Studies on Insects bred from Barley, Wheat, Maize and Oats

Larvae of a flea-beetle,Chaetocnema arida, were found mining in the stems of young barley shoots in June 1939. Chlorops pumilionislarvae infested barley most heavily in fields whereAgrioteslarvae were doing most damage. TheChloropsadults showed marked sexual dimorphism in both size and colour. The size range for this species is correlated with a proportionate size range in its parasitesCoelinius nigerandStenomalus micans. Perforations 1·3 mm. in diameter in the top of a cage were sufficient for the escape ofStenomalusbut not ofChloropsorCoelinius. Lasiosina cinctipeslarvae were commonly synoecious withChloropsin barley shoots, but in some cases (5–10 per cent.) they were living withoutChlorops. In these shoots the nodes were not swollen as inChloropsinfestation.Lasiosinawas not attacked by the above parasites ofChlorops. The larvae ofElachiptera cornutainfested shoots already badly damaged by other species and were accompanied by manyLasiosinalarvae. Wet weather in July favours these two species. Their puparia differ in the form of the posterior spiracles.Elachipteraalso occurred in maize and wheat. Meromyza saltatrixvar.nigriventriswas present in stunted barley shoots in small numbers, producing swelling of the nodes very like that due toChlorops. The summer pigmentation in both these species in Hampshire differed from that reported by Mesnil in France.Meromyzawas also bred from wheat.Meromyzapuparia, unlike those ofChlorops, were attached to barley sheathing-leaves by silk. Oscinella fritlarvae, infesting young sweet maize shoots at Gosden, Surrey, were either accompanied or followed by those ofAphanotrigonum trilineatumandElachiptera. Infesting oat shoots at Long Sutton, Hampshire,Oscinella fritlarvae were accompanied by larvae ofLasiosinaandCamarota curvinervis. Adults of the latter emerged from stunted barley shoots in September. They showed some resemblance to flea beetles, possibly protective.Oscinella fritwas also bred in small numbers from stunted wheat and barley shoots. The Chalcid,Callitula pyrrhogaster, was reared from pupae of this species found in oat shoots. Larvae of a Muscid,Hylemyia(Phorbia)genitalis, infested a winter wheat crop in large numbers in May 1940.Tropidoscinis albipalpis, Oscinella? graciliorandAgromyza nigripes, were bred in small numbers from potted plants of this crop kept in a cage in the laboratory during the summer.Hylemyia genitalisandAgromyza(Domomyza)ambiguapupated in the soil surrounding the roots of these plants. The adults (together with a Braconxd parasite,Phaenocarpa pullata, Hal.) emerged from the soil in the following spring.