Rearing parasitoids: Doirania & Leefmansia, PNG Minimize

March 2013. We have been rearing parasitoids from the eggs of Tettigoniidae (which are the size of rice grains); however, our technique is cumbersome and labour intensive, and I would like to ask if anyone has any techniques (however unspecialized) for mass rearing minute Doirania leefmansi (Trichogrammatidae) or Leefmansia bicolor (Encyrtidae), or any related parasitoids from Orthoptera eggs or other large insect eggs? Another problem, because of high humidity we have fungal contamination; I wonder if anyone has ideas on reducing infestations, as our conditions are fairly basic at present.

The techniques used at present are the following:

We collect host eggs and put a number (usually 100-200) into petri-dishes containing oasis (a green absorbent material used by florists). The Oasis is damp (a great cause of fungus that grows on the eggs, although not all the time!). Parasitoids are permitted access by being in a larger cage and they are given 10% honey as a food source.

After a few days (when we assume parasitism has taken place), a 10% sample of eggs is removed for us to be able to estimate parasitism rate, and also estimate numbers likely to be released.

The presumed (as there is no obvious way of telling) parasitised eggs are then put into IKEA spice jars with damp Oasis and kept until the parasitoids are emerging and can then be released. The parasitoids themselves are minute, and individual handling is not really possible. Doirania leefmansi is parthenogenetic and more than 200 adults may emerge from a single host egg. Leefmansia bicolor on the other hand has males and females and produces about 50 adults from a single egg.

We should be producing very large numbers, but this does not seem to happen! Your thoughts will be much appreciated (as for anyone else).

A member asked if alternative hosts had been tried? Probably, Ephestia or Corcyra cephalonica eggs would be suitable for your parasitoids. These moths probably will be easier to rear.

Other suggestions were as follows:

  • Treat the oasis with chlorine (Clorox) before using it or try other absorbent material like sponges or paper filter disks.
  • Test different parasitoid/host egg ratio and exposure times. Probably there is over-parasitism and this could be affecting emergence rates.
  • Is it really needed to damp the oasis after parasitism? If high humidity levels are needed probably another way of doing it should be explored (eg room humidifier).