I have this horrible caterpillar infestation on what I think is an Abelia. Every may after the shrub has flowered all leaves are completely devoured and the plant is left completely defoliated by a hoard of grey caterpillars. The caterpillars are grey on the top and have a whitish pale underside. There are place spots running across the body of the beast. I live in Asheville, NC. The attached photo was taken today (May 27, 2014).
Any help identifying these as well as suggestions on how to deal with the best without harsh pesticides would be greatly appreciated.
To be more specific, we would need to see the head of the caterpillar and photos of other stages. But from your description and photo it is a sawfly larvae. The larvae do vary a bit as they mature and molt thru the different stages.
This insect is related to wasps. The wasplike adult usually has dark wings and colorful heads or bodies. The adults feed on nectar. Sawflies are found thru out North America. Some larvae are host plant specific others are more general leaf feeders.
The larvae do look like caterpillars from Lepidoptera(moths or butterflies) but there are some differences. The most common difference is that the prolegs (rear leg-like appendages) do not have crochets (hooks) on the bottom. Also, there are more prolegs on sawfly larvae than the typical 3-4 found on Lepidoptera. Larvae of sawflies also curl or the tail end coils around the leaf when bothered.
Usually there is only one generation a year. Sawflies overwinter in the ground or protected areas as a pupa.
It is easiest to control when they are small by either picking them off dropping in warm soapy water (sounds like you have too many to do that!). You can try hosing off with a powerful stream of water. Some may make it back to the bush, but others will get eaten 🙂 You can control small larvae spraying with insecticidal soap. However, once they get bigger it is more challenging. Yours are probably gone for this year. Next year watch for them from early May on, so you can get ahead of the damage.
Organic/Natural products that can be use are Neem (an insect growth regulator – needs to be applied before the last stage) and Pyrethrin will control this insect. But Please follow all label directions for your county and state. These products can kill beneficial insects also.