sion 5.5 (Unistat Ltd. 1998, London, England). Homogeneity was tested with a Bartlett's Chi-Square-test and data were analysed with a Duncan's multi-.
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PARASITATION OF THE PARASITIC WASP EPHEDRUS PERSICAE (FROGATT) ON THE ROSY APPLE APHID DYSAPHIS PLANTAGINEA (PASSERINI) G. PEUSENS1, L. BUNTINX2 & B. GOBIN1
1 Proefcentrum Fruitteelt vzw, Department Zoology De Brede Akker 13, BE-3800 Sint-Truiden, Belgium 2 Katholieke Hogeschool Kempen Kleinhoefstraat 4, BE-2440 Geel, Belgium
SUMMARY The rosy apple aphid Dysaphis plantaginea is one of the most important leaf sucking pests in pome fruit. As damage, caused by an infestation of a relatively small number of fundatrices in spring, easily exceeds the economic threshold level, pest management is crucial. Besides the use of IPM-compatible pesticides, natural enemies (ladybird beetles, parasitic wasps, saw flies…) can play an additional role in controlling aphids. In Europe, the solitary endoparasitoid Ephedrus persicae (Hymenoptera: Braconidae, Aphidiinae) is the dominant parasitic wasp attacking rosy apple aphid. As this parasitoid develops later than its host, control is determined by the population density and the parasitising efficiency of the wasp. The population increase within a season is determined by generation turnover and parasitizing capacity, a factor poorly understood in E. persicae. To be able to estimate the number of wasps required for successful control the parasitic behaviour was studied in semi-field circumstances. Artificially infested colonies of rosy apple aphid on apple trees grown in a greenhouse, were covered with cages of gauze in which young, mated female parasitic wasps were released. The number of aphids (alatae, apterae and mummies) as well as the number of adult parasitic wasps were recorded weekly until the end of infestation or parasitation. This test method allowed a comparison of the parasitizing efficacy of Ephedrus with that of the well-studied parasitoid Aphelinus mali (Haldeman), that efficiently controls the woolly aphid Eriosoma lanigerum (Hausmann). Key words: parasitoid, rosy apple aphid, biological control
INTRODUCTION The holocyclic, heteroecious rosy apple aphid Dysaphis plantaginea (Passerini) is one of the most important leaf sucking pests in pome fruit. As damage caused by an infestation of a relatively small number in spring easily exceeds the economic threshold level, early pest management is crucial. In addition to the use of selective plant protection products, natural enemies can play an important role in controlling aphids. In Europe, the solitary endoparasitoid Ephedrus persicae (Frogatt) (Hymenoptera: Braconidae, Aphidiinae) is the dominant parasitic wasp attacking rosy apple aphid. Currently only two groups of active ingredients are registrated in Belgium for aphid control, i.e. carbamates (pirimicarb) and neonicotenoids (imidacloprid, thiacloprid, acetamiprid), a limitation that poses a potential resistance risk (Delmore 1998). Control strategies that solely rely on the use of chemicals are not the best option for sustainable agriculture (Hoehn et al, 2003) as IPM strategies should integrate a maximal use of natural enemies. In recent years, studies focussed on the release of aphid predators such as predatory midges, hover flies or ladybird beetles in crops (e.g. Wyss et al. 1999). On the
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other hand, specific vegetation managements, such as the use of weed or flower strips, were aimed to increase natural occurring numbers of these predators (Wyss, 1995; Vogt and Weigel, 1999). The presence of aphid mummies containing parasitic wasps indicate the possibility for biological control through parasitoids in our regions. Unlike other parasitic wasps (Christiansen-Weinger and Hardie, 1999) E. persicae enters diapause in summer which limits its possibility for population growth (Starý, 1975). E. persicae over winters in the orchard in aphid mummies (Evenhuis, 1958; Hagen & Van den Bosch, 1968; Mackauer and Chow, 1986; Tauber et al., 1986) and emerges in spring. To obtain an early control of the first aphids the time of emerging is important (Polgár et al., 1995). Little is known about the efficacy of the parasitation of E. persicae but several studies exist on another parasitic wasp in apple, A. mali, parasitizing the woolly apple aphid E. lanigerum (Hausmann). Monteiro et al. (2004) illustrated a parasitation rate of more than 50 % in apple orchards in South Brazil, in all seasons. In New Zealand parasitoids were able to keep the damage below the economic threshold level (Collyer & van Geldermalsen, 1975; Cameron et al., 1989). Shaw and Walker (1996) reported a parasitation rate higher than 80 % in New Zealand. In combination with a selective insecticide spraying scheme Von Kögler (1989) confirmed successful biological control of E. lanigerum by A. mali. in Pfalz (Germany). Observations made in an Australian orchard managed according to IPM-guidelines indicated the possibility of this parasitic wasp although control was only successful in combination with the European earwig Forficula auricularia (Nicholas et al., 2005) MATERIALS AND METHODS Trials with Ephedrus persicae Mummies of the rosy apple aphid naturally parasitized by E. persicae were collected in an orchard and reared in a climatic growth chamber until emerging (18/16°C day/night temperature, 16/8 h day/night photoperiod). After mating the adult wasps were used in the experiments. In the greenhouse experiment potted apple trees were inoculated artificially with D. plantaginea and reared in a greenhouse (20°C) until the infestation was established. After recording of the number of aphids in the colonies, infested shoots were enclosed with nylon insect sleeves (length: 45 cm, diameter: 21 cm) and adult parasitoids were introduced in the sleeves in relation to the degree of infestation aiming for a parasitoid/host ratio of 1/40 (see Table 1)). In the semi-field experiment naturally occurring colonies of D. plantaginea on apple trees (in an orchard were enclosed with the same type of insect sleeves (length: 80 cm, diameter: 21 cm) and introduction of parasitic wasps was similar as in the greenhouse experiment (see also Table 1). After introduction the number of aphids (alatae, apterae and mummies) on shoots, leaves and inner side of the sleeves was counted until the end of infestation or parasitation.
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Table 1. Number of adult parasitic wasps E. persicae introduced in relation to the degree of infestation by D. plantaginea in insect sleeves Number of E. persicae introduced 2 4 5 6 n.e.: not executed
Greenhouse experiment Degree Ratio of infestation parasitoid/host low (110) 1/55 medium (142) 1/36 medium (188) 1/38 high (231) 1/39
Semi-field experiment Degree Ratio of infestation parasitoid/host low (87) 1/44 medium (139) 1/35 n.e. n.e. high (248) 1/41
Trials with Aphelinus mali Potted apple seedlings were infected artificially with E. lanigerum collected in orchards and reared in a greenhouse under natural circumstances. All plants were placed individually in an wooden frame insect cage and divided into two groups: in one group 4 adult mated wasps of A. mali were introduced to the colony, the other group was left without parasitoids to serve as a control group. After introduction and until the end of infestation or parasitation the degree of infestation was estimated using a metric scale (Immik 2002) and the number of mummies and parasitic wasps were recorded. Statistical analyses were performed using Unistat Statistical package, version 5.5 (Unistat Ltd. 1998, London, England). Homogeneity was tested with a Bartlett’s Chi-Square-test and data were analysed with a Duncan’s multiple range test (p
