Defensive Gland Of Pheropsophus Occipitalis: Morphological Structure,Chemical Compositions And Defensive Behaviors

Pheropsophus occipitalis(Macleay, 1825) effectively resists the predators by a kind special chemical liquid secreted by defensive glands, meanwhile, with high temperature. This defense way is one of the most unique styles in class Insecta. It is quite important to expound the mystery of its life that reveal the morphological structure of defensive system, the chemical compositions of secretions, and a series of actions during the spraying. In the present paper, morphological characteristics, the living habitats and the spray behavior of the beetles were surveyed, morphological characteristics and tissue structure of defensive gland of the species were dissected and observed, and the chemical compositions of reactant, product and catalyst were analyzed, according to the above, we can infer the whole defensive mechanism of bombardier beetles.The conclusions as following:(1) Structures of defensive glands Defense system of P. occipitalis is composed of three parts: reservoirs, secretory tissue, and reaction chambers. Reservoir thin, transparent and tough, with a root-liked tube which formed by 12 thin tubes. The reaction chamber is composed of a pair of ossific horseshoe shaped structures, its surface with dense, different sized and pocket strumae. Inner surface of longitudinal section of the reaction chamber is complexly honeycomb shaped, and covered with various thorns to strengthen inner wall and control the liquid flow.At the entrance of reaction chamber, there is a V-shaped valve which control reactive substances unidirectionally flowed from tube, it plays key role on concrolling the time of spray and frequency of pulse, and it is very important for reducing temperature of reaction chamber and controlling injection time.(2) Chemical compositions Six components from reservoir which preserved in defensive system were determined by GC-MS techniques(The present results of GC-MS analyses were provided by Mass Spectroscopy Centre, Institute of Chemistry, Chinese Academy of Sciences), mainly containing Methyl on phenol, hydroquinone, Methyl-p-benzoquinone, and p-benzoquinone. In contrast, 13 components were determined from ejection, because benzene’s bonds break after the reaction. Besides p-benzoquinone, there are formic acid, acetic acid and some other substances which have stimulating and toxic functions. As a consequence, the bombardier beetles could effectively protect themselves from predators. The activity test of enzyme in reaction chamber in different temperature shows that the activity of enzyme is highest in 40℃, and slows down when the temperature higher than 40℃, it suggests that the catalyst in reaction chamber is peroxidase, not metal ions.(3) Its “spraying” behavior is an important field of the study. This bombardier beetle has a particularly high accuracy for aiming at the target, its secretion is accurately delivered via twin spray nozzles emanating from the tip of the beetle abdomen. The injection keep 0.01~0.03 s. There is a pulse every 0.002 s during the injection, and there is 5~15 pulse every spray.