Effects Of Temperature And Host-Plant On Fitness Of Parasitoid (Chelonus Murakatae) Of The Stripped Stem Borer (Chilo Suppressalis)

Chilo suppressalis is the major pest of rice and water-oat in China. Day by day increasing yield loss is a big threat for food security. Scientists are trying to find the most suitable ways for controlling pest insects to ensure food safety from last many decades. A number of management strategies are being experimented and even implemented in the field. These practices include pesticide application, cultural means of control, transgenic food, biological control and so on. Different techniques have their own limitations and drawbacks which sometimes becomes hazardous for human health. In such circumstances, biological control of insect pests is considered to be one of the safest management tactics.Morphology and DevelopmentThe Braconid parasite Chelonus muarakatae is one of dominant natural enemies of C. suppressalis. The morphology and development of this parasitoid developing in host larvae are rarely mentioned. In current study, the morphological characters and developmental duration of each immature stage of C. murakatae is recorded by dissecting parasitized hosts. The egg of C. murakatae is oval and hymenopteriform. Based on changes in number of body segments, visibility of anal vesicle and measurement of head capsule width, there are three instars for the larval stage. The third instar mature larvae drilled the host body and pupated as a cocoon. Development time from egg to adult emergence is about 34 days at 27.5 oC and a photoperiod of 15:9(L: D) h with relative humidity of 70-85 %. All stages were showed with photomicrographs.Mating BehaviorStudying mating behavior of a natural enemy aids in understanding reproductive ability to ensure mass rearing and optimizing sex ratio for field release. In this study, it was observed that the offsprings of unmated C. murakatae are the male under the experimental conditions and only mated females can produce female progeny. Male and female are mating in the daytime. And the mating average duration is(11.6 ± 14.6) seconds. This study provides some reference to investigate the biological characteristics and mating behavior of C. murakatae for biological control of C. suppressalis.Effect of temperature on development and adult longevity of C. murakataeEffects of temperature on development duration and longevity of adult of Chelonus murakatae was studied under five constant temperatures including 22.5, 25, 27.5, 30 and 32.5 °C under laboratory conditions. It was observed that as the temperature increases the development time decreases within the range of 22.5 to 32.5 oC. The results indicated that the optimum temperature for development ranged from 25 to 30 oC. Thermal threshold was estimated by linear model which was recorded as 15.5 and 18.5 oC for males and females respectively. The required number of degree days for complete development from egg to adult was 439.6 degree days in males and 336.8 degree days in females. Adult longevity also decreased with increase in temperature.Effect of host plant on fitness of C. Murakatae fed on rice and water-oatResearchers believe that host plant and host races are among most important factors to investigate their effect on fitness of natural enemy to ensure effective biological control of insect pests. The study of tritrophic interaction between host plant, host insect and its natural enemy can be very helpful in understanding parasitoid?s suitability for formulating and improving a control strategy. In this study, it was observed that populations fed on water-oat irrespective of host race took shorter duration to complete its development. Body weight of larvae fed on water-oat was also heavier than that of population fed on rice.Concluding, C. murakatae can be used as a potential biological control agent against stripped stem borer as the biology and morphology studied in this research will support in understanding physiological interactions of parasitic wasp and its host. Studies on temperature can be used for optimizing mass culturing and field release for an efficient biological control in this species. Feeding on rice can also increase the fitness of parasitoid as the development duration of parasitoid matches with that of stem borer while feeing rice.