Developmental plasticity and reduced susceptibility to natural enemies following host plant defoliation in a specialized herbivore

Abstract

Host-specific phytophagous insects that are short lived and reliant on ephemeral plant tissues provide an excellent system in which to investigate the consequences of disruption in the timing of resource availability on consumer populations and their subsequent interactions with higher tropic levels. The specialist herbivore, Belonocnema treatae (Hymenoptera: Cynipidae) induces galls on only newly flushed leaves of live oak, Quercus fusiformis. In central Texas (USA) episodic defoliation of the host creates variation in the timing of resource availability and results in heterogeneous populations of B. treatae that initiate development at different times. We manipulated the timing of leaf flush in live oak via artificial defoliation to test the hypothesis that a 6- to 8-week delay in the availability of resources alters the timing of this gall former's life cycle events, performance and survivorship on its host, and susceptibility to natural enemies. B. treatae exhibits plasticity in development time, as the interval from egg to emergence was significantly reduced when gallers oviposited into the delayed leaf flush. As a consequence, the phenologies of gall maturation and adult emergence remain synchronized in spite of variation in the timing of resource availability. Per capita gall production and gall-former performance are not significantly affected by the timing of resource availability. The timing of resource availability and natural enemies interact, however, to produce strong effects on survivorship: when exposed to natural enemies, B. treatae developing in galls initiated by delayed oviposition exhibited an order-of-magnitude increase in survivorship. Developmental plasticity allows this gall former to circumvent disruptions in resource availability, maintain synchrony of life cycle events, and results in reduced vulnerability to natural enemies following defoliation of the host plant.

Parallel Patterns of Morphological and Behavioral Variation among Host-Associated Populations of Two Gall Wasp Species

“…The sexual generation then develops within multi-chambered galls on oak roots (Figure 2B). Males and females emerge in the spring corresponding with spring bud break [37] and (or) leaf flushes following defoliation by insect herbivores [39]. Similarly, the asexual generation of D. quercusvirens develops within woody compound stem galls (Figure 2C) during early shoot expansion in the summer and fall and emerges in the winter [30], [38].…”

Galling Insect Community Associated with Copaifera langsdorffii (Fabaceae): The Role of Inter- and Intra-annual Host Plant Phenology

“…Thus, insects using these resources during unfavorable phenological stages may suffer reduction on their performance (Forister 2005 ). For instance, galling insect emerging after leaf maturation, and even those using late-produced foliage, may have insuffi cient resource to ideal development before leaf abscission (Egan and Ott 2007 ;Hood and Ott 2010 ). Thereby, synchronization of consumers with the resources upon which they depend is of fundamental importance to consumer fi tness.…”

Generational shape shifting: changes in egg shape and size between sexual and asexual generations of a cyclically parthenogenic gall former

“…Coinciding with spring bud break sexual generation adults emerge and mate, and females then oviposit into developing leaves (Hood & Ott, 2010). In central Texas, the asexual and sexual generations alternate to complete the yearly life cycle.…”