Host plant influence on chemical defense in conifer sawflies (Hymenoptera: Diprionidae)

Abstract

Host diet affects the defensive efficacy of Neodiprion sawflies. In laboratory assays with wood ants (Formica obscuripes), secretions from larvae reared on Pinus banksiana were the most repellent, while those from P. resinosa feeders were the least so. This was explained diterpene resin acid content, but not total monoterpene content. The terpene content of regurgitant generally reflected dietary concentrations. Compounds were sequestered nonselectively by larvae. Host-based differences in defense persisted at the behavioral level. P. banksiana feeders regurgitated greater volumes of fluid and were less likely to be disabled or killed by ants in one-on-one interactions than were larvae fed on P. resinosa. The defensive advantages of host diet conflicted with developmental requirements. N. sertifer reared on P. banksiana (the best diet for defense in all cases) had lower cocoon weights (a correlate of fecundity) than those reared on other diets, and had prolonged larval development compared to insects fed P. sylvestris. No such tradeoff was detected in N. lecontei. Larvae of both species strongly preferred P. banksiana over P. resinosa in feeding choice assays.

Plant chemistry and insect sequestration

“…Compounds are mainly sequestered by herbivory on leaves, but also by feeding on roots Nishida et al 1992), flowers (Klitzke and Trigo 2000), seeds Aldrich et al 1990) and fruits (Fletcher et al 1975;Braekman et al 1982). Plant families from which sequestration occurs, belong mainly to the angiosperms, but also a few examples were found for sequestration from gymnosperms (Rothschild et al 1986;Bowers and Larin 1989;Nash et al 1992;Codella and Raffa 1995) and even from lichens (Hesbacher et al 1995).…”

“…hydroxygeraniol, sterols) are not included in this review, although those substances clearly contribute to the aposematic colouration of many noxious insects and therefore play an important role in the defence strategy of these insects (for review see Harborne 2001). Furthermore, insects such as sawflies, which deposit plant compounds in pouches of the foregut and regurgitate them when disturbed (Codella and Raffa 1995), are not described in the main text, but are included in the table (Table 1). Furthermore, the review does not include insect species (e.g.…”

Effects of group size and pine defence chemicals on Diprionid sawfly survival against ant predation

“…DiVerent defences are not mutually exclusive; for example, herbivores can combine gregarious behaviour with unpalatability (Lawrence 1990;Boevé 1991;Codella and RaVa 1995b;Sillén-Tullberg and Hunter 1996;Sillén-Tullberg et al 2000;Hunter 2000). This combination is likely to be beneWcial, since the strength of a chemical defence increases in aggregations, and predators learn to avoid noxious prey faster when they are clumped (Endler 1991;Alatalo and Mappes 1996;Hunter 2000).…”

“…High resin-acid concentration reduces growth. Thus, there is a trade-oV between fast development and defence against predators (Larsson et al 1986;Björk-man and Larsson 1991;Codella and RaVa 1995b).…”

“…Pine sawXy (Diprionidae) larvae exhibit multicomponent defensive repertoires against bird and ant predation: they are cryptic, gregarious and unpalatable for most predators (Larsson et al 1986;Codella and RaVa 1995a, 1995b, Larsson et al 2000. After the Wrst instar, larvae have also defensive movements, such as rearing of the front end and emission of a droplet of resin Xuid when disturbed by a predator (Eisner et al 1974;Kalin and Knerer 1977;Larsson et al 1986;RaVa 1995b 1996;Hunter 2000).…”