They can be used as biological control as we have a research based evidence in indian rice fields and also in western kenya(http://www.parasitesandvectors.com/content/4/1/128)
I believe some work was done (possibly by Philip Corbet?) placing odonate nymphs in containers that collect water within communities to cut down on mosquito emergence within a village. I am having trouble finding a reference for this, but do have the following work looking at odonate use in midge control:
J. ARENA and M. C. CALVER. Biological Control Potential of Three Species of Nymphal Odonates against Polypedilurn nubifer (Skuse), a Nuisance Midge
(Diptera: Chironomidae) Australian Journal of Entomology, 1996, 35: 369-371.
Yes, Dragon flies can be used as biocontrol agents of mosquitoes specially bradinopyga geminata, Crocothemis spp, pantala flavescens etc Kindly see the book Dragon flies production technology written by Dr T V Sathe 2013 Astral international Private LTD, New Delhi
Yes, potentially very useful in certain situations. Dragon fly larvae are most useful for biological control in semi-permanent to permanent aquatic mosquito habitats such as rice fields and ponds, but much less useful in small, temporary habitats where predator populations are highly unstable. Lamborn (1980) http://www.biodiversitylibrary.org/item/25901#page/1/mode/1up. Dragon larvae can manually be placed in container habitats for temporary control [see Sabastian, Sein, and Thu (1990)], but many more cost effective biorational methods are also available for these types of habitats [see Biorational Control of Mosquitoes, Bulletin No. 7, Supplement ot the Journal of Mosquito Control Association 23(2)].
Dragonflies as well as their nymph are natural predators of mosquitoes and their larvae. We have to mass produce dragonflies to effectively control and reduce mosquito population
Dear Dr. Lawrence, Dragonflies larvae used for control the mosquito borne diseases. I published one paper in Odonatologica regarding this. Kindly go through it