Leaf Surface Lipophilic Compounds as One of the Factors of Silver Birch Chemical Defense against Larvae of Gypsy Moth

Abstract

Plant chemical defense against herbivores is a complex process which involves a number of secondary compounds. It is known that the concentration of leaf surface lipophilic compounds (SLCs), particularly those of flavonoid aglycones are increased with the defoliation treatment of silver birch Betula pendula. In this study we investigated how the alteration of SLCs concentration in the food affects the fitness and innate immunity of the gypsy moth Lymantria dispar. We found that a low SLCs concentrations in consumed leaves led to a rapid larval development and increased females’ pupae weight (= fecundity) compared to larvae fed with leaves with high SLCs content. Inversely, increasing the compounds concentration in an artificial diet produced the reverse effects: decreases in both larval weight and larval survival. Low SLCs concentrations in tree leaves differently affected larval innate immunity parameters. For both sexes, total hemocytes count in the hemolymph increased, while the activity of plasma phenoloxidase decreased when larvae consume leaves with reduced content of SLCs. Our results clearly demonstrate that the concentration of SLCs in silver birch leaves affects not only gypsy moth fitness but also their innate immune status which might alter the potential resistance of insects against infections and/or parasitoids.

Intrapopulation Genotypic Variation of Foliar Secondary Chemistry during Leaf Senescence and Litter Decomposition in Silver Birch (Betula pendula)

“…Foliar secondary metabolites (Keinänen and Julkunen-Tiitto, 1998; Laitinen et al, 2000), their genotypic variation and role in herbivore and stress responses (Mutikainen et al, 2000; Yamaji et al, 2003) are equally well known for B. pendula . For example, the flavonoid aglycones and triterpenoids found on B. pendula leaf surface can impair the growth and survival of Lymantria dispar larvae (Martemyanov et al, 2015). The ability of secondary metabolites to explain the link between herbivore resistance and litter decomposition rate in B. pendula has also been tested, with no obvious role found (Silfver et al, 2015), but the basic knowledge of alterations in the secondary metabolite profiles and their genotypic variation in leaf senescence and litter decomposition is lacking.…”

Phenological asynchrony between host plant and gypsy moth reduces insect gut microbiota and susceptibility to Bacillus thuringiensis

“…Ecologists consider the phenological synchrony between the emergence of overwintering herbivorous insects and the budding of their host plants to represent one of the crucial factors in the population dynamics of herbivores (van Asch & Visser, ; Feeny, ; Foster, Townsend, & Mladenoff, ; Hunter & Lechowicz, ; Ivashov, Boyko, & Simchuk, ; Martemyanov, Pavlushin, Dubovskiy, Belousova et al., ; Martemyanov, Pavlushin, Dubovskiy, Yushkova, et al., ). If the larvae hatch prior to the host plant budburst, the larvae may starve, whereas if the larvae hatch too late, the foliage quality may be reduced (reviewed in van Asch & Visser, and references therein), although the occurrence of this phenomenon is related to studied species (Kharouba, Vellend, Sarfraz, & Myers, ) and global climate processes (Uelmen et al., ).…”

“…In addition, dramatic changes in leaf quality during the first 20 days of development have been suggested to represent the main mode of action of asynchrony on insect antiviral immunity (Chernyak et al., ; Martemyanov, Pavlushin, Dubovskiy, Yushkova, et al., ). However, the effect of asynchrony on insect bacterial diseases, such as intestinal bacteria Bacillus thuringiensis , which is widely used for the pest management (Garczynski & Siegel, ), remains unclear because different insect immune parameters are affected in different ways by the same trophic factor (Martemyanov, Dubovskiy, Belousova, et al., ; Martemyanov, Dubovskiy, Rantala, et al., ; Martemyanov et al., ; Martemyanov, Pavlushin, Dubovskiy, Belousova et al., ). Therefore, in this study, we tested how phenological asynchrony would affect the interaction between L. dispar and B. thuringiensis Berliner and investigated the mechanisms underlying this interaction.…”

“…MarteMyanov et al Belousova et al, 2015;. If the larvae hatch prior to the host plant budburst, the larvae may starve, whereas if the larvae hatch too late, the foliage quality may be reduced (reviewed in van Asch & Visser, 2007 and references therein), although the occurrence of this phenomenon is related to studied species (Kharouba, Vellend, Sarfraz, & Myers, 2015) and global climate processes (Uelmen et al, 2016).…”

“…In addition, dramatic changes in leaf quality during the first 20 days of development have been suggested to represent the main mode of action of asynchrony on insect antiviral immunity (Chernyak et al, 2016;. However, the effect of asynchrony on insect bacterial diseases, such as intestinal bacteria Bacillus thuringiensis, which is widely used for the pest management (Garczynski & Siegel, 2007), remains unclear because different insect immune parameters are affected in different ways by the same trophic factor Martemyanov et al, 2013;Martemyanov, Pavlushin, Dubovskiy, Belousova et al, 2015).…”