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.     

Oviposition site selection and oviposition stimulation by conspecifics in the golden egg bug (<Emphasis Type="Italic">Phyllomorpha laciniata</Emphasis>): implications for female fitness

Phyllomorpha laciniata Vill. (Heteroptera, Coreidae) females lay eggs on the host plant and on the backs of conspecifics. Since egg survival is greater when eggs develop on the backs of conspecifics than when laid on plants, we predict that females should prefer to lay eggs on conspecifics. In addition, because conspecifics are a high-quality site that represents a limiting resource, females should experience oviposition stimulation upon an encounter with a conspecific. Our results reveal that, when both the host plant and conspecifics are available simultaneously, females lay eggs preferentially on conspecifics. The results also support the second prediction, since females housed with conspecifics lay more than twice the number of eggs than isolated females. Isolated females do not seem to retain eggs, suggesting that oviposition stimulation is the result of an acceleration of egg-maturation rates. Other studies have found oviposition stimulation by mating and have suggested that it is the result of male strategies to increase short-term male reproductive success at some cost to females. The evolutionary scenario of our model organism seems to be quite different since females benefit greatly from increasing egg laying when there are conspecifics, because the advantages in terms of offspring survival are likely to translate into substantial increases in female reproductive success.     

Parasitoid learning during interactions with ants: how to deal with an aggressive antagonist

Pauesia picta, P. pinicollis and P. silvestris (Hymenoptera: Aphidiidae) are common parasitoids of the conifer aphid Cinara pinea, which is regularly attended by red wood ants (Formica spp.). In this study, I tested whether females of these parasitoid species learned during interactions with honeydew-collecting Formica polyctena workers that caution is not necessary if searching behaviour is adapted, and whether parasitoids benefit from being able to learn. When searching on Scots pines, naive females of P. picta and P. pinicollis generally retreated to a pine needle when making contact with a honeydew-collecting ant, did not approach ants from the side or from the front and kept a ”safe distance” from ants when sitting on needles. After some non- aggressive ant encounters, experienced female parasitoids changed their behaviour: they reduced their searching speed, approached ants from the side and even from the front, retreated less often in response to an approaching ant and reduced the ”safe distance”. These experienced females had a significantly higher rate of oviposition than naive females or females foraging for an unattended host. Thus, the ability of the parasitoid to learn during interactions with an antagonist led to a prolonged retention time and a higher oviposition rate. By contrast, there was no evidence of learning in P. silvestris. Females of this species showed no behavioural change in response to ant encounters, and there was no difference in the foraging success of naive and experienced female parasitoids. Received: 7 December 1999 / Revised: 23 September 2000 / Accepted: 10 March 2000     

Chemical egg defense in Photuris firefly “femmes fatales”

Summary. Female Photuris fireflies contain defensive chemicals of two types. They sequester steroidal pyrones (lucibufagins) from male fireflies of the genus Photinus that they eat, and themselves produce the defensive betaine N-methylquinolinium 2-carboxylate. Chemical analyses of Photuris eggs showed that females that fed on Photinus males endow their eggs with both lucibufagin and the betaine, while those that did not feed on Photinus lay eggs that contain betaine, but virtually no lucibufagin. Photuris females collected in the field during the Photinus flight season laid eggs that invariably contained betaine, but lucibufagin only at times. Predation experiments showed that Photuris eggs are essentially unacceptable to larvae of a coccinellid beetle (Harmonia axyridis) and an ant (Leptothorax longispinosus), but moderately acceptable to an earwig (Forficula auricularia). When applied experimentally to palatable insect eggs, lucibufagin proved deterrent to these three predators, while the betaine proved deterrent to the ant and coccinellid larva only. Both types of defensive compound decreased egg predation in the field. By endowing their eggs with both exogenous and endogenous chemicals, Photuris females are essentially “maximizing their options”– when feeding on Photinus, their eggs are doubly protected, but they are not entirely defenseless when the females are unable to procure lucibufagin. Received 12 August 1999; accepted 27 August 1999     

A field test of the intraspecific brood parasitism hypothesis in the golden egg bug (<Emphasis Type="Italic"> Phyllomorpha laciniata</Emphasis>)

In natural populations of golden egg bugs ( Phyllomorpha laciniata), females lay eggs on plants where they develop unattended, or on conspecifics, where they remain firmly glued until the nymphs hatch and start an independent life. Mortality rates among eggs laid on plants are higher than among eggs carried by adults. Because females cannot lay eggs on themselves, in order to improve offspring survival, they have to lay eggs on other individuals. Two hypotheses have been proposed to explain egg carrying: (1) the mating pair intraspecific brood parasitism hypothesis suggests that females dump eggs on copulating pairs, and (2) the paternal care hypothesis suggests that the system is driven mainly by males accepting eggs to improve the survival rates of their own offspring. Our data from the field show that 77% of the eggs are carried by males, because more males than females carry eggs, and because males carry a greater number of eggs. In addition, we show that mating males carry more recently laid eggs than single males. These results support the view that egg carrying is performed predominantly by males and that eggs are laid on males by their current mating partner, probably between repeated copulations. Males are likely to accept eggs, despite intermediate levels of paternity, because they cannot discriminate in favour of their own eggs, because rejected eggs will face 97% mortality rates on plants, and because they do not suffer mating costs when they carry eggs. However, females carry 23% of the eggs, but no differences in egg carrying have been found between mating and single females, suggesting that this is not the result of egg dumping while females are copulating. Egg carrying by females could reflect low levels of intraspecific parasitism, which is likely to reflect the low rate of successful attempts by egg-laying females who try to oviposit on other conspecifics rather indiscriminately, in an effort to improve the survival of their offspring.     

Chemical communication and coevolution in an ant–plant mutualism

Protective ant–plant interactions provide valuable model systems to study mutualisms. Here, we summarise our recent research on chemical and physiological adaptations that contribute to the stabilisation of the mutualism between Mesoamerican Acacia host plants and their Pseudomyrmex ant inhabitants against exploiters, that is, species using host-derived rewards without rendering a service. Acacia hosts produce food bodies (FBs) and extrafloral nectar (EFN). Both types of reward are chemically adapted to their specific function as ant food and protected from different exploiters. FBs contained higher amounts of specific proteins than the leaves from which they originate. EFN possessed amino acids making it attractive for the mutualist ants and an invertase making its carbohydrate composition nutritionally suitable for the mutualists but unattractive for generalists. Moreover, pathogenesis-related proteins such as glucanases, chitinases and peroxidases were found in EFN, which likely serve as protection from microorganisms. Digestive adaptations were found that make workers of the ant mutualists dependent on the host-derived food sources, a mechanism that likely counteracts the evolution of cheaters. The ants also possessed a high diversity of bacterial associates, several of which appeared involved in nitrogen fixation, thus contributing to the nutrition of these ‘vegetarian’ ants. By contrast, a non-defending ant species that parasitises the host plants appeared physiologically less adapted to the host-derived food rewards; this species, thus, likely is competitively inferior when colony growth is limited by plant-derived rewards. In summary, several physiological adaptations of both host plants and ants stabilise the Acacia–Pseudomyrmex mutualism against exploitation.     

Host-plant leaf surface compounds influencing oviposition in Delia antiqua

Summary. Delia antiqua (Diptera: Anthomyiidae) females lay eggs between the leaves of onion plants or in the soil around the base of the plants, then the maggots feed on the onion bulb and roots causing rapid secondary infection by fungi and bacteria. It is well known that the first sensory modality used by the onion fly is vision, therefore the shape (vertical narrow cylinders) and colour (yellow) of the plant play a crucial role in the recognition of a potential host plant. In the past it has been shown that n-dipropyl disulfide (Pr₂S₂), a typical component of onion volatiles, is an important chemical host plant cue. We extracted host leaf surface to verify if Pr₂S₂ is the major chemical oviposition stimulant and to determine if other as yet unknown substances may play a role in host-plant selection. We confirmed that the females laid more eggs around onion plants with leaves than when only the onion bulb was present and that the odour of chopped onion stimulates oviposition. Extraction of the surface of onion leaves revealed that only the apolar fraction contained substances that stimulate egg-laying in D. antiqua. GC-EAD analysis indicated that a minor constituent, Pr₂S₂, is perceived by the olfactory receptor on the antennae of the onion fly females. This confirmed the importance of Pr₂S₂ as oviposition stimulant. Contact with the polar fraction did not stimulate egg-laying behaviour in this Delia species. We discuss the oviposition strategy of D. antiqua in comparison with its closely related species, D. radicum, in which the oviposition behaviour is stimulated mainly through contact with the cabbage leaf surface and only partially by the host volatiles.     

Dominance and fertility in a functionally monogynous ant

Summary Colonies of some leptothoracine ants may contain several inseminated but sterile females in addition to a single, fertile queen (functional monogyny). We here report the first observations on the behavior of these supernumerary females in the nearctic ant Leptothorax sp.A, a species belonging to the L. muscorum complex.In four colonies, each with up to eight intermorphic females, ritualized or openly aggressive interactions between individuals were observed, similar to those among workers of some other leptothoracine ants. The responses of individual females during encounters with nestmates apparently reflect the existence of linear dominance hierarchies. In each colony, the highest ranking individual was fed and groomed significantly more often than other females, and was the only one to oviposit after hibernation and to become fully physogastric during the first weeks of spring. When these -females were removed from three colonies, several other females started to lay eggs. However, in each colony only the highest ranking individual remained fertile; the others either were pushed out of the nest and finally killed by the workers, or their ovaries degenerated again.Aggressive interactions among females may also play an important role in the foundation of new colonies either by inducing intermorphs to leave the maternal nest to found new colonies solitarily or by inducing colony fission. Offprint requests to: J. Heinze at his new address     

Oviposition height increases parasitism success by the robber fly Mallophora ruficauda (Diptera: Asilidae)

For parasitoids, host finding is a central problem that has been solved through a variety of behavioural mechanisms. Among species in which females do not make direct contact with hosts, as is the case for many dipteran parasitoids, eggs must be laid in an appropriate part of the host habitat. The asilid fly Mallophora ruficauda lays eggs in clusters on tall vegetation. Upon eclosion, pollen-sized larvae fall and parasitize soil-dwelling scarab beetle larvae. We hypothesized that wind dissemination of M. ruficauda larvae is important in the host-finding process and that females lay eggs at heights that maximize parasitism of its concealed host. Through numerical and analytical models resembling those used to describe seed and pollen wind dispersal, we estimated an optimal oviposition height in the 1.25- to 1.50-m range above the ground. Our models take into account host distribution, plant availability and the range over which parasitic larvae search for hosts. Supporting our findings, we found that the results of the models match heights at which egg clusters of M. ruficauda are found in the field. Generally, work on facilitation of host finding using plants focuses on plants as indicators of host presence. We present a case where plants are used in a different way, as a means of offspring dispersal. For parasitoids that carry out host searching at immature stages rather than as adults, plants are part of a dissemination mechanism of larvae that, as with minute seeds, uses wind and a set of simple rules of physics to increase offspring success.     

Behavioral response of a generalist predator to chemotactile cues of two taxonomically distinct prey species

Chemotactile cues unintentionally left by animals can play a major role in predator–prey interactions. Specialized predators can use them to find their prey, while prey individuals can assess predation risk. However, little is known to date about the importance of chemotactile cues for generalist predators such as ants. Here, we investigated the response of a generalized predatory ant, Formica polyctena, to cues of two taxonomically distinct prey: a spider (Pisaura mirabilis) and a cricket (Nemobius sylvestris). In analogy, we studied whether crickets and spiders showed antipredator behavior in response to ant cues. When confronted with cues of the two prey species, Formica polyctena workers showed increased residence time and reduced movement speed, which suggests success-motivated searching behavior and thus increased foraging effort. The ants’ response did not differ between cues of the two prey species, coinciding with similar aggression and consumption rates of dead prey. However, the cuticular hydrocarbons, which likely resemble part of the potential cues, differed strongly between the species, with only few methyl-branched alkanes in common. This suggests that ants respond to multiple compounds left by other organisms with prey-search behavior. The two prey species, in turn, showed no detectable antipredator behavior in response to ant cues. Our study shows that ants can detect and respond to chemotactile cues of taxonomically and ecologically distinct prey species, probably to raise their foraging success. Using such chemotactile cues for prey detection may drastically increase their foraging efficiency and thus contribute to the high ecological success of ants.     

The dynamics of brood desertion among communally breeding females in the treehopper, Publilia concava

In species that exhibit extended parental care, females sometimes lay eggs communally in order to redistribute the costs of offspring care. Communal egg-laying often involves redundancy in female effort, such that the number of females contributing to reproduction is more than is needed to provide adequate parental care. As a result, a subset of females will often abandon the communal brood, with the time of departure ranging from immediate abandonment after egg-laying (brood parasitism) to delayed abandonment with prolonged care (cooperative breeding). In this paper I approach the parental care dynamics of female-female broods as a desertion game similar to that of mate desertion in species with bi-parental care. I describe a field study of the insect Publilia concava (Hemiptera: Membracidae), a species that exhibits communal oviposition and a full range of egg guarding. This species exhibits full redundancy in female care, with no difference in survival between singly and doubly guarded broods. I find that double guarding is extremely rare in the population, with most communal broods having only one female guard. While this guard was usually the female that initiated the brood, these same females were more likely to abandon when secondary females arrived and when secondary females exhibited longer guarding durations. Paradoxically, the secondary females usually abandoned the broods they visited, resulting in up to 50% of broods with double abandonment. These unguarded broods suffered a 50% reduction in hatching success, reflecting an important risk for primary females that abandon egg masses to secondary females. Overall, P. concava exhibits desertion dynamics similar to mate desertion in vertebrates and it is likely that the theoretical work in this area will be useful for future work that addresses the allocation of parental care among communal breeders.     

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.     

Induced responses to herbivory in the Neotropical ant-plant association between Azteca ants and Cecropia trees: response of ants to potential inducing cues

Plant defense against herbivores often involves constitutive and inducible mechanisms of resistance. Obligate ant-plants, which provide food and housing for ants, are thought to primarily rely on ants for defense against herbivores. This form of plant defense has largely been viewed as static. We have been investigating the dynamic nature of Azteca ants as an inducible defense of Cecropia trees. Ants rapidly recruit to and patrol sites of foliar damage. We propose that Azteca ants can be viewed as an inducible defense for Cecropia trees because of their sensitivity to cues associated with herbivory, their rapid and aggressive recruiting ability, and their reclaimable and redeployable nature as a plant defense. In this study, we examine ant behavior following plant damage, and the potential cues that indude ant recruitment. We found that ants present on leaves when the plant is damaged leave the damaged leaf and recruit other ants to it, presumably by laying recruitment trails. Volatile leaf cues associated with herbivory were important in eliciting an induced response in two experiments. However, we found that cues associated with a congeneric plant elicited a much stronger ant response than conspecific cues. Although the type of leaf damage (gaping wounds versus leaf edge wounds) did not affect the level of ant recruitment, the extent of damage did. Leaves with one hole punched showed a 50% increase in ants, while leaves with five holes punched in them elicited a 100% increase in ant numbers. In sum, it appears that multiple plant-related cues associated with herbivory are involved in induction of ant recruitment in the Cecropia-Azteca system. We discuss the generality of ant responses to herbivory in obligate ant-plant systems, and in facultative ant-plant associations, which may be more common. Received: 23 March 1998 / Accepted after revision: 5 July 1998     

Oviposition site guarding by male walnut flies and its possible consequences for mating success

Field studies showed that male Rhagoletis juglandis and R. boycei flies guard egg-laying punctures (and the eggs within) on host walnut (Juglans major) fruit and defend those sites from conspecific and heterospecific males. In field experiments with artificially punctured fruit,as well as field observations on unmanipulated fruit, males were consistently more likely to be sighted and stayed longer on damaged fruit than on undamaged fruit. On artificially punctured fruit, they consistently spent more time in the vicinity of a puncture than expected by chance alone. Males together on damaged fruit were more likely to engage in contests over those fruit than males together on undamaged fruit. Copulations were consistently more frequent for either species on damaged than undamaged fruit, both in observations of unmanipulated fruit and in artificial puncture experiments. Analyses which controlled for the longer male residence time on damaged fruit suggested strongly that copulations were consistently achieved at higher per capita rates on damaged than on undamaged fruit, indicating that puncture-guarding functions to increase access to females. An exception to the pattern in male mating success was noted at a site where both species used host fruit on the same trees. In this case, R. juglandis males were only slightly more common on punctured fruit than on control fruit and male success in copulation did not differ significantly between the two types of fruit. This anomalous result was apparently due to an almost absolute advantage enjoyed by R. boycei males in on-fruit contests with R. juglandis males. A likely basis for improvements in mating success associated with puncture guarding was a propensity for females to deposit eggs into existing punctures. Both in observations of unmanipulated fruit and in artificial puncture experiments, females consistently attempted oviposition more often in damaged than undamaged fruit. In artificial puncture experiments, both species at both sites deposited most clutches in damaged fruit. Mating generally took place as females initiated oviposition. The possible functions of puncture use by females as well as alternative functions of puncture guarding by males are discussed.     

Queen and worker policing in the monogynous and monandrous ant, Diacamma sp.

Policing behavior that prevents workers from laying male eggs was examined in the monogynous and monandrous ponerine ant Diacamma sp. from Japan, in which a singly mated worker called a “gamergate” reproduces as the functional queen in each colony. Since oviposition by virgin workers is rare in the presence of a gamergate, we separated a portion of workers from the gamergates and induced their oviposition experimentally. When orphaned workers had started to oviposit, they were returned to the original colonies, where they continued to lay eggs for a while. The gamergates and other workers interfered with the laying workers by aggressively taking and finally eating the eggs. In total, 60% and 29% of the worker-derived eggs were eaten by gamergates and non-mother workers, respectively. The observed worker-worker interactions were not driven simply by competition to leave own sons, because non-laying non-orphaned workers interfered with worker reproduction. Furthermore, orphaned workers were usually attacked by non-orphaned workers soon after colony reunification. These results indicate that both queen policing by gamergates and worker policing in this species are mechanisms inhibiting worker oviposition. The gamergate contribution to policing was proportionately larger than that of workers, but among virgin workers, the relationship between dominance rank and contribution to policing was not clear. But about 11% of the eggs were not policed and were added to egg piles, especially in large colonies. Worker policing in a monandrous and monogynous eusocial Hymenoptera contrasts to other recent findings, and possible genetic, social, and ecological factors for its evolution in Diacamma sp. are discussed. Received: 16 November 1998 / Received in revised form: 9 February 1999 / Accepted: 21 February 1999     

Eggs of cabbage root fly stimulate conspecific oviposition: Evaluation of the activity and determination of an egg-associated compound

Summary. Previous studies indicated the presence of antennally-active compounds in extracts of eggs laid by female cabbage root flies, Delia radicum, that stimulated oviposition by conspecific females. We confirmed that previously laid D. radicum eggs stimulated oviposition by other D. radicum females, in a dose-dependent manner. Methanol extracts of conspecific eggs stimulated oviposition by females D. radicum, whereas egg extracts of D. antiqua and Psila rosae had no effect. Electrophysiological recordings from the tarsal sensilla of D. radicum females indicated that neurones of the C₅ sensillum responded to the egg extracts from both D. radicum and D. antiqua, but not P. rosae. Chemical analysis revealed that the extract of eggs from D. radicum contained the thia-triaza-fluorene compound, 1,2-dihydro-3-thia-4,10,10b-triaza-cyclopenta[.a.]fluorene-1-carboxylic acid (CIF-1), an oviposition stimulant found previously only in cruciferous plants. Another potentially active component has yet to be identified.     

How identity of the homopteran trophobiont affects sex allocation in a symbiotic plant-ant: the proximate role of food

We provide evidence for the proximate role of food in sex allocation by an ant species, and demonstrate how identity of the homopteran partner affects benefits to colonies of a plant-symbiotic ant. The system studied includes a plant-ant that nests in swollen hollowed internodes of a myrmecophyte, and two species of homopteran trophobionts (a coccid and a pseudococcid) tended inside domatia by these ants, for which they are an essential source of food. Total investment in pupae was greater for ant colonies that tended solely or primarily coccids than for those that tended pseudococcids. In particular, biomass invested in sexuals increased more rapidly with size of the colony in trees where ants tended coccids. This greater investment in sexuals was not made at the expense of investment in workers, but reflected increased resources available to coccid-tending colonies. Higher reproductive output indicates that ant fitness may be greater when they tend coccids. These additional resources led to a greater increase in production of alate females than in that of males. Consequently, the sex investment ratio of coccid-tending colonies was more female biased than in those that tended pseudococcids. Differences in resource supply affected numbers of individuals produced but not per-individual investment, with one partial exception: in very small colonies, pseudococcid-tending colonies produced small workers while coccid-tending colonies did not, further underlining the higher resource supply to coccid-tending colonies. This study provides evidence for the proximate role played by food in sex allocation at the colony level. We discuss our results in the context of hypotheses aimed at explaining sex ratio at the colony and population levels.     

Daphne gnidium, a possible native host plant of the European grapevine moth Lobesia botrana, stimulates its oviposition. Is a host shift relevant?

Summary. We tested the hypothesis that Daphne gnidium is an ancestral host plant of Lobesia botrana. To this end, we studied the oviposition response of this moth to various aerial organs of this plant. Our results show that females prefer to lay eggs on daphne berries rather than on grapes (cv. chasselas) and that polar surface extracts of daphne berries and leaves strongly stimulate oviposition in a dosedependant way, whereas flower extracts are weakly stimulant and branch extracts are inactive or deterrent for oviposition. Furthermore, a total extract of daphne berries stimulates oviposition in semi-natural conditions when applied onto fresh grapes. Oviposition stimulants from berries were isolated by HPLC coupled with a dual-choice oviposition bioassay. The ecological value of D. gnidium for L. botrana is discussed and the possible use of oviposition stimulants from daphne, contrasting with the oviposition signal of the cultivated host plant, is proposed in the perspective of developing behavioural manipulation methods such as stimulo-deterrent diversionary strategies compatible with IPM programs.     

High genetic relatedness among nestmate queens in the polygynous ponerine ant Gnamptogenys striatula in Brazil

Gnamptogenys striatula is a polygynous ant species, in which all workers are potentially able to mate. The reproductive status, relatedness and pedigree relationships among nestmate queens and winged females in a Brazilian population were investigated. We collected all the sexual females of 12 colonies (2–44 queens per colony, plus 2–18 winged females in 3 colonies). Dissections revealed that 98% of the queens were inseminated and that the queens in the most polygynous colonies did not lay equal numbers of eggs. The sexual females and a sample of the population were genotyped using eight microsatellite markers. Relatedness among nestmate queens was among the highest recorded to date (0.65±0.25), and tests of pedigree relationship showed that they were likely to be full-sisters, and sometimes cousins. Mated winged females were always full-sisters, the estimated genetically effective queen numbers were low and tests of pedigree relationship showed that only a few queens in the colony could be the mothers. These results suggest that the high queen-queen relatedness in polygynous colonies of G. striatula is maintained by an unusual mechanism: winged females are mostly produced by only one or a few queens, and these groups of full-sisters are recruited back into their original nest after mating. Received: 26 November 1999 / Revised: 7 September 2000 / Accepted: 7 September 2000     

Disease resistance in a weaver ant, <Emphasis Type="BoldItalic">Polyrhachis dives</Emphasis>, and the role of antibiotic-producing glands

Parasites represent one of the main threats to all organisms and are likely to be particularly significant for social animals because of the increased potential for intragroup transmission. Social animals must therefore have effective resistance mechanisms against parasites and one of the most important components of disease resistance in ants is thought to be the antibiotic-producing metapleural gland. This gland is ancestral in ants, but has been lost secondarily in a small number of species. It is unknown whether these evolutionary losses are due to a reduction in parasite pressure or the replacement of the gland’s function with other resistance mechanisms. Here we used the generalist entomopathogenic fungus Metarhizium to compare the disease resistance of a species of a weaver ant, Polyrhachis dives, which has lost the metapleural gland, with that of the well-studied leaf-cutting ant Acromyrmex echinatior and two other ant species, Myrmica ruginodis and Formica fusca, all of which have metapleural glands. The P. dives weaver ants had intermediate resistance when kept individually, and similar resistance to A. echinatior leaf-cutting ants when kept in groups, suggesting that the loss of the metapleural gland has not resulted in weaver ants having reduced disease resistance. P. dives weaver ants self-groomed at a significantly higher rate than the other ants examined and apparently use their venom for resistance, as they had reduced resistance when their venom gland was blocked and the venom was shown in vitro to prevent the germination of fungal spores. Unexpectedly, the leaf-cutting ant A. echinatior also had reduced resistance to Metarhizium when its venom gland was blocked. It therefore appears that the evolutionary loss of the metapleural gland does not result in reduced disease resistance in P. dives weaver ants, and that this at least in part may be due to the ants having antimicrobial venom and high self-grooming rates. The results therefore emphasise the importance of multiple, complementary mechanisms in the disease resistance of ant societies.