Preliminary Study On The Mechanism Of Inter-colony Recognition In Coptotermes Formosanus Shiraki (Isoptera: Rhinotermitidae)

The Formosan subterranean termite, Coptotermes formosanus Shiraki, is native to China, and is one of the most destructive insect pests of buildings and timber structures. This species of termite commonly shows agonistic behavior when encountering the individuals from other colonies, however, the mechanism is complicated and the previous investigations have provided only somewhat ambiguous information. This paper tries to seek the cues for inter-colony recognition in the C. formosanus, through analysis of the protein content, intestinal microorganisms and chemosensory sensilla on the antenna. The main results are as follows:1 The relationship between variation of the protein content and inter-colony agonism(1) The effect of laboratory-rearing on the inter-colony agonism of C. formosanusEight colonies were collected from different sites of Zhejiang Province and Hubei Province. The termites of every colony were divided into two groups, one was used for the experiment of intercolonial agonism and protein analysis immediately, and the other was reared in the laboratory for 35 days. The agonistic behaviors of soldiers between any 2 colonies were tested. The result indicated the agonistic levels after a period of laboratory-rearing were much lower than that before laboratory-rearing.(2) Total protein content analysi of the soldiers of C. formosanusThe total protein content in soldiers of the two groups was determined with brilliant blue G-250 spectrophotometery method. The results suggested that after the 35 days of laboratory-rearing, the protein content of individuals from all colonies decreased besides the Yancang colony A.(3) The relationship between the variation of the protein content and the inter-colony agonismCombined the results of protein biochemical analysis with behavioral tests mentioned above, it implies that there was no correlation between the variation of the protein content and the inter-colony agonism in C. formosanus, whether the colonies had experiend 35 days of laboratory-rearing or not.2 The effect of intestinal microorganisms on the nestmate recognition in C. formosanus(1) The influence of dye-treating on the survival and agonistic behaviors of C. formosanusThe agonistic behaviors of workers between any 2 colonies of 6 colonies in C. formosanus were tested. The Yancang colony B (B), Hongqiao colony (H) and Yuhuangshan colony (Y) were selected as the testing materials according to the test results: the colony B was compatible to colony H and aggressive to colony Y. When the abdomens of termites were marked with token's pen, the dye-treatment had no influence on the survival and agonistic behaviors of the workers. It proved that the "token's pen dye" was a practicable way to mark individuals in the agonistic test of C. formosanus.(2) The influence of antibiotic-treatment on the survival and agonistic behaviors of C. formosanusTo determine the effect of antibiotic-treating on the agonistic behaviors of C. formosanus, the workers were fed with filter paper which was treated by different concentrations of penicillin, or streptomycin and tetracycline, respectively. The results indicated that antibiotic-treatment had negative influence on the survival of the termites, and the mortality increased gradually as the concentrations and time of treatment. When the concentration of treatment was <12mg/ml for penicillin, <6.25mg/ml for streptomycin and <50mg/ml for tetracycline, there were no obvious influences on the survival of termites (mortality was <5%) and the agonistic levels between colonies.(3) The influence of protozoan on the agonistic behaviors of C. formosanusBesides symbiotic bacteria, there are mass protozoan in the hindgut of C. formosanus. To clarify the influence of protozoan on the inter-colony agonism, we examined the agonistic levels of the workers from colony B, colony H and colony Y, in which the symbiotic protozoan had been killed through high temperature. The experiments showed that treatment of 36 °C for 24h had no effect on the survival and agonistic levels of C. formosanus. It means the intestinal microorganisms had no effect on the agonistic behaviors in C. formosanus.3 Study of chemosensory sensilla on the antenna in C. formosanus(1) Priliminary location of the chemosensory sensilla with the function of nestmate recognitionAgonistic test showed that 100% soldiers of colony B exhibited agonistic behaviors when encountering the workers of colony YC. To determine the location of the chemosensory sensilla on antenna with the function of nestmate recognition, after part of segments of antennae of soldier and worker had been removed, one soldier from the colony B and one worker from the colony YC were paired for agonistic tests. The behavior of the soldier towards the worker was observed during 5 min. The results showed thatsoldiers had ability to discriminate non-nestmates when their antennae were kept more than 6 segments. To prove these results, we used a soldier from the colony Y and a soldier from the colony H to do paired agonistic test, and mortality of soldiers was recorded after 24h. The results indicated that when the numbers of segment of antennae were less than 7, the agonistic behaviors between soldiers from two colonies disappered (the mortalities were <10.0 %). Both experiments mentioned above suggested that the chemosensory sensilla with the function of nestmate recognition located in the 7th-15th segments of antenna in C. formosanus.(2) Types and distribution of the chemosensory sensilla on antenna in C. formosanusTo clarify the type and distribution of the chemosensory sensilla, the antennae of the soldier and worker in C. formosanus were observed with the photomicrography and the scanning electron microscopy. The results showed that there were 6 types of sensilla on the antenna: sensilla trichodea, sensilla chaetica, sensilla basiconic, sensilla placodea, sensilla campaniformia, and mammilla-like sensilla which had been rarely reported. Moreover, a great number of sensilla placodea, sensilla campaniformia and mammilla-like sensilla were found in the joints between segments. The length joints were the longest in the middle of antenna and became graduaaly short near the ends. Behavior bioassay results indicated that the joints between segments maybe the key position receiving and processing signals in the nestmate recognition, and the sensilla placodea, sensilla campaniformia and mammilla-like sensilla might be responsible for the nestmate recognition in the C. foimosanus.