The role of volatile semiochemicals in mediating host location and selection by nuisance and disease-transmitting cattle flies.

The role of volatile semiochemicals in mediating the location and selection within herds of Holstein-Friesian heifers by nuisance and disease-transmitting cattle flies was investigated using coupled gas chromatography-electrophysiology (GC-EAG), coupled gas chromatography-mass spectrometry (GC-MS), electrophysiology (EAG), laboratory behaviour and field studies. Using volatile extracts collected by air entrainment from heifers in the Netherlands, a number of active peaks were located by coupled GC-EAG for Musca autumnalis (de Geer) (Diptera: Muscidae) and Haematobia irritans (L.) (Diptera: Muscidae). Volatile samples were also collected from two heifers in Denmark shown in previous counting experiments to differ significantly in their fly loads. Coupled GC-EAG using Ha. irritans antennae revealed differences in the EAG response to the samples, with additional EAG activity in the sample collected from the heifer with the lower fly load. To identify more EAG active compounds, volatiles were also collected from 48-h-old urine by air entrainment. In total, 23 compounds were located and identified by coupled GC-EAG and GC-MS. Further electrophysiological testing of these compounds with five fly species [M. autumnalis, Ha. irritans, Hydrotaea irritans (L.) (Diptera: Muscidae), Stomoxys calcitrans (L.) (Diptera: Musicidae) and Wohlfahrtia magnifica (Schiner) (Diptera: Sarcophagidae)] showed that only some of the compounds were physiologically active across the range of flies tested. These included 1-octen-3-ol, 6-methyl-5-hepten-2-one, (Z)-3-hexen-1-ol, naphthalene, and all EAG active compounds identified from urine. Compounds showing significant EAG activity were tested for behavioural activity using a wind-tunnel designed for measuring upwind flight behaviour. At certain concentrations, 1-octen-3-ol, 6-methyl-5-hepten-2-one and 3-octanol increased upwind flight, whereas naphthalene, propyl butanoate and linalool reduced upwind flight. In field studies using small herds of heifers ranked according to their fly load, individual slow-release formulations of 1-octen-3-ol and 6-methyl-5-hepten-2-one, when applied to low and high fly loading heifers, reduced fly loads on these individuals. This study provides evidence for the hypothesis that the natural differential attractiveness within herds of Holstein-Freisian heifers, i.e. a single host species, for cattle flies is partly due to differences in volatile semiochemicals emitted from the host. It is suggested that this phenomenon applies to other vertebrate host species and their associated insect pests.

Comparative rearing of Wohlfahrtia magnifica (Diptera: Sarcophagidae) in dead and living tissues and the impact of cold storage on pupal survival.

Larvae from adults of Wohlfahrtia magnifica (Schiner) emerging from pupal cold storage (4 degrees C for 80-100 d) were reared in wound and dead tissues. Of 2,150 first instars placed on a mixture of muscle + liver in a climate-controlled room, 47.1% molted to 2nd instar, 6.1% to 3rd instar, and 4.6% pupated. Two females emerged from these pupae after 14 d. To synchronize adult emergence, 191 pupae that were reared in living or dead tissues and were 2, 8, and 11 d old were cold-stored in lots according to age. Adult emergence was greatest in pupae of 2-d-old (57.1%) and, pupae developing in living and dead tissues, 22.5 and 8.7%, respectively. When the experiment was repeated with cold-stored pupae from 0 to 11 d old, developing in living tissues, the highest emergence was again in 2-d-old pupae (55.0%). These data have important implications for the control of adult emergence which may be used in further biological studies.