Abstract:The effect ofleafhairs on searching efficiency of adult female Phytoseiulus persimilis was investigated. For this purpose we used the ornamental crop Gerbera jamesonii and determined the predator's searching efficiency on three cultivars that differ largely in density of leaf hairs on the undersurface of the leaves. Walking speed of the mites was highest on the cultivar with the lowest leaf hair density. Walking activity, defined as the percentage of time spent walking, was not dependent on leaf hair density of the cultivars. At both prey densities tested, time until first predation increased with leaf hair density. Predation rate of adult female P. persimilis is affected by trichome density, especially when prey density is low. At prey densities of 1.3 and 2.5 T. urticae eggs/cm2, predation rate was inversely related to leaf hair density. At a prey density of 8.0 eggs/cm2 no significant effect of leaf hair density on predation rate was found. These negative effects on searching efficiency and predation success at low prey density of P. persimilis suggest that biological control of T. urticae on gerbera may be hampered by leaf hairs.

Muscidifurax raptorellusKogan & Legner is a gregarious pteromalid ectoparasitoid that attacks pupae and pharate adults from several families of the higher Diptera. Egg-to-adult development time, adult parasitoid size and emerging offspring ( = secondary) sex ratio ofM. raptorelluswere compared with clutch size in two hosts that differed greatly in mass, the smallMusca domesticaLinnaeus and the largerCalliphora vomitoriaLinnaeus. The mean number of emerging parasitoids did not vary significantly with host species, although slightly higher clutch sizes were recorded inC. vomitoria. Irrespective of offspring sex, parasitoids completed development more rapidly inM. domesticathan inC. vomitoria. In the small host, the development time and adult size ofM. raptorelluswere negatively correlated with clutch size. By contrast, female parasitoid size was unaffected by clutch size in the larger host,C. vomitoria. In both hosts, female parasitoids were significantly larger than male parasitoids. The secondary sex ratio (percentage males) of emerging parasitoids was significantly lower inC. vomitoria, and varied with clutch size in both hosts. InC. vomitoria, the greatest proportion of females emerged from hosts with the highest clutch sizes, whereas inM. domesticahosts with the highest clutch sizes produced the lowest proportion of female progeny. The results described here show that the development ofM. raptorellusis profoundly affected by interspecific differences in host quality. Our results suggest that mating structure and host quality have potentially different effects on sex ratio decisions inM. raptorellus, and perhaps other gregarious parasitoids.

Among the drimane compounds tested, the dialdehydes polygodial and warburganal were the most active as antifeedants against Colorado potato beetle larvae, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), in a dual‐choice assay with potato, Solanum tuberosum L., leaf discs. Lactones were less effective. Direct observations showed that decreased feeding on leaf discs treated with polygodial and warburganal was accompanied by increased locomotory activity. Topical application of these two compounds on the insect's cuticle decreased food intake of untreated leaf discs, indicating that besides deterrent effects, toxic properties of these molecules influence feeding behaviour.

Fifteen drimane compounds were tested for their feeding inhibiting activity in larvae of Pieris brassicae L. (Lepidoptera: Pieridae) when applied to leaf material of the host plant Brassica oleracea L. The antifeedant efficacy of the drimanes was related to their molecular structure in order to identify important functional groups. Of the drimanes tested, those with a lactone group on the B-ring were the most effective feeding inhibitors. Additionally, the sensory responses to 13 of the drimanes were measured. Neural activity was evoked in the deterrent cell in the medial sensillum styloconicum. Also, inhibition of sensory responses to feeding stimulants was found. Results of behavioural and electrophysiological tests were correlated in an attempt to elucidate the sensory code underlying feeding inhibition by drimanes in Pieris brassicae. It was concluded that the response of the deterrent cell in the medial sensillum styloconicum contributes significantly to inhibition of feeding behaviour in larvae of Pieris brassicae.

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