The Japanese beetle is an economically important pest to growers, landscape managers, and homeowners who rely on insecticides to manage the adult beetle and its grubs. Adults feed on foliage, fruits, or flowers of >300 species of wild and cultivated plants in 79 families (Potter and Held, 2002), including Rosaceae. Roses provide a useful system for exploring new ways of controlling adult Japanese beetles because both flowers and leaves are highly susceptible to adult feeding. Due to the attraction of floral scents, flowers are even more preferred by beetles than foliage (Held and Potter, 2004). Due to the long flight period of adult beetles (usually >8 weeks), multiple foliar applications of persistent insecticides like carbaryl are typically used to attain satisfactory control of adult beetles on blooms and foliage (Potter and Held, 2002).
With the implementation of the Food Quality Protection Act (FQPA), the U.S. Environmental Protection Agency (EPA) has revoked the registration of some of the common insecticides homeowners used to control Japanese beetles on roses (U.S. EPA, 2003). If the recent cancellation of diazinon for homeowners is indicative of a trend that will spread to the pyrethroids, there will be a strong need to look for alternatives to broad-spectrum foliar-applied pesticides. Studies that evaluate the ability of pesticides to reduce damage on flowers and leaves could provide simultaneous estimates of efficacy on highly preferred and somewhat less preferred plant substrates.
Imidacloprid is one of the most commonly used materials in landscapes because of its activity against leaf beetles (Chrysomelidae) and its long residual toxicity (Sclar and Cranshaw, 1996; Webb et al., 2003). A single systemic application of imidacloprid reduced adelgid (Adelgidae) populations to zero on healthy eastern hemlock trees (Tsuga canadensis) up to 816 d after the application (Webb et al., 2003) and provided control of aphids (Aphididae) and elm leaf beetle (Pyrralta luteola) on American elm (Ulmus rubra) for 1–2 years (Lawson and Dahlsten, 2003; Sclar and Cranshaw, 1996). When systemically applied to poplar (Populus deltoides and nigra) and silver maple (Acer saccharinum), imidacloprid was toxic to adult Asian long-horned beetles (Anoplophora glabripennis) (Wang et al., 2005). Although soil applications of imidacloprid do not protect Transvaal daisy (Gerbera jamesonii) blooms from western flower thrips (Frankliniella occidentalis) injury (Cloyd and Sadof, 1998), its outstanding ability to protect foliage makes it a good candidate for adult Japanese beetle control on rose leaves.
Despite its utility as a foliar protectant, soil applications of imidacloprid often result in pest outbreaks of tetranychid mites (Tetranychidae) and armored scales (Diaspididae) (Raupp et al., 2004; Rebek and Sadof, 2003; Sclar et al., 1998). Some of these outbreaks can be explained by reported toxicity of imidacloprid to lady beetles (Coccinelidae), predatory mites (Phytoseiidae), predatory plant bugs (Miridae), and parasitic wasps (Braconidae) (James and Coyle, 2001; James and Vogele, 2001; Sclar et al., 1998; Smith and Krischik, 1999). In contrast, azadirachtin extracted from the neem tree (Azadirachta indica) have fewer documented impacts on nontarget beneficial insects, reducing likelihood of secondary pest outbreaks (Schmutterer, 1990). The primary activity of azadirachtin is to inhibit the development of immature insects to adulthood by interfering with molting (Ladd et al., 1984). Azadirachtin also has repellent and antifeedant properties that are effective deterrents of >200 insect species, including adult Japanese beetles (Duthie-Holt et al., 1999; Held et al., 2001; Ladd et al., 1978). Systemic applications of azadirachtin extracts have been shown to affect a variety of pests on different hosts (Arpaia and van Loon, 1993; Nisbet et al., 1993). The systemic activity of azadirachtin can control sucking and root-feeding insects (Isman et al., 1991) as well as reduce boring insects, such as the pine engraver beetle (Ips pini) and the mountain pine beetle (Dendroctonus ponderosae) on lodgepole pine (Pinus contorta) (Duthie-Holt et al., 1999; Naumann et al., 1994). Effective translocation of azadirachtin, low toxicity to nonphytophagous natural enemies, and deterrence to adult beetles makes azadirachtin a viable control option that needs to be explored (Duthie-Holt et al., 1999; Held et al., 2001).
A recent study has demonstrated that imidacloprid and azadirachtin had both antifeedant and toxic effects against the Asian long-horned beetle and cottonwood borer (Plectrodera scalator) when fed toxic diet and “have potential for use in management programs” (Poland et al., 2006). In this experiment, we examine the use of the two systemic insecticides—azadirachtin and imidacloprid—for use in managing Japanese beetles on roses, by themselves and in conjunction with a range of foliar insecticides.
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