Morphology, Biology And Ecology Of The Terrestrial Firefly Pyrocoelia Pectoralis (Coleoptera: Lampyridae)

The terrestrial firefly Pyrocoelia pectoralis Olivier (Coleoptera: Lampyridae) iswidely distributed in mainland China. Since its description in 1883, no subsequent paperson P. pectoralis appear to have been published on this species. In this paper, we report themorphological, biological and ecological characteristics of P. pectoralis as a basis forfuture studies on protection and utilization.1. MorphologyThe morphological observation showed adults of P. pectoralis were typically sexualdimorphism. The males' pronotum were semicircular, yellow-orange, semitransparent,apical margin well reflexed and there a pair of small vitreous areolets at longitudinal ridge.Elytra were very strong and black. The zonary luminescent organs nearly occupy all ofventrites 6-7. Females were yellow-orange in the whole, brachypterous. Pronotum wassimilar to that of male but without vitreous areolets. At the lateral sides of abdomenventrites 6-7, each with a pair of spot-like luminescent organs. Eggs were subovate,yellow-orange. The color pattern of larval is usually a combination of black with yellow,red and white. It also employs the bold, repeating pattern of triangular red spots. Theluminescent organs of larvae were opalescent at lateral sides of abdomen ventrite 8. Theultra-structural of larva and adult were examined using scanning electron microscopy.Larva has well developed mandibles. Each of them is a hook, strongly curved inwards,sharply acuminate and with a canal running through its entire length. The antenna was 3segments and with a specially hemispheroidal structure on the apical flagellum. Thepygypodia was cylindraceous and Y-shaped. There were sensilla trichodea and sensillachaetica on the surface of antennae.The anatomical structure of adults reproductive systems showed that there were twotesticles, a pair of seminal duct and two accessory glands in males, and the ratio ofgenitalia is 2.0-2.5(length/width). There was no tumefacient copulatory pouch, and theovariole belongs to panoistic type in female.2. BiologyThe larvae inhabit moist grasslands, deserted farmlands and jungles, and mainly feedon two species of land snails, Bradybaena similaris (Ferussac) and Bradybaena ravidaravida (Benson) (Stylommatophora: Bradybaeniidae). A predator of adult fireflies is thespider, Tetragnatha praedonia (L. Koch) (Araneae: Tetragnathidae).The development and starvation ability of 1st instar larvae were influenced by eggssize. The starvation ability of 1st larvae hatched from defferent egg was 17.68±4.82 days (â… : 0.0041-0.0051g), 15.68±3.91 days (â…¡: 0.0031-0.0040g), 14.29±3.73 days (â…¢:0.0021-0.0030g) and 9.12±3.81 days (â…£: 0.0012-0.0020g), respectively. It was correlatedwith body length (y=5.58x-31.15; R²=0.5824, df=123, P＜0.01).The larvae are nocturnal. Larval glow is not regular. Usually, the duration of theglow is 1-15 sec, and the interval is 1-20 sec or longer. The sequence of the preyingbehavior of larvae is searching, preying, cleansing, break and searching again. The valuesof rectilinear distance, searching speeds and areas before feeding are bigger than that afterfeeding respectively.Larvae did not need favorable places for pupal cell construction. During pupation,the adult light organ developed and became functional. In addition, the larval light organcontinued to function throughout prepupal, pupal and teneral adult stages. The rhythm ofemergence is very obviously. Adults usually appeared at midnight, but male(approximately 23:06 PM) was earlier than female (approximately 01:53 AM).Light and chemical signals played an important role in the courtship and copulation.The duration of adults' glow is 1-8 sec, and the interval is 1-7 sec. The photic emission ofadult was 526.5-593.9 nm, with the peak emitted wavelength (λ_max) at 548.6 nm, thusproducing a yellow-green color. Males were attracted by compound extracted from thefemale abdomen significantly.The mating and ovipositing behavior was also observed in field and laboratory. Eachfemale can mate immediately after emergence and with several different males in wholelife. The competitive behavior among mating males was ubiquitous. The duration ofmating usually lasted for 82.5±34.8 min (n=15). The mated and unmated females can layeggs normally. The longevity of the former lasted for 8.87±2.06 d (n=30), and the averagenumber of eggs was 72.03±34.38 (n=30) at 25±2℃. The total number of eggs laid bymated female was correlated with female's initial mass (y=235.28x-20.38, R²=0.7283,df=43, p＜0.01), and the daily ovipositing rate was correlative to the day-age(y=159.685exp(-x/1.0684)-0.5293, R²=0.9974, dr=5, p＜0.01). The result of factor analysisshowed that there were two main factors, morphological and physiological factor, whichinfluenced female fecundity.Adults of P. pectoralis exhibit reflex bleeding when tactually stimulated. Maledischarge fluids from along elytral and pronotal margins and around the antennal sockets,but females only discharge from pronotal margins and antennal sockets, without the smallelytral buds. There were a series of circular, but irregularly pit which is surroundings by athin membrane is connected to the cuticle along the pronotal and elytral margins. It'sseems to be related to the reflex bleeding response. The viscid blood is a very effective deterrent against predators such as ergates of ants, Monomorium pharaonis andPolyrhachis vicina.3. EcologyEffects of four constant temperatures (20℃, 24℃, 28℃, 32℃) on developmentduriation, relative mortality rate, fecundity and longevity of P. pectoralis wereinvestigated. The 2nd instars larvae are all dead at 20℃. The development duriation ofmale pupa is longer than that of female pupa. The survival rate of whole unmature periodis higher at 28℃. The longevity of male adult is longer than that of female at 24℃-32℃.The oviposition rate is the highest (81.99±7.27%) at 28℃, and lowest (69.52±5.54%) at32℃. The peaks of oviposition period centralize on 1st day after mated, and it issignificantly shortened at 32℃. The relationship between age-specific fecundity and dailyovipositing rate are all accord with the first order exponential decay model at differenttemperatures. There are highest net reproduction rate (R₀) and lowest double time (t) ofexperimental population at 32℃.The spatial characteristics of larvae were analyzed using geostatical method fordensity at different period. The result of semivariograms of isotropic showed that theranges of spatial were 10.40m and 14.70m, and the spatial variations were 67.29% and50.06% at June and August, respectively. The theoretic models were exponential andspherical. The isovalue maps of interploted estimates of larval densities were analyaed byusing Kriging techniques.