Differentiation of two Bathyplectes species, B. anurus and B. curculionis, parasitoids of the Alfalfa weevil (Hypera postica) in Spain.

The alfalfa weevil Hypera postica Gyllenhal (Coleoptera: Curculionidae) is one of the most destructive alfalfa pests in the world, resulting in substantial economic losses. However, the amount of damage can be reduced by larval parasitoids of the genus Bathyplectes Förster (Hymenoptera: Ichneumonidae) as a conservation biological control strategy. Parasitoids are currently identified by morphological body characteristics, cocoon morphology, and/or DNA analysis, but geometric morphometrics (GM) applied to the wing vein arrangement may also reveal differences between specimens. We distinguished 61 B. anurus (Thomson) and 41 B. curculionis (Thomson) specimens, based on the appearance of the cocoon. GM revealed statistically significant differences in wing vein patterns and fore wing shapes between species, but not between sexes within the same species. The 1 M + 1R1 cell, also known as the horsehead cell, was revealed to be an easy and reliable morphological character for species differentiation. Despite the New World literature, this is the first European report providing a visual method to differentiate B. anurus from B. curculionis. This study highlights the importance of precise species identification methods, such as geometric morphometry. It can contribute to a better implementation of biological control strategies against the alfalfa weevil in Spain and other Mediterranean countries.