Actions of motor neurons and leg muscles in jumping by planthopper insects (hemiptera, issidae)

Abstract

To understand the catapult mechanism that propels jumping in a planthopper insect, the innervation and action of key muscles were analyzed. The large trochanteral depressor muscle, M133b,c, is innervated by two motor neurons and by two dorsal unpaired median (DUM) neurons, all with axons in N3C. A smaller depressor muscle, M133a, is innervated by two neurons, one with a large-diameter cell body, a large, blind-ending dendrite, and a giant ovoid, axon measuring 50 microm by 30 microm in nerve N5A. The trochanteral levator muscles (M132) and (M131) are innervated by N4 and N3B, respectively. The actions of these muscles in a restrained jump were divisible into a three-phase pattern. First, both hind legs were moved into a cocked position by high-frequency bursts of spikes in the levator muscles lasting about 0.5 seconds. Second, and once both legs were cocked, M133b,c received a long continuous sequence of motor spikes, but the two levators spiked only sporadically. The spikes in the two motor neurons to M133b,c on one side were closely coupled to each other and to the spikes on the other side. If one hind leg was cocked then the spikes only occurred in motor neurons to that side. The final phase was the jump movement itself, which occurred when the depressor spikes ceased and which lasted 1 ms. Muscles 133b,c activated synchronously on both sides, are responsible for generating the power, and M133a and its giant neuron may play a role in triggering the release of a jump.

Jumping mechanisms in flatid planthoppers (Hemiptera, Flatidae)

“…The Journal of Experimental Biology (2014) doi:10.1242/jeb.105429 muscles comprised ~10% of body mass, as also found in other planthoppers (Burrows and Bräunig, 2010), both adults and nymphs needed a power output of 14,799 to 29,160 W kg −1 of muscle in their fastest jumps.…”

“…This was the minimum time resolution possible with a frame rate of 5000 s −1 . In other planthoppers where jumps have been captured at six times this frame rate, the synchronisation was within 0.03 ms (Burrows, 2009;Burrows and Bräunig, 2010).…”

“…To propel the body forwards, and without losing energy to spin, requires that hind legs both move at the same time. To produce such synchrony of action, froghoppers and planthoppers activate muscles of the left and right hind legs with a tightly coupled sequence of motor spikes, thereby ensuring that similar levels of force are developed by both in their primed, pre-jump position (Burrows, 2007c;Burrows and Bräunig, 2010). The neural control alone cannot, however, deliver the close synchrony that is needed.…”

“…family Issidae (planthoppers) (Burrows and Bräunig, 2010) show that the muscles contract for a long time before the beginning of the propulsive movements of the hind legs. In hemipteran bugs, the muscle contractions during this preparatory stage of a jump, distort and bend part of the internal skeleton of the metathorax (the pleural arches) that link coxae to the hinges of the hind wings.…”

Jumping mechanisms in gum treehopper insects (Hemiptera, Eurymelinae)

“…This is the mechanism proposed for fleas (Bennet-Clark and Lucey, 1967) and demonstrated to be used by locusts (Bennet-Clark, 1975) and some other hemipteran bugs. Electrical recordings from the jumping muscles of froghoppers (Burrows, 2007c), leafhoppers (Burrows, 2007a) and the planthopper Issus (Burrows and Bräunig, 2010) show that they contract in advance of the rapid propulsive movements of the hindlegs. In froghoppers and Issus the slow contractions of the these muscles bend internal skeletal structures (pleural arches) that are built of a composite of hard cuticle and the rubber-like protein resilin.…”