This study was conducted to measure the host-searching behavior of Cardiochiles nigriceps (CN), a parasitoid of the tobacco budworm Heliothis virescens (HV), on tobacco and cotton. Behavioral studies with CN were conducted in the field with feral females, because laboratory-reared CN would not search for hosts in cages. Five potted plants of each species (tobacco and cotton) were placed in a 5 ha cotton field containing CN females; the pots were arranged in a random order in a row, 60 cm apart. Then, three HV early second instars were allowed to feed in the terminal of each potted plant for 2 h.

Before attempting to measure the host-searching behavior of CN females, their general behavior was observed and described. It included hovering, searching and oviposition. Once a foraging female located a host plant, she hovered around it, sometimes staying over a particular spot before moving on. When a female hovered near a host-damaged site on the plant, she landed on the plant and began searching for the host. Searching behavior involved antennating the plant until the female found the host. Antennation behavior can be described as “drumming” the antennae close to the plant. When a host was located, the CN female antennated the host, positioned herself over its body (away from the head, to avoid being bitten), inserted her ovipositor and deposited an egg in the host.

CN females sometimes used their ovipositors as a probe, to ‘stab’ a host down in the terminal or crevice of the plant, but often the host remained out of reach. Such unsuccessful searching was referred to as ‘agony-search’. On other occasions, attempted oviposition was unsuccessful because the host dropped from the plant as a defensive response to an encounter with the parasitoid. Searching associated with a dropped host was referred to as ‘drop-search’. At other times, some hosts whipped their heads back and forth and tried to bite the attacking CN female. The most common result of a successful head-whipping defense was that the female could not insert her ovipositor into the host. Searching associated with a host miss was termed ‘miss-search’.

Nest, five methods were evaluated for measuring the host-searching behavior of CN females in the field. First, a stopwatch was used to try to time behaviors. This did not work well, since observation, timing and recording could not be done simultaneously. Second, a tape recorder was used to try to keep a hands-free record of the times of behavioral events. However, it took too much time to transfer data from the recorded tape to the computer back in the lab. Third, a stationary video camera was used to try to record CN behavior. This did not work either, because when the CN female moved in and around the plant, she also moved out of sight. Fourth, we tried using a hand-held video camera. This did not work for several reasons, but mainly because it was difficult to keep the camera focused on a female hovering up and down and around a plant.

Finally, we tried using a Psion Organizer II Model LZ64 (Psion PLC, London, England) with The Observer software (Noldus Information Technology, Inc., Sterling, VA). This method worked very well. We could easily follow females wherever they went, and were still able to time each of the observed behaviors. The video camera would have been excellent for acquiring accurate data, but we were unable to obtain all of the necessary data with the camera. The data obtained with the Psion Organizer was accurate, user response time was quick and there was no significant difference in oviposition times obtained for CN females using a stopwatch versus the Psion Organizer.

Using the Psion Organizer, the searching behavior of CN females was observed and recorded for a total of 10 h. Analyses revealed that CN females spent more time searching in tobacco than in cotton. This supports an earlier finding that females preferred tobacco and expected an ovipositional reward in this crop.

Paper presented at Measuring Behavior 2002 , 4^th International Conference on Methods and Techniques in Behavioral Research, 27-30 August 2002, Amsterdam, The Netherlands

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