Functional response or Rhy nOClJr , is fuscipes Fabricius ( Heteroptera : Reduviidae ) to Ripldrtiuclavatus Thunberg ( Heteroptera : Alydidae )

Functioncil response of thereduviid predator, Rhynocoris iUsdpes Fabricius to the be'an bug Riptortus clava/us Thunberg was studied in pigeonpea branch terminals using' field cages. Rhynocoris ! iJscipe~ positively responded to the changing abundance of prey andexhiblted Holling's 'secOIid model of functional response. The searching capacity of R. mscipes increased with increasing prey density. The considerable number of prey consumed by the predator per day at higher prey density than at lower density reflected the predator's biocontrol potential KEY WORD~ : Functional response, handlinl! ; time •. prey density • Rhvnocoris iUscioes. Riptortus'ciavatus. searching time . ~ynocoris fUScipes Fabricius is anexceUent predfltor predominantly found in agro-ecosystems. scrub jungles and semi-arid zones bordering agroecosystems in India. It was found to be one of the most important predators of insect pests of cotton. maize, black gram and green gram (Singh and Singh, 1987; Ambrose, 1995). RiptortuscJavalllsThunberg is a serious pest of cotton, cereals and pulses. Rhynocoris filscipe,s was found voraciously predating upon nymphs of R, clavatus on pigeonpea. Caj.7J1us cajan L. Millsp . in the field. Hence, an attempt was made to ~tudy the functional response of R. fuscipes to R. clavatus to understand the basic mechanism . ", . underlying the prey-predator interaction and to evolve strategies f<? r mass rearing and subsequent release of this.predator into the agro-ecosystem to manage R. clavatllS. lYIATERIALS AND METHODS The nymphs and adults of R~ fuscipes collected at Sivanthipatti, Nellai Kattabomman District, Tamil Nadu (77 0 41' E and 8°30" N'}were reared in the laboratory (300 C 32 OC) in separate plastic containers (7 x. 7 x 4cm) on Corcyra cephalonica Stainton larvae. Newly mowtedadult females of R. fllscipeswere used . in this experiment. The functional response experiments were conducted in' pigeonpea agroecosystem atV.M. Chatramvillage five km.north east of Sivanthipatti. The branch terminals of flowering plants were covered with small nylon mesh branch cages (10 x 15 cm) (Pickett et ai., 1987). Predators starved for 48 Ii were used in thIS experiment. The functional response of adult. female R. iUscipesto fourth instar R. cia·vatus was assessed at six. differe~l densities viz., 1,2,4.8, 16 and 32 prey/predator. for 4 days. A predator and the prey were introduced into the mesh cage. Thus six different categories of experimental set ups with six different prey levels were maintained, separately. Six replications were maintained ~oreac~ category. }\Jter 24 h the number of prey consumed or killed was recorded and the prey number was maintained constant by replacing them with fresh prey throughout the experimental period . In the present study 'disc' equation of Holling (1959) was used to describe the functional response of R. iUscipesadults at six prey densities. The various parameters in the 'disc' equation ,are: x = prey density, . y = total numbe:r· of preY' killed in a· given period of time, y/x = the attack ratio, T t = total predator (Tt/k), and a time in days when prey was exposed to the predator, b= time spent for handling each prey by the = 'rate· of discovery' per u.nit of searching time [(y/x)/TsJ. The parameters 'b' and 'a' were directly measured in the present study. The handling time 'b' ",as estimated as the int~rvalbetween the time of completion of feeding and the time for the predator to attack again.