How does synchrony with host plant affect the performance of an outbreaking insect defoliator?

Abstract

Phenological mismatch has been proposed as a key mechanism by which climate change can increase the severity of insect outbreaks. Spruce budworm (Choristoneura fumiferana) is a serious defoliator of North American conifers that feeds on buds in the early spring. Black spruce (Picea mariana) has traditionally been considered a poor-quality host plant since its buds open later than those of the preferred host, balsam fir (Abies balsamea). We hypothesize that advancing black spruce budbreak phenology under a warmer climate would improve its phenological synchrony with budworm and hence increase both its suitability as a host plant and resulting defoliation damage. We evaluated the relationship between tree phenology and both budworm performance and tree defoliation by placing seven cohorts of budworm larvae on black spruce and balsam fir branches at different lags with tree budburst. Our results show that on both host plants, spruce budworm survival and pupal mass decrease sharply when budbreak occurs prior to larval emergence. By contrast, emergence before budbreak decreases survival, but does not negatively impact growth or reproductive output. We also document phytochemical changes that occur as needles mature and define a window of opportunity for the budworm. Finally, larvae that emerged in synchrony with budbreak had the greatest defoliating effect on black spruce. Our results suggest that in the event of advanced black spruce phenology due to climate warming, this host species will support better budworm survival and suffer increased defoliation.

Warming counteracts defoliation‐induced mismatch by increasing herbivore‐plant phenological synchrony

“…A phenological mismatch between antagonistic species can negatively affect herbivore feeding. A lower quality of food increases the risk of starvation for herbivores, thus decreasing their survival and reproduction (Fuentealba, Pureswaran, Bauce, & Despland, ). As a consequence of the phenological mismatch, the young larvae try to disperse to prospect for food elsewhere.…”

Host plant phenology, insect outbreaks and herbivore communities – The importance of timing

“…Non-significant interaction terms shown in the results are derived from the original, non-simplified models. For models with a quasi-distribution or a temporal correlation structure, significance was assessed with a marginal ANOVA using function anova.lme from the nlme package (Pinheiro, Bates, DebRoy, & Sarkar, 2017), while a type III ANOVA from the car package (Fox & Weisberg, 2011) was used for all other models. To account for variation among blocks, we included block as a random effect in each of the models described below.…”

“…Specialized herbivores can sometimes overcome these defenses (Roslin & Salminen, 2008), allowing them to utilize a highly nutritious resource. By contrast, herbivores feeding on older leaves can experience lower survival, body mass and growth rate (Fuentealba, Pureswaran, Bauce, & Despland, 2017;Tikkanen & Julkunen-Tiitto, 2003;Tikkanen & Lyytikainen-Saarenmaa, 2002), possibly due to lower nitrogen content and/or a tougher leaf surface in older leaves (Falk et al, 2018;Feeny, 1970;Salminen et al, 2004). Hence, many herbivores experience a short time window when the leaf quality is high.…”

Phenological synchrony between eastern spruce budworm and its host trees increases with warmer temperatures in the boreal forest

“…Emerging too late in relation to budburst also reduces fitness as lignified foliage is difficult for young larvae to feed on (Lawrence et al, ). Recent studies that manipulated the availability of new buds to second instar larvae showed that phenological asynchrony with both balsam fir and black spruce has a negative impact on spruce budworm performance (Fuentealba, Pureswaran, Bauce, & Despland, ; Fuentealba, Sagne, Pureswaran, Bauce, & Despland, ).…”