Depressant insect beta-toxins cause a transient contraction paralysis followed by a slow flaccid paralysis. They bind voltage-independently at site-4 of sodium channels (Nav) and block action potentials, primarily by depolarizing the axonal membrane and suppressing the sodium current. This depressant toxin is active only on insects. It is found in a relatively small amount in the venom. Expressed by the venom gland. Has the structural arrangement of an alpha-helix connected to antiparallel beta-sheets by disulfide bonds (CS-alpha/beta). PD(50) is 19 ng/100 mg of body weight of Sarcophaga larvae for contraction paralysis, and 85 ng/100 mg for flaccid paralysis. Belongs to the long (4 C-C) scorpion toxin superfamily. Sodium channel inhibitor family. Beta subfamily.