Temporal accumulation of phenylpropanoids in male fruit flies, <Emphasis Type="Italic">Bactrocera dorsalis</Emphasis> and <Emphasis Type="Italic">B. carambolae</Emphasis> (Diptera: Tephritidae) following methyl eugenol consumption

Summary. Males of dacine tephritids, Bactrocera carambolae and B. dorsalis are strongly attracted to, and compulsively feed on methyl eugenol (ME), a potent attractant for many Bactrocera species. While ME was shown to be biotransformed into phenylpropanoids, 2-allyl-4,5-dimethoxyphenol and (E)-coniferyl alcohol, and temporarily stored in the rectal gland of male B. dorsalis prior to release during courtship at dusk, B. carambolae male produces only the latter compound along with its de novo synthesized pheromone components. Both species were also shown to have different age-related response, sensitivity and consumption levels of ME. Here, we monitored and compared temporal changes in the accumulation profiles of these phenylpropanoids by the two sibling species, with male rectal glands being individually excised at different time intervals from 15 minutes to 20 days after initial ME feeding and analysed quantitatively. Results are discussed in light of plant-fruit fly co-evolution relationship.     

Lack of sequestration of host plant glucosinolates in <Emphasis Type="Italic">Pieris rapae</Emphasis> and <Emphasis Type="Italic">P. grarricae</Emphasis>

Summary. Sequestration of plant toxins in herbivores is often correlated with aposematic coloration and gregarious behaviour. Larvae of Pieris brassicae show these conspicuous morphological and behavioural characteristics and were thus suggested to sequester glucosinolates that are characteristic secondary metabolites of their host plants. P. rapaeare camouflaged and solitary, and are thus not expected to sequester. To test this hypothesis and to check the repeatabi-lity of a study that did report the presence of the glucosinolate sinigrin in P. brassicae, larvae were reared on three species of Brassicaceae (Sinapis alba, Brassica nigra and Barbarea stricta), and different leaf and insect samples were taken for glucosinolate analysis. The major host plant glucosinolates could only be found in traces or not at all in larval haemolymph, bled or starved larvae, faeces or pupae of both species or P. brassicae regurgitant. Haemolymph of both Pieris spp. was not rejected by the ant Myrmica rubra in dual-choice assays; the regurgitant of P. brassicae was rejected. This suggests the presence of compounds other than glucosinolates that might be sequestered in or produced by P. brassicae only. In faeces of both Pieris spp. a compound which yielded 4-hydroxybenzylcyanide (HBC) upon incubation with sulfatase was detected in high concentrations when larvae had been reared on S. alba. This compound may be derived from hydrolysis of sinalbin, the main glucosinolate of that plant. The unidentified HBC progenitor was apparently not sequestered in the two Pieris spp., and was not detected in faeces of larvae reared on B. nigra or B. stricta. Received 18 July 2002; accepted 11 September 2002.     

Interspecific transmission of Paederus endosymbionts: relationship to the genetic divergence among the bacteria associated with pederin biosynthesis

Summary. Endosymbiotic bacteria implicated in pederin production of Paederus (+)-females (Coleoptera: Staphylinidae) can be transmitted horizontally within and less frequently among the three species analyzed (P. melanurus, P. riparius, P. sabaeus). The 16S rDNA isolated from (+)-females reveals closely related bacterial sequences in the three species as well as in Paederus fuscipes and Paederidus ruficollis. This confirms the association of the undescribed endosymbiont and pederin biosynthesis in 5 of the 13 species that have been shown to contain the substance. In spite of the high sequence identities (> 99.5%), which suggest one species of endosymbiont, some of the heterospecific hosts were incompatible. This indicates adaptation and specific preferences of the endosymbiont for their natural host. Received 5 December 2001; accepted 11 March 2002.     

Foraging responses in the butterflies <Emphasis Type="Italic">Inachis io</Emphasis>, <Emphasis Type="Italic">Aglais urticae</Emphasis> (Nymphalidae), and <Emphasis Type="Italic">Gonepteryx rhamni</Emphasis> (Pieridae) to floral scents

Summary. For butterflies to be efficient foragers, they need to be able to recognize rewarding flowers. Flower signals such as colours and scents assist this recognition process. For plant species to attract and keep butterflies as pollinators, species-specific floral signals are crucial. The aim of this study is to investigate foraging responses to floral scents in three temperate butterfly species, Inachis io L. (Nymphalidae), Aglais urticae L. (Nymphalidae), and Gonepteryx rhamni L. (Pieridae), in behavioural choice bioassays. The butterflies were allowed to choose bet-ween flower models varying in scent and colour (mauve or green). Flowers or vegetative parts from the plants Centaurea scabiosa L. (Asteraceae), Cirsium arvense (L.) (Asteraceae), Knautia arvensis (L.) (Dipsacaceae), Buddleja davidii Franchet (Loganicaeae), Origanum vulgareL. (Lamiaceae), Achillea millefolium L. (Asteraceae), and Philadelphus coronarius L. (Hydrangiaceae) were used as scent sources. All visits to the models — those that included probing and those that did not — were counted, as was the duration of these behaviours. Both flower-naive and flower-experienced (conditioned to sugar-water rewards, the colour mauve, and specific floral scents) butterflies were tested for their preference for floral versus vegetative scents, and to floral scent versus colour. The butterflies were also tested for their ability to switch floral scent preferences in response to rewards. Flower-naive butterflies demonstrated a preference for the floral scent of the butterfly-favourable plants C. arvense and K. arvensis over the floral scent of the non-favourable plants Achillea millefolium (Asteraceae), and Philadelphus coronarius cv. (Hydrangiaceae). Most of the butterflies that were conditioned to floral scents of either C. arvense, K. arvensis, or B. davidii readily switched theirfloral scent preferences to the one most recently associated with reward, thus demonstrating that floral scent constancy is a result from learning. These findings suggest that these butterflies use floral scent as an important cue signal to initially identify and subsequently recognize and distinguish among rewarding plants. Received 2 September 2001; accepted 9 September 2002.     

Antennal responses to floral scents in the butterflies <Emphasis Type="Italic">Inachis io</Emphasis>, <Emphasis Type="Italic">Aglais urticae</Emphasis> (Nymphalidae), and <Emphasis Type="Italic">Gonepteryx rhamni</Emphasis> (Pieridae)

Summary. To better understand the biological role of floral scents for butterflies, electrophysiological responses to floral scents were investigated using combined gas chromatography and electroantennographic detection (GC-EAD). The antennal responses of three butterfly species, Aglais urticae L. (Nymphalidae), Inachis io L. (Nymphalidae), and Gonepteryx rhamni L. (Pieridae) to floral scent compounds from both natural and synthetic mixtures were examined. Floral scents were collected from the butterfly nectar plants Cirsium arvense (L.) (Asteraceae), and Buddleja davidii Franchet cv. (Loganicaeae) with dynamic head-space methods on Tenax-GR and eluted with pentane. These eluates, composed of natural floral scent blends, represent an array of compounds in their natural state. In the GC-EAD analyses eleven compounds were identified from C. arvense with the benzenoid compound phenylacetaldehyde in highest abundance. Seventeen compounds were identified from B. davidii with the irregular terpene oxoisophorone in highest abundance. Thirty-nine synthetic floral scent compounds were mixed in pentane, in equal amounts; about 35 ng were allowed to reach the antennae. The butterflies showed antennal responses to most of the floral scent compounds from both natural and synthetic blends except to the highly volatile monoterpene alkenes. Certain benzenoid compounds such as phenylacetaldehyde, monoterpenes such as linalool, and irregular terpenes such as oxoisophorone, were emitted in relatively large amounts from C. arvense and B. davidii, and elicited the strongest antennal responses. These compounds also elicited strong antennal responses when present in the synthetic scent blends. Thus, the butterflies seem to have many and /or sensitive antennal receptors for these compounds, which points to their biological importance. Moreover, these compounds are exclusively of floral scent origin. For B. davidii, which depends highly on butterflies for pollination, the exclusive floral scent compounds emitted in high abundance could be the result of an adaptive pressure to attract butterflies. Received 2 Septemter 2001; accepted 9 September 2002.     

Predatory behavior and chemical communication in two Metapone species (Hymenoptera:Formicidae)

Summary. Colonies of two species of Metapone (M. madagascarica, M. new species.) were collected in Madagascar and established in laboratory nests. It could be demonstrated that both species are specialist predators of termites (Cryptotermes kirbyi). During hunting the ants sting the termites and thereby paralyze and preserve the prey alive. In this way prey can be stored in the ant nest for extended periods. During foraging and colony emigrations the ants lay chemical trails with poison gland secretions. Among the seven compounds identified in the venom only methyl pyrrole-2-carboxylate elicits trail following behavior in both Metapone species. Received 11 February 2002, accepted 23 February 2002.     

Pyrrolizidine alkaloid content in <Emphasis Type="Italic">Senecio</Emphasis>: ontogeny and developmental constraints

Summary. The ontogeny of pyrrolizidine alkaloid (PA) synthesis and constraints on defence level during the seedling stage were examined in the annual Senecio vulgaris and the monocarpic perennial Senecio jacobaea. In both species, PAs were actively synthesized from the onset of seedling growth so that juvenile stages did not go through an undefended stage. Roots are known to be the exclusive sites where PAs are produced. Root biomass was the single most important biomass parameter explaining variation in total PAs per seedling. All correlation coefficients between—relative growth rate and PA concentration were negative, but none was significant. However, a significant negative—correlation was found between shoot to root ratio and PA concentration in S. jacobaeaseedlings, suggesting a dilution effect of the PAs. Earlier studies have shown that the shoot to root ratio is positively correlated with relative growth—rate of established S. jacobaea plants. It is therefore suggested that young S. jacobaea plants with a high shoot to root ratio and hence a high growth capacity necessarily have lower PA defence levels than plants with a low shoot to root ratio. Received 10 July 2002; accepted 16 November 2002.     

Uptake and metabolism of [<Superscript>14</Superscript>C]rinderine and [<Superscript>14</Superscript>C]retronecine in leaf-beetles of the genus <Emphasis Type="Italic"> Platyphora</Emphasis> and alkaloid accumulation in the exocrine defensive secretions

Summary. Sequestration and processing of pyrrolizidine alkaloids (PAs) by leaf beetles of the genus Platyphora were investigated. Tracer experiments with labeled alkaloids were performed with P. eucosma feeding on Koanophyllon panamense (Asteraceae, tribe Eupatorieae). P. eucosma catalyzes the same reactions previously demonstrated for P. boucardi specialized to Prestonia portobellensis (Apocynaceae): (i) epimerization of rinderine to intermedine; (ii) esterification of retronecine yielding insect-specific PAs; (iii) efficient transport of the PAs as free bases into the defensive secretions. P. bella feeding on Tournefortia cuspidata (Boraginaceae) shows the same sequestration behavior and ability to synthesize the specific retronecine esters. P. ligata, a species phylogenetically closely related to the PA adapted species and clustering in the same clade, but feeding on a host plant devoid of PAs, feeds easily on PA treated host-plant leaves, but does not sequester or metabolize PAs. P. kollari a species clustering outside the PA clade refused to feed on its food-plant leaves painted with PAs. The results are discussed in relation to host-plant selection of the PA adapted species and the role of PAs in chemical defense. Received 20 September 2002; accepted 18 November 2002.     

Pheromone-based aggregation behaviour of the firebrat, <Emphasis Type="Italic">Thermobia domestica</Emphasis> (Packard) (Thysanura: Lepismatidae)

Summary. We tested the hypothesis that aggregation behaviour of the firebrat, Thermobia domestica (Packard) (Thysanura: Lepismatidae), an inhabitant of enclosed microhabitats, is mediated, at least in part, by a pheromone. Individual insects were released into the central chamber of a 3-chambered olfactometer and test stimuli were placed in lateral chambers. Paper discs previously exposed for 3 days to 10 female, male, or juvenile T. domestica were all preferred by female, male, or juvenile T. domestica over unexposed paper discs, indicating the presence of an aggregation/arrestment pheromone. In additional experiments, frass and scales from female T. domestica, tested singly and in combination, proved not to be the source of the pheromone. Physical contact was required for pheromone recognition, indicating that the pheromone arrests rather than attracts conspecifics. Arrestment by the long-tailed silverfish, Ctenolepisma longicaudata Escherich (Thysanura: Lepismatidae), but not by the common silverfish, Lepisma saccharina L. (Thysanura: Lepismatidae), to T. domestica exposed paper discs suggests closer phylogenetic relatedness between C. longicaudata and T. domestica, than between C. longicaudata and L. saccharina. Whether C. longicaudata or L. saccharina produce an aggregation signal, and whether T. domestica respond to this signal is unknown. Received 10 June 2002; accepted 30 September 2002.     

Comparison of phenylpropanoid volatiles in male rectal pheromone gland after methyl eugenol consumption, and molecular phylogenetic relationship of four global pest fruit fly species: Bactrocera invadens, B. dorsalis, B. correcta and B. zonata

Males of many tephritid fruit fly species of the genus Bactrocera show a very strong affinity to methyl eugenol (ME). An attracted male compulsively ingests ME, which is then biotransformed before its metabolites are accumulated into the rectal gland. The glandular organ is known to serve as a reservoir for sex pheromone in some species. Upon ME-feeding, males of the oriental fruit fly, Bactrocera dorsalis, selectively accumulated two metabolites, 2-allyl-4,5-dimethoxyphenol (DMP) and (E)-coniferyl alcohol (E-CF), in the rectal pheromone gland. We compared the profiles of phenylpropanoid metabolites accumulated by three other species of very high economic and quarantine importance—Bactrocera invadens, Bactrocera zonata and Bactrocera correcta, with that of B. dorsalis. Males of each species were fed artificially on ME and the metabolites stored in the rectal glands were examined by means of chromatography and spectroscopy. Similar to B. dorsalis, males of laboratory-raised B. invadens accumulated DMP and E-CF, in almost equal quantities, in the rectal sac. The sum of DMP and E-CF increased gradually with time after ME consumption and reached as high as 150 μg/male 2 days post ME-feeding. Wild males of B. invadens captured in Kenya also possessed both the compounds in varying quantities. In contrast, males of B. zonata accumulated DMP and (Z)-coniferyl alcohol (Z-CF) in an approximate ratio of 1:1; whereas B. correcta is known to convert ME to (Z)-3,4-dimethoxycinnamyl alcohol (Z-DMC) and Z-CF also in an approximately 1:1 ratio. Thus, there are three types of binary combinations of rectal phenylpropanoid volatiles (i.e. DMP + E-CF; DMP + Z-CF; Z-CF + Z-DMC) utilized among the four Bactrocera species. Such differences in phenylpropanoid ingredients may play a critical role in differentiating these species if encountered in the natural habitat. In this context, the two putative sibling species—B. invadens and B. dorsalis, possess the identical subset of rectal volatiles (DMP and E-CF) in a similar proportion. Furthermore, the phylogenetic analyses of the four Bactrocera species by comparing nucleotide sequences in the mitochondrial genes showed that B. invadens clearly belonged to the same clade as B. dorsalis species. Therefore, we consider the two as the same biological species, and certainly not distinct.     

Communication ecology of webbing clothes moth: 4. Identification of male- and female-produced pheromones

Summary. We investigated the hypothesis that aggregation signals produced by male webbing clothes moths (WCM), Tineola bisselliella (Hum.) (Lepidoptera: Tineidae), and close-range male attractant signals produced by females have a pheromonal basis, at least in part. Gas chromatographic-electroantennographic detection (GC-EAD) and GC-mass spectrometric analyses of bioactive methanolic extracts of male WCM disclosed three candidate pheromone components: hexadecanoic acid methyl ester (16:Ester), (Z)-9-hexadecenoic acid methyl ester (Z9—16:Ester), and octadecanoic acid methyl ester (18:Ester). In bioassay experiments in a large Plexiglas™ arena, a blend of synthetic 16:Ester plus Z9—16:Ester was attractive to male and virgin (but not mated) female WCM; the 18:Ester was inactive. GC-EAD analyses of pheromone gland extracts from female WCM revealed (E,Z)-2,13-octadecadienal (E2Z13—18:Ald) and (E,Z)-2,13-octadecadienol (E2Z13—18:OH) as candidate sex pheromone components. In arena bioassay experiments, 1—5 female equivalents of synthetic E2Z13—18:Ald (0.2 ng) and E2Z13—18:OH (0.1 ng) were more attractive to male WCM than were two virgin female WCM. We anticipate that the combination of aggregation and sex pheromones, male-produced sonic aggregation signals, and habitat-derived semiochemicals will be highly effective in attracting male and female WCM to commercial traps. Received 12 January 2001; accepted 8 June 2001.     

Two herbivore-deterrent iridoid glycosides reduce the in-vitro growth of a specialist but not of a generalist pathogenic fungus of Plantago lanceolata L

Summary. Many secondary plant compounds are involved in defense against both insect herbivores and pathogens. Two secondary plant compounds of Plantago lanceolata, the iridoid glycosides catalpol and its precursor aucubin, are well known for their deterrent effects on generalist and non-adapted specialist insect herbivores. We tested the effects of these compounds on the in-vitro growth of a specialist and generalist fungal pathogen of this host species. Two chemical forms of these iridoids were tested. The glycosides and their aglycones, the products of enzymatic conversion by specific $/Beta$-glucosidase enzymes. The glycosides enhanced growth of both the specialist fungus Diaporthe adunca and the generalist fungus Fusarium moniliforme var. subglutinans. The positive effect of these glycosides on the generalist fungus is in sharp contrast with the generally negative effects of these glysosides on generalist insect herbivores. The aglycones of aucubin and catalpol reduced the growth of the specialist fungus D. adunca, but, contrary to expectation, enhanced the growth of the generalist fungus F. moniliforme var. subglutinans. Effects of aucubin on D. adunca were stronger than effects of catalpol. This was true both for the growth stimulating effects of the glycosides and for the fungitoxic effects of the aglycones. We therefore expect that the effects of these iridoids in P. lanceolata on the specialist fungus will strongly depend on the ratio between catalpol and its precursor aucubin and the chemical form (glycoside or aglycone) in which these compounds are encountered by the fungus during growth. Our results suggest that iridoid glycosides in P. lanceolata can be used as defense against both herbivores and pathogens, but that their effects are highly specific with respect to the natural enemy species that is encountered. Received 11 April 2002; accepted 9 August 2002     

Preferences of six leaf beetle species among qualitatively different leaf age classes of three Salicaceous host species

Summary. As Salicaceous plants produce new leaves for a prolonged period of time, they expose a wide range of differentially aged leaves to herbivores during the growing season. In this work, I show that young leaves of three Salicaceous species, Populus tremula L., Salix phylicifolia L. and S. pentandra L., contain more nitrogen than conspecific old leaves. In P. tremula and S. pentandra young leaves also contained more low-molecular weight secondary compounds, phenolic glucosides. Leaves of S. phylicifolia did not contain phenolic glucosides in detectable amounts. Furthermore, in P. tremula and S. pentandra young leaves contained less polymeric digestability-reducing phenolics, condensed tannins, than old leaves. In S. phylicifolia, higher concentrations of condensed tannins were found in young leaves. In laboratory feeding trials with six leaf beetle species, young leaves of the studied plants were invariably preferred in all tested herbivore × host species combinations. In particular, it is remarkable that three leaf beetle species with known different overall relationships to phenolic glucosides equally preferred more glucoside-containing young S. pentandra leaves over conspecific old ones. Four beetle species were found to prefer young leaves of S. phylicifolia despite the higher content of condensed tannins in young leaves. These results indicate that the general preference of leaf beetles for young leaves of Salicaceous plants probably does not primarily result from variable distribution of secondary compounds. Apparently, the preference for young leaves is fundamentally due to variation in leaf nutritive traits, such as nitrogen content. Received 9 February 2001.     

Spray mechanism of crepidogastrine bombardier beetles (Carabidae; Crepidogastrini)

Summary.   The defensive glandular apparatus of primitive bombardier beetles of the tribe Crepidogastrini (Carabidae) is described for the first time. As exemplified by two African species (Crepidogaster ambreana and C. atrata), the apparatus conforms to the basic bombardier plan, in that the glands are bicompartmented and the secretion is quinonoid (it contains 1,4-benzoquinones and hydrocarbons), hot, and discharged audibly. In a number of morphological respects the crepidogastrine apparatus resembles that of the classical bombardiers of the tribe Brachinini (rather than that of bombardiers of the paussoid lineage), reinforcing the view, already held on taxonomic grounds, that the Crepidogastrini and Brachinini are closely related. That the Crepidogastrini may be primitive relative to Brachinini is underscored by the finding that, unlike brachinines, crepidogastrines do not pulse their secretory emissions. Moreover, they discharge their secretion as a mist, rather than forcibly in the form of jets. Received 22 May 2001; accepted 29 May 2001.     

Effects of hydrolysable tannins on a herbivorous insect: fate of individual tannins in insect digestive tract

Summary. We investigated the effects of four chemically characterised galloylglucoses (GGs, a subgroup of hydrolysable tannins) and their hydrolysis product, gallic acid (GA), on consumption and performance of larvae of the autumnal moth Epirrita autumnata. Larvae were fed with birch (Betula pubescens) leaves that had been painted individually with each of the compounds at two levels, 5 and 20 mg/g. In addition, we investigated the fates of the leaf-painted GGs and GA in the E. autumnata digestive tract by comparing phenolics in leaves consumed and in faeces. In general, GGs reduced leaf consumption by E. autumnata during the second and fourth instars, although there was high compound- and instar-specific variation. However, GGs did not affect the leaf consumption rates by the most voracious fifth instar larvae. This resulted in approximately the same loss of total biomass by the experimental tree, regardless of the nature and level of GGs enriched to its foliage. The characteristic fate of hydrolysable tannins, i.e. hydrolysis, was evidenced in the larval digestive tract for three of the four leaf-painted GGs. In addition to hydrolysis, the almost total absence of GGs in larval faeces was presumably related to the oxidation of GGs. The dose-dependent excretion percentage of ingested GA showed that it's faecal content should not be used, although it commonly is, to calculate the level of GG hydrolysis. Moreover, by comparing the non-uniform appearance of faecal tetragalloylglucoses, whether ingested as such or hydrolysed from pentagalloylglucose, we concluded that a major part of oxidation of GGs occurs before their hydrolysis in the digestive tract of E. autumnata. Criticism against the common use of tannic acid, a heterogeneous mixture of GA and GGs, in ecological studies is presented. Received 15 May 2002; accepted 16 July 2002     

The roles of nicotine and natural enemies in determining larval feeding site distributions of Manduca sexta L. and Manduca quinquemaculata (Haworth) on tobacco

Summary. Field observations indicated that hornworms select feeding sites non-randomly on tobacco. We tested the hypotheses that differences in feeding site locations of larvae of Manduca sexta L. and Manduca quinquemaculata (Haworth) (Lepidoptera: Sphingidae) on tobacco could be explained by differential nicotine concentrations within plants and leaves, species-specific responses to nicotine, or pressure exerted by natural enemies. Results showed that third-instar larvae of M. sexta fed more proximally and centrally on the leaf, whereas M. quinquemaculata fed more distally. Within-plant selection of leaves did not differ; both species selected leaves in the middle region of the plant. Nicotine concentrations in a high nicotine genotype, NC95, varied within each leaf, increasing 2—3 fold from the basal to apical portion of the leaf, and within each plant, increasing 7—10 fold from the first fully expanded leaf to the twelfth (lowest) leaf. In laboratory bioassays, both Manduca species responded to nicotine as a feeding deterrent. Electrophysiological studies demonstrated that gustatory organs of both species responded to nicotine at concentrations found in tobacco leaves and that M. quinquemaculata generally showed a less vigorous response to nicotine than M. sexta. Field mortality of M. sexta due to parasitism by Cotesia congregata (Say) and to parasitism and predation combined differed among feeding sites; predation alone did not. Results suggest that although nicotine concentration and species specific responses to nicotine play a role in determining feeding site locations, pressure exerted by natural enemies, especially parasitism by C. congregata, is more important. Received 22 February 2000; accepted 20 July 2001.     

Variation in metabolism of BOA among species in various field communities – biochemical evidence for co-evolutionary processes in plant communities?

Summary. The capacity of benzoxazolinone metabolization of dicotyledonous species characteristic for the former vegetation classes Secalietea (grain field weed communities) and Chenopodietea (hoed vegetable communities) was estimated by the production of BOA-6-OH, BOA-6-β-O-glucoside, and BOA-N-glucoside. Except for Urtica urens, Galinsoga ciliata, and Polygonum aviculare (Chenopodietea), all species tested were able to synthesize BOA-6-OH, its glucoside, and BOA-N-glucoside, but effectiveness of BOA metabolism differed highly depending on species and plant organ. There was no correlation between bacterial phenoxazinone production and appearance of metabolites in the plants. Bioassays demonstrated that N-glucosylation is more efficient in BOA detoxification than O-glucosylation. The intermediate BOA-6-OH, however, is more harmful than BOA itself. It is therefore assumed that the ability to synthesize BOA-N-glucoside reduces the sensitivity to BOA strikingly. Since the detoxification capacity did not correlate with the taxonomic position, the affiliation of the species tested with the corresponding plant communities was taken into consideration. Evidently, the ecobiochemical potential of species to detoxify benzoxazolinone, regarded as an essential secondary compound in rye and wheat fields, reflects their occurrence in those plant associations. The ability to cope with the compound could be the result of co-evolutionary processes and presents a hidden aspect of allelopathic interaction. Received 4 January 1999; accepted 14 June 1999.     

Individual variation in pheromone emission and termination patterns in female Anomala cuprea

Summary. Individual variations in pheromone emission patterns were examined in a scarab beetle, Anomala cuprea Hope (Coleoptera: Scarabaeidae), by headspace collection of airborne volatiles from individual females. The amount of pheromone obtained varied among virgin females, and about 16% of these females (“silent” females) did not emit detectable amount of pheromone throughout the experimental period. There was no clear temporal pattern of peak pheromone emission for 19 days after the onset. More than half of the laboratory mated females completely stopped releasing pheromone after the first mating, while the rest of them continued releasing pheromone, frequently followed by additional mating. Received 26 March 2001; accepted 28 January 2002.     

How does salinity tolerance influence the distributions of <Emphasis Type="Italic">Brachionus plicatilis</Emphasis> sibling species?

Environmental salinity is important in defining Brachionus plicatilis sibling species distributions. However, while salinity influences distributions, sibling species often co-exist. Three different mechanisms potentially account for the partial co-occurrence of sibling species: (1) siblings have differing salinity tolerances that partially overlap; (2) siblings physiological tolerances may be commonly broad, but relatively small differences in tolerances differentiate distributions via interactions e.g. competition; or (3) siblings distributions may be influenced by physical factors other than salinity. Here, we assess the extent of salinity tolerance in three B. plicatilis sibling species (B. plicatilis 6TUR, B. plicatilis IOM and B. rotundiformis 6TOS) by measuring population growth rate (μ, day⁻¹) and egg development time in response to salinity (5–60‰) and salinity fluctuations (≤ Δ40‰). Sibling species were identified by analysis of the mitochondrial COI gene, and salinity responses were compared by regression analysis. Responses differed significantly between siblings, although the broad trends were similar. Positive growth occurred at all salinities, and highest growth rates ranged between 0.93 and 1.08 day⁻¹ at 16–18‰. Rapid changes in salinity reduced growth rates, but net mortality occurred only in one treatment (100% mortality on transfer from 10 to 40‰). Egg development time was largely invariant with salinity except for B. plicatilis IOM and where rotifers were transferred from 30 to 60‰. We indicate that several siblings are similarly euryhaline and tolerate salinity fluctuations. Undoubtedly, wide tolerances in B. plicatilis are adaptations to ephemeral and seasonally variable habitats. Given common broad salinity tolerances, it is unlikely that the differential distributions of sibling species are a direct result of physiological constraints. Instead, we illustrate using a simple model that subtle differences in physiological tolerances may have important impacts on interactions between sibling species, which may in turn influence distributions.