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Appl. Entomol. Zool. 42 (1): 121–128 (2007) http://odokon.org/ Appraisal of the acceptability of subtropical rutaceous plants for a swallowtail butterfly, Papilio protenor demetrius (Lepidoptera: Papilionidae) Mamoru CHACHIN, Keiichi HONDA* and Hisashi ÔMURA Department of Biofunctional Science and Technology, Graduate School of Biosphere Science, Hiroshima University; Higashi- hiroshima 739–8528, Japan (Received 18 August 2006; Accepted 20 October 2006) Abstract A Rutaceae-feeding swallowtail butterfly, Papilio protenor demetrius, exploits only a few plant species as hosts in the field. We examined in detail the acceptability of five potential rutaceous hosts occurring in the subtropics for oviposit- ing females of a Hiroshima population of the butterfly. The plants tested were Citrus depressa, Toddalia asiatica, Evo- dia meliifolia, Melicope triphylla, and Murraya paniculata, which are distributed mainly in the Southwestern Islands of Japan, thus in allopatry with the butterfly. Female responses to the foliage, methanol extracts and partitioned frac- tions from these plants were assayed for the presence of oviposition stimulants and/or deterrents. The foliage of C. de- pressa and T. asiatica strongly stimulated egg-laying, whereas ovipositing females only marginally accepted E. meli- ifolia and Me. triphylla, and virtually rejected Mu. paniculata. Further experiments with methanol extracts and frac- tions derived from the respective plants revealed that both C. depressa and T. asiatica contained potent oviposition stimulant(s) particularly in the aqueous fractions, and that the aqueous fractions of E. meliifolia and Mu. paniculata, despite their poor or little acceptability, contained moderate and weak stimulant(s), respectively. However, certain volatile deterrent(s) seemed to be responsible for the rejection of Mu. paniculata by females. Me. triphylla appeared to have neither appreciable stimulant(s) nor deterrent(s). Larval survival on these plants was also recorded as an estimate of fitness. Larvae performed very well on C. depressa. Unexpectedly, however, larvae did not survive on T. asiatica at all, but successfully grew on E. meliifolia. Larvae altogether failed to grow on both Me. triphylla and Mu. paniculata, suggesting the involvement of antifeedant(s) and/or toxic substance(s) in those plants to which larvae were mal- adapted. Key words: Host selection; oviposition; larval performance; Papilio protenor demetrius; Rutaceae made on the basis of a reciprocal balance of posi- INTRODUCTION tive and negative inputs from the plant which are Most butterfly species are phytophagous and ultimately transmitted to the central nervous sys- usually utilize only a limited range of host plants in tem for further processing (Renwick and Chew, nature. Although the host range of an insect is de- 1994; Honda, 1995). Extensive investigations car- termined by a diversity of ecological, geographical, ried out during the last two decades have revealed physiological, and behavioral factors, the key ele- an array of stimulants and deterrents of plant origin ments underlying the host range determination are responsible for oviposition by butterflies and moths phytochemicals; stimuli evoked, in particular, by (Renwick and Chew, 1994; Honda, 1995, 2005; plant secondary metabolites which are thought to Nishida, 1995; Honda and Nishida, 1999). The have a significant effect on host utilization by her- most crucial phase of host assessment in butterflies bivores (e.g. Städler, 1992). It has been fully estab- is “drumming” on the leaf surface with foretarsi lished that phytophagous lepidopterans can detect endowed with gustatory sensila. The majority of specific plant chemicals, which they use to assess phytochemicals directly associated with host recog- the suitability of potential hosts, and the decision nition and discrimination by ovipositing females to accept a given plant by ovipositing females is are those characterized mostly as non-volatile *To whom correspondence should be addressed at: E-mail: [email protected] DOI: 10.1303/aez.2007.121 121 122 M. CHACHIN et al. secondary metabolites (Honda, 2005). However, allowed to copulate in an outdoor cage (7 mϫ10 m, volatile compounds from host plants, in certain 3.5 m high). These were derived from laboratory cases, are also believed to stimulate egg-laying be- stock cultures originated from females collected in havior and thus promote egg deposition (Feeny et Higashihiroshima City (Hiroshima Prefecture). al., 1989). Larvae were reared on potted plants of Citrus spp. While papilionid butterflies are known to exploit (mainly C. natsudaidai) or F. ailanthoides at 25°C a wide range of plant families as hosts, most under a photoregime of 16L : 8D. Females were fed species of the genus Papilio exclusively utilize ru- with 15% aqueous sucrose solution once daily taceous plants, showing a differential use of allied throughout the experiments. plants depending on the species (Miller, 1987). De- Extraction and fractionation of plant materi- spite extensive work by many scientists, phyto- als. Young leaves of C. depressa, T. asiatica, E. chemical cues and sensory mechanisms regulating meliifolia, Me. triphylla, and Mu. paniculata col- host selection and host preference in these butter- lected in Okinawa Pref. (0.5–1 kg each) were ex- flies remain poorly understood. For a better under- tracted separately with methanol (4–8 l) at room standing of the physiochemical background of temperature for one month. Subsequent fractiona- present-day host utilization and host range evolu- tion of each extract was carried out according to tion in Papilio butterflies, further attempts are the method of Honda (1990), as outlined below. needed to investigate the chemical basis for differ- Each methanolic extract was concentrated in vacuo ential acceptance of potential host plants. below 50°C, and an aliquot of the whole concen- Papilio protenor is a specialist on the Rutaceae. trate, after being dispersed in water, was succes- P. protenor demetrius, a subspecies distributed sively partitioned with chloroform and isobutanol from the main island (Honshu) to the Amami Is- to give three fractions (one aqueous and two or- lands of Japan, utilizes several Citrus plants and a ganic fractions). The chloroform-soluble fraction few species of other genera (Fagara, Zanthoxylum, (Fr. 1) was stored in chloroform. The isobutanol- and Skimmia) as hosts. Another subspecies, P. pro- soluble fraction (Fr. 2) was evaporated to dryness tenor liukiuensis, inhabits more southerly regions, below 50°C, and the residue was re-dissolved in i.e. Okinawa and Yaeyama Islands, where many ru- methanol. The water-soluble fraction (Fr. 3) was taceous plants such as Murraya paniculata, Evodia dissolved in 50% aqueous methanol. All these frac- meliifolia, Fagara ailanthoides, Toddalia asiatica, tions were stored below 0°C until use. Fractions Citrus depressa, Melicope triphylla, Skimmia prepared from the respective plants will hereafter japonica var. lutchuensis, and Zanthoxylum ni- be abbreviated: Fr. 1 of C. depressa and Fr. 2 of T. tidum grow. We have previously reported on the asiatica, for instance, will be designated as Cd-1 affinity of P. protenor demetrius for four temperate and Ta-2, respectively. Concentrations of test sam- rutaceous plants occurring in Honshu; Citrus ples are all shown in % w/v. An initial extract and unshiu, Fagara ailanthoides, Phellodendron three partitioned fractions (Frs. 1–3) of a given amurense, and Orixa japonica (Honda and concentration prepared from the respective plants Hayashi, 1995a). This study of P. protenor were tested for their stimulatory or deterrent effect demetrius deals with a comparative appraisal of fe- on oviposition. male oviposition responses to and the suitability Bioassay for oviposition response. Behavioral for larval growth of five subtropical rutaceous bioassays were conducted by a method similar to plants, C. depressa, T. asiatica, E. meliifolia, Me. that reported previously (Honda, 1986), employing triphylla, and Mu. paniculata. In Japan, these are a green heart-shaped plastic plate (2–5 cm2) as a distributed in the Southwestern Islands, though E. leaf surrogate. Before testing, females were meliifolia is also found in Kyushu and Shikoku. screened daily to assess their responsiveness, and only those that showed positive responses to the fo- liage of C. natsudaidai (one of the major host MATERIALS AND METHODS plants of P. protenor demetrius; Honda, 1990) and Insects. Adults of P. protenor demetrius sub- negative responses to water alone (control) were jected to behavioral bioassays were 3- to 10-day- chosen. Appraisal of female responsiveness to each old gravid females, which had been hand-paired or sample was made basically in accordance with the Butterfly Host Selection 123 criteria given in previous papers (Honda et al., 1997; Nakayama et al., 2002): In each trial (sample presentation), the response of an individual was scored as 100% for actual egg-laying or equivalent behavior (trying to bring the ovipositor in contact with the underside of the leaf without egg de- position), 50% for half-curling the abdomen with continuous drumming (this behavior took place in- frequently), and 0% for drumming only with no positive response. Trials were replicated more than three times for each individual and the responses of an individual to a given sample were averaged. For all trials, merely alighting on ovipositional sub- Fig. 1. Oviposition responses (meanϮSE) of P. protenor strates without drumming was not

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