Physiology of the post-pharyngeal glands and comparative morphology of glands associated with the mouthparts among castes of the red imported fire ant, Solenopsis invicta Buren

Abstract

Morphology has been determined from serial sectioning and dissections of the post-pharyngeal, maxillary, mandibular, and labial glands of the red imported fire ant, Solenopsis invicta Buren. Various parameters such as weight, length, width, and number of lobes of the post-pharyngeal glands, cellular and nuclear diameters of the labial and maxillary glands, length and width of the mandibular glands, and the number of cells of the maxillary glands have been compared and contrasted among castes. Ratios of gland measurements to body length indicate the post-pharyngeal glands are most highly developed in the queen caste. All other glands associated with the mouthparts are most highly developed on a relative size basis in the minum caste and least developed in the queen caste. The lumen of the post-pharyngeal glands of all castes of the red imported fire ant is empty at the time of emergence. After seven days of colony exposure to sugar water, the lumen of the glands remains empty. The glands in all castes are still colorless and flaccid even though the crop is filled with a sugar solution. Only after feeding on materials high in lipid does the lumen become full, acquiring the characteristic turgid, yellow color typical of glands from older worker and reproducer castes. The post-pharyngeal glands selectively absorb and hold lipids from ingested foods for long periods of time. These lipids come from the food only, since the post-pharyngeal glands from queens do not sequester triglycerides or fatty acids from the haemolymph. Lipid classes from the post-pharyngeal glands of worker and queen castes separated by column fractionation are not attractive to members of the colony. Excision of the post-pharyngeal glands from a mated, established queen causes no noticeable change in her behavior or the behavior she elicits from the remainder of the colony. Therefore, the post-pharyngeal glands are not the source of any specific pheromone...