Plant chemistry and insect sequestration

Abstract

Most plant families are distinguished by characteristic secondary metabolites, which can function as putative defence against herbivores. However, many herbivorous insects of different orders can make use of these plant-synthesised compounds by ingesting and storing them in their body tissue or integument. Such sequestration of putatively unpalatable or toxic metabolites can enhance the insects' own defence against enemies and may also be involved in reproductive behaviour. This review gives a comprehensive overview of all groups of secondary plant metabolites for which sequestration by insect herbivores belonging to different orders has been demonstrated. Sequestered compounds include various aromatic compounds, nitrogen-containing metabolites such as alkaloids, cyanogenic glycosides, glucosinolates and other sulphurcontaining metabolites, and isoprenoids such as cardiac glycosides, cucurbitacins, iridoid glycosides and others. Sequestration of plant compounds has been investigated most in insects feeding or gathering on Apocynaceae s.l. (Apocynoideae, Asclepiaoideae), Aristolochiaceae, Asteraceae, Boraginaceae, Fabaceae and Plantaginaceae, but it also occurs for some gymnosperms and even lichens. In total, more than 250 insect species have been shown to sequester plant metabolites from at least 40 plant families. Sequestration predominates in the Coleoptera and Lepidoptera, but also occurs frequently in the orders Heteroptera, Hymenoptera, Orthoptera and Sternorrhyncha. Patterns of sequestration mechanisms for various compound classes and common or individual features occurring in different insect orders are highlighted. More research is needed to elucidate the specific transport mechanisms and the physiological processes of sequestration in various insect species.

Herbivore pressure increases toward the equator

“…3 and Tables S1 and S3) translate into greater qualitative herbivore pressure closer to the equator. The distinct evolutionary makeup of each additional herbivore lineage is likely to influence the response of that particular taxon to the mechanical and chemical defenses of its host (11). Piper aequale in Ecuador was attacked by caterpillars from four families not found on that plant species in either Mexico or Bolivia, and P. aduncum by seven additional families ( Fig.…”

“…Herbivore pressure is expected to increase with greater tissue loss when damage reduces growth and reproduction (quantitatively) (9) but also with changes in the identity of the herbivore species (qualitatively) (7). Increased number of species attacking a given plant host should result in a qualitatively different set of selective pressures compared with attack by fewer species because each herbivore reacts idiosyncratically to the defensive arsenal of a plant and may, therefore, influence plant fitness in different ways (10)(11)(12)(13). From the point of view of the plant, each combination of traits embodied by a specific herbivore species may represent an additional and potentially unique evolutionary hurdle that the plant may need to overcome and may be manifested as a tradeoff in defense allocation.…”

Phyllotreta striolataflea beetles use host plant defense compounds to create their own glucosinolate-myrosinase system

“…To avoid deleterious effects from plant toxins, herbivores require appropriate biochemical adaptations allowing them to deal with these metabolites, for example, by developing insensitive target sites or by enzymatic detoxification. Many specialized insects are able to sequester plant defense compounds and exploit them for their own protection against natural enemies and/or as semiochemicals in interspecific communication (2,3).…”

A Pharm-Ecological Perspective of Terrestrial and Aquatic Plant-Herbivore Interactions

“…Of the parameters outlined in Figure 1, dose (e.g., total intake), metabolism, excretion and foraging response have received the most attention by ecologists (Haley et al, 2008;McLean and Duncan, 2006;. Distribution, specifically associated with the amount and site of sequestered PSMs, is well described in terrestrial insects (Opitz and Muller, 2009;Dobler et al 2011) and a small number of marine invertebrate systems (Pennings and Paul, 1993;Whalen et al, 2010). The mechanisms of absorption of PSMs and the resultant kinetics (i.e.…”