Taste receptor activity and feeding behaviour reveal mechanisms of white spruce natural resistance to Eastern spruce budworm Choristoneura fumiferana

Abstract

The pattern of feeding of Eastern spruce budworm Choristoneura fumiferana (Clem.) (Lepidoptera, Tortricidae) is compared on foliage from white spruce Picea glauca (Moench) Voss. (Pinaceae) trees previously determined to be susceptible and resistant to defoliation by budworm. No differences are observed in electrophysiological responses from taste sensilla to aqueous extracts of the two foliage types, nor is there a preference for either extract type in a choice test. Acetone extracts from the two foliage types are both preferred to a control sucrose solution, although neither elicits a preference relative to the other. These results suggest that there is no difference in phagostimulatory power of internal leaf contents of the two foliage types. Longer‐term observation of feeding behaviour in a no‐choice situation shows no difference in meal duration, confirming the lack of difference in phagostimulatory power. However, on average, intermeal intervals are twice as long on the resistant foliage, leading to an overall lower food consumption during the assay. This result suggests an anti‐digestive or toxic effect of the resistant foliage that slows behaviour and limits food intake. Previous research has shown that waxes of the resistant foliage deter initiation of feeding by the spruce budworm and that this foliage contains higher levels of tannins and monoterpenes. The data suggest that the resistant foliage contains a post‐ingestive second line of defence against the spruce budworm.

Phenolic compounds that confer resistance to spruce budworm

“…In brief, these results most likely provide one explanation for reduced spruce budworm populations on resistant white spruce in the Drummondville forest. Tannins, a group of (high molecular-weight rather than mono-) phenolics implicated in natural resistance mechanisms (Harborne, 1984), have been shown to have negative effects on performance and their actions create intestinal lesions and disrupt development of budworms (Bauce et al, 2006;Despland et al, 2011), gypsy moths (Barbehenn et al, 2009), and grasshoppers (Bernays & Chapman, 2000). Furthermore, a hypothesis was proposed that phenolic compounds increase in response to insect attack in insecthost plant or tritrophic interactions (Bahnweg et al, 2000;Faccoli & Schlyter, 2007).…”

Larval experience induces adult aversion to rearing host plants: a novel behaviour contrary to Hopkins' host selection principle

“…We examined the pattern of feeding of sixth‐instar larvae, which provides information on the quality of the food source and the ways in which it influences the insect's behaviour (Despland et al , 2011). When an insect probes a plant, it receives chemical information about stimulatory or deterrent compounds that direct further feeding.…”

“…The behaviour can be quantified by counting the number and duration of probing events; faster transition to feeding indicates a food source with higher phagostimulatory power (Simpson, 1995; Daoust et al , 2010). The duration of the first feeding bout is also an indication of the overall phagostimulatory power of a food source; strong phagostimulatory responses from taste cells lead to a high level of feeding excitation, which then decreases gradually during the meal as a result of post‐ingestive feedback, until it reaches a threshold and ingestion ceases (Simpson, 1995; Simpson & Raubenheimer, 2000; Despland et al , 2011). Insects feeding on foliage containing phagodeterrent compounds are therefore expected to take shorter meals.…”

“…The present study examined information transfer across larval stages and from larval to adult stages using the eastern spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae), and two recently described distinct types of white spruce tree, Picea glauca (Moench) Voss (Pinaceae), defined by their differential susceptibility to attack by the budworm (Bauce & Kumbasli, 2007; Daoust et al , 2010; Despland et al , 2011). Resistant trees support lower spruce budworm survivorship and have been shown to contain more monoterpenes and condensed tannins than susceptible trees (Daoust et al , 2010).…”

“…Resistant trees support lower spruce budworm survivorship and have been shown to contain more monoterpenes and condensed tannins than susceptible trees (Daoust et al , 2010). Experiments suggest the presence of anti‐digestive or toxic compounds within the resistant foliage (Delvas et al , 2011; Despland et al , 2011). To investigate whether spruce budworm that were laid and developed on a resistant white spruce tree showed differences in feeding behaviour or oviposition preference compared with insects reared on susceptible trees, we examined: (i) the feeding behaviour of sixth‐instar larvae in a no‐choice test; and (ii) the oviposition behaviour of adult females in a two‐choice test.…”