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Watch for Bagworm Egg Hatch.
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Readers in southwest Ohio should start monitoring for 1st instar COMMON BAGWORMS (Thyridopteryx ephemeraeformis). Joe Boggs reported that the Growing Degree Day (GDD) accumulation for his location in the southwest part of the state has reached 616; the GDD for bagworm egg hatch is 630. A percentage of the tiny 1st instar caterpillars will produce a strand of silk upon hatching from overwintered eggs. The silk catches the wind to transport the caterpillars to new locations. This method of distribution is known as "ballooning"; it is one of the reasons bagworms often appear on hosts that were not infested last season. Once the 1st instars find a suitable feeding site, either by ballooning or remaining on the host selected by their mother, they begin to construct their characteristic sack-like bags. | ||||||||||||
| The 1st instar bagworm caterpillars carry their bags held upward making them look like tiny dunce caps. Also, major portions of the 1st instar bags are constructed of tiny pieces of reddish-brown, sawdust-like frass stuck to the outside of the silk. The 2nd instar bagworm caterpillars, as well as all the succeeding instars, carry their bags held downward like pine cones. From the second instar stage onward, the bags are constructed with plant debris woven into the bag's silk. The plant material provides structural stability and camouflage to the caterpillar bag-abodes. Late instar bagworms can be highly destructive, particularly to evergreens. The best way to avoid damage is to monitor for egg hatch and target early instar caterpillars for control. It is a common misconception that bagworms only eat evergreens; however, the caterpillars can feed on over 130 different species of plants including a wide range of deciduous trees and shrubs. Indeed, deciduous trees and shrubs are sometimes overlooked during bagworm inspections allowing the plants to become reservoirs for reinfestation of neighboring evergreens. |
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| Early instar bagworms can be effectively controlled using the biological insecticide Bacillus thuringiensis var. kurstaki (Btk) (e.g. Dipel, Thuricide, etc.). The bacterium will not kill bio-allies such as predators and parasitoids. Once eggs begin to hatch, bagworm populations should be closely monitored since egg hatch can occur over an extended period of time. Btk is a stomach poison which means it must be consumed to kill the caterpillars, and its residual activity is very short-lived. Thus, two applications may be required. The efficacy of Btk declines once bags reach 3/4" so a standard insecticide will need to be used after bags exceed this length. |
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