dual effect of wasp queen pheromone in regulating insect sociality · 2015-05-14 · current...

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Dual Effect of Wasp Queen
Pheromone in RegulatingInsect Sociality
Highlights

d Specific queen pheromones induce sterility in social insect

workers

d One of these queen pheromones is shown to also signal egg

maternity

d The pheromone enables workers to recognize or ‘‘police’’

eggs laid by cheater workers

d This shows that queen pheromones regulate insect sociality

in several distinct ways

Oi et al., 2015, Current Biology 25, 1–3June 15, 2015 ª2015 Elsevier Ltd All rights reservedhttp://dx.doi.org/10.1016/j.cub.2015.04.040

Authors

Cintia A. Oi, Annette Van Oystaeyen, ...,

Jelle S. van Zweden, Tom Wenseleers

[email protected] (C.A.O.),[email protected] (T.W.)

In Brief

Social insect queens use pheromones to

stop the workers from reproducing. Oi

et al. show that in wasps, one of these

sterility-inducing pheromones is also

used by the queen to mark her eggs and

enable the workers to recognize and

‘‘police’’ eggs laid by other workers. This

shows that queen pheromones regulate

insect sociality in several distinct ways.

mailto:[email protected]


http://dx.doi.org/10.1016/j.cub.2015.04.040

Please cite this article in press as: Oi et al., Dual Effect of Wasp Queen Pheromone in Regulating Insect Sociality, Current Biology (2015), http://dx.doi.org/10.1016/j.cub.2015.04.040

Current Biology

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Dual Effect of Wasp Queen Pheromonein Regulating Insect SocialityCintia A. Oi,1,* Annette Van Oystaeyen,1 Ricardo Caliari Oliveira,1 Jocelyn G. Millar,2 Kevin J. Verstrepen,3,4

Jelle S. van Zweden,1 and Tom Wenseleers1,*1Laboratory of Socioecology and Social Evolution, KU Leuven, Naamsestraat 59, 3000 Leuven, Belgium2Department of Entomology and Department of Chemistry, University of California, Riverside, Riverside, CA 92521, USA3VIB Laboratory for Systems Biology, KU Leuven, Gaston Geenslaan 1, 3001 Leuven, Belgium4CMPG Laboratory for Genetics and Genomics, KU Leuven, Gaston Geenslaan 1, 3001 Leuven, Belgium

*Correspondence: [email protected] (C.A.O.), [email protected] (T.W.)


SUMMARY

Eusocial insects exhibit a remarkable reproductivedivision of labor between queens and largely sterileworkers [1, 2]. Recently, it was shown that queensof diverse groups of social insects employ specific,evolutionarily conserved cuticular hydrocarbons tosignal their presence and inhibit worker reproduction[3]. Workers also recognize and discriminate be-tween eggs laid by the queen and those laid byworkers, with the latter being destroyed by workersin a process known as ‘‘policing’’ [4, 5]. Workerpolicing represents a classic example of a conflict-reducing mechanism, in which the reproductivemonopoly of the queen is maintained through theselective destruction of worker-laid eggs [5, 6]. How-ever, the exact signals used in worker policing havethus far remained elusive [5, 7]. Here, we show thatin the common wasp, Vespula vulgaris, the phero-mone that signals egg maternity and enables theworkers to selectively destroy worker-laid eggs is infact the same as one of the sterility-inducing queensignals that we identified earlier [3]. These resultsimply that queen pheromones regulate insect social-ity in two distinct and complementary ways, i.e., bysignaling the queen’s presence and inhibiting workerreproduction, and by facilitating the recognition andpolicing of worker-laid eggs.

RESULTS AND DISCUSSION

Even though social insects may appear to work together in total

harmony, social insect colonies are in fact rife with conflict [1, 5].

A case in point is the queen-worker conflict over male produc-

tion, observed in many species, whereby rogue workers will sur-

reptitiously lay unfertilized eggs, destined to become males,

instead of working for the benefit of the colony [5]. To keep

such transgressing workers at bay, many species have evolved

a ‘‘policing’’ system in which eggs laid by workers are selectively

detected and cannibalized [5, 8]. First discovered in the honey-

bee a quarter of a century ago [4], this phenomenon of worker

Current Biolo

policing has since been reported in more than a dozen social in-

sect species, including bees, ants, and wasps [8]. It has long

been hypothesized that the workers’ ability to discriminate be-

tween queen-laid and worker-laid eggs might be aided by a

pheromone mark left on the queen’s eggs [5]. Such a queen

egg-marking pheromone should be evolutionarily stable

because the pheromone would benefit both the queen, by

increasing her share of the colony’s reproduction, and the

workers, by reducing the chance of them accidentally destroying

the queen’s eggs and thereby reducing their inclusive fitness

[5, 8–10]. However, despite decades of research, no social in-

sect queen egg-marking pheromone has been unambiguously

identified [5, 7, 11].

Cuticular hydrocarbons provide a waxy protective layer on the

cuticles of all insect life stages, including eggs [12, 13]. The pro-

files of cuticular chemicals are known to show pronounced dif-

ferences between castes [3, 11] and have acquired important

signaling functions in social insects, including as queen phero-

mones [3]. We hypothesized that the same hydrocarbons that

function as queen pheromones might also play a role in signaling

eggmaternity. That is, based on evolutionary parsimony, we pre-

dicted that the co-option and repurposing of an existingmaternal

signal might be easier than evolving an entirely new signaling

system from scratch. To test this hypothesis, we carried out ex-

periments with the common wasp, Vespula vulgaris (Figure 1A),

fromwhichwe recently identified several sterility-inducing queen

pheromones [3], and in which the workers, as in the honeybee,

police each other’s eggs [14]. To shortlist possible egg-marking

pheromones, we first carried out a detailed comparison of the

hydrocarbon profiles of queen-laid and worker-laid eggs ([15];

Figure S1 and Supplemental Experimental Procedures). Our

analysis showed that two compounds were consistently more

abundant on the surface of queen-laid eggs than on the surface

of worker-laid eggs, namely 3-methylnonacosane (3-MeC29),

which we earlier found to act as a sterility-inducing queen signal

[3], and 3-methylheptacosane (3-MeC27), which shows weaker

caste differences on the cuticle but is highly characteristic of

queen-laid eggs (Figure S1).

Subsequently, we collected six colonies of the commonwasp,

from which we isolated about half of the worker force from their

mother queen to stimulate egg laying. We then treated worker-

laid eggs with synthetic versions of the queen-characteristic

pheromones 3-MeC27 and 3-MeC29, either individually or as a

blend (‘‘mix,’’ Figure 1B), dissolved in acetone. These treatments

gy 25, 1–3, June 15, 2015 ª2015 Elsevier Ltd All rights reserved 1




B

A

Figure 1. Experimental Setup Used to Test the Role of Queen Pher-

omones in Signaling Egg Maternity during Worker Policing in the

Common Wasp

(A) To test the hypothesis that hydrocarbon queen pheromones, which

stop workers from reproducing [3], could also play a role in signaling queen

egg maternity, we performed experiments with the common wasp Vespula

vulgaris. As in most social insects, common wasp queens have a near

monopoly over reproduction [14]. This reproductive monopoly is enforced

partly via a mechanism of ‘‘worker policing,’’ whereby workers selectively

detect and destroy eggs laid by transgressing workers [14].

(B) In bioassays, we determined whether treatment with an acetone solution of

the hydrocarbon 3-methylnonacosane (3-MeC29), one of the main sterility-

inducing queen signals in this species [3]; 3-methylheptacosane (3-MeC27),

which is characteristic of queen-laid eggs; or a mix of both caused worker-laid

eggs to become more ‘‘queen-like’’ and thus acceptable to the workers upon

reintroduction into their mother colony.

A

B

Figure 2. A Sterility-Inducing Queen Pheromone Also Protects the

Queen’s Eggs against Worker Policing in the Common Wasp

(A) Treatment of worker-laid eggs with acetone solutions of the queen egg

characteristic compounds 3-MeC29 and 3-MeC27, either as single compounds

(‘‘single’’) or as a blend of the two compounds (‘‘mix’’), caused their relative

abundance to significantly increase relative to the control and to approach

those found naturally on queen-laid eggs (mean ± SEM, Tukey’s post hoc

tests, n = 18 eggs each per egg type and treatment from N = 6 colonies each;

Table S1). Compound concentrations were compared separately but signifi-

cance levels are presented only once, given that the results were the same for

both compounds (***p < 0.001; NS, not significant).

(B) Our bioassays confirmed that 3-MeC29 also signals eggmaternity, because

the percentage of eggs that were policed was significantly reduced when

3-MeC29 was applied onto worker-laid eggs compared to the solvent-only

control (mean ± 95% confidence level, binomial mixed model, Table S1; N = 6

replicate colonies, n = 625–724 eggs per treatment; ***p < 0.001; NS, not

significant).


rendered worker-laid eggs chemically more similar to queen-laid

eggs (Figure 2A; Table S1), and our hypothesis was that applica-

tion of these compounds should therefore reduce the rate at

which these eggs were policed. By reintroducing the chemically

manipulated eggs into the mother colony (Figure 1B), we

confirmed this hypothesis. Specifically, the bioassays confirmed

that 3-MeC29 was strongly correlated with signaling egg mater-

nity because it significantly reduced the rate at which worker-

laid eggs were policed compared to solvent-treated controls

(Figure 2B; Table S1). By contrast, 3-MeC27, which is present

in significantly higher amounts on queen-laid eggs than on

2 Current Biology 25, 1–3, June 15, 2015 ª2015 Elsevier Ltd All right

worker-laid eggs, did not inhibit policing, and the blend of both

compounds was not significantly different from 3-MeC29 used

alone. The fact that applying the compound 3-MeC29 onto

worker-laid eggs only partially protected them against policing,

however, indicates that our treatments were only partially effec-

tive at mimicking the complete profiles of queen-laid eggs. This

could be explained either by small concentration mismatches

(Figure 2A) or by the fact that worker-laid eggs also contain

some specific cues that give away their maternal origin, and

which we could not experimentally remove. Indeed, our chemi-

cal analysis reveals several short-chain mono- and dimethyl

s reserved


alkanes that are specific to worker-laid eggs (Figure S1) and

might be produced as some intrinsic side effect of worker-spe-

cific physiological processes [16]. Hence, 3-MeC29 forms an

important part of the queen signal, but an additional contribution

of other queen- or worker-specific compounds cannot be

entirely excluded. In fact, a recent study has shown that in

ants, a hydrocarbon fertility signal is maximally effective only

when perceived within its full chemical context [17]. It is likely

that the same is true for the queen egg-marking signal that we

have documented here.

Overall, our study is the first to unambiguously identify a social

insect queen egg-marking pheromone used in worker policing.

Furthermore, our results show that the egg-marking pheromone

appears tobe the sameasoneof themain sterility-inducingqueen

signals in this species [3]. Fromanevolutionaryperspective, these

findings make sense because a queen pheromone has all the

necessary attributes to be a marker of maternal origin and could

easily be co-opted into a valuable secondary function as an

egg-marking pheromone. A dual function of queen pheromones

in inducing sterility and egg marking had been suggested previ-

ously for volatile queen pheromone components in the termite

Reticulitermes speratus [18, 19], as well as for non-volatile hydro-

carbons in theantsCamponotusfloridanus [20] andPachycondyla

inversa [11]. In the latter two cases, particular long-chain hydro-

carbons are highly specific for queens and their eggs, but a dual

function in communication and regulation of sociality was not

confirmed with defined blends of pure compounds, causing the

functional roles of these compounds to remain speculative in

these cases. Nonetheless, these results together with ours clearly

suggest that hydrocarbon queen pheromones have a central role

in regulating the spectacular reproductive division of labor of

diverse lineages of hymenopteran social insects.

SUPPLEMENTAL INFORMATION

Supplemental Information includes one figure, one table, and Supplemental

Experimental Procedures and can be found with this article online at http://

dx.doi.org/10.1016/j.cub.2015.04.040.

AUTHOR CONTRIBUTIONS

C.A.O., J.S.v.Z., and T.W. designed and contributed to all aspects of this

study. A.V.O. first conceived the experiments and provided some of the

bioassay results. R.O.C. helped to collect nests and perform bioassays.

J.G.M. synthetized the methyl-branched hydrocarbons. K.J.V. provided the

GC-MS instrument used to analyze the chemical profiles of eggs. C.A.O.,

J.S.v.Z., and T.W. wrote the manuscript.

ACKNOWLEDGMENTS

This study was supported by Research Foundation Flanders grant G.0A51.15

and KU Leuven Centre of Excellence grant PF/2010/007 (to T.W.), postdoc-

toral fellowship 12Q7615N of the Research Foundation Flanders (to

J.S.v.Z.), CNPq-Brazil scholarships 201959/2012-7 and 238127/2012-5 (to

C.A.O. and R.C.O.), and Hatch project CA-R*ENT-5181-H (to J.G.M.). We

are grateful to A. Vollet-Neto and A. Vandoren for assistance with fieldwork.

Received: March 7, 2015

Revised: April 20, 2015

Accepted: April 20, 2015

Published: May 7, 2015

Current Biolo

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http://dx.doi.org/10.1002/bies.201400180

http://dx.doi.org/10.1002/bies.201400180

Current Biology

Supplemental Information

Dual Effect of Wasp Queen Pheromone

in Regulating Insect Sociality

Cintia A. Oi, Annette Van Oystaeyen, Ricardo Caliari Oliveira, Jocelyn G. Millar,

Kevin J. Verstrepen, Jelle S. van Zweden, and Tom Wenseleers

FD padj FD padj

3-MeC27 1.8 0.0075 1.4 0.012

3-MeC29 2.1 0.045 7.4 0.0054

C25 1.2 0.047 -1.1

C26 1.3 1.6 0.0025

C27 1.2 3.6 0.0059

7-MeC27 1.6 -1.1

C29:1 1.6 1.2

11,17-, 13,17-, 15,19-diMeC31 1.9 5.5 0.0025

C31:1 1.4 1.4

5,9-diMeC29 1.3 -2.0 0.039

11-, 13-, 15-MeC31 1.3 1.5

C28 1.1 3.2 0.019

11-, 13-, 15-MeC29 1.2 1.0

10-, 12-, 14-, 16-MeC28 1.1 -1.5

C27:1 (+isomer) 1.1 -1.2

4-MeC26 1.0 -1.9 0.029

7-MeC29 1.1 1.2

x,y-diMeC30 -1.0 1.2

5-MeC27 -1.1 -1.3

3-MeC25 -1.0 -2.8 0.039

11-, 13-MeC27 -1.1 -2.0 0.037

4,x-diMeC28 -1.1 -1.4

11,15-diMeC27 -1.2 -2.1 0.039

C25:1 (+isomer) -1.2 -2.0 0.039

C24 -1.2 -2.3 0.0069

4,x-diMeC26 -1.4 -2.6 0.039

4-MeC28 -1.3 1.8 0.032

C23 -1.3 -3.6 0.012

C31 -1.2 3.3 0.012

5,x-diMeC27 -1.2 -1.9

C30 -1.1 -1.2

10-, 12-, 14-MeC26 -1.2 -2.6 0.034

C29 -1.2 5.2 0.0057

7-MeC25 -1.3 -3.4 0.032

4-MeC24 -1.7 -3.8 0.031

4,x-diMeC24 -1.6 -2.8 0.021

3,x-diMeC27 -1.4 -2.4 0.034

6-MeC24 -1.6 0.045 -3.4 0.023

3,x-diMeC25 -1.6 0.045 -2.8 0.039

5-MeC25 -1.4 0.045 -3.3 0.031

5,x -diMeC23 -2.1 0.034 -2.6 0.049

3,x-diMeC23 -1.9 0.034 -3.3 0.039

5,x-diMeC25 -1.5 0.034 -2.5 0.039

3-MeC23 -2.0 0.034 -4.9 0.029

10-,12-,14-MeC24 -1.8 0.034 -3.7 0.034

11-, 13-, 15-MeC25 -1.5 0.030 -3.2 0.034

7-MeC23 -2.0 0.030 -4.0 0.032

5-MeC23 -2.0 0.030 -4.0 0.032

9-, 11-MeC23 -2.1 0.012 -3.9 0.034

Queen vs worker-laid eggs Queen vs worker cuticle

1 2 3 4 5 6 2 4 5 6

Colony

QLE vs WLE Q vs W

Fold difference

-8 -2 2 4 8-4 0

Supplemental Information Supplemental Figure S1 Figure S1. Queen‐characteristic hydrocarbons in the common wasp Vespula vulgaris (related to Fig. 1B). Based on a reanalysis of the data from our earlier study [S1], it can be seen that only two hydrocarbons, 3‐methylheptacosane (3‐MeC27) and 3‐methylnonacosane (3‐MeC29), are much more abundant on the surface of queen‐laid eggs (QLE) than worker‐laid eggs (WLE) (fold difference in relative peak area > 1.5 and FDR corrected p‐level < 0.05, highlighted in red in the QLE vs. WLE columns). One of these compounds, 3‐MeC29, was earlier shown to act as a queen signal that stops workers from reproducing [S2], together with the queen‐characteristic linear alkanes C27, C28 and C29 (highlighted in red in the Q vs. W columns). Analyses of the cuticle are based on the comparison of relative peak areas, and for egg extracts are based on the average relative peak areas of 5 to 10 QLEs and WLEs each per colony from a total of 6 colonies, whereas for cuticle extracts they are based on the average relative peak areas of 10 workers per colony as well as that of their mother queen from a total of 4 colonies. Subsequently, colony‐average Log2 transformed relative peak areas of the 49 hydrocarbon peaks present were compared using paired t‐tests, after which significance levels were FDR corrected using the Benjamini‐Hochberg procedure. Further methodological details can be found in ref. [S1]. (FD = fold difference in relative peak areas, padj = Benjamini‐Hochberg FDR corrected p values, QLE and WLE = hexane extract of queen‐laid and worker‐laid eggs, Q and W = cuticular hexane extract of mature egg‐laying queens and nonreproductive workers, Cx and Cx:1 = linear alkanes and alkenes with chain length x, y‐MeCx = monomethyl branched alkanes, y,z‐diMeCx = dimethyl branched alkanes)

Supplemental Table S1. Significance of the effect of treating worker‐laid eggs with queen‐characteristic hydrocarbons and of the treatments on egg policing rates. Application of synthetic versions of the queen‐characteristic compounds 3‐methylheptacosane (3‐MeC27, A) and 3‐methylnonacosane (3‐MeC29, B), or a mix of both, onto worker‐laid eggs (WLE) resulted in relative peak areas of 3‐MeC27 and 3‐MeC29 that were significantly higher than in the control WLEs, and non‐significantly different from the levels observed in queen‐laid eggs (QLE). Significance levels are based on Tukey posthoc tests carried out on a mixed model in which the relative peak area of each of the two compounds were coded as the dependent variable and colony and treatment were coded as a random and fixed factors, respectively (***: p < 0.001, n = 18 eggs each per egg type and treatment condition from 6 replicate colonies each). Policing bioassays (C) confirm that treatment of eggs with the queen pheromone 3‐MeC29 [S2], either alone or in a mix with 3‐MeC27, significantly reduced the odds for eggs to be policed compared to the control. Egg policing rates also showed a significant positive association with the number of workers present in each discriminator colony, but this was not confounded with treatment due to the paired experimental design that we used. Significance levels are based on a binomial mixed model in which discriminator colony and treatment were coded as random and fixed factors and the number of cells in each test comb and the number of workers in the discriminator colony were included as continuous covariates. (***: p < 0.001, odds ratio = odds of worker‐laid eggs being policed relative to control eggs) A) Effect of 3‐MeC27 treatment Coefficient SE z value p‐value

3‐MeC27 vs Control WLE 0.017 0.0043 3.85 < 0.001 ***

Mix vs Control WLE 0.017 0.0043 3.79 < 0.001 ***

QLE vs Control WLE 0.024 0.0061 3.97 < 0.001 ***

3‐MeC27 vs Mix 0.00027 0.0040 0.067 1.00

3‐MeC27 vs QLE ‐0.0073 0.0066 ‐1.12 0.67

Mix vs QLE ‐0.0076 0.0066 ‐1.16 0.65

B) Effect of 3‐MeC29 treatment Coefficient SE z value p‐value

3‐MeC29 vs Control WLE 0.0087 0.0017 5.05 < 0.001 ***

Mix vs Control WLE 0.0072 0.0017 4.18 < 0.001 ***

QLE vs Control WLE 0.012 0.0023 5.34 < 0.001 ***

3‐MeC29 vs Mix 0.0015 0.0016 0.94 0.78

3‐MeC29 vs QLE ‐0.0036 0.0024 ‐1.46 0.46

Mix vs QLE ‐0.0050 0.0024 ‐2.06 0.16

C) Effect on egg policing rates Coefficient SE Odds ratio

z value p‐value

(Control) ‐2.22 0.41 ‐5.40 6.9 x 10‐8

3‐MeC27 ‐0.19 0.12 0.82 ‐1.60 0.11

3‐MeC29 ‐0.44 0.12 0.65 ‐3.61 0.0003 ***

Mix ‐0.44 0.12 0.64 ‐3.55 0.0004 ***

Nr. of cells 0.0012 0.0027 0.45 0.65

Nr. of workers 0.0067 0.0014 4.83 1.3 x 10‐6 ***

Supplemental methods Identification of putative egg‐marking pheromones To identify putative queen egg‐marking pheromones in the common wasp Vespula vulgaris, we reanalyzed the raw hydrocarbon profile data of queen‐laid eggs (QLEs) and worker‐laid eggs (WLEs) as reported on in our earlier study [S1]. Comparison of the average profiles of 5 to 10 WLEs and QLEs from a total of 6 colonies (total n QLE=44, total n WLE=39) demonstrates that only two hydrocarbons, 3‐methylheptacosane (3‐MeC27) and 3‐methylnonacosane (3‐MeC29), were consistently much more abundant on the surface QLEs than WLEs (avg. fold difference in relative peak area > 1.5 and FDR corrected p‐level < 0.05, based on paired t‐tests on Log2 transformed relative peak areas, Fig. S1). One of these compounds, 3‐MeC29, was earlier shown to act as a queen signal that stops workers from reproducing [S2], together with the queen‐characteristic linear alkanes C27, C28 and C29 (Fig. S1). Based on this, we hypothesized that 3‐MeC29 could act as a maternal marker in two different contexts, and play a role both as a sterility‐inducing queen signal as well as a queen egg‐marking pheromone used to signal maternity and stop workers from accidentally policing the queen’s eggs. Policing bioassays To test the bioactivity of the putative egg‐marking pheromones 3‐MeC29 and 3‐MeC27 we treated worker‐laid eggs with an acetone solution of synthetic versions of the two compounds, either alone or in a mix of both, to make them more queen‐like (Fig. 1B) and tested if this reduced the rate at which these eggs were policed compared to a solvent‐only sham treated control. This was done by pipetting 5 µl of a 0.15 µg/µL (for 3‐MeC29) or 0.35 µg/µL (for 3‐MeC27) acetone solution of either compound, or a mix of both, onto each worker‐laid egg (Fig. 1B). These concentrations were chosen to optimally mimic the concentration of these compounds present naturally on queen‐laid eggs. Fig. 2A and Tables S1A and S1B show that this treatment was indeed effective, as the application of 3‐MeC27 and 3‐MeC29, or a mix of both, onto worker‐laid eggs resulted in relative peak areas of 3‐MeC27 (Table S1 A) and 3‐MeC29 (Table S1 B) that were significantly higher than in the control eggs, and non‐significantly different from the levels observed in queen‐laid eggs (GLMM with colony as random factor). Subsequently, the acetone was allowed to evaporate for 10 min and the test combs filled with worker‐laid eggs exposed to our different queen pheromone treatments were placed on a wire mesh support inside a discriminator colony to check egg policing rates (Fig. 1B). A comb containing brood and the mother queen was placed on second mesh above the test comb, after which the workers were added (ca. 200‐300 individuals). The wire mesh acted as a queen excluder, as it had a size that enabled the workers, but not the queen, to pass through. In this way, the queen was confined to the upper compartment and prevented from depositing new eggs in the lower test comb during the experiment. The two combs were placed on strips of cardboard to provide an air space between the wire mesh and to allow the workers free access to all the cells. The nest box was connected to a foraging box in which food and water (mealworms, Apifonda sugar paste and a moist cotton ball) were provided ad libitum in falcon tubes. At the start of each experiment, a cell map was drawn of the test comb in which the location of all the worker‐laid eggs inside the cells as well as the treatments they were exposed to were indicated. Then, 24 hours later, we recorded the number of eggs that were policed by the workers in the different treatments (cf. [S3]) and also counted the total number of workers that were present inside the discriminator colony (average number in the end of the experiment: 271, SD = 115, N=6 replicates). Combs with fresh worker‐laid eggs were obtained from queenless colonies containing ca. 200‐300 workers each, kept in

the same type of nest box but provided with just a single empty comb for egg deposition. Ca. 10 days after queen removal, these workers started to lay eggs [S3], thereby enabling us to collect nearly full combs of worker‐laid eggs a couple of days later (i.e. after ca 14 days). Colonies were

placed in a temperature controlled climate room at 30 C. The total dimension of the nest plus foraging box was 36 x 15 x 15 cm (width x depth x height). The box was covered with a perspex lid and provided with a ventilation mesh, and the nest box was kept in the dark using a black plastic cover. All experiments were replicated six times, using six common wasp colonies collected in the vicinity of Leuven (Belgium) in July and August 2014, which were split in two parts, to serve as a source of worker‐laid eggs (for the part without a queen) or as a discriminator colony (for the part with the mother queen). Synthesis of 3‐MeC29 and 3‐MeC27 was performed as described in [S2].

Egg policing rates were compared across the different treatments using a binomial mixed model with logit link function using lme4 v. 1.1‐8 in R v. 3.1.1. In this model, discriminator colony and treatment were coded as random and fixed factors, respectively, whereas the number of cells in each test comb and the total number of workers present in the discriminator colony were included as continuous covariates. Statistical significance of the difference relative to the solvent control was assessed using Wald z tests. Overdispersion was checked for, but found not to be significant. Final results were expressed in terms of the estimated mean percentage of eggs eaten in the different treatments and control, and were calculated using the effects package, together with asymptotic 95% confidence limits. Supplemental references S1. Bonckaert, W., Drijfhout, F.P., d'Ettorre, P., Billen, J., and Wenseleers, T. (2012). Hydrocarbon

signatures of egg maternity, caste membership and reproductive status in the common wasp. J. Chem. Ecol. 38, 42‐51.

S2. Van Oystaeyen, A., Oliveira, R.C., Holman, L., Van Zweden, J.S., Romero, C., Oi, C.A., d'Ettorre, P., Khalesi, M., Billen, J., Wäckers, F., et al. (2014). Conserved class of queen pheromones stops social insect workers from reproducing. Science 287, 287‐290.

S3. Foster, K.R., and Ratnieks, F.L. (2001). Convergent evolution of worker policing by egg eating in the honeybee and common wasp. Proc. R. Soc. Lond. B 268, 169‐174.

dual effect of wasp queen pheromone in regulating insect sociality · 2015-05-14 · current...

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