Insect mandibles—comparative mechanical properties and links with metal incorporation

Abstract

A number of arthropod taxa contain metals in their mandibles (jaws), such as zinc, manganese, iron, and calcium. The occurrence of zinc and its co-located halogen chlorine have been studied in relation to the mechanical properties and shown to be linked in a direct fashion with increasing concentration. Hardness along with elastic modulus (stiffness) has also been linked to zinc and halogen concentration in some marine polychaete worms. The metal appears to be incorporated within the biological matrix, possibly bonding with proteins. However, the comparative advantage of metal inclusion has not been tested. It is possible that without metals, alternative mechanisms are used to achieve hardness of equal value in similar 'tools' such as mandibles. This question has direct bearing on the significance of metal hardening. In the present article, we compare across mandibles from six termite species, including samples with major zinc concentration, minor manganese, and no metals. Nanoindentation, electron microscopy, and electron microanalysis are used to assess metal concentration, form, and mechanical properties. The data demonstrate that termite mandibles lacking metals when fully developed have lower values for hardness and elastic modulus. Zinc is linked to a relative 20% increase in hardness when compared with mandibles devoid of metals. The similar transition metal, manganese, found in minor concentrations, is not linked to any significant increase in these mechanical properties. This raises the question of the function of manganese, which is as commonly found in insect mandibles as zinc and often located in the same mandibles.

Arsenic accumulation, biotransformation and localisation in bertha armyworm moths

“…In insects, a variety of metals including zinc, manganese, iron and copper are found concentrated within the mandibles, ovipositors and various body parts. [34][35][36] Insects also need small amounts of metals and metalloids as enzyme cofactors and as constituents for metalloenzymes. Both zinc and copper are found to be associated with the gut.…”

“…4d) is observed highly concentrated in the mandibles (which appear as two bright spots near the top of the image) in addition to the midgut. The presence of zinc in mandibles of herbivorous insects has been known for some time [34,35] and reduces the abrasive wear that mandibles would suffer through chewing hard plant material. Enhanced levels of zinc have also been observed in grasshoppers and leaf-cutter ants where high levels of zinc are linked with greater hardness of the cuticle.…”

“…Enhanced levels of zinc have also been observed in grasshoppers and leaf-cutter ants where high levels of zinc are linked with greater hardness of the cuticle. [34,35] Manganese is also commonly found in insect mandibles. However, in the case of bertha armyworm, we find that manganese is not concentrated in the mandibles of the larvae, but is observed on the cuticle (Fig.…”

Not just the usual suspects: Insect herbivore populations and communities are associated with multiple plant nutrients

“…Carbon (C), nitrogen (N), and phosphorus (P) have been the most frequently examined elements because of their importance in major classes of biological molecules (e.g., protein [C, N], carbohydrates [C], lipids [C], nucleic acids [C, N, P], and energetic nucleotides [C, N, P]), and because of their critical structural roles and relatively high concentrations in organisms (Sterner and Elser 2002). However, insect herbivores require multiple nutrients, many of which contain elements other than C, N, or P. For instance, we currently know little about how other nutrient-linked elements might be associated with insect herbivore population-and community-level processes, particularly elements that occur in plants as free ions, and which serve important physiological and maintenance functions (e.g., Na, K, Ca, Mg), or structural purposes (e.g., Fe, Zn, Mn; Cribb et al 2008). …”

Evolutionary optimization of material properties of a tropical seed

“…The tunnel surfaces are smooth and plastically 'smeared' ( figure 3a,b). Once inside the shell, the females lay eggs and die, their mandibles being completely worn down during a single entry: severe wear is inevitable since the hardness of insect mandibles, even with metal impregnation [29], is comparable to that of the M. parviflora shell. Hatched larvae then feed on the seed's fatty endosperm, develop and mate.…”