|Weathersbee Iii, Albert|
|Elliott, Norman - Norm|
Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2003
Publication Date: 6/28/2004
Citation: Shufran, K.A., Weathersbee III, A.A., Jones, D.B., Elliott, N.C. 2004. Genetic similarities among geographic isolates of Lysiphlebus testaceipes (Hymenoptera: Aphidiidae) differing in cold temperature tolerances. Environmental Entomology. 33(3):776-778.
Interpretive Summary: Biological control of insect pests is a very desirable approach to pest control. While many insect natural enemies are imported and released into the US, there are many that are native species. One native species parasitic wasp, Lysiphlebus testaceipes, attacks aphid pests (especially the greenbug) of wheat and sorghum. This wasp attacks many other aphid pests on a variety of crops as well, and is found in all states, plus Central and South America and the Caribbean Islands. Because of these factors, it is likely that populations of Lysiphlebus testaceipes have evolved and become specialized on specific crops and aphid pests. Therefore, Lysiphlebus testaceipes attacking one aphid on one crop may not be as effective attacking a different aphid on another crop. Parasitic wasps from different geographic regions may also differ in their effectiveness as biological control agents. One way of initially looking for this type of variation is to study genetic differences between wasps from different locations, crops and aphid pests. Using DNA sequencing, we determined that Lysiphlebus testaceipes attacking greenbug on sorghum were virtually identical across a 900 mile transect from Corpus Christi, TX, to Lincoln, NE. However, this same wasp species from FL attacking brown citrus aphid, was genetically distinct. This suggests that evolution has caused various Lysiphlebus testaceipes populations to diverge. We will next evaluate the wasp's ability to attack various aphid species and look for other biological differences. This will be of value in maximizing the effectiveness of this native wasp to control pest aphids in sorghum, wheat and other crops.
Technical Abstract: Lysiphlebus testaceipes is a solitary endoparasitoid of aphids. It is widely distributed and native to the US, but also found in South America and Europe. Lysiphlebus testaceipes is the primary parasitoid attacking cereal aphids in the Great Plains from Texas to North Dakota, especially Schizaphis graminum. In a previous study of L. testaceipes collected from S. graminum on sorghum (Royer et al., 2001), it was found that a Lincoln, Nebraska population had a much higher survivorship at cold temperatures than a population from Stillwater, Oklahoma and Corpus Christi, Texas. This suggested local adaptation to the northern environment and perhaps partitioning of populations farther to the south. To test this hypothesis, we examined DNA sequence divergence (about 440 b) in the COI and 16S mtDNA genes. We also examined a Florida population of L. testaceipes reared from Toxoptera citricida on Citrus, and L. fabarum from Europe as an outgroup. The Great Plains populations (NE, OK and TX) were very homogeneous, with zero sequence divergence in the COI, and a maximum of 0.2% in the 16S. There was weak evidence that the OK and TX populations were more closely related, and the NE population formed its own clade, suggesting a degree of divergence possibly due to cold temperature selection. Homogeneity of the Great Plains populations may be explained by a lack of geographic barriers and a continuous landscape containing wheat and sorghum hosts from southern TX to NE. This would allow uninhibited gene flow in both parasitoid and host. The FL population was divergent from the Great Plains populations in both genes. Phylogenetic analysis placed the FL population of L. testaceipes basal to the Great Plains populations alongside L. fabarum, suggesting a possible species complex within L. testaceipes.