240 H O ST PREFEREN CE, STAGE PREFEREN CE AN D FUN CTI O N AL RESPO N SE O F ASSASSI N BUG, RH YN O CO RI S KUM ARI I AM BRO SE AND LIVINGSTONE (HEMIPTERA: REDUVIIDAE) TO ITS MOST PREFERRED PREY TO BACCO CUTWO RM , SPO DO PTERA LI TURA (F.) J. MUNIYANDI, A. GANESH KUMAR, K. NAGARAJAN AND DUNSTON P. AMBROSE * Entomology Research Unit, St. Xavier’s College (Autonomous), Palayamkottai – 627 002, Tamil Nadu, India. email: eruxavier@gmail.com ABSTRACT The assassin bug, Rhynocoris kumarii Ambrose and Livingstone preferred larvae of tobacco cutworm, Spodoptera litura (F.) (35.29%) followed by the larvae of castor semilooper, Achaea janata L. (29.41%) and slant-faced grasshopper, Tyloprobidus variecornis Walker (21.57%). A low preference was expressed towards the blister beetles, Mylabris indica Thunberg (13.45%) and Mylabris pustulata Thunberg (8.03%). Among the blister beetles M. pustulata was the least preferred one. Among the different size groups of its most preferred prey S. litura, R. kumarii preferred 5-10 mm size group (44.64%) followed by other size groups (0-5 mm, 26.95%) and (10-15 mm, 18.16%). The least preferred (10.23%) size group was 15-20 mm. R. kumarii also exhibited type II functional response to S. litura larvae. A positive correlation was obtained between the prey density and the prey killed (y = 0.598 + 0.279x; r = 0.926). The attack ratio decreased as the prey density increased (y = 0.496 - 0.011x; r = -0.732). The maximum predation represented by ‘k’ value (4.53) was always found restricted to higher prey density. A negative correlation was obtained between the searching time and the prey density (y = 4.383 - 0.311x; r = -0.975). Key words: Rhynocoris kumarii, assassin bug, host preference, stage preference, functional response, Spodoptera litura Predators are regarded as ‘keystone species’ because of the great prey suppression impact they promote (Begon et al., 1996; Paine, 1966) due to their abilities by adjusting their numerical and functional responses to changes in prey density (Hassell, 1978; Ambrose, 1999, 2000, 2003). Hence, an understanding on predatory-prey interactions is essential to realize the biological control potential of predators in agroecosystems. The family Reduviidae is considered as an economically important taxon because it includes important generalist predators associated with a wide array of pests in diverse agroecosystems (Ambrose, 1999, 2000, 2003). Among reduviid predators, Rhynocoris kumarii Ambrose and Livingstone was reported as a key predator on various insect pests belonging to Lepidoptera such as American bollworm, Helicoverpa armigera (Hübner), tobacco cutworm, Spodoptera litura (F.) and hairy caterpillar, Earias vittella (F.); Coleoptera such as blister beetles, Mylabris pustulata Thunberg and Mylabris indica Thunberg and Hemiptera like red cotton bug, Dysdercus cingulatus F. (Ambrose, 1999). Although R. kumarii is polyphagous, it certainly exhibited certain degree of host specificity (Ambrose, 1999) and also preferred a particular stage of prey. Hence, knowledge on prey preference of this polyphagous predator is imperative before employing it in biological warfare (Nordlund and Morrison, 1990; Hattingh and Samways, 1992; James, 1994). Moreover, * Corresponding author Insect Pest Management, A Current Scenario, 2011 (ed.), Dunston P. Ambrose, Entomology Research Unit, St. Xavier’s College, Palayamkottai, India, pp.240-248.