Chemical basis for differential acceptance of two sympatric rutaceous plants by ovipositing females of a swallowtail butterfly, Papilio polytes (Lepidoptera, Papilionidae)

Summary. In the natural habitat of Papilio polytes, a Rutaceae feeder utilizing Toddalia asiatica as a major host plant, some other rutaceous plants such as Murraya paniculata (abundant) and Glycosmis citrifolia (relatively rare) occur sympatrically as potential hosts. Whereas G. citrifolia is occasionally infested in the field, M. paniculata remains entirely unexploited by the butterfly. We thus examined the phytochemical mechanisms that can explain the differential acceptance of the two plants by ovipositing females of P. polytes. The foliage of G. citrifolia was found to readily induce oviposition and females deposited eggs in response to a methanolic extract of the plant. Stimulatory activity-directed fractionation of the extract revealed the presence of two characteristic compounds, trans-4-hydroxy-N-methylproline and 2-C-methylerythronic acid, known to serve as oviposition stimulants for the butterfly. In addition, larvae performed as well or better onG. citrifolia as on T. asiatica. Similar examination of the inhibitory chemical constituents of M. paniculata led to the isolation of an oviposition deterrent. The compound, identified as trigonelline (N-methylpyridine- 3-carboxylic acid), exhibited moderate oviposition deterrency to females. These results combined with our previous data are in agreement with the observed differential utilization of the two plants by P. polytes in the field.     

Oviposition stimulant for the zebra swallowtail butterfly, Eurytides marcellus, from the foliage of pawpaw, Asimina triloba

Summary. We have isolated a caffeoylcyclohexane-1-carboxylic acid derivative, 3-caffeoyl-muco-quinic acid (3-CmQA), as a contact oviposition stimulant for the zebra swallowtail butterfly, Eruytides marcellus (Papilionidae), from the foliage of its primary host plant, Asimina triloba (Annonaceae). This compound alone was as active in stimulating oviposition by females as were the parent ethanolic plant extract and the host plant itself. Other tested isomers of 3-CmQA, including 5-caffeoylquinic acid (5-CQA or trans-chlorogenic acid), were inactive. We found, however, that experienced female butterflies responded strongly to host volatiles, which enhanced landing rates and hence oviposition.? This is the first report of an oviposition stimulant for a swallowtail butterfly of the tribe Graphiini. We found 3-CmQA to be the major caffeoylcyclohexane-1-carboxylic acid isomer in plants of the genus Asimina. These plants lack appreciable amounts of 5-CQA, which has been shown previously to be one of the oviposition stimulants for certain Rutaceae- or Apiaceae-feeding swallowtails of the related tribe Papilionini.? Our findings, along with earlier results from the tribes Troidini and Papilionini, suggest that responses by swallowtails to hydroxycinnamic acid derivatives as oviposition cues date back at least to the ancestor of the subfamily Papilioninae. Received 24 March 1998; accepted 27 May 1998.     

Autecology of the common mormon butterfly,Papilio polytes (Lepidoptera : Rhopalocera : Papilionidae)

The adults of the common mormon butterfly Papilio polytes Linn. feed on a variety of floral species. The larval food plants in the study area included Citrus limon and Murraya koenigii both of the family Rutaceae. The eggs are laid singly, and the hatching time is three days. The larvae pass through five instars. The larval growth is directly correlated with the quantity of food consumed. The AD (approximate digestibility) values decreased from first instar to the last, whereas the ECD (efficiency of conversion of digested food) and ECI (efficiency of conversion of ingested food) values increased, thus bearing an inverse relationship with AD. The development time from egg to adult is 28-30, giving 11-12 generations in a year, but with better breeding during August-February. Thus P. polytes is multivoltine.     

Clutch size in the swallowtail butterfly,Battus philenor: the role of host quality and egg load within and among seasonal flights in California

Summary Clutch size in the pipevine swallowtail of California (Battus philenor hirsuta) varies widely within and among two seasonal flights, early and late spring. Pilson and Rausher (1988) proposed that variation in clutch size in a Texan B. philenor population is due to assessment of host quality with subsequent adjustment of clutch size and to differences in motivational state. The assessment hypothesis and a nonexclusive alternative that clutch size is determined by mature egg load were tested for populations in Sacramento, California. Weak and sporadic correlations between host quality and clutch size were found, suggesting that host assessment with adjustment of clutch size is not a strong factor in this population. Clutch size was highly correlated to mature egg load in the early but not in the late spring flight. Yet, females from both flights had similar loads of mature eggs. It is proposed that females lay clutch sizes proportional to egg load, up to a maximum threshold. The threshold may be lowered in the late spring flight in response to changes in overall host quality or to increased egg predation, reducing both the mean clutch size and the correlation between clutch size and egg load. Potential mechanisms for the change in behavior among flights, based on changes in the threshold, are discussed.     

Behavioral and electrophysiological responses of the emerald ash borer, Agrilus planipennis, to induced volatiles of Manchurian ash, Fraxinus mandshurica

Summary. We investigated the volatile emissions of Manchurian ash seedlings, Fraxinus mandshurica, in response to feeding by the emerald ash borer, Agrilus planipennis, and to exogenous application of methyl jasmonate (MeJA). Feeding damage by adult A. planipennis and MeJA treatment increased volatile emissions compared to unexposed controls. Although the same compounds were emitted from plants damaged by beetles and treated with MeJA, quantitative differences were found in the amounts of emissions for individual compounds. Adult virgin female A. planipennis were similarly attracted to volatiles from plants damaged by beetles and those treated with MeJA in olfactometer bioassays; males did not respond significantly to the same volatiles. Coupled gas chromatographic-electroantennogram detection (GC-EAD) revealed at least 16 antennally-active compounds from F. mandshurica, including: hexanal, (E)-2-hexenal, (Z)-3-hexen-1-ol, 3-methyl-butylaldoxime, 2-methyl-butylaldoxime, (Z)-3-hexen-1-yl acetate, hexyl acetate, (E)-β-ocimene, linalool, 4,8-dimethyl-1,3,7-nonatriene, and E,E-α-farnesene. Electroantennogram (EAG) dose–response curves using synthetic compounds revealed that females had a stronger EAG response to linalool than males; and male responses were greater to: hexanal, (E)-2-hexenal, (Z)-3-hexen-1-ol, 3-methyl-butylaldoxime, 2-methyl-butylaldoxime, and hexyl acetate. These results suggest that females may use induced volatiles in long-range host finding, while their role for males is unclear. If attraction of females to these volatiles in an olfactometer is upheld by field experiments, host plant volatiles may find practical application in detection and monitoring of A. planipennis populations.     

Autotoxic effects of essential oils on photosynthesis in parsley, parsnip, and rough lemon

Summary. Many plant species contain essential oils with allelochemical properties, yet the extent to which these same chemicals can be autotoxic is unclear. In this study, we tested the toxicity of several essential oil components to three species that produce them—Pastinaca sativa and Petroselinum crispum (Apiaceae), and Citrus jambhiri (Rutaceae). The effects of exogenous application of small amounts of essential oil components to the surface of foliage, followed by a pinprick to allow entry into the leaf, were monitored by chlorophyll fluorescence imaging. Rapid and spatially extensive declines in photosynthetic capacity were detected within 200 s. The most toxic constituents were monoterpenes. Two sesquiterpenes, caryophyllene and farnesene, and the phenylpropanoid myristicin, by comparison, were not toxic. Autotoxicity of endogenous essential oil was investigated by slicing through containment structures (glands or tubes); significant toxicity, manifested by reduced photosynthetic activity, was observed in all three species but was most pronounced in P. sativa and P. crispum, both of which possess oil tubes.     

Oviposition stimulants for the pipevine swallowtail butterfly,Battus philenor (Papilionidae), from anAristolochia host plant: Synergism between inositols,aristolochic acids and a monogalactosyl diglyceride

Aristolochia macrophylla (Lam.) is a major host of the pipevine swallowtail butterfly,Battus philenor (L.), in the eastern United States. The female butterflies use a synergistic mixture of inositols, acids and a lipid as oviposition cues in recognizing this plant on contact. The acids and lipid, all isolated from the Et₂O-CHCl₃ fraction of an alcoholic extract of fresh foliage, were identified as aristolochic acid I (1), aristolochic acid II (2) and 1,2-[di(9Z,12Z,15Z)-octadeca-9, 12, 15-trienoyl]-3-galactosyl-sn-glycerol (3). Identifications were facilitated by UV, MS (EI and FAB) and NMR (1D and 2D) spectral techniques and by analysis of the hydrolysis products of 3. The active inositols were identified as D-(+)-pinitol, reported previously, and sequoyitol. Though this is apparently the first report of oviposition responses to a diacyl glycerol glycoside by a phytophagous insect, responses to aristolochic acids and sequoyitol have been reported previously for anAristolochia-feeding swallowtail of a different genus in Japan. This indicates substantial evolutionary conservatism in chemical oviposition cues within the tribe Troidini.     

Antennal responses of four species of tree-killing bark beetles (Coleoptera: Scolytidae) to volatiles collected from beetles,and their host and nonhost conifers

Summary. Host selection in tree-killing bark beetles (Coleoptera: Scolytidae) is mediated by a complex of semiochemical cues. Using gas chromatographic-electroantennographic detection (GC-EAD) and GC-mass spectrometric analyses, we conducted a comparative study of the electrophysiological responses of four species of tree-killing bark beetles, the Douglas-fir beetle, Dendroctonus pseudotsugae, Hopkins, the mountain pine beetle, D. ponderosae Hopkins, the spruce beetle, D. rufipennis Kirby, and the western balsam bark beetle, Dryocoetes confusus Swaine, to volatiles captured by aeration of 1) bole and foliage of four sympatric species of conifers, Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, lodgepole pine, Pinus contorta var. latifolia Engelm., interior spruce, Picea engelmannii x glauca, and interior fir, Abies lasiocarpa x bifolia, and 2) con- and heterospecific beetles at three stages of attack. We identified 13 monoterpenes in the conifers and nine compounds in the volatiles of beetles that elicited antennal responses. There was no qualitative difference in the terpene constitution of the four species of conifers and very little difference across beetle species in their antennal response to compounds from conifers or beetles. The lack of species-specific major or minor components in conifers suggests that beetles would need to detect differences in the ratios of different compounds in conifers to discriminate among them. Attraction to hosts and avoidance of nonhost conifers may be accentuated by perception of compounds emitted by con- and heterospecific beetles, respectively. The 22 compounds identified are candidate semiochemicals with potential behavioural roles in host location and discrimination.     

Behavioural and electrophysiological responses of the olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae), to male- and female-borne sex attractants

In the olive fruit fly, Bactrocera oleae, females attract males by producing 1,7-dioxaspiro[5.5]undecane (olean), the main component of the sex pheromone secreted by rectal glands. It has been recently demonstrated that males are able to produce (Z)-9-tricosene (muscalure) in rectal glands, a compound that selectively attracts females. In this study, a male grooming reaction that may transfer the male-borne compounds from rectal to urotergal glands was observed, suggesting that urotergal glands could be involved in B. oleae sexual communication. GC/MS, EAG, GC/EAD analyses and behavioural assays were carried out to compare the role of male rectal and urotergal glands during courtship. In both male glands, olean and muscalure amounts were age dependent. Extracts of rectal glands contained higher amounts of olean and/or muscalure than urotergal ones. Extracts of rectal and urotergal glands of males and females elicited EAG responses in both sexes. GC/EAD showed that female EAG response to male rectal extracts was mainly due to olean and muscalure. Synthetic compounds evoked EAG dose-dependent responses in both sexes, and the EAG response to muscalure was higher as compared to olean. Rectal and urotergal glands from old males were able to attract females, while urotergal glands from young males attracted only males. Overall, our results add knowledge to the mating system of B. oleae, giving first evidences on the electrophysiological activity of muscalure towards both sexes, as well as on the involvement of male urotergal glands in the chemical sexual communication of this pest.     

Behavioral and antennal electrophysiological responses of a predator ant to the pygidial gland secretions of two species of Neotropical dung roller beetles

The pygidial gland secretions of Neotropical dung roller beetles appear to function as defensive agents against predator ants. Behavioral and electrophysiological tests were used to evaluate the responses of the ant Camponotus sericeiventris to pygidial compounds secreted by the dung roller beetles Canthon cyanellus cyanellus and Canthon femoralis femoralis (Coleoptera: Scarabaeidae). Our behavioral investigation revealed a lower aggressive response of C. sericeiventris to the dung roller beetles compared to their response to the fly Anastrepha ludens. Additionally, C. sericeiventris workers attacked C. f. femoralis more often than C. c. cyanellus. The behavioral aggression of C. sericeiventris was greater toward male than female C. c. cyanellus. Electroantennography showed that the antennae of C. sericeiventris react to pygidial extracts from C. c. cyanellus and C. f. femoralis. Three compounds from male and female C. f. femoralis and C. c. cyanellus elicited coupled gas chromatography-electroantennogram (GC-EAD) activity in the antennae of C. sericeiventris. Geraniol and an unknown compound (A) were specific for C. f. femoralis, whereas guaiacol and another unknown compound (B) were specific to C. c. cyanellus; phenol was shared by both beetle species. This is the first report confirming that the pygidial gland secretions of dung roller beetles play a role in their defense against predators.     

Use of genetic,climatic, and microbiological data to inform reintroduction of a regionally extinct butterfly

Species reintroductions are increasingly used as means of mitigating biodiversity loss. Besides habitat quality at the site targeted for reintroduction, the choice of source population can be critical for success. The butterfly Melanargia russiae (Esper´s marbled white) was extirpated from Hungary over 100 years ago, and a reintroduction program has recently been approved. We used museum specimens of this butterfly, mitochondrial DNA data (mtDNA), endosymbiont screening, and climatic‐similarity analyses to determine which extant populations should be used for its reintroduction. The species displayed 2 main mtDNA lineages across its range: 1 restricted to Iberia and southern France (Iberian lineage) and another found throughout the rest of its range (Eurasian lineage). These 2 lineages possessed highly divergent wsp alleles of the bacterial endosymbiont Wolbachia. The century‐old Hungarian specimens represented an endemic haplotype belonging to the Eurasian lineage, differing by one mutation from the Balkan and eastern European populations. The Hungarian populations of M. russiae occurred in areas with a colder and drier climate relative to most sites with extant known populations. Our results suggest the populations used for reintroduction to Hungary should belong to the Eurasian lineage, preferably from eastern Ukraine (genetically close and living in areas with the highest climatic similarity). Materials stored in museum collections can provide unique opportunities to document historical genetic diversity and help direct conservation.     

Fecundity,egg weight and longevity in relation to multiple matings in females of the monarch butterfly

Summary In many insects nutrients transferred by the male at mating are later incorporated into both the eggs and soma of the mated females. Accordingly, it has been suggested that insect females can use these male-derived nutrients for somatic maintenance and enhancement of their fecundity and fitness of their offspring. I this paper we tested the validity of these predictions by studying the longevity and reproductive output of 1, 2, 3, 4 or 5 times mated female monarchs Danaus plexippus, a nectar-feeding butterfly that is long-lived and strongly polyandrous and emerges as an adult without mature eggs. Females mated five times received ejaculates that corresponded to an average of 38% of their body weight at eclosion. However, we found that the number of times females had mated had no effect on their longevity, life-time fecundity, or egg weight. Although negative evidence should always be interpreted with caution, our study suggests that male-derived nutrients are less important for female longevity and reproductive output than are larval and adult food.     

d-Pinitol as a key oviposition stimulant for sulfur butterfly, Colias erate: chemical basis for female acceptance of host- and non-host plants

The sulfur butterfly, Colias erate, utilizes various legumes as host plants. We examined the chemical constituents of its primary host plant, Trifolium repens (white clover), to identify phytochemicals inducing oviposition by C. erate females. Since one of the four aqueous subfractions prepared from a methanolic extract of the plant has previously been shown to be the most responsible for the oviposition-stimulatory activity exerted by the plant, chemical analyses were conducted of the fraction concerned. Activity-directed fractionation of the subfraction by ion-exchange chromatography revealed that the key substance(s) resided in the neutral fraction. Preparative TLC of the neutral fraction and subsequent spectral analyses identified d-(+)-pinitol, glycerin, methyl β-d-glucoside, and myo-inositol as characteristic components together with ubiquitous sugars (e.g., sucrose and glucose). Of these, only pinitol singly evoked significant oviposition responses at concentrations over 0.05%. In dual-choice bioassays, however, females laid significantly more eggs on pinitol solutions admixed with glycerin or methyl β-d-glucoside than on pinitol alone. Two cyanoglucosides, linamarin, and lotaustralin, occurring in the other aqueous subfractions, also synergistically increased the oviposition response in combination with pinitol. The results clearly indicated that pinitol is a crucial oviposition stimulant involved in host recognition, while glycerin, methyl β-d-glucoside, linamarin, and lotaustralin function as synergists. We further examined the oviposition responses of C. erate females to aqueous fractions, along with their chemical compositions, that had been prepared from five other host plants and a non-host plant, Aristolochia debilis (Aristolochiaceae), on which oviposition occasionally took place in an outdoor cage during the experiments. The plant species accepted by ovipositing females were all found to contain pinitol in amounts enough to induce egg laying by the butterfly, thus leading to the conclusion that pinitol serves as the essential mediator in recognizing and accepting potential host plants.     

Relation of spawning of the giant scallop,Placopecten magellanicus,to temperature fluctuations during downwelling events

We examined the relation of spawning to biological and physical factors for the scallop Placopecten magellanicus (Gmelin, 1791) over 8 yr (1984 to 1991) in the Baie des Chaleurs, southwestern Gulf of St. Lawrence, Canada. Spawning was always abrupt and occurred between July and mid-September. It did not appear to be related to the abundance of phytoplankton or particulate organic carbon and nitrogen in the water. It further showed no relationship to lunar or tidal phascs or to current velocity. Spawning consistently occurred during the summer temperature maximum, but did not coincide with any critical temperature or cumulative temperature threshold. All but one of the 33 spawning events, for which temperature data were recorded, were associated with temperature changes; 25 of these were sharp temperature increases and 7 were during strong temperature fluctuations when the mean temperature was 9 to 14°C. Both types of temperature changes were caused by downwelling of warm surface water. The delay by about 1 d in time of spawning between sites coincided with the rate at which downwelling events propagated into the bay. Virtually all of the spawning events resulted in gametes being ejected into warm water masses where conditions are likely to favour larval development.     

Chemosensory and behavioural responses of the turnip sawfly, Athalia rosae, to glucosinolates and isothiocyanates

Summary. The turnip sawfly Athalia rosae sequesters glucosinolates from its cruciferous host plants in the larval stage. Investigation of the chemosensory and behavioural responses of adult A. rosae to glucosinolates and their volatile hydrolysis products, isothiocyanates, revealed that females detect glucosinolates by contact chemoreception and isothiocyanates by antennal olfaction. In electroantennogram recordings, four isothiocyanates (allyl [2-propenyl] isothiocyanate, benzyl isothiocyanate, butyl isothiocyanate and iberverin [3-methylthiopropyl isothiocyanate]) were active at all doses presented, including the lowest (0.1 μg), whilst the threshold for detection of three others, iberin [3-methylsulphinylpropyl isothiocyanate], methyl isothiocyanate, and sulforaphane [4-methylsulphinylbutyl isothiocyanate], was higher, at between 1 and 10 μg (source concentration of volatiles). Allyl isothiocyanate attracted experienced females in a four-chambered olfactometer, whilst na?ve females showed no response. Allyl isothiocyanate also attracted mature females to baited yellow water traps in field trials, although immature females were repelled at high isothiocyanate concentrations. In laboratory behavioural bioassays the glucosinolates sinigrin (allyl [2-propenyl] glucosinolate) and sinalbin (p-hydroxybenzyl glucosinolate), stimulated ovipositor probing in mature female A. rosae to an extent comparable to hot-water extracts of their host plants. These responses show that glucosinolates and isothiocyanates play an important role in host finding and host recognition in A. rosae.     

The costs and benefits of cooperation between the Australian lycaenid butterfly,Jalmenus evagoras,and its attendant ants

Summary The larvae and pupae of the Australian lycaenid butterfly, Jalmenus evagoras associate mutualistically with ants in the genus Iridomyrmex. Four ant exclusion experiments in three field sites demonstrated that predation and parasitism of J. evagoras are so intense that individuals deprived of their attendant ants are unlikely to survive. Larvae and pupae of J. evagoras aggregate, and the mean number of attendant ants per individual increases with larval age and decreases with group size. Field observations showed that young larvae could gain more attendant ants per individual by joining the average size group of about 4 larvae than by foraging alone. Aggregation behaviour is influenced by ant attendance: young larvae and pupating fifth instars aggregated significantly more often on plants with ants than on plants where ants had been excluded. In return for tending and protecting the larvae, ants were rewarded by food secretions that can amount to as much as 409 mg dry biomass from a single host plant containing 62 larvae and pupae of J. evagoras over a 24 h period. Larval development in the laboratory lasted approximately a month, and larvae that were tended by ants developed almost 5 days faster than larvae that were not tended. However, tended individuals, particularly females, pupated at a significantly lower weight than their untended counterparts, and the adults that eclosed from these pupae were also lighter and smaller. On average, pupae that were tended by ants lost 25% more weight than untended pupae, and in contrast with larvae, they took longer to eclose than pupae that were not tended. These experimental results are discussed in terms of costs and benefits of association for both partners, and of aggregation for the lycaenids.     

Effects of mating history on ejaculate size, fecundity, longevity, and copulation duration in the ant-tended lycaenid butterfly, Jalmenus evagoras

The mating system of the Australian lycaenid butterfly, Jalmenus evagoras, is highly unusual compared to most other Lepidoptera. Characteristics of this system, which has been termed an ’explosive mating strategy,’ include the formation of an intensely competitive mating aggregation of males, a highly male biased operational sex ratio, a lack of discrimination and mate choice by both sexes, a high variance in male mating success, and female monogamy. In this study, we tested the hypothesis that multiple mating by males imposes physiological costs resulting in smaller spermatophores, and that this results in a fitness cost to females. We found that male J. evagoras transferred only 2.2% of their eclosion weight during their first mating, consistent with the hypothesis that males of monandrous species produce a relatively small investment. The wet weight of the ejaculate declined by an average of 27% at the second mating and the dry weight by 29%, and an intermating interval of 5–9 days was needed for the ejaculate to return to the size at the first mating, regardless of male size or age. Wet ejaculate mass increased proportionally with male size, though dry mass was proportionally larger in smaller males. Ejaculate mass tended to increase with male age at both first and second matings. Female characteristics, in general, did not affect ejaculate mass, although the wet weight of the ejaculate was positively associated with female weight at the second mating. Copulation duration increased from 2.4 h to approximately 3 h at the second mating, and to over 4 h at the third and fourth matings. Fecundity was positively correlated with female size but not with mating history, copulation duration, or any other characteristics measured for either males or females. Female longevity declined significantly as the number of times the male partner had previously mated increased. We conclude that despite the small male investment in ejaculate, the costs of multiple mating may nonetheless be significant, as indicated by the reduction in ejaculate mass, an increase in copulation duration, and reduction in female lifespan with increasing mating number. Received: 22 January 1999 / Received in revised form: 28 July 1999 / Accepted: 18 September 1999     

植物对污泥的响应及根系对重金属的活化作用

为了研究植物对污泥的改良作用及植物根系对重金属的活化作用,在温室盆栽条件下对生长于污泥中的几种耐性植物遏蓝菜属(Thlaspi goesingense)、羽叶鬼针草(Bidens maximowicziana Oett)、酸模(Rumex acetosa L.)、紫苜蓿(Medicogo sativa L.)和印度芥茉(Indian mustard)的植物干重、体内重金属(Cu、Zn、Pb、Cd)的含量、叶片中叶绿素含量和植物根系对重金属的活化率做了研究。结果表明,生长于污泥中的植物其干重比对照均有不同程度的增加,其中羽叶鬼针草与对照相比差异极显著;不同植物对不同重金属的吸收量亦不同;各种植物叶片中的叶绿素含量变化不同,与对照相比,差异不显著;遏蓝菜对Cu、Zn的活化率最高,印度芥茉对Cd的活化率最高。     

A field study of the toxicity of two oils and a dispersant to the mangrove Avicennia marina

The relative toxicities of Arabian Light crude oil, Tirrawarra crude oil, Dispersant BP-AB, and mixtures of oils and dispersant were assessed on 30 mangroves, Avicennia marina (Forsk.) Vierh. var. resinifera (Forst.) Bakh., in a coastal fringe on the eastern shore of Gulf St. Vincent, South Australia. Five treatments were applied: 100% Arabian Light crude oil, 100% Tirrawarra crude oil, Arabian Light crude oil plus dispersant (1:1), Tirrawarra crude oil plus dispersant (1:1) and 100% dispersant. Five mangroves were used for each of the treatments and five as controls. Defoliation, leaf damage, pneumatophore damage, flowering and fruiting were monitored for three years (September 1982–September 1985). Initially, the toxicity of both oils was increased by the addition of dispersant; Tirrawarra crude oil plus dispersant caused significant defoliation. 100% Tirrawarra crude oil was more toxic than 100% Arabian Light crude oil; the former caused significant leaf damage from Week 4 to Week 12 after treatment. After Week 49 production of new leaves was significantly greater in the Arabian Light crude oil plus dispersant treatment than with the Arabian Light crude oil. No such difference was found between the Tirrawarra treatments. Twelve to 26 weeks after treatment, partial pneumatophore damage was observed in all treatments. No atypical flower or fruit production was observed.