Sorghum halepense (L.) Persoon (Poaceae), a new larval host for the South American corn rootworm Diabrotica speciosa (Germar) (Coleoptera: Chrysomelidae)

Authors: CABRERA WALSH, GUILLERMO - USDA/ARS/SABCL

Submitted to: The Coleopterists Bulletin
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2007
Publication Date: 4/30/2007
Citation: Cabrera Walsh, G. 2007. Sorghum halepense (L.) Persoon (Poaceae), a new larval host for the South American corn rootworm Diabrotica speciosa (Germar) (Coleoptera: Chrysomelidae). The Coleopterists Bulletin - 61(1):pp. 83-84

Interpretive Summary: Diabrotica speciosa is a South American corn rootworm (Coleoptera: Chrysomelidae: Galerucinae) the adult of which is a pest on many crop and ornamental plants. The list of known larval hosts, however, is limited to maize, wheat, potatoes and peanuts. In March, 2005, larvae of D. speciosa were found feeding on roots and rhizomes of Johnson grass, Sorghum halepense (L.) Persoon (Poaceae), in the locality of Mercedes, Buenos Aires province. The larvae were transported together with the root mat to the laboratory, and incubated until adult emergence on the same, in 500-ml containers with potting mix. The resulting adults were of normal size and appearance. The plants hosting the larvae were located more than 8 meters away from the nearest maize plants, ruling out the possibility of the eggs having being laid near the corn plants, or partly developed on them and then moved through the soil to the S. halepense plants where they were collected. This is the first report of a non native wild plant hosting D. speciosa larvae in the field. The significance of this find is that Johnson grass is an invasive grass that can be found worldwide at present, and is considered one of the worst weeds in the world. So this find is a forewarning regarding the dispersal of the western corn rootworm, Diabrotica virgifera virgifera, since the chances of controlling its dispersal, especially in the areas where it is not present yet, or uncommon, depend in great measure on it not finding substitute host plants.

Technical Abstract: Diabrotica speciosa is a South American corn rootworm (Coleoptera: Chrysomelidae: Galerucinae) the adult of which is a pest on many crop and ornamental plants. The list of known larval hosts, however, is limited to maize, wheat, potatoes and peanuts. In March, 2005, larvae of D. speciosa were found feeding on roots and rhizomes of Johnson grass, Sorghum halepense (L.) Persoon (Poaceae), in the locality of Mercedes, Buenos Aires province. The larvae were transported together with the root mat to the laboratory, and incubated until adult emergence on the same, in 500-ml containers with potting mix. The resulting adults were of normal size and appearance. The plants hosting the larvae were located more than 8 meters away from the nearest maize plants, ruling out the possibility of the eggs having being laid near the corn plants, or partly developed on them and then moved through the soil to the S. halepense plants where they were collected. This is the first report of a non native wild plant hosting D. speciosa larvae in the field. Johnson grass is an invasive grass of Eurasian origin. It can be found worldwide at present, and is considered one of the worst weeds in the world. More significantly so, it is a very common plant in Europe, where the western corn rootworm, Diabrotica virgifera virgifera Le Conte, was accidentally released in the early 1990’s. The chances of controlling the dispersal of D. v. virgifera, especially in the areas where it is not present yet, or uncommon, depend in great measure on it not finding substitute hosts native to Eurasia.