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Biological Journal of the Linnean Society (1983) 20: 175-184. With 4 figures Body size and alternative mating tactics in the beewolf Philanthus zebratus (Hymenoptera; Sphecidae) K.M. O’NEILL AND H. E. EVANS Department of <oology and Entomology, Colorado State University, Fort Collins, Colorado, U.S.A. 80523 Accepted 5 3uh 1982 A study of the mating behaviour of males of the beewolf Philanthus Zebratus revealed that in one population males display variability in mating tactics and that this variability is related to male body size. There was a tendency for large males to patrol the airspace above the nesting area while smaller males were territorial adjacent to it. The mean sizes of the two groups of males were significantly different, although the size ranges of the two groups overlapped. Only 2 . 5 O b of the males were obsened to undertake both mating tactics, at different times. Observations are presented on daily and seasonal activity patterns and on the relative location of nests, territories, and patrolling males. A second population, with lower nest density, was observed for several days, revealing only territorial males. It is suggested that the presence of patrolling males is related to the higher nest density of the one population. The fact that patrolling males tend to be relatively large is possibly related to flight energetics or simply to the ability of large males to seize females, which are usually larger than males, in mid-air. KEY WORDS :-Philunthus ~ body size ~ mating strategy - territoriality - intraspecific variation CONTENTS Introduction . . . . . . . . . . . . Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . Results Locations of nests, territories, and patrolling males . . Seasonal activity patterns . . . . . . . . . . . . . . . . Daily activity patterns Patrolling behaviour . . . . . . . . . Territorial behaviour . . . . . . . . . Mating behaviour . . . . . . . . . The role of body size variability in the mating system . Some observations on a second aggregation o f P . zebratus Discussion . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 . 176 . . . . . . . . 177 177 177 178 178 179 180 180 181 182 . . 183 184 INTRODUCTION Philanthus is a large genus of solitary wasps commonly called beewolves, the females of which nest in the ground and prey upon bees and wasps. The normal 0024-4066/83/060175 + 10$03.00/0 175 tQ 1983 The Linnean Society of London 176 K. M. O’NEILL AND H . E. EVANS pattern in the mating system of this genus is for males to defend small perches which they scent-mark, the pheromone evidently serving to attract females. I n 14 species of Philanthus in which males have been observed, 13 exhibit territoriality of this basic form (Alcock, 1975a,b; Gwynne, 1978, 1980; Borg-Karlson & Tengo, 1980; Gwynne & O’Neill, 1980; O’Neill, unpubl. data). One Species, P. albopilosus, is evidently not territorial and indeed lacks the large mandibular glands and hair brushes associated with scent-marking (O’Neill, 1979). We have previously reported that males in a population of P. zebmtus in Jackson Hole, Wyoming, display a mating strategy that is unique not only in the genus, but among sphecid wasps generally (Evans & O’Neill, 1978). Males were found patrolling the airspace above the nesting area and attempting to intercept females flying to and from their nests. The position of the males at a height of 3-5 m above the nesting area coincides with the altitude that females achieve on orientation flights and on returning to nests with prey. I n this same paper, we reported an alternative mating strategy in this species, basing this assertion on several Colorado populations in which males were territorial, as in other species of the genus. Since the paper was published, it has become clear that these Colorado populations are not conspecific with zebratus but belong to the closely related species basilarix (G. F. Ferguson, pers. comm.; O’Neill & Evans, 1978). Further observations on P. zebrutus in Jackson Hole during the summers 1978 through 1981 revealed that both patrolling and territorial males do in fact occur in this population, something we did not observe in 1977. Hence our assertion that alternative strategies occur in zebratus remains valid, although originally based on a taxonomic misinterpretation and now found to be intrapopulational rather than interpopulational. This paper reports observations on territorial males, further describes patrolling behaviour, and in particular presents results concerning the relation of a male’s size to the type of mating tactic it employs. Observations on a second Wyoming population of zebratux also suggest that density of female nests may influence male behaviour. METHODS Observations on this species were made at the same location as the previous study (i.e. at Deadman’s Bar, 14 km SW of Moran P.O., Teton County, Wyoming) on 7-1 1 July, 1978; 9-16 July, 1979; 4-16 July, 1980; 11-24 July, 1981. Except as otherwise indicated in the text, all observations reported were obtained from this population. A few additional observations were made on a second population at Huckleberry Hot Springs, Teton County, Wyoming from 17 to 19 July, 1981. This site is approximately 40 km north of the previous locality. The results from this second population are presented for comparison. In 1979, 79 males and in 1980, 179 males were captured, measured to the nearest 0.1 mm (maximum head width), marked on the dorsum of the thorax with one to three small dots of coloured enamel paint, and released. Head widths were measured with a VWR Scientific Products Micrometer accurate to 0.05 mm. Males for dry mass analysis were dried for 7 days in an oven at 65°C to a stable weight. In 1979 and 1980 all individuals that were seen were captured, if possible, regardless of their behaviour at the time. Subsequently, we recorded the type of mating tactic (territoriality or patrolling) being displayed by marked males each MATING TACTICS IN THE BEEWOLF 177 time they were seen again. Locations of nests and territories were recorded to the nearest 10 cm. RESULTS Locations of nests, territories, and patrolling males The main aggregation of nests at Deadman’s Bar occurred in an area of alluvial sand, covered with sparse vegetation, along a dirt road within 100 m of the Snake River. Nest density was high in all 5 years of study; density in 1980 is shown in Fig. 1. Nest entrances were commonly within several centimetres of one another, although a few outliers occurred. Females build one nest per season, which may contain up to 17 cells. The cells vary in depth from 8 to 18 cm and are each stocked with from four to nine prey. Prey identified included members of 10 families and at least 46 species of Hymenoptera (Evans, 1970; Evans & O’Neill, unpubl. data). As in other species of Philanthus, territories are within small (i.e. approximately 1 m 2 ) areas relatively devoid of vegetation, but with at least several nearby tall plants, usually grass stems, which are used as substrate for scent-marking. Territories were never within the nesting area, but usually adjacent to it (Fig. 1). 00 Phtlanthus zebratus 0 0 .. . , . .. . I I - . . 0 . \\ - .-Territory = ......= . -b-. 3 *----., - road ‘-. -.__ 0 0 0 ,_-- .._ ..._ . . ...._ ~. . . .. . .~ ~...~ .~~ ~ _ .. -----.--------.~ Nest opprox.area potrolled c3 5m Figure 1. Map of P. Zebrutlcc study site at Deadman’s Bar showing locations of territories, nests, and area patrolled by males in 1980. Patrolling flights were generally made directly above the nesting area, but were commonly extended beyond the immediate boundaries. Between flights males usually landed among the nests, but would also land in that section of the territorial area that was near the nests. Seasonal activity patterns In 1978 and 1980, observations of the nesting area commenced before the first wasps emerged, so that we were able to record early season emergence patterns of both sexes. The degree of proterandry is slight relative to many other sphecid wasps (e.g. Lin, 1963). I n 1978, the first males were seen two days before, and in 1980 one day before the first females. I n both years, nests, territories, and patrolling flights were all initiated on the first clear day after the females first emerged. 178 K.M.O’NEILLA N D H.E. EVANS Thus, male activity seems to be synchronized with the beginning of female nesting behaviour. This is confirmed by observations made on three marked females which were observed mating. One of these females had initiated her nest on the previous afternoon, but had yet to bring in prey. The other two marked females mated and then initiated their nests later in the same day. Both females caught in copula in 1981 were dissected and the condition of their ovaries examined. I n both cases, the ovaries were relatively undeveloped, indicating that these females were relatively recently emerged. Based on this and the above evidence, it appears that females mate early in their nesting cycle. We have no evidence that females mate later in the cycle. In 1980, the number of nesting females increased each day, from 11 on 8 July, to 151 on 16 July, when observations on this population were terminated. The nesting area was still expanding on this last day. I n 1981, there were at least 186 active nests on 16 July. Males made patrolling flights on all of the 7 clear days from 8 July through 16 J L I ~ Y , 1980. However, territories were present on only 4 of these days. Territorial males were not found on 11 through 13 July 1980 although patrolling males were present. Territories were present both before and after these dates. It is not known why territories were not present on every day on which patrolling flights occurred. Daily activity patterns Females began working at nest entrances between 10.15 and 10.50 hours Mountain Daylight Time (MDT).T h e first prey were brought in between 10.30 and 12.54 hours. The latter time was observed on the first day of nesting in 1980. The usual beginning of the hunting period was between about 10.30 and 11.00 hours. However, a t this time most females were still digging. Another 30-60 min usually passed before most of the females were provisioning. When males first emerged in the morning from sleeping burrows in the nesting area (at about 10.30 to 11.00 hours) they fed on flowers near the nesting area and perched on low plants or the ground. During this period they showed no apparent site attachment and did not interact with conspecific males and females. O n clear days the first patrolling flight was made between 11.13 and 11.55 hours ( N = 9 days). The frequency distribution of patrolling flights (during the day) for 5 days is presented in Fig. 2. The last flights were made between 16.30 and 17.12 hours. At this time, few females were bringing in prey. Most were digging at their nest entrances. The time at which the first territories were initiated was harder to determine because this is a less conspicuous event. O n 5 days in 1978 and 1979, territories were first noted between 11.58 and 13.10 hours. O n the only 2 clear days on which the last territorial males and patrolling males were observed, both activities ceased within 10 min of one another (at about 16.45 hours). Patrolling behaviour A detailed description of patrolling behaviour of males of this species is given by Evans & O’Neill (1978). Here, we pill only briefly summarize the form of this behaviour. From a perch on the ground in or near the nesting area, males make a MATING TACTICS IN THE BEEM’OLF 179 U t :: $ Phdanfhus zebraius I I1111 30- I 939 flights 5 days observations I = copulation I1 P a-* -a E m .; 0 0 Bm r c c al a =/a 1030 1130 12 30 \a \ \\ a\ *\= 1330 13.30 1430 14.30 1530 15.30 I6 3 0 16.30 1730 17.30 Time (hours) Figure 2. Daily schedule of number of patrolling flights observed in 10 min intervals throughout 5 days. Data for 3 days from 1977 (Evans & O’Neill, 1978) were combined with 2 days from 1980. quick ascent to a height of 3-5 m. Upon reaching this altitude, a horizontal flight path is assumed, with the males hovering or flying slowly over a distance of 1-10 m. During this period, they actively pursue passing insects, including conspecific males and females. Upon completion of the flight, the males descend swiftly to the ground. While perching on the ground, they remain sedentary, but may pursue another male upwards as the latter begins a patrolling flight. While perched, males ignore females at nest entrances. One further observation of patrolling males was made in order to determine the relative amounts of time spent by males in flight and on the ground. O n one day in 1981, beginning at 11.15 hours and ending at 14.15 hours, as many patrolling flights and perch durations as possible were timed with a stopwatch (to the nearest second). The duration of 61 flights had a mean of 9.9 s ( S . D = 3.24; range: 3-18 s). The mean duration of 110 perches on the ground between flights was 12.9 s (s.D. = 3.63; range: 6-23 s ) . Comparison of these means indicates that males spent more time on the ground doing nothing that contributes directly to obtaining females than they did actively patrolling for females (t-test for difference in means is significant, P < 0.001 ). We may have slightly underestimated the mean duration of high flights because of the difficulty in following some of the longer flights to completion, but the important point is that males undertaking patrolling tactics spend a substantial proportion of their time not actively pursuing females. Territorial behaviour Few extensive observations of individual territorial males over long periods of time were made. However, the behaviour of males on territories seems similar to that of males of other species of Philanthus. Philanthus Zebratus males mark territories and interact vigorously with conspecific males in contests that involve butting and grappling. Four of seven interactions observed in 1979 resulted in usurpation of the territory by the intruder. Occasionally, interactions between a territorial male and a patrolling male that had landed on a territory were observed. They were short, did not involve physical contact, and were rare since 180 K.M. O’NEILL AND H.E. EVANS most territories were outside the patrolled area. Males also pursued passing insects in a manner similar to that described for other species of Philanthus. Butting of several airborne insects was observed. Territorial males did not react to other males that were patrolling at the height of the swarm. Mating behaviour From 1977 through 1980, 11 matings by patrolling males and none by territorial males were observed. It is true that the initiation of matings on territories might be much less conspicuous. The 11 copulations occurred between 12.39 and 15.05 hours (Fig. 2). Pairing of males and females probably occurred primarily within the aerial swarm, after which the pair descended to the ground. Nine of the 11 mating pairs were found after they were already at ground level. The other two were first observed a t a height of 2 and 5 m. After coupling they completed the copulation on low vegetation in and around the nesting area. The role of body sire variability in the mating system Males of this species collected in 1979 and 1980 ranged from 2.4 to 4.1 mm in head width (2 = 3.20 m m ; S.D. = 0.25; .N = 258). The range of this sample is misleading because of the presence of one male with a head width of 4.1 mm. Excluding this male, the upper size limit of males was 3.7 mm. It is possible that the 4.1 mm male represented a mistake in sex determination, whereby a male (unfertilized) egg was laid in a cell provisioned for a female (fertilized) egg. This has been previously discussed in relation to such a phenomena in bees of the genus Osmia (Raw & O’Toole, 1980). Females of this species were larger than males on the average ( 2 = 3.81 mm: S.D. = 0.18; N = 120; t-test for difference P<c 0.00 1). This difference is typical of the direction of sexual size dimorphism in Philanthus (O’Neill, 1981). Head width of males is highly significantly correlated with dry mass ( r = 0.93; P < 0.001). Of 1 1 matings observed (including four from the previous study), the size of six males was determined, one of which was observed to mate twice. The six males ranged in size from 3.2 to 3.6 mm (ii = 3.41 mm; S.D. = 0.17; ”V = 7). Although this sample is too small to allow for statistical analysis, it is interesting to note that they were all of mean size or larger. Alcock, Jones & Buchmann (1977) reported that males of the bee Centris pallida undertake alternative mating strategies, and that large males tended to be patrollers and small males tended to be ‘hoverers’ (i.e. territorial). This population of P. rebratus was investigated in order to determine if there was any relationship between the mating tactic that a male undertook and his size. In 1979 and 1980, 78 different males were caught after they were seen to make patrolling flights. They had a mean head width of 3.36 mm (s.D. = 0.20; Fig. 3). O n the other hand, 44 different males found to be territorial had a mean head width of 3.06 mm (s.D. = 0.26). The means of all patrolling males and territorial males were significantly different (t-test, P<c 0.001). The difference between 3.36 mm and 3.06 mm males becomes more apparent and biologically significant when one considers mass rather than linear dimensions such as head width. The regression of dry mass on head width for P. eebratus males indicates that a male of 3.36 mm should weigh about 39(y0 more than a 3.06 mm male. MATING TACTICS IN T H E BEEWOLF I 181 High Flight Moles f = 3.36 mm N.78 -g z 0'30..,LLLL_ 0.20 'i; 0.10 = 2 P <0.0001 3.06 mm N=44 f = m g B 0.20 ? E 0.10 n 2.4 2.6 28 3.0 3.2 3.4 3.6 . . 3.8 . , . , 4.0 Head width (mm) Figure 3. Size-frequency distributions of patrolling males and territorial males of P. zebrutus in Jackson Hole from 1979 and 1980. Hollow portions of bars in lower histogram indicate the size of three males that both held territories and made high flights. I t is also instructive to compare the range of values for the head widths of the two groups. Only one male (2.9 mm) with a head width of less than 3.0 mm was seen to undertake a patrolling flight, although 40 males in this size range were found in the population (16% of all males). I n contrast, although 58 males (22O/,,, of all males) had head widths greater than 3.3 mm, only four of these males were found to hold territories. Males descending from high flights were easy to follow against the backdrop of spruce trees near the nesting area, so we feel confident that the above is not a function of differential visibility of males of different sizes. Only three of the 122 males were seen to undertake both territoriality and patrolling flights (i.e. at different times). These males had head widths of 3.3, 3.4 and 3.6 mm (Fig. 3). Two of these males were observed to be territorial before switching to patrolling, while the third male held a territory between two observations of it making patrolling flights. The behaviour of these males while they were territorial was not obviously different from that of other territorial males. Seven interactions between territory residents and intruders, in which the size of at least one of the males was known, were observed. The smaller of two males never won a fight (.N=5). The mean size of the winners was 3.23 mm (s.D. = 0.11; . V = 7 ) . The mean size of the losers was 2.77 mm (S.D = 0.21; .N=6;Mann-Whitney test for difference; PGO.001). Even with such a small sample of observed fights we are confident of the advantage of large males in fights given results from other species of Philanthus. In 133 territorial contests observed in P. basilaris, P. pulcher, and P. crabroniformis, between males of different size, the larger male of the pair won 131 contests (O'Neill, 1981 and unpubl. data). Some observations on a second aggregation of P. zebratus As noted earlier, we made a brief study of a population about 40 km north of our major study area, at Huckleberry Hot Springs. These studies began at midseason and lasted only 3 days. This was a much smaller aggregation and the K. M. O’NEILL AND H. E. EVANS 182 Philantbus zebrotus t 0 = Territory = Nest 10 rn Figure 4. Map of P. Zebratus study site at Huckleberry Hot Springs. nests were much more scattered; hence it is of interest to note differences in male behaviour which may be related to population size and nest density. Although nests were scattered along the centre and sides of a little-used dirt road and in a sandy field adjacent to the road, they were relatively conspicuous and we feel that we found most that were active during the study period. We found 23 nests, separated by distances of from 0.5 to 45 m (Fig. 4). As in the other population, territories were usually adjacent to the nests, though here they seemed more intimately associated. We also found four territories about 50 m from the nests. Territorial males scent-marked grass stems and interacted with intruding males and other insects. We saw no evidence of patrolling flights above the nests. In this population a larger area containing far fewer nests was involved, and patrolling may be much less effective under these conditions. We had earlier suggested (Evans & O’Neill, 1978) that under the conditions of high population density in the Deadman’s Bar population, the cost of territorial defence within the aggregation may be too great. This was presumably not true at Huckleberry Hot Springs, and males were territorial. However, because of the brevity of our study we cannot be certain that patrolling flights do not sometimes occur in this population. We measured the head width of 12 different males that held territories in this population. They ranged from 2.8 mm through 3.4 mm and had a mean size of 3.13 mm (s.D. = 0.18). This mean was not significantly different from that obtained for the 44 territorial males in the Deadman’s Bar population (t-test; t = 1.07). DISCUSSION Territoriality and scent-marking appear to be ancestral forms of mating behaviour in male Philanthines. Not only do most Philunthus spp. display these strategies, males of the related genus Eucerceris have also been observed behaving in this manner (Alcock, 1975b; Evans, unpubl. data). Therefore, it is likely that MATING TACTICS I N T H E BEEWOLF 183 the patrolling behaviour in the Deadman’s Bar population of P. zebratus is a derived tactic. Under conditions of high nest density P. rebrutus males probably practise a type of conditional strategy based upon size. The presence of at least three males that performed both beha\iours in the 1980 population indicates that there is not a fixed polymorphism in which males of different genotypes are programmed to exhibit totally different mating behaviours. Patrolling males collected and dissected in 1977 had the large mandibular glands associated with scent-marking (Evans & O’Neill, 1978) and all males examined had mandibular and abdominal hair brushes typical of Philanthus males. We can infer that, relative to territoriality, the patrolling tactic is more successful, at least when nests are closely aggregated. We know from this and especially other species of Philanthus that large males are much more successful at the territorial tactic than are small males. If there is not a fixed polymorphism, and if large males have been selected to abandon territoriality for patrolling, it follows that the latter tactic is more profitable in this population. Patrolling is a form of scramble competition polygyny (Alcock, 1980) which may be more profitable than territoriality because patrolling males intercept receptive females before the latter reach territories. Because of the high nest density, the cost of defending a territory and repeatedly soliciting non-receptive females in the nest area would be correspondingly high. A similar situation may be occurring in the bee Centris pallidu (Alcock et al., 19771. This is the only other reported case of size-related alternative behaviours in the solitary Hymenoptera. In that species, large males patrol the emergence area and copulate with emerging females. By virtue of their large size, they are able to fend off other males attempting to usurp possession of the female. Many of the smaller males hover near plants outside the emergence area and intercept females that have not copulated upon emerging from the ground. It should be noted that, although a size-conditional strategy is the most parsimonious explanation for size-related male behaiiour in Philanthus, without genetic analysis i t is not possible to rule out a stable polymorphism in which size and a tendency to behave in a particular manner are genetically predetermined (Cade, 1980). The question arises as to why small Philanthus males do not also switch to patrolling beha\riour under high nest density. The fact that males spend more time on the ground between patrolling flights, on a\rerage, than they do in the air, suggests that the flights are energetically expensi\.e to undertake. It may be that, during flight, large males are energetically more efficient than small males and can, therefore, sustain longer flights or more flights per day. Between species of insects comparisons do suggest that in flight, larger insects have a lower ‘cost of transport’ than smaller insects (Tucker, 1975), but it is not known whether this analysis can be extended to intraspecific body size comparisons. Again, as suggested by interspecific comparisons (Bonner, 1965), larger males may have higher flight speeds. A simpler reason for sex-related behavioural variability may be that large males are better able to seize the usually larger females in mid-air. ACKNO\VLEDGEhlENTS Keith Christian contributed valuable help with the field work. FVe thank Kenneth L. Diem of the University of Wyoming, National Park Service Research 184 K. M. O’NEILL AND H. E. EVANS Centre and Robert Wood of Grand Teton National Park for their co-operation and hospitality. Robert Longair commented on the manuscript. Financial aid was supplied by the National Science Foundation Grant Nos BNS 76-09319 and BNS 79-26655 to Howard E. Evans and by the National Park Service. REFERENCES ALCOCK, J., 1975a. Territorial behaviour by males ofPhilanthus multimaculatus (Hymenoptera, Sphecidae) with a review of territoriality in male sphecids. Animal Behauiour, 23: 889-895. ALCOCK, J., 1975b. Male mating strategies of some Philanthine wasps (Hymenoptera: Sphecidae). Journal of the Kansas Entomological Socieiy, 48: 532-545. ALCOCK, J., 1980. Natural selection and the mating systems ofsolitary bees. American Scientist, 68(2): 146-153. ALCOCK, J., JONES, C. E. & BUCHMANN, S. L., 1977. Male mating strategies in the bee Centris pallida (Hymenoptera: Anthophoridae). American Naturalist, 111(977): 145-155. BONNER, J. T., 1965. Size and Cycle: an Essay on the Structure of Biology. Princeton, New Jersey: Princeton University Press. BORG-KARLSON, A-K. & TENGO, J., 1980. Pyrazines as marking volatiles in Philanthine and Nyssonine wasps (Hymenoptera: Sphecidae). 3 0 u r d of Chemical Ecology, 6(4) : 827-835. CADE, W., 1980. Alternative male reproductive behaviors. Florida Entomologist, 63(1) : 3G44. EVANS, H. E., 1970. Ecological-behavioural studies of the wasps of Jackson Hole, Wyoming. Bulletin of the Museum of Comparatizle ~ o o l o ~ Haruard y, University, 140: 45 1-51 1. EVANS, H. E. & O’NEILL, K. M., 1978. Alternative mating strategies in the digger wasp Philanthus zebratus. Proceedings of the National Academy of Sciences 75(4): 1901-1903. GWYNNE, D. T., 1978. Male territoriality in the bumblebee wolf, Philanthus bicinctus (Mickel) (Hymenoptera: Sphecidae). Zeitschrftfur Tzerpgchologie, 47: 89-103. GWYNNE, D. T., 1980. Female defense polygyny in the bumblebee wolf, Philanthus bicinctus (Hymenoptera: Sphecidae). Behauioural Ecology and Sociobiology, 7 : 21 3-225. GWYNNE, D. T. & O’NEILL, K. M., 1980. Territoriality in digger wasps results in sex-biased predation on males (Hymenoptera: Sphecidae, Philanthus). Journal of the Kansas Entomological Sociep, 53(1) : 220-224. LIN, N., 1963. Territorial behaviour in the cicada-killer wasp Sphccius speciosus. Behaviour, 20: 115-133. O’NEILL, K. M., 1979. Territorial behavior in males of Philanthus psyche (Hymenoptera: Sphecidae). Psyche, & ( I ) : 19-43. O’NEILL, K . M., 1981. Male mating strakgies and body size in three species of beewolues (Hymenoptera: Sphecidae; Philanthus). Dissertation, Colorado State University. O’NEILL, K . M. & EVANS, H . E., 1981. Predation on conspecific males by females of the beewolf Philanthus basilaris Cresson (Hymenoptera: Sphecidae). Journal of the Kansas Entomological Sociefy, 54: 553-556. RAW, A. & O’TOOLE, C. 1979. Errors in the sex of eggs laid by the solitary bee Osmia rufa (Megachilidae). Behaviour, 70(1-2): 168-170. TUCKER, V., 1975. The energetic cost of moving about. American Scientist, 63: 413-419.