Insect hemolymph factor promotes muscle histolysis in Solenopsis

Hemolymph was collected from both normal (virgin) females (control hemolymph) and artificially inseminated females (experimental hemolymph) of Solenopsis, ssp., the imported fire ant (primarily S. invicta and S. geminata). When the control hemolymph was injected into normal females, breakdown of the thoracic flight musculature was not seen 24 hr postinjection. In contrast, when the experimental hemolymph was injected into normal females, flight muscle histolysis was marked 24 hr postinjection. When the experimental hemolymph was heated to 70 degrees C prior to injection into normal females, subsequent flight muscle breakdown was not seen. The injection of freshly collected semen into normal females produced no effect on flight muscle structure. Also, the injection of the experimental hemolymph into normal, alate males produced no muscle histolysis. These observations suggest that the hemolymph from inseminated females contains a factor (or factors) that induces the specific breakdown and subsequent dissolution of the complex thoracic flight musculature. Other thoracic muscles (leg muscles, intersegmental muscles, etc.) are not affected. Based on observations made in both insect muscles as well as vertebrate skeletal muscles, it is suggested that such a hemolymph factor may act by disrupting the structural integrity of muscle cell membranes, resulting in significant changes in membrane permeability, especially with regard to calcium ions.