Jumping strategies and performance in shore bugs (Hemiptera, Heteroptera, Saldidae)

The jumping movements of the hemipteran shore bug (Saldula saltatoria, sub-order Heteroptera, family Saldidae) were analysed from sequences of images captured at 5000 frames s(-1). Adult Saldula weigh approximately 2.1 mg and are approximately 3.5 mm long. The hind legs that propel jumping are 180% longer than the front legs and 90% of body length, but non-jumping species in the same family have longer hind legs relative to the lengths of their bodies. Jumps were powered by large trochanteral depressor muscles in the thorax in two different strategies. In the first (used in 24% of jumps analysed), a jump was propelled by simultaneous extension of the two hind legs powered by rapid depression movements about the coxo-trochanteral joints, while both pairs of wings remained closed. In the second strategy (74% of jumps), the wings were opened before the hind legs began to move. At take-off, the position of the wings was variable and could be 8-21 ms into either elevation or depression. When the hind legs alone propelled a jump, the body was accelerated in 3.97+/-0.111 ms at a take-off angle of 52+/-6.5 degrees to a take-off velocity of 1.27+/-0.119 m s(-1); when the wings also moved, the body was accelerated in 3.86+/-0.055 ms at a take-off angle of 58+/-1.7 degrees to a take-off velocity of 1.29+/-0.032 m s(-1). These values are not different in the two jumping strategies. In its best jumps the take-off velocity reached 1.8 m s(-1) so that Saldula experienced an average acceleration of 529 m s(-2), equivalent to almost 54 g, expended 3.4 microJ of energy, while exerting a force of 1.1 m N. The power requirements for jumping indicate that a catapult mechanism must be used in which the trochanteral depressor muscles contract and store energy in advance of a jump. These jumps should propel it to a height of 105 mm or 30 times its body length and distances of 320 mm. The two jumping strategies achieve the same jumping performance.