Submitted to: Biological Control
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/22/2003
Publication Date: 1/14/2004
Citation: Stuart, R.J., Shapiro Ilan, D.I., James, R.R., Nguyen, K.B., Mccoy, C.W. 2004. Virulence of new and mixed strains of the entomopathogenic nematode steinernema riobrave to larvae of the citrus root weevil diaprepes abbreviatus. Biological Control. v.30. p.439-445. Interpretive Summary: The naturally occurring round worm called S. riobrave kills harmful insect pests but does not hurt people or the environment. One of the insects that this worm (called a nematode) is used for control of is a very serious pest of citrus in Florida called the diaprepes root weevil. However, only one strain (kind) of S. riobrave is currently available and it does not always kill the diaprepes root weevil effectively (sometimes it does and sometimes not). Our goal was to find new strains of this nematode so that maybe the new ones would work better than the old one. Therefore, we revisited the general area in which the original strain was isolated in Texas and Mexico and found ten new strains of S. riobrave. Several of the new strains were found to be better at killing the diaprepes root weevil and a mixture of all the strains was the best of all. Thus, the new strains may have great value in development of environmentally friendly methods to control the diaprepes root weevil and other weevil pests as well.
Technical Abstract: Steinernema riobrave generally ranks as the best entomopathogenic nematode for biological control applications against larvae of the root weevil Diaprepes abbreviatus in Florida citrus groves. However, only one strain of S. riobrave is known. The objective of this study was to find new strains of S. riobrave and determine if they may have greater biocontrol potential than the currect strain. We revisited the general area in which the original strain was isolated (the low Rio Grande Valley near Weslaco, TX) and used insect baiting to obtain 10 new isolates of S. riobrave. Incidentally, a new species of entomopathogenic nematode in the genus Heterorhabditis was also found. Laboratory assays indicated several of the new strains have superior virulence compared to the old strain, and a mixed strain (created by pooling all the new strains) had the highest virulence. These data indicate that some of the new strains or the mixed strain could be more effective for biological control of D. abbreviatus than the current commercial strain.