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 various pests that damage rice crops. Alongside the oriental eyed waterfly, there are several other related species such as the gray-horned waterfly and the rice fly (*Ephydra macellaria*). Five species have been identified globally, all with similar physical characteristics. These pests are widespread in rice-growing regions across the country.
This pest primarily attacks rice plants, but it can also affect wild grasses like white grass, British grass, and Lee's cricket. The larvae feed on the leaf sheaths and inner leaf tissue, causing significant damage. Infested areas develop yellow-brown debris inside the stalks, and the affected plants may become wilted or folded.
Morphologically, adults measure between 1.7 to 2.3 mm in length, with a wingspan of about 4.6 mm. Their bodies are gray-brown to dark gray, and their heads are lead-gray. They have black compound eyes with short hairs, and their antennae are short. The abdomen is black, covered with fine, greenish-gray hairs, while the back of each abdominal segment has a dark gray band. In males, the tip of the abdomen features a flat protrusion, and the base of the lateral leaf has a distinct structure. Eggs are small, measuring 0.5 to 0.7 mm, oval-shaped, initially white, and later turn gray. The last instar larvae grow up to 6-8 mm long, starting off white and turning light yellow to yellow-green. They are cylindrical with 11 segments, smooth but with fine bristles. Their mouthparts are dark brown, and the rear end is bifurcated. The pupa is 5-9 mm long, 2-3 mm wide, and has 12 segments. It is cylindrical, initially yellow-brown, and later turns tan or brown. At the tail end, there are two black protrusions.
In terms of life habits, in Xiangzhou, Guangxi, this insect completes eight generations annually, while in Taiwan, it also has multiple generations. Overwintering larvae begin to move in mid-March of the following year. They migrate from the rhizomes of Lee's cricket, late rice, and winter 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 appear from early July to mid-August, early August to mid-September, and early September to mid-October, respectively. Each female lays between 10 to 40 eggs, and adults live for 4 to 8 days. Eggs hatch within 2 to 4 days, larvae develop over 11 to 20 days, and the pupal stage lasts 5 to 11 days. Similar to other rice stem pests, these insects are most active from early May to mid-October, with peak damage occurring between late July and early October. The third and fourth generations are particularly abundant throughout the season.
For control, regular monitoring of the crop is essential to predict adult emergence and egg hatching periods, with inspections conducted every 5 to 10 days. Before March each year, all remaining rice stubble should be completely removed, either by deep plowing or burning. The first and second generations are key targets for control, with efforts focused on eliminating the third and fourth generations by killing newly hatched larvae and treating adults. Pesticides such as 25% Ekar EC diluted at 1500 times, 2.5% deltamethrin at 2500 times, 10% PVP at 2500 times, 50% fly nectar, or 35% PF at 2000 times can be applied. Additionally, strict quarantine measures must be enforced to prevent the transport of infected seedlings.
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