Insect pests of mushrooms: Sciaridae

Sciarids

 

Adult sciarids are small (c.3-4 mm), delicate, two-winged flies which are dark grey/ black with large compound eyes and long, threadlike antennae. Females are generally larger than males and their abdomens are often distended with eggs.  Adults do not fly readily but move rapidly across the growing surface in brief jumping flights.  They may also be found "roosting" in tight spaces and on the walls of production houses.

Adult flies may be present on mushroom production sites throughout the year but are most numerous during May - November.  On average, a mated female can lay 150-170 white, oval eggs singly, or in groups within the growing substrate.  Depending on temperature, these eggs will hatch within three to four days to produce larvae.

Sciarid larvae are white, elongate, legless maggots with a distinctive black shiny head.  At this stage the larvae feed on developing mycelium and uncontrolled will burrow into pinheads and small buttons forming a sponge-like mass.  Mature larvae are approximately 8.0 mm in length and can remove mycelial attachments at the base of the stalk and in severe infestations may enter stalks and caps.

It has been demonstrated that a mean of one sciarid larva in 125g of casing causes 0.5% loss in total yield.  As the cost for recommended sciarid control measures also accounts for 0.5% of the value of the crop, this represents an economic threshold for this pest.

Larval development is temperature-dependent but after approximately 12-15 days, the larvae transform into pupae.  This is an inactive stage, which does not feed.  Adult emergence normally occurs following 5-7 days pupation.

Sciarid life cycle

• Adult flies may be present on mushroom production sites throughout the year but are most numerous during May – November.
• On average, a mated female can lay 150-170 white, oval eggs singly, or in groups within the growing substrate.  Depending on temperature, these eggs will hatch within three to four days to produce larvae.
• The larvae feed on developing mycelium burrow into pinheads and small buttons forming a sponge-like mass.
• Mature larvae are approximately 8.0 mm in length and can remove mycelial attachments at the base of the stalk and in severe infestations may enter stalks and caps.
• Sciarid infestations in Phase I compost should be eliminated by efficient pasteurisation.
• Subsequent infestations are caused by adult females, which are attracted to the fermentation odours produced during compost cool-down.
• Environmental conditions during the spawn-running period facilitate the completion of a generation of sciarids within 2-3 weeks.