Bruchophagus roddi Gussakovskii
Common name: Alfalfa seed chalcid
Taxonomic placing: Insecta, Holometabola, Hymenoptera, Eurytomidae.
Geographical distribution: Cosmopolitan.
Host plants: Various species of Medicago (lucerne/alfalfa).
Morphology: The adult is about 1.7 mm long, black except for some yellow-brown parts of the legs. Both pairs of wings have only a single, anteriorly placed vein. The fully grown larva is white except for its brown head, apodous, ‘C’-shaped and about 1.8 mm in length.
Life history: The pest inserts its eggs (up to 60/female) into green alfalfa seeds. Only a single larva develops within each seed and destroys its contents, leaving only the coat. A generation takes about 1 month to complete. In Europe the chlacid usually has two annual generations and diapauses in the pre-pupal stage, but in the Middle East it has continuing, overlapping generations. In India the pest completes 6 annual generations. All stages of the pest, which can disperse locally by flight, may thus be present at any time in one area.
Economic importance: The larvae destroy the seeds as they feed and develop therein; losses can reach up to 80%. The pest has spread through the world in the seed trade.
Management
Monitoring: Sweep nets, swept through alfalfa plots, can reveal the presence of the pest. Extent of damage may be estimated prior to adult emergence by placing seeds in a 20% salt solution. Infested seeds, being lighter in weight, rise to the surface
Horticultural methods: Soil management by deep plowing or disking the plots. Crop rotation, in which alfalfa is not grown again for 2-3 years, or at a distance from old alfalfa fields. Sanitation by eliminating volunteer flowering alfalfa around fields and farm sheds, even at roadside. Clipping-back plants to delay blooming to limit green pod exposure to the pest. Irrigation reduces its numbers in infested seeds at the soil surface
Plant resistance: Winter-hardy alfalfa cultivars with early autumn dormancy have a lower level of damage than less hardy cultivars. Cultivars whose pods bear glandular hairs and are tightly-coiled are resistant. Pod-wall lignification may also reduce pest damage. In some cases resistance is due to non-preference.
Chemical control: Organophosphates and pyrethroids are still being used, but in some regions the pest has developed resistance to the chemicals. Pesticides with low toxicity to honeybees and to natural enemies are currently being used. If treatments are necessary, they should be applied during evening when bees have left the fields.
Biological control: Significant natural enemies of this seed chalcid were listed in various regions. They include endoparasitoids of the families Torymidae, Eupelmidae, Eulophidae and Pteromalidae. In the Middle East the pteromalid Pteromalus sequester Walker (formerly known as Habrocytus medicaginis Gahan) reduces pest numbers.
References
Brewer, G.J. Sorensen, E.L. and Horber, E.K. 1983. Trichomes and field resistance of Medicago species to the alfalfa seed chalcid (Hymenoptera: Eurytomidae). Environmental Entomology 12: 247-251.
Harpaz, I. 1978. Cultural control of the alfalfa seed chalcid, Bruchophagus roddi, in Israel. FAO Plant Protection Bulletin 26: 158-162.
Prashar HK, Dhaliwal JS, 1984. Biology of lucerne seed chalcid, Bruchophagus roddi Gussakovsky (Hymenoptera: Eurytomidae). Indian Journal of Agricultural Sciences 54: 935-940.
Săpunaru, T., Mateiaş, M. C., Pricop, M., Pricop, M., Bild, I. and Nechita, A. 2000. Experiments with some new insecticides to prevent and control of pests in annual legumes for grains and lucerne for seed at ARS Podu Iloaiei. Probleme de Proteçtia Plantelor 28: 283-293 (in Romanian with an English abstract).
Springer, T.L., Kindler, S.D. and Sorensen, E.L. 1990. Comparison of pod-wall characteristics with seed damage and resistance to the alfalfa seed chalcid (Hymenoptera: Eurytomidae) in Medicago species. Environmental Entomology 19: 1614-1617.
Tingey, W.M. and Nielson, M.W. 1975. Developmental biology of the alfalfa seed chalcid on resistant and susceptible alfalfa clones. Journal of Economic Entomology 68: 167-168.