Bagworms "Appear"

Yes, it may seem that this bug just appeared but bagworms have been feeding since early June. Most folks don’t notice bagworms until they have devoured most of the foliage of their favorite host plants such as arborvitae and juniper. Bagworms seem to prefer conifers but they are known to feed on more than 125 different plant species including sycamore, honeylocust and elm. Bagworms can be deadly to some plants. Evergreens that are defoliated do not recover. Deciduous plants can tolerate the feeding much better.
It is important to realize that the treatment time for this insect has passed. You may have the urge for revenge… but hold off. You can get ‘em next year when they are vulnerable.

Here’s a quick review of the bagworm life cycle. Right now they are mature larvae (caterpillar form) encased in a cocoon-like “bag” made up of parts of the plant they are feeding on. Soon, they will stop feeding and pass into a resting stage (pupae). Later this summer the moth-like adults emerge. Actually, only the males leave the bag. Females lure in the males, mate and then die, leaving 500-1000 eggs to overwinter. So, some bags that you see from September through Spring are empty. These are remnants of male bagworms. Some contain eggs… remains of the female insects.

About Memorial Day, 2009, we can expect the little buggers to hatch. They begin feeding in June but go un-noticed by most folks as they blend into the background of the plants they are feeding on. But this is the time to drop the hammer on them. By mid -June most of the eggs should have hatched and small larvae are feeding. The biological insecticide called Bt can be effective if your timing and spray coverage is good. Conventional insecticides such as carbaryl (Sevin) and synthetic pyrethrins are also effective. So, if you have signs of bagworm feeding, mark your 2009 calendar for Flag Day and plan to treat then.
What? You want to pick off all of the bags. OK. Have fun. But don’t call me if you off the ladder. Seriously, hand picking is OK but your chances of getting them all are slim. There is some gratification in hand picking but it ain’t worth breaking a leg.

PS Photo by Sarah Pickel, PA Department of Agriculture. Look closely and you can see the pupal case protruding from the open end of the bag.