The effect of air resistance on the jump performance of a small parasitoid wasp, Anagyrus pseudococci (Encyrtidae).

Abstract

The distance a small insect moves through the air during a jump is limited by the launch velocity at take-off and by air resistance. The launch velocity is limited by the length of the jumping legs and the maximum power that the jump apparatus can provide for pushing against the ground. The effect of air resistance is determined by the insect mass-to-area ratio. Both limitations are highly dependent on body size, making high jumps a challenge for smaller insects. We studied both effects in the tiny Encyrtid wasp Anagyrus pseudococci. Males are smaller than females (mean body length 1.2 and 1.8 mm, respectively), but both sexes take off in a powerful jump. Using high-speed cameras, we analyzed the relationship between take-off kinematics and distance traveled through the air. We show that the velocity, acceleration and mass-specific power when leaving the ground places A. pseudococci among the most prominent jumpers of the insect world. However, the absolute distance moved through the air is modest compared with other jumping insects, as a result of air resistance acting on the small body. A biomechanical model suggests that air resistance reduces the jump distance of these insects by 49% compared with jumping in the absence of air resistance. The effect of air resistance is more pronounced in the smaller males, resulting in a segregation of the jumping performance between sexes. The limiting effect of air resistance is inversely proportional to body mass, seriously constraining jumping as a form of moving through the air in these and other small insects.