J. Asia-Pacific Entomol. 5 (2) : 215 -220 (2002) www.entomology.or.kr Life Cycle and Predation Potential of the Black Cricket, Methioche vittaticollis (Orthoptera: Gryllidae) and Its Population Density in the Rice Field Geon-Hwi Lee*, K. L. Heong', Chae-Hoon Paik, Doo-Ho Kim, Seung-Yeoung Na and Man-Young Choi National Honam Agricultural Experimental Station, Iksan 570-080, Korea 'Entomology Division, The International Rice Research Institute, Los Banos, Philippines Abstract Life cycle and predation potential of a predatory black crickets, Methioche vittaticollis (Stal), were studied in the laboratory at the conditions of 27 ± 1 °C and 70 ± 5% RH with a photoperiod of 14: 10 (L: D). Average life cycle was 90 days. The cylindrical eggs were laid singly within the leaf sheath and hatched in 17 days. Total nymphal period lasted 33 days. There were four nymphal stadia that lasted for 7.2, 7.7, 8.7, and 9.0 days, respectively. Adult male and female lived an average of 35 and 43 days, respectively. The female lay an average of 45 eggs during her life span. The number of striped stemborer (SSB) eggs consumed per day by lst, 2nd, 3rd and 4th instar nymphs of M vittaticollis was 1.7, 2.5, 13.3 and 184.3, respectively. Also, The number of SSB eggs consumed per day by male and female adults were 102.7 and 158.7, respectively. The fourth instar nymph consumed the most number of preys. The functional response curve of 4th instar nymph, male and female adults of M vittaticollis to the densities of SSB eggs indicated Holling's TYPE II. The consumption of prey by the M vittaticollis increased with the prey density but the consumption rate decreased. The attack rate of 4th instar of M vittaticollis was the highest compared to the adults, and handling time was the shortest. Population densities of hoppers and lepidoptera in unsprayed field consisted of rice variety "PSBRc 20" were very low throughout the cropping period. This could be due to the high density of M vittaticollis. M vittaticollis was collected from the field and bunds, its population inside the field increased as crop matures. Bunds served as refuge for predators when the crop is maturity stage. Key words prey consumption, Methioche vittaticollis, striped stemborer, rice field, functional response, population density *Corresponding author. E-mail: Leejhwi@rda.go.kr Tel: 063-840-2291; Fax: 063-840-2118 (Received August 13, 2002; Accepted October 21, 2002) Introduction Biological control of rice insect pest is an important component of an IPM program. There are many species of natural enemies which contribute to the suppression of rice pest populations below economic injury levels. In order to use biological control more efficiently, it is a need to identify beneficial species and determine their roles in possible regulation of insect pests. There is a rich complex of biological control agents in rice fields (Nishida, 1967; Yasumatsu and Torii, 1968; Yasumatsu, 1975). Among them, insect predators are considered to be one of the most important groups. Some crickets are defoliators and damaging to early stages of rice plants (Natarajan et al., 1979). However, many species of crickets are omnivorous (Criddle, 1925; Severin, 1935). Crickets like Methioche vittaticollis (Stal.) are an important predator of several insect pests of rice. M vittaticollis is an egg predator of several defoliators, stemborers (Wongsiri et al., 1980) and leaffolders (Bandong and Litsinger, 1986). Also, their potential as predators has been indicated by their attack on grasshopper eggs (Criddle, 1925; Smith, 1959). However, very little information is available in the literature about this predator due to the fact that limited studies has been done. The objectives of this study are 1) to determine the developmental period, fecundity and longevity of M vittaticollis in the laboratory, 2) to determine the prey consumption and functional response of 4th instar nymph, male and female of M vittaticollis when provided with striped stemborer eggs as prey and 3) to investigate change in population density of M vittaticollis and its prey groups in unsprayed field and bunds in relation to crop age.