across rice-growing regions in various countries.
This pest primarily attacks rice plants, but it can also affect other grasses such as wild white grass, wild British grass, and Lee’s cricket. The larvae feed on the leaf sheaths and the inner flesh of the leaves, causing significant damage. As a result, yellow-brown debris accumulates inside the stems, and the affected plants often become wilted or folded, leading to reduced crop yield.
Morphologically, the adult *Hydrellia philippina* measures between 1.7 to 2.3 mm in length, with a wingspan of about 4.6 mm. Its body color ranges from gray-brown to dark gray, while the head is lead-gray. The compound eyes are black and covered with short hairs. The antennae are short. The abdomen is black, but it has fine grayish-green hairs, with the back part appearing dark gray and featuring a gray ring on each segment. In males, the end of the abdomen has a flat protrusion, located near the base of the lateral leaf. The eggs are elongated, measuring 0.5–0.7 mm, initially white and turning gray after hatching. The last instar larvae are 6–8 mm long, starting off white and gradually turning light yellow to yellow-green. They are cylindrical in shape with 11 segments, smooth but with bristles along their bodies. Their mouthparts are dark brown, and the posterior end is bifurcated. The pupal stage is 5–9 mm long, 2–3 mm wide, and has 12 segments. It is cylindrical, initially yellow-brown, then turning tan or brown. At the tail end, there are two black valve-like protrusions.
In terms of life habits, in Xiangzhou, Guangxi, there are approximately eight generations per year, while in Taiwan, the number of generations is similar. Overwintering larvae begin to move in mid-March of the following year. These larvae migrate from the rhizomes of Lee’s cricket, late rice, and winter white grass. The migration period occurs from mid-April to early June and again from late May to mid-July. The fourth, fifth, and sixth generations occur from early July to mid-August, early August to mid-September, and early September to mid-October, respectively. Each female lays 10–40 eggs, and adults live for 4–8 days. Eggs hatch within 2–4 days, and larvae develop over 11–20 days, followed by a pupal stage lasting 5–11 days. Rice damage typically begins in early May and continues until mid-October. From late July to early October, the infestation reaches its peak, with the third and fourth generations being most active throughout the year.
Control methods include regular field inspections to monitor the development of the pest and predict the peak emergence of adults and egg hatching, conducting monitoring every 5–10 days. Before March each year, all remaining rice stubs should be completely removed and either deeply buried or burned. The first and second generations should be targeted for control, with efforts focused on eliminating the third and fourth generations by killing newly hatched larvae and treating adults. Spraying solutions such as 25% EkaSS EC at 1500 times dilution, 2.5% deltamethrin at 2500 times, 10% PVP at 2500 times, 50% fly nectar, or 35% PF at 2000 times are effective. Additionally, strict quarantine measures should be enforced, prohibiting the transport of rice seedlings infected with waterflies.
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