‘Mushroom
Flies’
Damn! some bugger fly just flew out of my terrarium! wtf?
yaaaarrrgghhh! is my crop ruined?
At
some time or other, all mycologists will encounter 'fungus gnats', the
pesky flies that are real pests, and need action. these gnats are very
closely associated with fungi and decaying vegetation and highly
attracted to mycelium and mushrooms. (In fact, I often wonder whether I
am really a fungus gnat myself.) They lay eggs in the compost or casing
layer, which hatch into critters that, like the adult flies, nibble and
tunnel through mycelium, growing and marture mushroooms. Flies flit
from tub to tub, often in swarms like locusts on a wheatfield. They may
also be the primary vectors for spreading fungal, bacterial and viral
diseases, mites and nematodes. Also, the wounds created by larval
feeding provide an entry site for secondary soil-borne pathogens.
can you spot him in this picture?
what about up close?
Uncontrolled
populations of any of the main mushroom pests can result in substantial
losses in yield due to both direct larval action and associated disease
spread by adult flies. Problems caused by flies found in cropping
houses include reduced yield by damaging the compost and feeding on the
mycelium, acting as vectors of diseases, a nuisance to the
growers/pickers, and possible crop rejection at market. who would go
back to again buy a packet of mushrooms that had flies flitting out of
it?
Mushroom flies fit into several categories, only one of which
(sciarids) represents the true
‘fungus gnat’.
[Wherever I refer to ‘fungus gnats’ in the rest of this document, the
same will largely apply also to phorids, cecids and sphaerocids.]
Like
all flies, fungus gnats have four developmental stages: egg, larva,
pupa and adult. The female adult flies deposit between 50 to 300 eggs
(0.2mm) in the compost and the developing larvae pass through four
moults (varying in size from 1 to 8 mm) before pupating.
Outbreaks
of high fungus gnat populations are linked to high humidity and soil
moisture levels - this may have something to do with the insect's
vulnerable egg stage. Fungus gnat eggs are very much subject to
desiccation.
When the moist conditions that favour egg
development are present in a species that goes from egg to adult in
only 10 to 14 days, populations are likely to boom. High humidity and
soil moisture encourage the growth of the larval stage.
If allowed to enter and uncontrolled, fungus gnat numbers can sometimes
soar into an explosion of winged insects.
A : KNOW YOUR ENEMY
Without
close examination, these small flies appear to be very similar and are
hard to distinguish from each other. However, it is important to know
which pest you are dealing with, as treatments are often very species
specific - different species of fly might have different susceptibility
to munchers and to insecticides so is also important to know which
species is present on a crop.
1) True Fungivorids - Sciarid Flies:
Lycoriella
castanescens (auripila) and Lycoriella ingenua (mali); Bradysia
difformis (paupera), Bradysia coprophila, and Bradysia lutaria.
Adult
flies are usually 3 - 4 mm long and with the naked eye can be
distinguished from the other fly pests of mushrooms by their long
antennae, black shiny heads, long legs and long thin wings. They look
like bonsai mosquitoes.
Sciarids
are compost feeders and really prefer unspawned compost to that
colonised by Agaricus mycelium. The adult flies are attracted by
volatiles given off by the compost so are a danger at any time after
pasteurisation when the compost is cool. They feed on rotting
vegetation, so compost is an ideal substrate for them.
Although
exudates produced by the growing mycelium inhibit the larvae, they have
been observed browsing on the growing tips and when there is a large
infestation the larvae will even burrow right up into the mushroom
stipes, the little fuckers. The accumulation of their waste (called
frass) also renders the area unsuitable for mushroom growth and makes
the place generally unsavoury.
2) Phorid flies:
Megaselia species eg. Megaselia halterata
The
phorids, also known as humpbacked flies, resemble fruit flies in
appearance but do not have the red eye classic trademark of the fruit
fly. Phorid flies are larger than sciarids, with very short antennae
and a characteristic hump-back.
Phorid
larvae are obligate mycelial feeders therefore the adult flies are not
attracted until after spawning. They are unable to fly when the
temperature falls below 12C and are therefore unlikely to re-infest
mushroom houses between late Autumn and early Summer. The larvae are
white, 1 to 6 mm long, are stubby at one end and have a pointed head at
the other. They feed on the growing mushroom mycelium but rarely feed
on the fruiting body itself, although some species are known to do so.
They can be distinguished from sciarid larvae by the absence of the
black head and they develop more rapidly into a pupa.
The
trademark of the adult Phorids is running, betraying their evil trait
of cowardice: even with the naked eye you can watch adult Phorid flies
dashing rapidly across surfaces with a rapid, jerky, running movement
instead of immediately flying when disturbed.
3) Sphaerocid flies
eg. Pullimosina heteroneura
These
are an occasional pest but are usually an indication of poor compost
preparation. These small flies have dark colored bodies and are about
3-4mm in length, making proper identification difficult without
magnification: the tarsi (last 5 segments of the hind leg) are the key
to identifying the Sphaerocerid fly - the first segment is greatly
enlarged in sphaerocids.
Most
flies of this family generally breed in animal manure and can also be
known as small dung flies. There are a few species that feed in any
decaying organic matter, meaning that they can be found in mycologists’
compost.
4) Cecids:
eg. Heteropeza pygmaea and Mycophyla speyeri
Cecids
are only usually seen as larvae. Cecid flies are rarely seen as the
larvae reproduce paedogenetically - i.e. new generations are produced
within the body of a 'mother' larva without sexual reproduction - and
the flies are very small.
The
larvae are obligate mycelial feeders as with the phorids. In a mushroom
cultivation environment i.e. high temperature and humidity, cecids can
produce a new generation every 4 to 7 days and each 'mother' larva can
produce up to 12 new larvae so numbers can increase exponentially. When
there is a bad infestation the larvae clump together and (get this)
flow over the sides of the mushroom beds onto the floor where they can
be inadvertently transported to healthy crops on feet and equipment.
Ewwwww.
Cecids are less common nowadays as hygiene and careful
selection of casing materials eliminate them as a problem. However, as
with the phorids, there is no pesticide available for use against them.
5) Not actually mushroom flies : Thrips, Fruit Flies
Although many growers also refer to their infestations as
‘thrips’ or
‘fruit flies’,
this is a misnomer - neither of these are actually mushroom flies :
thrips lust after not fungus but flowers and leaves, and fruit flies
(similar to phorids, but with red eyes) prefer …. (can you guess?)
..fruit!.
thrip 
...
fruit fly 
Perhaps in time of famine, these may pay a visit to a mushroom growing
aea, but mostly these have other fish to fry.
B : PREVENTION:
The
best control for flies is strict sanitation, exclusion and farm
cleanliness. Stop the buggers ever getting a sniff. Mushroom houses
must be airtight and all air vents must have filters. If you can afford
to make your growing area a positive pressure zone, with filters on all
air intakes, you'll be doing youtself a major favour in pest prevention.
Water
management is crucial to controlling fungus gnat buildups: avoid
overwatering, and provide adequate indoor ventilation. Moving air is
not good news to fungus twats ... er gnats.
ADDITIVES AS DETERRENTS:
dried
coffee grounds,
tobacco water (from soaking cigarette
butts),
chilli spray and
garlic water have all also been touted
as possible deterrents.
citronella candles
are reputed to deter many flying insects, including fungus gnats. also,
crushed leaves of the herb '
tansy'
can be sprinkled around the growing area: In Europe and in colonial
America in the 1840s, meat was packed in tansy or rubbed with it to
prevent decay and to repel flies. The oil distilled from the plant,
made a 'mosquito dope' useful to hunters and fisherman and others who
had to work where mosquitoes are troublesome.
One major source
of gnats is in their (microscopic) egg and larvae forms, in coco-coir
and under-pasteurised manure-based substrates. Increase pasteurisation
times and temperatures (being wary not to accidentally sterilise).
Remove any standing water, or treat it with the long-term biological
mosquito larvicide
Bacillus Thuringiensis (variants H-14
[Gnatrol] or
Israelensis, BTI)
weekly for two or three weeks as routine preventative control of fungus
gnat larvae. This larvicide gradually settles in water where it is
eaten by any mosquito or fungus gnat larvae growing there, which will
be killed continuously.
BTI is used to make ‘skeeter dunks’ that
look like little donuts (designed to float on water and kill
mosquitos), and will keep on working for 30 days or longer under
typical environmental conditions. While floating they slowly release at
the waters surface. Put some in water to be used for a day or two, to
load it with the stuff.
BTI:-
tansy:-
You can also drench soil with
neem
extract. the fascinating Indian Neem Tree (Azadirachta indica) and its
unique extracts have an enormously broad range of applications. The
oil, extracted from neem tree kernels, has nourishing qualities and is
used in India today in many toiletry ranges, including hair-care
products, toothpaste and soap. Mahatma Gandhi believed firmly in the
goodness of neem and ate neem leaf chutney as part of his everyday
diet. The main substance azadirachtin, a tetranortriterpenoid,
influences the hormonal system of insects, exerting thereby a
pesticidal effect. Feeding activity, reproduction and flying ability of
insects are also affected. Azadirachtin has a very low toxicity to
mammals, its biologically degradable and can be easily extracted from
the seeds of the trees - it can be found as leaves, oil, powder or
coir. Note, though that Azadirachtin [Diazinon] has been withdrawn due
to fly resistance from many areas.
Neem:-
ADDITIVES AS ATTRACTANTS:
"You
get more with honey than vinegar" is suggested by some as ways to tempt
the flies from an already-infected casing to their place of execution,
to be swatted, stuck, drowned, electrocuted, poisoned, eaten or
otherwise assassinated.
Others see this as folly, fearful of
bringing more baddies in by attracting them from outside, where they
were previously not troublesome. This is one you'll have to decide for
yourself.
dishes of
vinegar,
bourbon,
beer,
watered
dish soap, ‘minty
mouthwash’ have all been touted here
at the shroomery. Most entertaining of all is the ingenious and
old-fashioned '
fly agaric'
in a dish of milk, the first to get em stoned and the second to drown
them. This inventive use is behind this nickname of the amanita
muscaria. It has been used as a fly killer - hence the name. Small
pieces of the fungi were added to a saucer of milk. Flies came to feed
from the saucer and were killed.
More recommended are those yellow (they love the colour) sticky
pheromone-scented
flypaper cards
near lights to trap the first few arriving critters for monitoring
purposes or to minimise numbers.
'fly agaric':-
C : 'MILD ATTACK' MODE:
Starting low-tek, there's manual removal with clean
tweezers,
applying the business end of a
vacuum cleaner hose,
drowing the caing inhabitants with a 24h water dunk or a 6h
bleachwater (1:200) dunk.
Also heavily supported by myco-enthusiasts are the microscopic
exoskeletons of diatoms, sea-dwelling microbes. You can use
diatomaceus earth
at 3-5% volume in casing mixture or even in compost: it acts like
ground glass in grinding their little maggoty bodies up from the
inside. Ouch! Good!
And don't forget
electric bug zappers,
which both lure and kill in one snap.
'DE', Diatomaceous Earth:-
D : 'FULL ATTACK MODE' - BIOLOGICAL AND CHEMICAL
WARFARE:
BIOLOGICALS
means employing living nature to do its circle-of-life thing and work
for you. This can be as passive as a plant, a loose frog or mantis, or
as aggressive as sending mites, worms or wasps to eat their eggs and
developing children.
Venus flytraps
will survive in a humid growroom, look teriffic, and should eat the
critters (though some worry that the fine hairs may not be triggered by
the even finer gnat legs).
Green treefrogs
will be grateful to eat flies all day, if you can be sure they're not
harbouring any unwelcome pests and microscopics of their own. Still,
they're good enough for Fungi Perfecti, who made one an 'employee of
the month'!
Praying mantises
(tinodera sinesis) may sound like a scary option, but i'm not talking
about the 4-inch scaryass-looking adults, but the babies, freshly
hatched from egg cases. I suggest you move 'em on out by the time they
get as big as your hand.
Professional mushroom house kepers release
predatory
mites (Hypoaspis miles)
and nematodes (see below) to control fungus gnat larvae. When fungus
gnat food resources are exhausted, Hypoaspis mites will turn to feed on
the nematodes -- and be present when fungus gnat populations rise
again. Hypoaspis mites are used at a quantity of approx 10/sq foot for
prevention, 30-50/sq foot for damage control.
Predatory nematodes - Steinernema feltiae
-(the more common species Steinernema carpocapsae offers less
impressive results) are naturally occurring tiny worms which live in
the water-coated spaces between soil particles. These nematodes have a
specialized third juvenile stage, the dauer larva, or infective
juvenile, which is the stage which attacks insects: it is nonfeeding,
and thus can survive in the soil for extended periods until it is able
to find a susceptible host by orienting to carbon dioxide, and host
excretory products.
Infective
juveniles enter hosts through natural openings, such as the mouth, anus
or breathing pores (spiracles). These nematodes carry specific species
of bacteria in their intestines. Upon entering the host, the nematode
releases the bacteria, where they rapidly multiply, killing the host
through release of protein-destroying enzymes, usually within 24 hours.
Nematodes then feed on the host remains, and complete two or three
generations inside the host. Sounds horrible, but good on em - these
are OUR ninja assassins.
When the host resources are gone,
large numbers of infective juvenile nematodes leave the host and begin
to search for new hosts. At room temperature, it takes steinernematid
nematodes about 7-10 days from infection to the emergence of new
infective nematodes. Insects infected by steinernematid nematodes are
limp, and cream to dark brown in color.
The combination of mite
and nematode seems to work very well, but can't always be counted on
for the long run, because once they've consumed their pest hosts,
they'll die or depart, leaving the plant unprotected.
Another biological control agent is the naturally occurring
parasitic wasp
Synacra pauperi. This parasitoid is very noticeable on yellow sticky
cards. In fact, they are more attracted to yellow sticky cards than
adult fungus gnats. The adults are approximately the same size as
fungus gnat adults (1/8 inch long) and have a noticeable constriction
between the head and the thorax, and the thorax and the abdomen, which
tapers to a sharp tip. Antennae are elbowed and the tips are dark and
swollen. Females are reddish-brown with black eyes. Males are black
with long antennae approximately the same length as the body.
Female
synacra wasps insert eggs into fungus gnat larvae. They can develop in
each of the three larval instars. The parasitized larvae live until
pupation, then die, after which the wasp pupates. However, the
parasitized fungus gnat larvae may still cause damage during the
interval between parasitization and death. Synacra wasps have been
demonstrated to be a useful biological control agent of fungus gnats in
Swedish greenhouses to the point that insecticides are generally not
needed.
A rule of thumb with biologicals is you can't wait
until you get an infestation. All these organisms seem to work best as
preventive measures before pest levels build up, and when pest
populations are lower. Many commercial growers just monitor with yellow
strips, and you can wait until monitoring indicates it's time to act.
CHEMICALS i.e. insecticides may
be necessary when the sticky panels or direct evidence indicate
significant fly populations in the house:
Those used in commercial mushroom houses include
Methoprene to casing and spawn,
Diflubenzuron
[Dimilin, used in aquaculture, possibly found in aquarium shops] to
composts and casing layers. Diflubenzuron is an insect growth regulator
(IGR) which inhibits the production of chitin in the larvae thus
preventing their moulting process. Over the past few years, cases of
insect resistance to diflubenzuron have appeared.
Azadirachtin [Diazinon] to
mushroom house walls and floors (withdrawn due to fly resistance from
many areas, and
Permethrin, Piperonyl butoxide and Pyrethrins
to fog mushroom houses for flies (these latter three are not used when
mushrooms are present).
SUMMARY
prevention is better than cure
give pasteurising manure an extra half hour, and stick to 170s
rather than lower temps
consider getting a bug zapper, and some yellow flypaper strips
hung vertically near the trays.
get hold of, and use, some diatomaceus earth (also deters
slugs and snails in outdoor beds)
remove all infected casings from the grow area to minimise
cross-contamination, and clean up well after yourself.
consider a permethrin-based insecticide in compost and casing
layers.
if you have a big operation, consider getting some bugs to
work for you as gnat assassins
hope this was useful!
shirley xxx
