Effects of starvation on the search path characteristics of Orius majusculus (Reuter) (Het., Anthocoridae) Y. He´naut 1,3 , C. Alauzet 1 and M. Lambin 2 1 Laboratoire d’Ecologie terrestre-UMR 5552, Universite´ Paul Sabatier, Toulouse Cedex, France; 2 Laboratoire de Neurobiologie et Comportement, Universite´ Paul Sabatier, Toulouse Cedex, France; 3 El Colegio de la Frontera Sur, Tapachula, Chiapas, Mexico Ms. received: January 16, 2001; accepted: June 11, 2002 Abstract: Orius majusculus (Reuter) is a polyphagous predator bug used to control western flower thrips Frankliniella occidentalis (Pergande). As physiological factors may be highly influential upon the predatory behaviour of Orius spp. we studied the possible impact of starvation on the search path of this bug. Orius majusculus was maintained on a diet of Ephestia kuehniella Zeller (Lep., Pyralidae) eggs in laboratory. Adults were collected immediately after the imaginal moult and were individually placed in Petri dishes with abundant food. Each adult was randomly assigned to one of the following five treatments: immediate observation or starved for 2, 6, 9 or 12 h prior to observation. The observation procedure consisted of placing a single O. majusculus adult at the centre of an empty arena. The displacement of each insect was recorded with a video camera until it had reached the limits of the arena. The recorded paths were digitized and the digitized search path was used to calculate the mean walking speed, the number of stops per second, the duration of stops and the diffusion rate. The results clearly show that, in comparison with unstarved bugs, insects that experienced 6 h of prey deprivation walked more slowly, stopped more frequently and for longer periods, and had a lower rate of diffusion away from the release point. In contrast, all search path variables returned to the levels measured in unstarved bugs in the group that experienced the longest period of starvation (12 h), whereas groups of O. majusculus that had experienced 2 or 9 h of prey deprivation presented intermediate values for all the variables tested. Starvation produced evident changes in the search path characteristics that we assume to be related to physiological states of hunger and energy availability. These behavioural changes related to physiological state could have consequences for the use of this pirate bug in biological control. 1 Introduction Orius majusculus (Reuter) is a polyphagous predator bugusedingreenhousestocontrolwesternflowerthrips Frankliniella occidentalis (Pergande) (Trottin-Caudal et al., 1991; Fisher et al., 1992; Maisonneuve, 1993). This pirate bug appears to hold promise as an biological control agent of thrips pests, although predator releases may not always result in adequate levels of pest control in some cases (Grasselly, 1994). Several published studies indicate that the efficiency of Orius spp. may be influenced by environmental factors such as tempera- ture (Coccuza et al., 1997), the type of prey available (Fritsche and Tamo, 2000) or the experience of different prey types acquired during larval development (Henaut et al., 2000). The bug may also use visual cues during prey search related to prior experience of prey-associ- ated stimuli (Henaut et al., 1999). Physiological factors may also be highly influential in the predatory behaviour of Orius spp. although this has not been studied as far as we are aware. In this respect, predator starvation may be particularly relevant, given that commercially reared Orius are deprived of prey for considerable periods prior to release for insect biocon- trol in glasshouse or field crops. Observations on the searching behaviour of insects reveal different phases: the first, ranging search in which the insect forages over a large stretch of substrate in fast linear paths, followed by a phase of local search, in which the insect forages over a smaller area with a slower more sinuous path and with a greater frequency of stopping (Jandler, 1975). In the current study we attempted to determine the effect of various degrees of starvation on the search path characteristics of O. majusculus and the possible impact that starvation may have on the efficiency of this species as a pest control agent. 2 Materials and methods A laboratory culture of O. majusculus was maintained on a diet of Ephestia kuehniella Zeller (Lep., Pyralidae) eggs following established methods (Alauzet et al., 1992). Adults were collected immediately after the imaginal moult at different times during 5 days. These adults were individually placed in Petri dishes with abundant food [E. kuehniella eggs and Acyrtosiphon pisum Harris (Hom., Aphididae)] for 6 h. After this time, all food was removed and each adult was randomly assigned to one of the following five treatments: JEN 126 (2002) J. Appl. Ent. 126, 501–503 (2002) Ó 2002 Blackwell Verlag, Berlin ISSN 0931-2048 U. S. 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