Yong Ihl Park

Nymphs of the Formosan Subterranean Termite (Isoptera: Rhinotermitidae): Aspects of Formation and Transformation

Abstract Mature colonies of the Formosan subterranean termite, Coptotermes formosanus Shiraki, like most other termite species, produce a reproductive caste in the form of nymphs that subsequently give rise to alates. Temporal production of nymphs in C. formosanus was monitored in monthly collections from four field traps in New Orleans, LA. Nymphs were present throughout the year with peak numbers observed during October/November and May. Large nymphs first occurred in December and peaked in March. Fewer than 1.5% workers formed nymphs within 3 months after collection from the field and after removal of the preexisting nymphs. Collections from other colonies, kept in the laboratory for >2 yr, did not produce any nymphs. It is speculated that a nymph induction factor (NIF), possibly coming from a mature physogastric queen, elicits nymph formation. The same or a similar factor may also be responsible for further development of nymphs and their transformation to alates. In the absence of this latter factor, the nymphs, except those in the most advanced stage of development, are either cannibalized or transform into brachypteroid neotenics. A scheme for the formation and transformation of various developmental stages within each caste of C. formosanus is presented.

Premating Behavior of Dealates of the Formosan Subterranean Termite and Evidence for the Presence of a Contact Sex Pheromone

Swarming by alates of the Formosan subterranean termite, Coptotermes formosanus Shiraki, occurs around dusk during April–June in Louisiana and adjoining states. Dispersal is the primary purpose for swarming. We studied the premating behavior, following swarming. Loss of wings, especially in females, was essential for successful formation of tandem pairs between the two sexes. No calling was observed and apparently a long-range volatile sex pheromone, reported in some other species of termites, may not be involved in mate attraction in C. formosanus. Males moving randomly use their antennae to detect a female, and, together with maxillary and labial palps, contact is maintained with her while in tandem. Previously mated males paired with virgin females showed tandem behavior. The incidence was very low when both males and females were previously mated and then paired. Males with complete ablation of antennae did not form tandem pairs. Ablation of 10 terminal antennal segments or the labial palps caused a significant increase in the time to initiate tandem behavior. Electrophysiological recordings from gustatory sensilla on both antennae and maxillary palps revealed increased neural activity in response to female abdominal tip extracts compared to activity elicited by a solvent control. Analysis of extracts of male and female abdominal tips using high-performance liquid chromatography showed a peak unique to the female extract. We discuss the presence of a nonvolatile chemical in female C. formosanus and its involvement in the specific premating behavior.

Structure of Spermatheca, Sperm Dynamics, and Associated Bacteria in Formosan Subterranean Termite (Isoptera: Rhinotermitidae)

Abstract Primary reproductives of the Formosan subterranean termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), complete their first reproductive cycle in ≈60 d after nest formation. During this period, the pairs mate several times. The spherical, aflagellate sperm, after transfer by the male, are stored in the female’s spermatheca. Sperm numbers in the spermatheca increase significantly between day 20 and 40, and thereafter they show a steep decline, indicating that the pairs may not be mating after day 40. The spermatheca is bean shaped with an extremely narrow duct. The thick wall of the spermatheca consists mainly of type 3 cells made up of secretory and duct cells. Cuticle-lined ducts are interspersed throughout these cells. Finger-like extensions of the cuticle-lined interior wall project into the spermathecal lumen. The secretory cells presumably provide nutrition for the sperm during their long storage. Eleven anaerobic and six aerobic species of bacteria were cultured and identified from the spermatheca. The role of these bacteria is unknown.

Defaunation Leads to Cannibalism in Primary Reproductives of the Formosan Subterranean Termite, Coptotermes formosanus (Isoptera: Rhinotermitidae)

Abstract Soon after swarming, the alates of the Formosan subterranean termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), drop their wings, form tandem pairs, and look for new nesting sites to form incipient colonies. In ≈10% of the several hundred incipient colonies kept in laboratory, both the male and female were found to cannibalize their progeny and die of starvation. Examination of such adults revealed that all of them had lost most of their gut fauna, essential for the digestion of wood. We used antibiotic (gentamicin) and a combination of gentamicin and antiprotozoal (metronidazole) compounds during 2002 and 2003, respectively, to induce defaunation in 30-d-old adults after they had laid 30–40 eggs. The progeny of treated pairs compared with control pairs was significantly lower 30 and 60 d after treatment. Feeding on these chemicals during 2003 caused total loss of spirochetes and one of the three flagellates, while the numbers of the other two flagellates were greatly reduced. It is suggested that, in the absence of gut fauna, the adult termites cannot effectively feed on wood, and the ensuing hunger results in cannibalism of their progeny.

Ecdysone agonist halofenozide affects corpora allata and reproductive physiology of the Formosan subterranean termite, Coptotermes formosanus

Following a short swarming flight, winged adults of the Formosan subterranean termite, Coptotermes formosanus lose their wings and form tandem pairs. These dealates or primary reproductives then form incipient colonies. Topical application of 5 microg of the non-steroidal ecdysone agonist RH-0345 (halofenozide) in 0.1 microl DMSO to the primary reproductives during the 2000 season resulted in significant reduction in the number of eggs laid. There was however complete recovery of the treated females. Apparently the non-treated partner removed the treatment chemical while grooming indicating oral activity. In 2001 both topical application as well as feeding methods were tried. Significant effects were observed only in the topical treatment group, perhaps because of inconsistency in feeding. In this group, total progeny, the number of ovarioles in ovaries and the size of the females corpora allata (CA) were all significantly reduced. Ultrastructure of the CA of treated females showed extensive vacuolation near the surface of the gland. The experiment was repeated in 2002 using both topical application and an improved oral feeding method. Whereas there was apparent recovery in the topically treated group after 90 days, the oral treatment was more persistent in its effect perhaps due to a higher amount of halofenozide consumed during feeding.

Trilinolein identified as a sex-specific component of tergal glands in alates of Coptotermes formosanus

Hexane extracts of the tergal glands from female alates of the Formosan subterranean termite Coptotermes formosanus were analyzed by high performance liquid chromatography—atmospheric pressure chemical ionization—mass spectrometry with collision-induced dissociation. Double bond configuration was determined by chemical modifications with gas chromatography—mass spectrometry. A single component, identified as the triacylglycerol, trilinolein, was unique to the female tergal glands. This compound was not found in other areas of the female alate abdomen or in the corresponding area of male alates. Neither gland extract nor trilinolein caused a behavioral response from male alates. However, significant differences were found between males and females for responses from neurons within sensilla of the maxillary palps.