A univoltine species: late June (earlier in the south) to early August.
Notes In Britain, M. dimidiata is apparently associated with the native strain of Onobrychis viciifolia (referable to subspecies montana). This plant has deep pink flowers and is procumbent to erect in form, but significantly less so than the variety described below (Dony, 1953; Grose, 1957). During the 17th Century, another variant (subspecies sativa), was introduced as a fodder plant (Aubrey, 1685). This taxon differs from the wild strain in being taller and erect, the stems bearing paler flowers and with more leaves than its sibling. This introduction is now found as a relict of former cultivation. Intermediates between the two are probably hybrid stock. The introduced strain also seems to flower earlier in the season; e.g. in late May 1990, it was in full flower in east Dorset, yet the procumbent form flowered about a month later in Wiltshire (S.P.M. Roberts, pers. comm.). There are records of O. viciifolia in the writings of Gerard (1597) and Goodyer (1624) who noted it in areas which today support strong populations of subspecies montana. Significantly, both of these dates are prior to the earliest reported introduction of the plant as a fodder crop, and it seems reasonable to regard subspecies montana as the native form (P.F. Yeo, pers. comm.). The difference in flowering periods of the two variants would of necessity restrict Melitta dimidiata to the native form. There are late-glacial British pollen records of O. viciifolia (Godwin, 1975), and it is presumed that M. dimidiata subsequently arrived in Britain in Boreal or Sub-boreal times (Baker, 1964).
Parasites and predators None confirmed from Britain or elsewhere in Europe. Nomada flavopicta has been found several times within Melitta dimidiata sites in Wiltshire (pers. obs.). This Nomada is a cleptoparasite of M. leporina and probably of M. tricincta and M. haemorrhoidalis. It is possible that M. dimidiata is also a host of this Nomada.