Oecologia (1993) 95:241 245 Oecologia 9 Springer-Verlag i993 Thynnine wasps discriminate among heights when seeking mates: tests with a sexually deceptive orchid Steven N. Handel 1,2, Rod Peakall 1,. 1 School of Biological Sciences, Macquarie University, Sydney, N.S.W. 2109 Australia 2 Department of Biological Sciences, Rutgers University, Piscataway, NJ 08855-1059, USA Received: 5 August 1992 / Accepted: 19 April 1993 Abstract. The flower of a sexually deceptive orchid, Chi- loglottis reflexa, mimics both the sex pheromone and the appearance of a female thynnine wasp (Neozeloboria nr. proxima). The flower is pollinated when visited by male wasps, who attempt mating with the flower. We have used these mimetic flowers to investigate mating behavior of the male wasps. In field choice experiments, males strongly prefer to visit flowers that are very low in the habitat, 15 cm, vs. flowers that are placed at 55 or 105 cm. These studies suggest that male precopula- tory response is strongly dependent on the microlocation of the female (or female mimic). Other insect-mimicking orchids, which together attract several groups of Hyme- noptera, may be useful in analogous experiments on mating behavior. Additionally, these experiments help elucidate features of the mimetic flowers, particularly stature, that act to efficiently attract potential pollina- tors. Key words: Orchids - Thynnines - Chiloglottis reflexa - Pollination - Mimicry The behavior of male Hymenoptera has received little attention relative to that given to females (Alcock et al. 1978), even though male mate choice is predicted to evolve in species such as thynnines, where males invest time and energy to feed the females (Alcock 1981; A1- cock and Gwynne 1987). For example, such choice has been shown to occur for males of Megalothynnus klugii who prefer larger females over smaller ones (Alcock and Gwynne 1987). However, in general, studies of reproduc- tive behavior in groups like thynnines are difficult be- cause females spend much of their time underground * Current address. Division of Botany and Zoology, Australian National University, Canberra, ACT 2601 Australia Correspondence to." S.N. Handel, Department of Biological Sci- ences, Rutgers University, Piscataway, NJ 08855-1059, USA and at any given time few are available for observation or experimental manipulation. In this paper we use a new method for investigating the behavioral ecology of this insect group. In particular, we use a species of orchid whose flowers mimic the fe- males' attractive cues. Because the orchid flowers are often easily located and manipulated they provide a powerful tool for studying the reproductive behavior of the male insects attracted to their mates. For example, more than 70 species of Australian orchids exploit the reproductive behavior of thynnine wasps by mimicking the sex pheromones and morphology of the females. Sex- ually deceived males pollinate the flowers during a pre- copulatory routine or attempted copulation (Stoutamire 1974, 1975, 1983; Peakall 1990; Peakall and Handel 1993). Similar interactions occur with other insect groups and orchids in Europe, the Mediterranean, and Australia (Dafni 1984; Borg-Karlson 1990; Dafni and Bernhardt 1990). In the thynnine-orchid system, when the orchid flow- ers are presented within appropriate wasp populations, the pollinators are readily attracted to the flowers, often in a matter of seconds (Peakal11990; Peakall and Handel 1993). Given this finding, mark and recapture experi- ments using the orchid 'baits' to attract males can be exploited to provide information about the extent of male patrols. In addition, a behavioral response that is difficult to observe in nature was discovered: males were found to avoid the orchid flowers following an initial encounter, despite continuation of the stimulus. The same behavior occurred when females were experi- mentally presented but prevented from being taken. These data suggest a learned response that may be asso- dated with male choice. Anecdotal observations suggest that mate search in thynnines may be restricted to a narrow flight zone that is close to the ground although the males are known to forage more broadly on shrubs and trees (Ridsdill Smith 1970a, b; Peakall 1990). In this study we use the orchid Chiloglottis reflexa that mimics females of one wasp species to test whether mate search is restricted