nestmate recognition in sweat bees - Science Direct

Anita. Behav.,1981, 29, 802-809

NESTMATE RECOGNITION IN SWEAT BEES (LASIOGLOSSUM AN INDIVIDUAL RECOGNIZE ITS OWN ODOUR OR ONLY ODOURS OF ITS NESTMATES?

ZEPHYRUM): DOES

BY G R E G O R Y R. B U C K L E & LES G R E E N B E R G *

Department of Entomology, University of Kansas, Lawrence, Kansas 66045, U.S.A. Abstract. We investigated the olfactory mechanism by which guard bees of Lasioglossum zephyrum decide whether to admit conspecifics to their nests. First we set up colonies of young bees, consisting of sisters from a single family or a mixture of bees from two distinct families. These bees were then introduced into colonies other than their own. Our experimental evidence shows that guards learn the odours of their nestmates, then accept or reject other bees on the basis of the similarity of the latters' odours to those of the guards' nestmates. Guards act as though they do not use their own odour as a reference for nestmate recognition. This recognition mechanism enables individuals with different odours to live together; it may also enhance the operation of kin selection by providing a more complete basis for discriminating relatives from non-relatives. No evidence was found that nestmates acquire one another's odours. Such lack of odour transfer may be characteristic of early stages in the evolution of recognition mechanisms. differences are well known in Drosophila (Ehrman & Parsons 1976). Possible genetic as well as environmental influences on odour production in other social insect species are reviewed by Ribbands (1965), Wilson (1971), Crozier & Dix (1979), and H~511dobler & Michener (1980). Little is known of the effects of environmental influences on odour in L. zephyrum. Bell (1974) found that bees exposed to soil and faeces taken from another nest did not absorb sufficient odour to be accepted by the guards of that nest. When reciprocal introductions were made between nests into which peppermint had been blown, no increase was found in acceptance rates of non-residents. Greenberg (unpublished data) set up 'kin nests' (defined below), which he fed either Typha (cattail) pollen or a mixture of Typha pollen and pollen substitute. In introductions between sister nests, guards reared on the mixture were significantly more aggressive toward bees fed Typha alone than were guards raised on the same food source as the introduced bees. (This increased aggression was not usually sufficient, however, to prevent such introduced bees from eventually passing the guard.) Higher levels of aggression were not seen when bees fed the mixture were introduced into colonies that had received only Typha pollen. The significant difference obtained in the first comparison suggests that diet can affect a bee's odour or its perception of other bees' odours. However, the fact that bees fed the mixture still accepted sisters raised on Typha pollen alone at significantly higher rates than unrelated bees accepted

Introduction

Guards

at

nest

entrances of sweat bees (Lasioglossum zephyrum) distinguish nestmates (residents), which are allowed to enter, from non-residents, which are rejected, on the basis o f individual differences in odours (Bell 1974). Bell hypothesized that guards either learn or become habituated to the odours o f each colony member. When bees with an odour different from the set of odours that a guard has learned or become habituated to are introduced into the nest, they elicit aggressive behaviour by the guard and are rejected. Greenberg (1979) demonstrated that these odours are genetically specified. By taking bees from one nest and introducing them into another, he found a strong positive correlation between rate of acceptance and r, the degree of relatedness between the introduced and the guarding bee. Each of the colonies Greenberg tested was composed of a group of sisters. Thus, the odours that guards were exposed to were those of closely related individuals. If the bees that guards allowed into their nests were those that could not be distinguished from nestmates, then it follows that close relatives have similar odours more often than do more distantly related bees. Such a relationship between emitted odour and r would exist only if the syntheses of at least some odours are under genetic control. This demonstration of genetically specified odour differences among conspecifics is the first of its kind for a social insect, although such *Present address: Department of Entomology, Texas A & M University, College Station, Texas 77843, U.S.A. 802

BUCKLE & GREENBERG: NESTMATE RECOGNITION IN BEES one another indicates that genetic factors continue to play a prominent role in the face of environmental variation. Though unrelated sweat bees usually have different odours, a high degree of relatedness is not necessary for them to live together. Colonies of bees artificially assembled from different families have been repeatedly established in the laboratory. The success of these non-kin colonies (see Kukuk et al. 1977) is dependent upon the age at which the bees are put into the nest. Bees brought together as callows nearly always go on to develop a social organization and produce brood. Attempts to establish such colonies with unrelated older bees are rarely successful. These observations suggest that bees can learn the odours o f unrelated individuals. In non-kin colonies, this enables unrelated bees to leave and re-enter the nest. (Unlike Bell (1974), we define 'learning' in the broadest sense. Thus, when we state that a bee has learned an odour, one of the possibilities is that the bee has become habituated to that odour. Memory is similarly broadly defined to include any stored information.) The importance of a learning component in the olfactory recognition of nestmates is also suggested by the effects of isolation on the guard's ability to discriminate nestmates from non-residents (Kukuk et al. 1977). Bees in nonkin colonies were isolated from one another for 1 to 12 days. The guard in each nest was then returned and allowed to resume normal guarding behaviour. The ability of such guards to discriminate nestmates from non-residents was inversely related to the length of their prior isolation. Those isolated for the entire 12 days rejected nearly all bees, including nestmates. A progressive loss of memory may have been responsible for this change. Alternatively, the isolation period imposed on the guards may have altered their motivational levels or ability to coexist with other bees. The present study was designed to investigate further recognition o f non-resident bees, both related (sisters) and unrelated. The following questions were addressed: (1) Does a guarding bee whose nestmates are from two source colonies, its own and another with whom no common ancestor is shared, respond differently to the odours of the two families ? (2) Do bees use their own odours as a reference for accepting or rejecting other bees ? (3) Are odours transferred among nestmates ?

803

Methods Experiment 1 Twenty colonies of bees, divided into four groups of five colonies each, were established in artificial nests similar to those described by Michener & Brothers (1971) and K a m m (1974). A plastic tube 5 to 10 cm long connected each nest to a vial containing honey water and Typha pollen. Each colony was built up over a period of 3 to 8 days by adding one or more new young bees every day or two. The bees used were taken from laboratory nests ('source nests') in which only the queen was mated. These nests were from 1 to 10 generations removed from field-collected bees. Most lines had undergone some inbreeding. Bees were removed from their cells as callows to prevent contact with the adult members of their colonies. They were marked with a fast-drying paint for individual recognition and then isolated in plastic vials for 12 to 24 h before being put into nests. A pair of nests with no known common ancestor served as the source nests for each experimental group. Two experimental colonies were set up with sisters from one source nest and two with sisters from the other. Six bees were put in each. The fifth experimental colony of each group was set up with three bees from each source nest. A colony composed of bees from the same source nest is called a 'kin colony'; a colony (like the fifth experimental colonies above) composed of bees from two unrelated source nests is called a 'mixed colony'. Tests for recognition of odours were made by introducing bees from one experimental colony into another. Such introductions were performed only between colonies in the same group. No group was tested until the youngest bee in each nest was at least 7 days old. Procedures for introducing bees were similar to those described by Greenberg (1979). All the bees in a particular experimental nest were removed and placed in separate plastic tubes approximately 2 cm long. The tubes were closed at each end by double sections of pipe cleaner. The vials on the other four nests in the group were then removed. Each of the sequestered bees was individually introduced into these nests by (1) placing the end of a tube with a bee in it against the entrance of a nest (after removal of one of the pipe cleaners) and (2) prodding the bee inside with the remaining pipe cleaner until it moved from the tube into the nest and encountered the guard. In many cases prodding was not necessary as the bee

804

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BEHAVIOUR,

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moved into the nest of its own accord. The response of the guarding bee was recorded as either Pass (allowed introduced bee to pass) or No Pass (did not allow introduced bee to pass). A description of the various behaviours exhibited by introduced and guarding bees is given in Bell & Hawkins (1974). Each introduced bee was usually tested against several members of each colony. This was possible because of the presence of queues of two or more bees at most nest entrances. Introduced bees permitted to pass the guard in nests in which such queues were present would encounter one or more additional bees. I f the introduced bees were rejected by the guard, it was usually still possible to obtain the responses of other bees by either (1) waiting until a different bee was in the guard position or (2) temporarily removing the guard from the nest, thereby enabling one of its nestmates to take its place. Only one set of introductions was performed each day. Bees from different colonies were introduced on subsequent days until the members of each colony had been introduced into every other colony in the group. Tests involving the same bee were assumed to be independent since Greenberg (1979) has shown that the use of a given introduced or guarding bee in more than one trial does not significantly alter acceptance rates in later trials. Bees were never introduced into their own nests. Thus, when we speak of guards in mixed or kin nests being tested against their sisters, the sisters were always members of other artificial colonies. A summary of the experimental design and the types of introductions is given in Fig. 1 (see Results).

make reference to O's nestmates, O's sisters (in kin colonies), and sisters of O's nestmates (also in kin colonies). (2) N o t all colonies were tested against one another. Figure 2 illustrates the experimental design and the types of introductions that were made.

Experiment 2 This experiment differed from experiment 1 in two respects: (1) Fourteen sets of either three, four, or five experimental nests each were set up. Each set consisted of one or two kin colonies of bees from one source nest, one or two kin colonies of bees from a different source nest, and one mixed colony of bees from both source nests. O f the mixed colonies, 13 consisted of five bees from one source nest and one bee from the other. The other colony contained two bees from one source nest and one bee from the other. The single bee in each mixed colony from a source nest different from that of its nestmates will be called the odd bee or 'O'. We will also

Results Experiment 1 Section A addresses the first question in the Introduction; sections B and C deal with the third. Letters a - f refer to the different types of introductions made in experiment 1 (Fig. 1). Associated with each type of introduction is an acceptance rate. A. Are bees introduced into mixed nests accepted at a higher rate by their sisters than by their sisters' unrelated nestmates ? N o . They were accepted at similar rates by both groups. These rates, 67 % (a, Fig. 1) and 64 % (b), respectively, are not significantly different from the rate at which bees in kin colonies accepted sisters (65 %, c). Fignre 1 also shows how often, in introduc-

Statistical Analyses The data from the four groups in experiment 1 were pooled. Differences in the guards' acceptance rates of sisters and unrelated bees in mixed and kin colonies were examined for significance with the ;~ test. To provide for an experiment-wise error rate of 5 %, we assumed that all possible pair-wise comparisons were made (a total of 15). By the Bonferroni inequality (Harris 1975) the necessary error rate for each comparison is therefore P = 0.05/15 : 0.003. The critical ;~2 value for each comparison with df= 1 is 8.81. The data from experiment 2 were tested for significance with the Wilcoxon matched-pairs signed-ranks test. Comparisons were made by computing separately for each group the acceptance rate for each of the different types of introductions. Considerable variability existed in the number of interactions recorded for each group of nests, due in part to differences in group size. A combined analysis based on. the Z ~ test would not have given each group equal weight. For this reason the Wilcoxon test was selected as the preferred method of analysis. Because of experimental problems, certain interactions involving an odd bee were not obtained in two groups of nests. This resulted in an N of 12 groups instead of 14 for certain comparisons.

BUCKLE & GREENBERG: NESTMATE RECOGNITION IN BEES tions between kin colonies, bees from one source nest were accepted by bees from the other (d). Only 23 % of such introductions were successful. This acceptance rate is significantly lower than those associated with (a), (b), and (c). (We do not know why this rate of acceptance is higher than the rate of acceptance of unrelated bees recorded by Bell et al. (1974), Kukuk et al. (1977) and Greenberg (1979). Many of our bees were a greater number of generations removed from field-collected bees than those tested by other authors. This may have had some effect on guards' acceptance of non-relatives. Another possibility is that despite efforts to maintain constant laboratory conditions over the past several years, changes may have occurred that have affected odour recognition.) It is of particular interest to compare how often guards in mixed and kin colonies accepted non-relatives (a and d). These two cases differ

K~n

Colony

Kin

Colony

(N6_Z

K~n Colony

Kin

Colony

Fig. 1. Types of introductions (a-f) performed in experiment 1. Boxes represent nests. Arrows point in the direction bees were introduced. Not all introductions are shown; in actuality, the bees in each colony were introduced into each of the other four colonies in the group. The numbers next to each arrow correspond to the acceptance rate (expressed as a percentage) and the number of bees introduced (in parentheses) for that type of introduction. The symbols in boxes refer to the number of bees from a particular source nest. 3X and 3Y in the middle box, for example, represent 3 bees from source nest X and 3 bees from source nest Y.

805

in that members of mixed colonies lived with the sisters of the bee being introduced, whereas bees in kin colonies did not. The significantly higher acceptance rates exhibited by members of mixed colonies (a) demonstrates that living with bees from a different family group increases the likelihood of guards accepting other bees from that family. B. Does mere living with unrelated bees increase the likdihood of being accepted by the sisters of those unrelated nestmates ? No. Bees in mixed colonies were accepted by sisters of their unrelated nestmates (e) at a rate (23 %) equal to that at which their own sisters in kin colonies were accepted (d). This suggests that sharing a nest with bees from another source nest does not, in itself, make an individual more acceptable to other bees from that source nest. C. Does living with females from another source nest decrease the likelihegd of being accepted by one's own sisters ? No. An acceptance rate of 77 % resulted when bees from mixed colonies were introduced into colonies made up of their sisters. This is similar to the rate at which sisters in kin colonies accepted one another (65 %, c). However, the four experimental groups were heterogeneous. Two showed significantly higher acceptance rates of sisters from mixed colonies than sisters from kin colonies (81% and 56%, respectively, Z2 = 11.1). The other two groups showed the opposite trend (69% and 9 2 ~ , Z~ = 5.75). We are unable to account for this heterogeneity. Experiment 2 This experiment investigates whether bees use their own odours as a reference for accepting or rejecting other bees (question 2 in the Introduction). Letters a-d refer to Fig. 2. We begin by asking whether the odd bee's odour was present in sufficient quantities to influence its nestmates' behaviour as guards. That is: A. Does living with a single bee from a different source nest increase the likelihood of accepting other bees from that source nest? Yes. This question was tested by comparing the rate at which O's sisters were accepted by O's nestmates (b) and by sisters of O's nestmates (c). The only difference between these two groups of guarding bees was that the former (O's nestmates) were exposed to the odour of a bee (O) from another source nest; their sisters in kin colonies were not. In all 14 groups O's sisters were accepted at a higher rate by O's nestmates (b) than by O's

ANIMAL

806

BEHAVIOUR,

nestmates' sisters (c; P < 0.005). The average rates of acceptance of these two groups of bees were 56% and 20%, respectively. This significant difference demonstrates that the odd bee's odour was not 'swamped' by odours of its nestmates and that enough of O's odour was present to alter its nestmates' acceptance rate of its sisters. This suggests that sufficient quantities of the odour were present to influence its own behaviour. B. Do O and its nestmates show different acceptance rates of O's sisters (a and b)? Yes, but the difference is a most surprising one. In 13 of 14 nests, O accepted its own sisters less often than did its nestmates ( P < 0 . 0 0 5 , Wilcoxon test). The average rates of acceptance of these two groups of bees were 29 % and 56 %, respectively. This difference suggests that O's nestmates used O's odour as a basis for accepting or rejecting other bees to a greater extent than did O itself. However, it does not preclude the possibility that O's own odour had some influence on its behaviour as a guard. H o w much, if any, influence its own odour had on its responses to introduced bees can be examined by comparing Kin Colony

~.

Mixed Colony "

0%

N ~ k 2 (N:412) el

,

[

l (]y) Bee II,] Odd Nestmates [ (5X) " I Odd

/1

Bee's

I

_J

7)

4

~

--N5~7)

Kin Colony

Fig. 2. Types of introductions (a-d) performed in experiment 2. Boxes represent nests. Each group had up to five nests, one mixed colony and one or two of each type of kin colony. Numbers adjacent to arrows and symbols in boxes have the same meanings as in Fig. 1.

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the acceptance rates of O's sisters by O (a) and by its nestmates' sisters (c). To understand why we employed this comparison, consider the set of odours to which O and its nestmates' sisters were exposed in their respective nests. O was exposed to its own odour and those of five other bees from a different source nest. Each of O's nestmates' sisters was also exposed to six odours, its own and those of the other five members of its colony. The important point is that the six odours in the kin colony of O's nestmates' sisters were probably quite similar to those emitted by O's five nestmates. Therefore, should consistent differences be found in the rate at which O's sisters were accepted by O (a) and by its nestmates' sisters (c), these differences can only be due to one of two possibilities: either (1) O had an odour available to it (its own) that its nestmates' sisters did not (and this odour was probably similar to at least some of its sisters' odours) or (2) O learned the odours of its family while dosed in its cell as a larva, prepupa, pupa, or early callow (this opportunity would not have been available to sisters of O's nestmates). Prior learning either of its relatives' odours or of its own odour may lead an odd bee to accept its sisters at a higher rate. Is there any evidence for this ? That is: C. Are O's sisters accepted at a higher rate by 0 (a) than by sisters of O's nestmates (e) ? No. In seven nests O's acceptance rate was higher, in two nests it was the same, and in five it was lower (P > 0.25, Wilcoxon test). The average rates of acceptance of O's sisters by O (a) and by sisters of its nestmates (c) were 29 % and 20 %, respectively. (Much of this difference is attributable to a single nest in which O's acceptance rate of its sisters was 100 %, whereas its nestmates' acceptance rate was 0%. This odd bee was different from the other 13 in that it began 'suicide tunnelling' upon being placed in a colony with bees from another source nest. We stopped it from doing so a day later by removing it from the nest. When we reintroduced it shortly thereafter, it behaved in a more normal manner. Bees that 'suicide tunnel' dig a tunnel without clearing away the excavated dirt to the rear; they fail to maintain contact with the rest of the nest, their nestmates, and the food source. Death results within a day or two. Such behaviour is typical of older bees that fail to find their way back to the nest entrance after being introduced into a foreign nest. Why this one odd bee behaved in this manner is unknown, though

BUCKLE & GREENBERG: NESTMATE RECOGNITION IN BEES it seems likely it was responding to foreign features of the nest into which it had been placed.) These data argue against the hypothesis that a bee uses knowledge about its own odour for nestmate recognition. Of course, it could be that odd bees tend to reject all bees irrespective of odour. This possibility is tested in the following section by comparing O's behaviour toward its sisters and its nestmates' sisters. D. When 0 is a guard, does it show similar acceptance rates of its sisters (a) and its nestmates' sisters (d)? No. O accepted its sisters less often in 11 nests and at the same rate in one (P < 0.005, Wilcoxon test). The average rates of acceptance of sisters and nestmates' sisters were 29 ~o and 73 %, respectively. This significant difference indicates that odd bees do not show high rejection rates of all bees. Although their acceptance rates of their own sisters were low, their rates of acceptance of their nestmates' sisters were as high as the rates at which bees in mixed nests in experiment 1 accepted their own and their nestmates' sisters. Discussion Odour Recognition In experiment 1 bees in mixed nests accepted the sisters of their unrelated nestmates more often than members of kin colonies accepted unrelated bees. This indicates that bees learn at least some odours of their nestmates and then accept non-residents with similar odours. The fact that bees in mixed nests accepted their own sisters and sisters of their unrelated nestmates at similar rates shows that guards do not distinguish between relatives (sisters) and bees to whom they are unrelated but whose family odours they have learned (sisters of their unrelated nestmates). In experiment 2, O's sisters were accepted at similar rates by O and by its nestmates' sisters: This result argues against any sort of recognition mechanism in which a guard's response to an introduced bee is influenced by its own odour. This finding also suggests that bees do not learn the odours of their nestmates prior to the adult stage. Based on these results, we propose the existence of a 'nestmate recognition memory' which stores the odours of all the bees in a nest except for the individual's own odour. Opportunities to learn nestmates' odours would occur when sitting near, contacting, or passing other bees. An odd bee would not have the chance to interact with

807

another individual like itself; therefore, its own class of odours would not be represented in its recognition memory. This hypothesis assumes that the specific context of interacting with another bee is important since an individual can, for instance, contact itself. Since the learning mechanism is unknown, we cannot speculate about its similarity to habituation, associative learning, or latent learning (Thorpe's terminology, 1963). The principal advantage of a recognition mechanism dependent upon learning is that it enables bees with different odours to live together. Otherwise, if females tolerated only those individuals with odours identical to their own, related bees with many alleles in common but different alleles at the loci controlling odour would not be able to live together. This would often be disadvantageous, especially in an outbreeding system. A recognition mechanism in which a bee uses its own odour as a basis for admitting bees into its nest would enhance the likelihood that beneficiaries of its actions were kin. Can the same be said of the mechanism we have proposed for L. zephyrum? We think so. The odours a bee learns in a natural nest are usually those of relatives (sisters, mothers, aunts, nieces, etc.). Many nestmates, in fact, are apt to have odours identical to one another. In such cases, a bee that learns its nestmates' odours also learns its own odour. In those cases in which related colony members do not all have the same odour, the sum of the nestmates' odours provides a more complete basis for discriminating kin from non-kin than does a bee's own odour. This should enhance rather than adversely affect the operation of kin selection. Learning seems to play an important role in nestmate recognition in other species of social insects. Forel (1874) and Fielde (1903) established mixed colonies of ants by bringing together pupae or callows from different species. 'The implication to be drawn from this demonstration', Wilson (1971, page 276) states, 'is that newly eclosed workers accept whatever odours they first encounter, even if the odours are very different from those they would normally experience in undisturbed nests'. Partial success of mixed colonies has also been reported for bees (Apis, Bombus, and Trigona; see review in Michener 1974) and wasps (Polistes; see review in Spradberry 1973). The mechanism we have proposed may also explain such phenomena as (1) ant workers of

808

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one species, stolen as pupae, becoming the willing slaves of other species and (2) symbionts of social insects being treated as nestmates (see Wilson 1971). Preference for touching siblings rather than non-siblings has been reported tbr spiny mice pups (Porter et al. 1978). Porter & Wyrick (1979), in a follow-up study, hypothesize that the ability to recognize siblings results from the learning of cues associated with littermates during early development. Because of variability in cues emitted by littermates, the authors believe learning rather than inborn discrimination is 'a more parsimonious solution to the problem of littermate recognition' (page 766). Porter & Wyrick's studies focus on whether prior exposure to kin is sufficient, not whether it is necessary, to discriminate related from unrelated individuals. Experiments that bear upon this latter question have been conducted on infant pigtail macaques (Macaca nemestrina, Wu et al. 1980). Though reared apart from relatives, infants preferred to interact with halfsiblings rather than non-kin. Wu et al. point out that such results do not preclude a discrimination mechanism based on learning since 'each subject experienced itself during rearing'. Regardless of whether various organisms do or do not use their own phenotypes as a basis for discriminating kin from non-kin, we suspect most will show some dependence upon learning for recognition of siblings and other relatives. In most cases the relevant cues will be learned early in the organism's life when it is living with or in close proximity to parents, siblings, or other close kin. Later these cues can be used to discriminate among conspecifics.

Odour Transfer Our final topic is the effect of living in mixed colonies on emitted odour. Experiment 1 showed that (1) bees in mixed colonies were accepted by sisters of their nestmates at a rate similar to that at which their sisters in kin colonies were accepted and (2) bees in mixed colonies were accepted by their sisters in kin colonies at a rate at least equal to that at which such sisters accepted one another. Are these findings consistent with the hypothesis that bees acquire the odours of their nestmates? To answer this question, we must consider what stimuli elicit rejection by guards. There are (at least) two possibilities: either the introduced bee may lack some odour or it may have one o1" more odours different from those the guard has learned.

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Suppose rejected bees lack some necessary odour and odour transfer occurs among nestmates. Under these conditions, bees in mixed nests, having had the opportunity to acquire the odours of bees from a different family, should have been accepted by other bees of that family more often than were their sisters in kin colonies. This did not happen. Alternatively, suppose that rejected bees are so treated because they emit an odour unfamiliar to the guard. If nestmates acquire one another's odours, bees in mixed colonies should have been accepted by their sisters in kin colonies less often than sisters in kin colonies accepted one another. No such difference was found. Nene of these results supports the notion of odour transfer among nestmates. In the presence of bees from different families, bees seem to retain their individual odours. Crozier & Dix (1979) have proposed two models of nestmate recognition in species in which odour production is in part genetically determined. Their 'Gestalt' model assumes that odours are transferred among individuals by trophallaxis or grooming. Eventually all the members of a colony carry the same mixture of odours. Their 'individualistic' model supposes that no odour transfer occurs and that workers recognize each other as nestmates if they share at least one allele at each locus controlling odour production. If the individualistic model is modified to include the possibility of learned recognition of odours, then the results of our study support it and not the Gestalt model. Our bees seem to carry predominantly, in quantities detectable by guards, only those odours produced by their own genes. Though Crozier & Dix (1979) favour the Gestalt model, they acknowledge that the individualistic model may pertain to some species, representing an early stage in the evolution of recognition mechanisms. The fact that L. zephyrum is a primitively eusocial species and seems to have a recognition mechanism akin to some aspects of the individualistic model supports this speculation. Since the individualistic model is the only one that makes sense with respect to solitary bees (Shinn 1967; Steinmann 1976), it is not surprising that it has survived in a primitively social species like L. zephyrum.

Acknowledgments This study was supported by a grant from the National Science Foundation (No. BNS 7807707), C. D. Michener, principal investigator. We thank Drs C. D. Michener, W. J. Bell, R.

BUCKLE & GREENBERG: NESTMATE RECOGNITION IN BEES Jander, and W. G. H o l m e s for their criticisms o f this manuscript. This is c o n t r i b u t i o n n u m b e r 1750 fi'om the D e p a r t m e n t o f E n t o m o l o g y , University o f Kansas. REFERENCES Bell, W. J. 1974. Recognition of resident and non-resident individuals in intraspecific nest defense of a primitively eusocial halictine bee. J. comp. Physiol., 93, 195-202. Bell, W. J., Breed, M. D., Richards, K. W. & Michener, C. D. 1974. Social, stimulatory and motivational factors involved in intraspecific nest defense in a primitively social halictine bee. J. comp. Physiol., 93, 173-181. Bell, W. J. & Hawkins, W. A. 1974. Patterns of intraspecific agonistic interactions involved in nest defense of a primitively eusocial halictine bee. J. comp. Physiol., 93, 183-193. Crozier, R. I-I. & Dix, M. W. 1979. Analysis of two genetic models for the innate components of colony odor in social Hymenoptera. Behav. Ecol. Sociobiol., 4, 217-224. Ebrman, L. & Parsons, P. A. 1976. The Genetics of Behavior. Sunderland, MA: Sinauer Associates. Fielde, A. M. 1903. Artificial nests of ants. BioL Bull., Marine Biological Laboratory, Woods Hole, 5, 320-325. Forel, A. 1874. Les Fourmis de Ia Suisse. Zurich: Soci6t6 Helv&ique des Sciences Naturelles (revised and corrected, 1920). Greenberg, L. 1979. Genetic component of bee odor in kin recognition. Science, N.Y., 206, 1095-1097. Harris, R. 1975. A Primer of Multivariate Statistics. New York: Academic Press. HOlldobler, B. & Michener, C. D. 1980. Mechanisms of identification and discrimination in social Hymenoptera. In: Evolution of Social Behavior: Hypotheses and Empirical Tests, Dahlen Konferenzen (Ed. by H. Markl), pp. 35-57. Weinheim, Basel & Deerfield Beach, FL: Verlag Chemie. Kamm, D. R. 1974. Effects of temperature, day length, and number of adults on the sizes of cell and offspring in a primitively social bee (Hymenoptera: Halictidae). ar. Kansas EntomoL Soc., 47, 8-18.

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Kukuk, P., Breed, M. D., Sobti, A. & Bell, W. J. 1977. The contributions of kinship and conditioning to nest recognition and colony member recognition in a primitively eusocial bee, Lasioglossum zephyrum (Hymenoptera: Halictidae). Behav. EcoL Sociobiol., 2, 319-327. Michener, C. D. 1974. The Social Behavior of the Bees. Cambridge, MA: The Belknap Press of Harvard University Press. Michener, C. D. & Brothers, D. J. t971. A simplified observation nest for burrowing bees. J. Kansas EntomoL Soc., 44, 236-239. Porter, R. H. & Wyrick, M. 1979. Sibling recognition in spiny mice (Acomys cahirinus): influence of age and isolation. Anita. Behav., 27, 761-766. Porter, R. H., Wyrick, M. & Pankey, J. 1978. Sibling recognition in spiny mice (Acomys cahirinus). Behav. Ecol. SociobioL, 3~ 61-68. Ribbands, C. R. 1965. The role of recognition of comrades in the defence of social insect communities. Symp. ZooL Soe. Lond., 14, 159-168. Shinn, A. F. 1967. A revision of the bee genus Calliopsis and the biology and ecology of C. andreniformis (Hymenoptera, Andrenidae). Univ. Kansas Sci. Bull., 46, 753-936. Spradberry, J. P. 1973. Wasps: An Account of the Biology and Natural History of Solitary and Social Wasps. Seattle: University of Washington Press. Steinmann, E. 19'76. ~ber die Nahorientierung der Einsiedlerbienen Osmia bicornis L. und Osmia cornuta Latr. M. H. Schweizer. Ent. Gesellsch., 49, 253-258. Thorpe, W. H. 1963. Learning and Instinct in Animals. Cambridge, Mass.: Harvard University Press. Wilson, E. O. 1971. The lnsect Societies. Cambridge, MA: The Belknap Press of Harvard University Press. Wu, H. M. H., Holmes, W. G., Medina, S. R. & Sackett, G. P. 1980. Kin preference in infant Macaca nemestrina. Nature, Lond., 285, 225-227. (Received 27 June 1980; revised 16 October 1980; MS: number: A2504) Reprint requests should be addressed to: C. D. Miehener, Dept. of Entomology, University of Kansas, Lawrence, Kansas 66045, U.S.A.