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The oviposition behaviour of Dendrocerus carpenteri (Curtis), an ectophagous hyperparasitoid of aphidiine wasps inside mummified aphids was examined. Hyperparasitoids were provided in the laboratory with pea aphids (Acyrthosiphon pisum) which had been parasitized by three different species of aphidiine wasps (Aphidius ervi, Ephedrus californicus and Praon pequodorum) ranging in physiological age from the late larval stage to the late pupal stage. Females accepted only the hosts inside mummified aphids; they ignored live aphids, and did not accept dead, but not yet mummified aphids, although the latter were sometimes probed with the ovipositor. Female behaviour in handling A. ervi or E. californicus mummies did not change with experience; handling and oviposition times were stereotypic. However, naive females needed experience to locate the cocoon of P. pequodorum and distinguish it from the empty aphid mummy. Host acceptance and specificity were influenced more by the developmental stage than the species of the primary parasitoid. In dichotomous choice tests, hyperparasitoids ‘preferred’ prepupae over younger pupae of A. ervi, but they did not distinguish between these stages of E. californicus; older pupae were accepted at a low rate. Host preference was not influenced by conditioning on the rearing host. We consider several constraints on the host range of D. carpenteri, and discuss alternative explanations of differential hyperparasitism in the field.

Fertilization reduction could be a useful pest management tactic for floriculture crops if it reduced pest populations with little loss in crop yield and quality. We evaluated the response of the twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), to different fertilization levels for cut roses, Rosa hybrida L. 'Tropicana' and quantified fertilization effects on (1) management of T. urticae on roses, (2) abundance and distribution of T. urticae on roses, and (3) yield and quality of the cut rose crop. We tested two fertilization levels, 10% (15 ppm N) and 100% (150 ppm N) of the recommended level for commercial production, and three control methods: no control measure; a predatory mite, Phytoseiulus persimilis Athias-Henriot; and a miticide, bifenazate. Combinations of both bottom up (fertilization) and top down (biological or chemical control) tactics provided a greater degree of T. urticae control than either tactic alone. Rose productivity was reduced with fertilization at 10% of the recommended level; therefore, we conducted studies with T. urticae on roses fertilized with 33% (50 ppm N), 50% (75 ppm N), and 100% (150 ppm N) of the recommended level. Mean numbers of T. urticae and T. urticae eggs per flower shoot were twice as high on roses fertilized with 100 versus 33% or 50% of the recommended level. Number of rose leaves and total leaf area infested by T. urticae were similar at all fertilization levels. Cut rose yield and marketability were not compromised on plants fertilized with 50% of the recommended level.

Abstract. We test the hypothesis that a solitary parasitoid wasp may gain in fitness if she lays more eggs in a host. Using heterospecific superparasitism (=multiparasitism) between the solitary aphid parasitoids, Aphidius smithi Sharma & Subba Rao and Ephedrus californicus Baker, we show that (i) a superparasitizing female's chance that her offspring will survive competition is an increasing function of egg density, and (ii) survival among same‐aged larvae is independent of the oviposition sequence. These findings on asymmetric larval competition provide indirect evidence that supports two fundamental, but untested, assumptions underlying models of adaptive superparasitism between conspecific wasps.