Some observations on the diet of the backswimmer, Anisops wakefieldi (Hemiptera : Notonectidae)

In a series of laboratory experiments, A. wakefieldi was presented with a v ariety of prey from different systems to investigate its potential for cann ibalism and for eating cladocerans, copepods and rotifers. Large (ca. 7 mm) Anisops decreased the survivorship of small (ca. 3 mm) Anisops, but ate on ly 0.1 individual predator(-1) d(-1). Ingestion rates of small Anisops on s mall (< 0.5 mm) and large (0.5-0.9 mm) Ceriodaphnia dubia were 53 and 28 in dividuals predator(-1) d(-1), while those of large Anisops on these prey we re about twice as high. Clearance rates showed that small Anisops ate small and large C. dubia with similar efficiencies, while large Anisops ate larg e C. dubia much more efficiently. Anisops ate C. dubia much more efficientl y than the calanoid copepod Boeckella hamata. Only the large Anisops ate ad ult B. hamata. Large Anisops had a very low ingestion rate (0.6 individuals predator(-1) d(-1)) on the larger congener, B. triarticulata. Small, but n ot large, Anisops ate the rotifer Synchaeta pectinata and small Anisops pre sented with a natural assemblage of rotifers ate S. pectinata and Polyarthr a dolichoptera, but not four other species with a more well-developed loric a - Anuraeopsis fissa, Brachionus angularis, Keratella cochlearis and K. sl acki. Ingestion rates on Synchaeta and Polyarthra were 14-20 individuals An isops(-1) d(-1).