Fungus gnats are a major pest harming orchids

[Editor's note: This article gives aorchidvery thorough and scientifically sound introduction to the control of one of the insect pests. There is very little reporting in various orchid books and orchid journals on the situation of fungus gnats harmingorchids.] Inorchidcultivation, the common major pests include red spider mites, scale insects, aphids, thrips, ants, earthworms, slugs and snails, and so on, and these pests are generally introduced in orchid books. But there is one pest that occurs commonly in orchid cultivation and causes relatively severe damage toorchids, yet in the orchid materials the author has seen, there has been no report concerning this insect harmingorchids. According to the author's identification, this pest is the fungus gnat (Bradysia minpleuroti yang et zhang), belonging to Insecta - Diptera - Nematocera - Sciaridae. The occurrence and damage, morphological characteristics, occurrence features and control methods of the fungus gnat onorchidsare introduced as follows. 1. Occurrence and damage situation This insect has a wide range of hosts and a miscellaneous diet. According to the author's surveys over many years of someorchid-growinghouseholds in Dali City (105 households), whether it is courtyardorchid growing, greenhouseorchid growing, orbalcony orchid growing, and whether in the city or in the countryside, in orchid-growing sites, different places and different cultivation methods only differ in the severity of occurrence, but the pest occurrence rate among orchid-growing households was 100%. The survey results show that this insect mainly causes harm to orchids in three aspects: first, the larvae of this insect gnaw orchid roots in the pot, causing the orchid roots to die; second, this insect is mainly saprophagous, accelerating the decomposition of organic matter in the potting soil; third, the adults of this insect fly around in orchid-growing sites, stay on orchid leaves and deposit feces, contaminating orchid leaves and spreading orchid diseases. The results are manifested in affecting the growth and development, overall appearance and economic value of orchids. Therefore, all orchid growers should attach importance to the control of this insect. 2. Morphological characteristics Adult: The greatest characteristic of this insect is that the body is relatively small. The male body length is 2.7-3.2 mm, dark brown, with the head darker in color, compound eyes with eye hairs, thorax blackish brown, wings pale gray, 1.8-2.2 mm long and 0.8-0.9 mm wide, abdomen dark brown; the female is larger, with a body length of 3.4-3.6 mm, wing length 2.8 mm, width 1 mm, and a relatively large abdomen. Egg: oblong, initially milky white. Larva: about 0.6 mm long when newly hatched; 0.8-1 mm long when mature. Pupa: pupates inside a thin cocoon, 3-3.5 mm long, initially milky white, turning black after three days. 3. Occurrence features This insect mainly occurs in potting soil rich in humus and organic matter. On potted orchids in Dali City, the main occurrence period is from February to November each year. March to May, when the average temperature is 15-20°C, is the peak occurrence period, with an average of more than 50 insects per pot. The life cycle of each generation of the pest is 30-35 days. A pair of adults lays an average of more than 300 eggs, and there are 8-10 generations per year. The reproduction speed is quite fast, and if control is neglected, it is easy to cause an outbreak of damage. Indoors, the number and timing of pest occurrence are related to watering and soaking. Generally, 3-5 days after watering and soaking, the number of adults occurring increases markedly. 4. Control methods 4.1 Strictly prohibit bringing pest-infested orchids into the orchid garden For newly purchased orchids, especially those with growing medium, carefully inspect them, and do not bring pest-infested potting soil into the orchid garden; for ventilation openings in the orchid garden, such as doorways, doors and windows, it is best to install 60-mesh gauze to prevent adults from flying in. 4.2 Strengthencultivationmanagement When changing the soil for orchids, for pest-infested potting soil, it is best not to use it again. If it is used again, the potting soil must be treated at a high temperature above 50°C; in view of this insect's preference for moisture, after each watering, timely control should be carried out. 4.3 Rational use of pesticides Since potted orchids are mostly indoors, special attention should be paid to human safety when using chemical pesticides, and the idea of safety first should be established. Pesticides must not be used indiscriminately, and safe, efficient, low-toxicity agents should be selected. Through testing, a 1500-fold dilution of 5% cyhalothrin emulsifiable concentrate has a certain control effect on both adults and larvae of this insect, but spraying causes great indoor pollution and affects human health; after years of research, the author has now successfully developed a granular formulation with no pollution and good control effect. For an orchid pot with a pot rim diameter of 22-25 cm, it is only necessary to evenly broadcast 5 grams on the pot surface and add a little water. The effective period reaches more than 2 months. Under normal circumstances, applying the pesticide only twice each year in March and May is sufficient. Author's affiliation: Plant Protection and Plant Quarantine Station of Dali Prefecture, Yunnan Province Address: No. 219 Jianshe East Road, Xiaguan, Dali City Telephone: 0872-2123713, 2175070 13099848056