Tuesday, November 21, 2017

Life on a leaf-Braconid

When I find signs of life on a leaf, it usually follows me home.  Stored on our table (thanks, Barb) it can wait weeks before there is an answer, if any. Here are some examples.  A yellow spot on the underside of a maple leaf turned out to be eggs.  I stored them on August 24th and expected to see some larvae emerge but when I checked them on October 17th we had lots of little adult bodies gone past their prime.

Chris Barnhart explained that they had been moth eggs laid in a cluster, possibly oakworm moth eggs of Anisota spp.  Instead they had hatched parasitoid wasps, likely chalcid wasps.  These are parasitoids attacking the eggs or larvae of a large number of insect families.  They tend to be black or brown, often metallic, and have reduced veins in their wings.

Barb brought in this leaf of kale from the garden with cocoons attached.  They soon hatched out these tiny wasps.

Chris explained that they are braconids, probably Cotesia.  They have a distinctive black stigma on the forward edge of their wings.  The larvae can choose to leave the caterpillar entirely and cocoon in a mass.  Bugguide has several examples of these cocoon collections with no evidence of the parasitized larvae left.

Braconid wasps - Microgastrinae - Joy Markgraf 
If you like raising tiny insects and have an understanding spouse or roommate, wasp parasitoids may be for you.  Start looking on leaves.
A number of you have mentioned the late Monarch migration we witnessed this year and asked what it meant for the population.  Here is the opinion from the expert from Monarch Watch.