Oulema duftschmidi (Redtenbacher, 1874)

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POLYPHAGA Emery, 1886

CHRYSOMELOIDEA Latreille, 1802

CHRYSOMELIDAE Latreille, 1802

CRIOCERINAE Latreille, 1804

Oulema des Gozis, 1886

This species is known to be widely distributed throughout the Palaearctic region from Europe through Central Asia to north-west China and also from Morocco but the details probably need to be more precisely defined because until recent decades there has been confusion with the sibling species, O. melanopus (Linnaeus, 1758). In the UK they were recognized as distinct in the 1990’s and since that time the present species, originally identified as O. rufocyanea (Suffrian, 1847) which is a rare south and central European species not extending to the UK, has proved to be widespread in England and Wales but very local and scarce in Scotland. O. melanopus has long been considered a pest of cereal crops in many regions of Europe but the economic importance of the present species is unknown due to confusion between the two and the fact that for much of the distribution the two are sympatric. Here the biology is much the same as O. melanopus; adults occur year-round and are active from early until very late in the year, overwintering among litter and stubble, in the soil and under bark etc. Host plants include a range of both wild and cultivated grasses, mating occurs in the spring after a period of feeding and oviposition begins shortly afterwards. Larvae cover themselves with a layer of excrement and plant debris and feed on the upper layers of leaves producing long and narrow translucent marks on the foliage, they develop quickly and enter the soil to pupate in a cell lined with secretions, and new generation adults occur in early summer.

4.0-4.8mm. Very similar to O. melanopus but otherwise distinct among our UK fauna; the overall habitus is less elongate and the form less convex but without comparative material many specimens are not convincingly different, the body is at least 1.46X longer than the elytra and each elytron is at most 3.3X longer than wide (Duff), and there is also a general difference in the fifth antennomere, being less elongate in the present species, but we have not found this to be generally helpful. Head and elytra dark metallic blue, pronotum pale orange or

red, antennae dark metallic and the legs mostly pale. Vertex with variable transverse wrinkles and fine punctures, often with a longitudinal furrow, frontal tubercles shiny and rather flat or indistinct among the sculpture, clypeus finely punctured, pubescent and raised medially, eyes very strongly convex and emarginate anteriorly. Pronotum convex and finely punctured, rounded anteriorly and constricted before the base. Scutellum dark, as the elytra and very finely punctured. Elytra metallic blue to almost black, each with ten strongly punctured striae and an abbreviated scutellary striole which may be less strongly punctured, interstices with sparse and very fine punctures which may form indistinct rows in places. Lateral margins weakly sinuate behind prominent shoulders and smoothly rounded to the apex. Legs vary from entirely pale or with the femora and tibiae darker apically and the tarsi entirely black.

Similar Species

Among the UK fauna this species might only be confused with the closely similar O. melanopus (Linnaeus, 1758). In general most specimens will need to be dissected and the genitalia examined to be sure of the identification. The abdomen should be removed and soaked in KOH (or NaOH which is more readily available) until it is soft and swollen, then opened with a lateral cut and laid out flat with the contents exposed on a cavity slide. Among the dark fatty tissue the male structure will be obvious and can be removed onto the slide, more solution can be added and soaked off with a small twist of tissue to remove the mass of fatty substance but this needs to be done very carefully with females as the structures of interest are small and delicate, the median lobe can then be opened to reveal the endophallus which is the diagnostic bit; long and slender in melanopus, thick and truncate in duftschmidi, in some cases the endophallus can be extruded by applying pressure on the lobe, it will often appear at the apex and then slide back in but a glance at the apex is all that is needed. Females are more delicate, the spermatheca is well-sclerotized and will be seen first, once found be sure to identify the spermathecal duct and the bursa copulatrix to avoid any damage when sliding the structure off to the side of the slide. During this delicate operation the KOH may start to crystallize, especially after the structure has been transferred to the flat part of the slide, in which case a drop of organic acid can be added to neutralize the solution; colourless vinegar works well. The form and attachment of the spermathecal duct is diagnostic; in melanopus it is short and attached laterally before the apex of the spermatheca and bursa copulatrix, in duftschmidi it is long and curved and attached to the apex of both structures. After neutralizing with acid and washing with a drop of water a few times then allowing to dry the various structures can be mounted on the same card as the specimen using a drop of DMHF.