Variability in plant nutrients reduces insect herbivore performance

Abstract

, but recent studies showing the importance of plant genetic diversity for herbivores suggest that plant trait variance may be equally important 5,6 . The consequences of plant trait variance for herbivore performance, however, have been largely overlooked. Here we report an extensive assessment of the effects of withinpopulation plant trait variance on herbivore performance using 457 performance datasets from 53 species of insect herbivores. We found that variance in plant nutritive traits substantially reduces mean herbivore performance via nonlinear averaging of performance relationships that were overwhelmingly concave-down. In contrast, relationships between herbivore performance and plant defense levels were typically linear, such that plant defense variance does not affect herbivore performance via nonlinear averaging. Our results demonstrate that plants contribute to the suppression of herbivore populations by having variable nutrient levels, not just by having low average quality as is typically thought. We propose that this phenomenon could play a key role in the suppression of herbivore populations in natural systems, and that increased nutrient heterogeneity within agricultural crops could contribute to the sustainable control of insect pests in agroecosystems.Decades of research have established the importance of plant nutritive and defensive traits for herbivore performance and population dynamics 1 . Recent studies, showing that plant genetic diversity influences herbivore community patterns, suggest that plants influence herbivores not just through average trait values but also through variance in trait values 5,6 . The literature on plant defenses and herbivore nutritional ecology, however, focuses on mean relationships and mostly ignores the consequences of trait variance 2,3 . This is an oversight because intraspecific plant trait variance pervades natural systems, from among tissues within individuals to among individuals within populations 4 . In modern agroecosystems, however, plant functional diversity has been replaced by extensive homogeneous monocultures of single crop varieties or genotypes 7 . How the loss of trait diversity influences higher trophic levels and ecosystems services like pest control is unexplored relative to how much is known about the consequences of genetic diversity 8,9 . Elucidation of the direct effects of variability in plant defensive or nutritive traits on herbivore performance would inform management of agroecosystems-perhaps revealing new ways to use crop heterogeneity for sustainable pest management-and advance our fundamental understanding of plant-insect interactions. Here we test for general patterns in the effects of plant trait variance on herbivore performance using 457 datasets relating plant traits to herbivore growth and survival for 53 species of phytophagous insects from seven orders.Plant variance could influence herbivores in several ways, including reducing the opportunity for herbivore populations to adapt evolutionarily to plant defenses 10 ....

Survival, body mass and potential fecundity of the invasive moth Cameraria ohridella (Lepidoptera: Gracillariidae) on its original host plant Aesculus hippocastanum and Aesculus glabra

“…In phytophagous insects the chemical and physical quality of the host plant can affect fecundity (Awmack & Leather, 2002), and potential fecundity has been shown to be correlated with female body mass in Lepidoptera (Honek, 1993). However, not only the number of eggs but also egg size and quality may be infl uenced by plant quality (Awmack & Leather, 2002;Wetzel et al, 2016). On low-quality host plants, females may lay a smaller number of larger eggs, as has been shown for Lepidoptera (Wickman & Karlsson, 1989;Karlsson & Wickman, 1990;Moreau et al, 2006).…”

“…development time, survival, pupal mass, fecundity) is strongly affected by the quality of the host plant upon which they feed (Awmack & Leather, 2002;Wetzel et al, 2016). Phylogenetically related plants are more likely to be similar in structural, chemical and nutritional traits, and therefore novel host plants are suitable for colonization if they are related to the native host (Connor at al., 1980;Odegaard et al, 2005;Pearse & Hipp, 2009;Bertheau et al, 2010;Ness et al, 2011).…”

From plant fungi to bee parasites: mycorrhizae and soil nutrients shape floral chemistry and bee pathogens

“…Specifically, we asked whether floral traits (flowering phenology, nectar volume, and mean value or variation in pollen and nectar alkaloid and sugar concentrations) change in response to plant nutrient or mycorrhizal status; and whether AMF and nutrient effects on pollen and nectar affect pathogen levels in bumble bees infected with Crithidia. Furthermore, because variation in diet quality could affect plant-pollinator interactions (Kessler et al 2012, Wetzel et al 2016, we assessed mean value and variation in floral chemical traits. Alternatively, if AMF effects on alkaloid levels are due to up-regulation of defense pathways, rather than nutrient status (Vannette and Hunter 2009), we would expect plants grown with AMF to have higher floral alkaloids regardless of fertilizer treatment.…”

Diet alters performance and transcription patterns in Oedaleus asiaticus (Orthoptera: Acrididae) grasshoppers

“…Although ecological factors such as susceptibility to predation and other aspects of habitat association have been identified as important in selection, plant chemistry is critical, including nutrition, nutritional barriers, and secondary compounds [26,28, 56–58]. Phenotypic plasticity of individuals, genetic variability of populations, and detoxification mechanisms are just some of the mechanisms allowing herbivorous insects to overcome plant defenses and variable diets [1, 51, 59].…”