Impact of balsam fir flowering on pollen and foliage biochemistry in relation to spruce budworm growth, development and food utilization

Abstract

The impact of balsam fir (Abies balsamea (L.) Miller) flowering on nutritional and allelochemical quality of pollen, current-year and one-year-old foliage is studied in relation to spruce budworm (Choristoneura fumiferana Clem.) (Lepidoptera: Tortricidae) growth, development and utilization of food and nitrogen. In the laboratory, using fresh food from the field, we simulated conditions of low larval population density, in which there is no current-year foliage depletion during the spruce budworm feeding period. Similarly, we simulated conditions of high larval population density when current-year foliage depletion occurs.Because of the high nutritive value of pollen (high amounts of amino acids and minerals, especially nitrogen; low monoterpene content), insects from flowering trees reached the fifth instar five days earlier than those from non-flowering trees, and had heavier dry-and nitrogen-weights at the beginning of the fifth instar. At budbreak, switching from pollen to current-year foliage negatively affected conversion efficiencies and digestibilities of food and nitrogen (AD; ADN; ECDN; ECI; ECIN). The switch from pollen to new foliage had a detrimental impact on fifth-instar survival and on newly-moulted sixth-instar dry-and nitrogen-weights. Moreover, during the fifth instar, balsam fir flowering reduced the nutritive value of current-year foliage, which in turn, might have contributed to the reduced larval growth. Nevertheless, during the sixth instar, balsam fir flowering affected the biochemistry of current-year foliage in ways that enabled larvae to compensate for their low fifth-instar biological performance; larvae also managed to reach pupal dry weight similar to larvae reared on non-flowering trees. Current-year foliage from flowering trees contained less nitrogen, total soluble sugars and total monoterpenes. Those foliar characteristics enabled larvae to increase food and nitrogen consumption rates (RCR; RNCR), because of lower repellency and/or post-ingestional feedback from monoterpenes.As for current-year foliage, balsam fir flowering reduced nitrogen, total soluble sugar and total monoterpene contents in one-year-old foliage during the sixth-instar feeding period. These characteristics enabled sixth-instar larvae, fed on old foliage from flowering trees, to have high relative food and nitrogen consumption rates (RCR; RNCR). Larvae were also able to reach higher relative growth rates (RGR) and relative nitrogen accumulation rates (RNAR) compared to larvae reared on one-year-old foliage from non-flowering trees. Finally, larvae on flowering trees had pupal dry weight similar to those from non-flowering trees, but reached the adult stage nine days earlier.Regardless the foliage type consumed by spruce budworm larvae during the sixth instar, pollen consumption during early larval stages reduced total development time, and thus exposure time to natural enemies. This phenomenon might increase larval survival. Balsam fir flowering changed the biochemistry of one-year-old and current-year foliage...

How many species of arthropods visit flowers?

“…Flowers offer high-quality food resources in the form of nectar and pollen (Roulston and Cane 2000), while the flowers themselves may also represent less well-defended material for chewing herbivores compared to leaves (Carisey and Bauce 1997). Consequently, a great multitude of invertebrates visit flowers, especially from the four most species-rich insect orders: Coleoptera, Diptera, Lepidoptera, and Hymenoptera (Kevan and Baker 1983).…”

Advantages of a mixed diet: feeding on several foliar age classes increases the performance of a specialist insect herbivore

“…However, older age-classes of foliage may not all have the same nutritional quality. For example, aging of foliage is often associated with increased shading, declines in foliar levels of carbohydrates and nitrogen (Schoettle 1994;Carisey and Bauce 1997a;Tissue et al 2001), increased infection by endophytic fungi (Clark et al 1989), and other processes that eventually lead to leaf senescence. Consequently, there could be an optimal leaf age for the development of a herbivore.…”

Spruce budworm biological and nutritional performance responses to varying levels of monoterpenes

“…1 -Monoterpenes concentrations measured in A. balsamea foliage and doses used in the experiment. (a) sources: Bauce et al 1994, Bauce 1996, Carisey & Bauce 1997a, 1997b, 1997c. …”

“…The principal monoterpenes that are produced by host tree foliage and their concentrations have been determined in several previous studies (Bauce et al 1994, Bauce 1996, Carisey & Bauce 1997a, 1997b, 1997c, Kumbasli et al 2011. Based on these data, six monoterpenes (α-pinene, bornyl acetate, camphene, δ-3-carene, terpinolene, tricyclene -Sigma-Aldrich, Milwaukee, WI, USA) were tested at different concentrations (Tab.…”

“…We focused upon sixth-instar larvae to understand the effects of monoterpenes because 87% of spruce budworm total food consumption occurs during this larval stage (Miller 1977). Further, Carisey & Bauce (1997b) found that foliar monoterpene concentrations had no effect on nutritional indices calculated for fifth-instar larvae. The monoterpenes used were in a volatile form, with preliminary tests showing that 7 days was a sufficient period of time for deploying the diets without marked decreases in their monoterpene concentrations.…”