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Some aspects ofthe host:parasite relationships between adult blackflies (Diptera; Simuliidae) and larvae ofthe water-mite Sperchon setiger (Acari; Hydrachnellae) in a small chalk stream in southern England T. GLEDHILL, JUDITH COWLEY and R. J. M. GUNN Freshwater Biological Association, River Laboratory. Warehatn. England.SUMMARY. In Bcrc Stream three species of adult simuliids, 5. ornatum.S. eqiiinum and 5. angustipes were parasitized by Sperchon setiger larvae. Trapped adult 5. ornatum were more often parasitized than corresponding adults of 5. eqttimtm. The lower 95^1 confidence limits were used as an indication of the relative importance of the statistically signiricant differences and were high {10.4-33.6'^). Laboratory experiments on the occupation of host pupae by pre-parasitic5/7erc/io«5e/iger larvae also indicated that pupae of 5. ornattim were more often occupied than S. eqiunum. This was confirmed by tests on the difference in percentage occupation of more than 4000 held-collected host pupae. In tests that indicated a significant difference in percentage parasiti/alion between the sexes of the three host species, females were more t)ften parasitized. However, the lower 95% confidence limits for the increase in percentage parasitization of females compared to males were low (0.9-10.2%). The majority of adult simuliids carried only one parasite. The mean number of larvae per trapped parasitized host was significantly greater for 5. ortiattitn (2.69) than for S. eqtiinum (1.77). There was no significant difference between the mean number of parasites carried by the sexes of 5. ornattmi for each year from 1975 through 1978 but females were significantly more heavily parasitized than males during 1979. The ventral neck region of ali three host species is the main attachment site for Sperchon setiger larvae.The morphology ofthe pupae oiS. ornatum and 5. equinum is related to differences in levels of percentage parasitization between these two species. It is suggested that pupal morphology may be the most important factor in the selection of host simuliids by Sperchon setiger larvae.1)046-5070/82/0800-0345 $02.00

The effectiveness of 2 traps for Queensland fruit fly, Bactrocera rryoni was compared for 1 year amongst relatively low populations at Applethorpe-Stanthorpe in southeast Queensland. The Lynfield trap which is an inexpensive, non-sticky, pot-type trap was significantly more effective than the Jackson trap and was at least as reliable in the detection of fruit fly populations. Use of Lynfield traps in quarantine surveillance programs should allow for a greater trap density and a more sensitive detection system to be established without vastly increased operational costs.

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