Nesting biology, morphological remarks, and description of the mature larva of Mellinus arvensis obscurus (Hymenoptera: Crabronidae) in Nepal

Recently re-named as a sub-species of Mellinus arvensis, Mellinus arvensis obscurus Handlirsch 1888 was investigated ecologically and morphologically in Nepal, in order to underline the most important differences with the well known M. arvensis arvensis. Mellinus arvensis obscurus females nested in clumped aggregations on inclined plains at high altitudes, both on sunny bare soil and on a shaded grassy one. Beginning of monsoon season probably interfered with wasp activity, and females performed few provisioning flights during the day. Prey consisted of a broad range of Diptera, except for one case of a spider. Many females were observed not provisioning a nest but floating on the nesting site, and many intraspecific interactions suggested a high degree of usurpation attempts. At least one species of flies and two of ants probably acted as natural enemies of the wasp. Morphological observations on females showed that the Nepal population shares more similarities (shape of tergite I, body punctation) with the European populations than with the closer Japanese population; melanization is strong, according to west-east and altitudinal cline. The mature larva of M. arvensis obscurus Handlirsch is described, illustrated, and compared with the other mature larva of the genus. The differences between both larvae mainly lie in the presence/absence, and number or differentiation of integumental structures. We conclude that morphological traits are more important than ecological and behavioral ones in distinguishing M. arvensis obscurus from M. arvensis arvensis. (author) [Spanish] En el presente articulo se aportan los resultados y conclusiones de un estudio, llevado a cabo en Nepal, en el que se abordaron aspectos ecologicos, comportamentales y morfologicos (tanto del ultimo estado de la fase larvaria como del adulto) de Mellinus arvensis obscurus Handlirsch 1888. El principal objetivo del estudio radicaba en mostrar las principales diferencias que separan a esta subespecie de la bien estudiada subespecie nominal. Mellinus arvensis obscurus nidifica a gran altitud, en terreno inclinado, con y sin vegetacion, expuesto en mayor o menor medida al sol y en agregaciones muy compactas. Durante la estacion lluviosa la hembras llevan a cabo pocos vuelos de aprovisonamiento. Las presas pertenecen al orden de los dipteros, aunque, en una ocasion se observo el aporte de una arana. Gran numero de las interacciones intraespecificas observadas sugieren un alto grado de intentos