Wear Mechanics of the Female Locust Digging Valves: The “Good Enough” Principle

Abstract

Adult female desert locusts (Schistocerca gregaria) dig underground to lay their eggs, ensuring optimal conditions for successful hatching. Digging is performed using the two pairs of oviposition valves at the tip of the female's abdomen. These valves are subjected to considerable shear forces during the repeated digging cycles, potentially leading to wear over time. The resilience of the valves is investigated by analyzing the relationship between digging experience and valve damage and wear throughout the female locust's life. The findings reveal the ability of the valves to withstand the significant shear forces encountered during digging. Despite this resilience, however, perceptible limitations in the valves’ mechanical durability against wear are observed. Toward the end of the female locust's life, the valves show substantial signs of wear, indicating effective performance but with limited longevity, i.e., a designated life span that enables successful oviposition for ca. four oviposition cycles. A comparison of the valve material with that of the animals’ mandibles, which are used continuously throughout their life and show remarkable wear-resistance, further highlights the evolutionary adaptation of the valve materials to their specific function, suggesting a trade-off between energetic investment and the sufficient, or “good-enough”, performance that is required for survival.