Hello Fakhar, welcome. How long was the poultry manure composted? You are certain it was completely composted? It smells fresh and earthy?

Do you know what kind of larvae these are? Flies, fruit flies...?

If you can, post a picture. There are some knowledgeable posters who might be able to get an identification of the larvae. Know the larvae, learn what attracted them. Learn what attracted them, alter the conditions.

@toxcrusadr we are dealing with poultry manure (Layer,s ) and converting it through aerobic wind row composting . It does,nt smell earthy as its source is just Nitrogen (PM) , we don,t add further material into it

What is the moisture level of that material? Maggots, the larva of flies, need a fairly most environment to hatch and grow.

kimmq is kimmsr

@rgeen. Thank you for response .I am from pakistan ,we are doing this project near Islamabad (The Capital) .it is japanese technology of windrow composting. Larvae showed up after few days of tray filling. Now i did the same as you suggested , one main thing is noticed is " These white larvas are inverting /Manipulating the compost so it appears on top of trays" it splits out.

@kimmq , as we have to irrigate seedling trays after seed plantation so it remains moist almost whole day

That is a very large and organized operation!

Is the poultry manure mixed with bedding - sawdust, wood chips, straw? If not, it is going to be very high in N and too low in C to compost well by itself. The composting process will result in losing a lot of N. And the high N manure will attract flies.

yes exctly the manure is as it treated. And organic carbon is around 30-35 % and N is 1.5- 1.7 % . Suggest me what should we do?

The flies lay eggs in you growing medium and they hatch into those maggots in about a day, total time from egg laying to emergence of adults is 7 to 10 days. Maggots need warmth and moisture to hatch from the eggs and to grow and you provide both as well as a good food source. Perhaps this article might be of some use. http://animals.howstuffworks.com/insects/housefly4.htm

Covering the medium, to keep the adult flies away, is one solution, although on that scale it may be difficult.

kimmq is kimmsr