Many organisms utilize plant nutrients, from bacteria to insects to vertebrates. Although there is an absence of immune systems, plants use a variety of techniques to defend themselves against herbivorous insects and beetles. Familiar methods include structural and chemical mechanisms. Examples include physical barriers (such as bark , waxy epidermal cuticle or spines) or the use of volatile organic compounds that can repel these harmful insects.
Can nutrient levels also contribute to defence mechanisms?
A lesser known “defence” are the nutritive traits and their respective variability of plants. Qualities include carbon, nitrogen, and defensive metabolites. This may seem odd. However, this is due to the effects of herbivore performance based on variation in plant nutrient levels largely being overlooked. A recent study performed by Wetzel et al performed an extensive assessment on how within-population plant trait variance impacted herbivore performance using datasets from 53 species of insect herbivores.
It was discovered that variance in plant nutritive traits substantially reduces mean herbivore performance via nonlinear averaging. This meant that plants contribute to the suppression of herbivore populations by having variable nutrient levels. Host plant quality is also a key determinant of the fecundity of these insects. Many insect herbivores can alter both inter- and intraspecific interactions. Higher–trophic level interactions, such as the performance of predators and parasitoids, may also be affected by host plant quality. Thus, reproductive strategies can be affected at the individual and the population scale.
Why do we care?
Knowledge on suppression of herbivore populations in natural systems, and increased nutrient heterogeneity within agricultural crops could contribute to the sustainable control of pest outbreaks in agroecosystems. Long-term experiments can be set up that consider the impacts of global climate change and the respective impacts on herbivorous insects to gradual changes in the nutritional and defensive quality of their host plants. Schuler et al also looked at a different perspective: genetic modification that express novel insecticidal toxins can also set up a model that assesses the performance of herbivorous insects when exposed to rapid and dramatic changes in the quality of their host plants.