The Galerucella Life Cycle
Galerucella beetles have a fairly simple life cycle. The adult beetles begin emerging from hibernation by May, feeding voraciously on the newly-emerging leaves of purple loosestrife plants. Eggs are laid in sets of ten, from May to early June, and take up to two weeks to hatch. The eggs often have a distinctive line of frass, or beetle excrement, on each egg after being laid.
Galerucella eggs on a loosestrife leaf.
Once they hatch, the larvae crawl to the tips of the plants to hide from predators and feed on the plant buds (thus preventing flowering). They will go through 3 molts, or “instars”, as larvae, with the third instar causing the most damage to loosestrife through its “window pane” feeding. It consumes everything but the thin cuticle of the plant. We had a few cages where all the leaves were consumed, leaving nothing but crispy brown cuticles hanging from the loosestrife stalks.
Early damage to the top of a loosestrife plant from Galerucella larvae
After feeding for 2-3 weeks, the larvae will crawl down to the soil in your pots (or ground soil, if they are in the wild) and pupate, emerging after 2-3 weeks as pale new beetles. These beetles will want to eat right away, so putting your pots out into the wild once you see new beetles will help ensure their survival.
A released Galerucella in its new home!
Biological Control of Purple Loosestrife: A Guide for Rearing Leaf-feeding Beetles, University of Minnesota:
Galerucella rearing guide, Rachel Carson National Wildlife Refuge: