Lycoriella solani Winnertz, L. inguenua /Dufour/, L. auripila /Winnertz/, Bradysia brunnipes Meig
The most significant pests of button mushroom cultivation. In nature they can be found feeding on wild grown mushrooms, living in composts, manure and decaying wood, from where the adults find their way into the mushroom farms.
The larvae
The larvae feed on the mycelia in the compost and the casing. The infested parts of the compost and the casing soil are moisture, smell bad and only weakly colonized by the mycelium. The females lay eggs in the not yet spawned or colonized compost. The first larvae appear in the first flush and feed on the base of the fruitbodies, where they eat away the mycelia, which causes the mushrooms to stop growing, turn brown and get slimy. The mature larvae bore through the stem (and sometimes the cap) of the bigger fruitbodies. The tunnels created by the pest are filled with the faecal matter of the feeding larvae, which cannot be seen from the outside (only when the mushrooms are cut in half).
Fruitbodies damaged by larvae of Sciarid flies The adult
By spreading a number of diseases (and sometimes even other pests), adult mushroom flies cause secondary damage in mushroom cultivation. Unlike Phorid species, Sciarid flies clean themselves rarely. The mites get on them (as many as 30 mites at the same time), and get transported by the flies. Additionally, bacteria can be found on the mites, thus not only the pests, but the microorganisms are carried by the flies as well. Sciarid flies have an important role in spreading the spores of the dry bubble disease (Lecanicillium fungicola).
The anatomy and biology of the pests
The mature larvae are 8-12 mm long maggots, which have distinctive chewing mouthparts on their shiny black heads. 2 generations can develop, if the females lay eggs around spawning.
Sciarid larvae with the characteristic shiny, black head The adults are 3-4 mm black flies with long, thin antennae which are held characteristically (in 45˚).
Sciarid fly with the quite distinguishable antennae
The female lay 140-170 eggs in the not yet colonized compost or in the casing soil (during cropping, even on the surface of the fruitbodies). The eggs can either be found one by one or in groups (10-15 pieces). On 24˚C the pest reaches adult state in 18-22 days.
The temperature is above 24˚C during colonization, thus the larvae could appear as soon as the first flush begins. During cropping the development from egg to adult takes more time (35-38 days), as the temperature is lower, only 18˚C. The more larvae and adults are present, the more crop loss can be expected. Sciarids, in contrast to Phorid species which are seasonal pests, usually stay on the farm throughout the whole year.
Prevention and treatment
Chemicals or biological products are available against mushroom flies. Adequate production method and strict sanitary actions are essential in prevention.
Once the compost is colonized, the females do not lay eggs there (since the growing mycelia inhibit larval development), thus the most important thing is to prevent flies getting near the phase II. compost. That is why the rooms where colonization takes place are overpressure. In less modern mushroom houses the doors, windows and ventilation ducts have to be covered with screens.
Grower using phase II. compost should cover the bags or sacs with paper or plastic sheets after placing them on the floor or on the shelves. This way the female flies cannot lay eggs into the compost (only on the covering material). The covers should only be used once.
Any type of waste has to be removed from the surroundings of the growing area. The spent substrate cannot be left on the farm.
Dimilin 25 WP (active ingredient: diflubenzuron) can be used against larvae as prevention. It can be added to the water following the first irrigation in 4 g/m2 dose.
The biological product (Nemacel, Nemasys-M) used against mushroom flies contains the eelworm species Steinernema feltiae and is also effective.
Sticky traps can catch a large number of flies. Electric traps are not as effective, since the flies avoid light.
Phorid (hump-backed) flies (Megaselia halterata, M. nigra)
Phorid flies are common all over the world. They feed on decaying and composting organic materials, wastes. Since Phorid flies reproduce quickly, they can cause serious problems short after appearing in the crop. The flies can fly long distances (10 km in 24 hours). That is why disposing of the spent compost has to be done by special care. Phorids are seasonal pests, as they only appear from spring until autumn. Although the descriptions of Megaselia halterata and M. nigra are similar, there are differences between the feeding of the two species. M. halterata larvae feed solely on mycelium in the compost or in the casing soil, but do not bore into the fruitbodies, whereas M. nigra larvae tunnel the mushroom tissue right after emerging.
Megaselia halterata
The larvae are rarely seen, since feed in the compost or in the casing. The adults can be found easily especially in summer and early-autumn. These flies are one of the most effective vectors of the dry bubble disease (Lecanicillium fungicola), as they can carry hundreds of spores on their bodies (in spite of the fact that they clean themselves more often than Sciarid flies). Nowadays the indirect damage caused by the disease spreading adults is more significant than of that of the larvae.
Phorid flies are small (2-3 mm) hump-backed pests with practically inconspicuous antennae. The larvae are cream white, 1-6 mm long legless maggots with a pointy head and a blunt rear end. Unlike in case of Sciarids, Phorid flies do not have black heads. The female lays around 50 eggs near the mycelium. After that they live (and spread diseases) for weeks. Phorids do not fly below 13˚C, which explains why they are not infesting the farm from the surroundings during winter.
Phorid fly with the characteristic hump back
Megaselia nigra
M. nigra feed on both wild grown and cultivated mushrooms. The female lays eggs on the casing next to the developing fruitbodies or directly on the mushrooms, so food is instantly available for the emerging larvae. As a result of larvae activity, the fruitbodies get completely tunneled (both stem and cap) and finally the collapse. After a serious infection nothing is left on the surface but a mass of mushroom tissue, faecal matter and a group of larvae. Sciarids never bore into the cap, while Phorids tunnel through the entire fruitbody. M. nigra is slightly bigger and darker than M. halterata, otherwise they look the same. One female is capable of laying 500 eggs, 20 at a time and 40 within 12 hours. Larvae emerge in 3 days (on 18˚C), feed for 5 days before turning into pupa. On 24˚C the insect develop from egg to adult in 13-14 days and lives for 36 days. Since females prefer laying eggs on surfaces that get natural light, the occurrence of the pest is more likely in tents (and not in cellars or artificially lid Dutch-type houses).
Prevention and treatment
Just like in case of all pests (and diseases) prevention is first. The females can smell mycelia, start to look for it and try to get into the growing area. This can be prevented by thoroughly covering the openings with screens.
Every used material (plastic or paper covers, bags and especially the spent compost) have to removed and transported far from the farm, since they contain the pest (in different developmental stages), which can infest new crops.
Electric traps should be used, since the flies prefer light. Yellow sticky traps are also effective in catching flies.
Since the larvae hid in the mushrooms and do not come to the surface, the only opportunity to use chemicals against them is to add Dimilin 25 WP (4 g/m 2) to the first irrigation as prevention.
The biological products containing eelworms are not effective against Phorids.