Opportunistic Carnivory by Romalea microptera (Orthoptera: Acrididae)

Abstract

Grasshoppers generally are considered to be phytophagous. However, increasing evidence shows that many are better classified as omnivorous. The eastern lubber grasshopper Romalea microptera (Beauvois) (Orthoptera: Acrididae) not only consumes plants, but also dead or wounded arthropods in the field. We tested the potential range of arthropod taxa scavenged by R. microptera by offering fresh-killed carcasses to adult females in the laboratory. We predicted that they would eat all arthropods except those that the grasshopper's mandibles could not cut and chemically defended arthropods. We offered grasshoppers 104 arthropod species and life stages, representing 20 orders in five classes (Arachnida, Chilopoda, Diplopoda, Insecta, and Malacostraca). The grasshoppers completely consumed the entire body of all individuals of 42% of the arthropod species and life stages, and another 32% were highly consumed. Overall, 96% of the arthropod species and life stages, representing 19 of the 20 total orders, were consumed to some extent, suggesting that R. microptera is an opportunistic carnivore. Chemical defense in arthropods did not deter feeding by R. microptera, but the hardness of integument did: harder-bodied Hymenoptera and Coleoptera were consumed less than softer-bodied arthropods. Our results confirm that R. microptera is not strictly phytophagous, but readily eats a wide range of arthropod taxa. Carnivory within phytophagous clades may have important physiological, ecological, and evolutionary consequences.

Bottom‐up when it is not top‐down: Predators and plants control biomass of grassland arthropods

“…Auchenorrhyncha, by contrast did not. We suggest that one reason for this dietary flexibility is the chewing mandibles of the Orthoptera, which can easily partake of both plants and meat (Richardson, Reagel, Mitchell, & Whitman, 2012; Simpson, Sword, Lorch, & Couzin, 2006) while the piercing stylet of Auchenorrhyncha is restricted to plant fluids. The switch to a diet with more meat when plant biomass increases likely has two complementary causes.…”

Bite force transmission and mandible shape in grasshoppers, crickets, and allies is largely dependent on phylogeny, not diet

“…Many species feed indiscriminately on plant matter but do not refuse protein sources like dead arthropods when provided (Bernays and Chapman, 1970; Ingrisch and Köhler, 1998). Even strictly defined grass-feeders like the Gomphocerinae or Romalea microptera can be observed to feed on other arthropods (Clark, 1948; Richardson et al, 2012). The advantage of an omnivorous approach is that animals always have access to sustenance in form of abundant plant matter as well as highly nutritious protein-rich food sources like animal matter.…”

Ancestral gene duplication enabled the evolution of multifunctional cellulases in stick insects (Phasmatodea)

“…We also now have evidence that Phasmatodea can fully degrade plant cell wall components into monomers that could be used as energy, and their large number of endogenous ß-glucosidases strongly implies that their digestion of cellulose to glucose is entirely microbe-independent. Complete folivory without occasionally cheating on one's diet and engaging in carnivory or necrophagy, as documented frequently in grasshoppers (Richardson et al, 2012), likely could not have evolved in Phasmatodea without the neofunctionalizations from their ancestral cellulases. Experimental manipulation of some or all of these Phasmatodea genes and subsequent observation of their feeding rate, survival, and possible acceptance of non-leaf diets may help test the importance of enzyme diversity on maintaining such a specialist diet.…”