Illinois Natural History Survey - University of Illinois

Mass Rearing of Galerucella the Illinois Natural History Survey

Since 1995 the Illinois Natural History Survey has been mass rearing two species ofGalerucella for release throughout Illinois. A stock colony is maintained throughout the winter in our greenhouse.

Preparing the Host Plants

There is no purple loosestrife in the Champaign area so it is necessary for us to travel to N. E. corner of Illinois to dig roots. Enough roots are needed for potting approximately 1,000 plants each year. Twice a year we head for an infested wetland and dig a truck full of roots. Roots are maintained outdoors, in the winter they are covered with straw and a tarp, in the summer they are shaded, covered and watered periodically.

Roots are brought into the greenhouse and left under a mistbed until they sprout, then divided as necessary and potted into 11 inch pots along with a time release fertilizer. Each pot has a 4 ft. tomato cage stuck in it to hold the growing plant upright and is also covered with a mesh cage made of no-see-um netting. With plenty of water, light, heat and nutrition they grow rapidly and are ready to receive beetles.

Beetle Production in the Greenhouse

Once the plants are near the top of the cages, (as is the case in the photo above) they are ready to receive the parental beetles. Each cage receives 25 beetles that function as parental stock. Ideally they will have just emerged from diapause. They will feed for a few days then begin mating and layin eggs. In approximately 6 weeks the next generation of beetles will begin emerging into these cages. Each large plant yields between 500 and 2,000 offspring. Production begins to get into gear in April and continues throughout the summer.


Beetle Production Outdoors

During the spring and summer, large cages shown to the right are set up with a small plastic swimming pool each holding 12 pots of purple loosestrife. These are inoculated with about 300 beetles per cage and can produce many thousands of offspring.


Overwintering Beetles

Galerucella calmariensis and G. pusilla have an obligatory diapause and in nature have a single generation each year. It is possible to maintain them in the greenhouse for more than one generation by keeping the photoperiod long and the temperatures high. However, under these conditions fitness drops significantely after the second generation. To maintain a viable colony it is necessary to hold beetles in cold storage for periods of 2 to 6 months. Beetles are preconditioned by holding recently emerged adults in progressively cool temperatures and shortened photoperiods until they will no longer feed. By this time they have built fat body and can survive the dormant period. Once they enter diapause they are kept in a refrigerator at about 4 deg. C. Beetles emerging from diapause are very vigorous and fecund.

It is quite easy to overwinter beetles outdoors by collecting numbers of reared beetles and placing them on a large, caged plant outdoors. The beetles will feed on this plant and disappear into the duff at the base of the plant where they will remain until spring. For plant and beetle survival it is best to keep these thoroughly mulched and shaded throughout the fall and winter months.

Information on this page maintained by David Voegtlin.

Illinois Natural History Survey

1816 South Oak Street, MC 652
Champaign, IL 61820

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