Baracchi, David

Meucci, Fabio

Pradella, Duccio

Turillazzi, Stefano

English

Sydney eScholarship

Nest architecture and colony composition of a Malaysian sphecid waspTurillazzi1 S., Pradella1 D., Meucci1 F. and Baracchi1,2 D.1 Dipartimento di Biologia, Università di Firenze, Firenze, Italy2 School of Biological and Chemical Sciences, Queen Mary University, London, U.K.INTRODUCTIONEusociality evolved various times independently in thesuperfamily Apoidea (Michener 1969) including among theapoid wasps of the family Crabronidae. The majority of themore than 8000 described crabronid species arecharacterized by solitary nesting habits but some membersof one clade in the subfamily Pemphredoninae, theSpilomenina, have evolved relatively complex socialbehaviour (Matthews 1991). Division of labour and altruisticbehaviours have only been ascertained in Microstigmuscomes (Matthews 1968; Ross and Matthews 1989a and b).The present poster deals with an interesting, yetundescribed, species of Spilomena found in the CentralMountain Range of Peninsular Malaysia. This speciesforms multi-female colonies and builds nests characterizedby a peculiar architecture. We report preliminary data oncolony composition and other features of the biology,including a description of the nest.MATERIALS AND METHODSColonies and abandoned nests of Spilomena sp. were found at Bukit Fraser (1500 m; 03° 42.774 N -101° 46.319 E) a mountain resort at the higher elevations of the Central Range of PeninsularMalaysia, between the states of Pahang and Selangor. Colonies were collected at various times. Foreach colony all adults present were captured and the nest cells were removed from the substrate.Eggs, larvae and pupae were recorded for each nest.Adult females were dissected to determine ovarian development, classified from 0 to 3 according totheir relative size. We photographed the head of each adult present in each colony and used the opensource software ImageJ to measure the maximum width of the head (reported in pixels).Brief ethological observations were performed on some colonies, and some simple experiments wereconducted in an attempt to ascertain the defensive reactions of the adults against ants.Head of female (up) and male ofSpilomena sp.Nest architecture. The nest of Spilomen a sp. has a peculiar architecture. It consists of cylindricalcells attached to a vertical plane substratum. This substratum makes nests, usually dark brown, highlyvisible to a human observer; evidently nests are well camouflaged on natural substrata as we neverfound any except those on artificial nest sites. The substratum forms part of the walls of each cell.Cells are placed, vertically, one beside the other forming clusters containing up to several cells. Eachcell is attached to the substratum and clusters of cells have been never found superimposed, so nestswhich are composed of different clusters of cells (which is quite common) have always a flatextension.CONCLUSIONSPossession of a nest has always been regarded as an important (and probablyobligatory) characteristic of eusocial insects (Hansell 1996). The “invention” of thetube connecting cells in the nest of Spilomena sp. serves as a good system for theprotection of immature brood and of the adults but, in our opinion, it also constitutesa barrier to more advanced sociality in this species by imposing a limit to morecomplex interactions and altruistic behaviours. Indeed, only very limited interactionsamong these wasps has been observed outside of the nest or in the areasurrounding the nest clusters. That nest architecture can stongly influence socialwasp evolution, is generally accepted. More detailed and wider studies on thisspecies and other insects at the border of eusociality will be needed to furtherconfirm this hypothesis.We thank Prof. R. Matthews , Univ of Goergia U.S.A.,for his help and advicesNestFemalesMales Cells Larvae PupaeCollectedYear1 5 4 17 0 3 night 20042 6 1 23 3 6 night 20043 1 0 3 0 0 night 20044 3 0 8 1 1 night 20045 3 1 6 0 5 night 20046 8 2 12 3 3 night 20047 8 0 20 4 2 night 20048 8 0 26 2 2 night 20049 6 1 14 4 2 night 200410 1 0 3 1 0 night 200413 4 0 7 2 2 night 200414 8 2 21 10 1 night 200416 4 2 7 2 5 night 200417 4 3 23 3 7 night 200718 11 4 35 5 1 night 200719 5 0 13 1 3 night 200720 3 1 23 3 3 night 200721 7 0 39 5 4 night 200722 6 0 15 3 0 night 200723 6 4 35 6 11 night 200724 8 1 32 2 7 night 200725 5 0 19 0 11 day 200726 3 0 14 2 4 day 200727 3 0 30 4 11 day 200728 7 1 23 3 3 day 200729 3 0 7 2 3 day 200730 6 0 14 4 5 day 200731 1 0 14 0 4 day 200432 4 0 14 0 0 day 200433 2 1 15 2 2 day 200434 2 1 3 0 0 day 200435 2 0 5 0 0 day 2004Number of adults. The total number ofadults found in nests collected at nightvaried from 1 to 15 (N = 21 colonies)(females 1-11, males 0-4.). For othercolonies (N = 11) we collected adults atdifferent times of the day (females 1-7,males 0-1). Females present in the nestscollected at night were more numerousthan in those collected during the day (x =5.47 vs 3.45, Mann Whitney U = 59.5, P =0.025). However there was no differencein the total number of individuals (orfemales) collected on nests at night orday if this was normalized for the cellnumber of each nest.Ovarian development of the females. We dissected a total of 124 females from 25 colonies. Twenty-nine ofthem had very small ovaries (ovarian development = 0), 37 females had ovarian development = 1, 28 females= 2, and 30 females = 3 (MOIF).In each colony the number of females with the maximum ovarian index (= 3) did not increase significantly withthe total number of females present in the colony (Spearman ρ = 0.3019, P = 0.1, N = 25). In 8 colonies (outof 20) with three or more females we found only one MOIF. The presence of only one female with fullydeveloped ovaries was particularly evident in three colonies with 8 females each.The number of MOIF in a colony was positively correlated also with the total number of larvae and pupaefound in the nest (N = 18, Spearman ρ = 0.6558, P = 0.0042).Body size and ovarian development. In the 8 colonies, in which we measured the maximum head width ofthe 48 females present, we did not find any significant relationship between this parameter and the respectiveovarian development (Spearman ρ = 0.16, P = 0.28, N = 48), even excluding the females with an ovarianindex of 0 (i.e. assuming these to be very young individuals) (Spearman ρ = 0.267, P = 0.18, N = 8).Behavioural observations. We performed only limited ethological observations owing to the difficulty ofindividually marking each wasp due to their very small size. In two nests where we succeeded we observedparticular females patrolling and defending the nest from individuals coming from neighboring colonies (afemale from nest 6, for example, emerged from the tunnel of a cell group every now and then patrolling theentire nest and then dipping inside the tunnel again). In nest 7 two marked females shared the periodicpatrolling of the left and right part of the nest.Daily activity. Over two consecutive days we video recorded five adjoining nests, from 09.00 to 19.00 h.From this video we determined diurnal activity (with external activity condensed in one morning and oneafternoon peak) and also observed that individuals can shift from one nest to the other.The cell opening isalways situated at thehigher part and is coveredby a hood-like roof whichprotects the entrancefrom one side when thecell is isolated. Whencontiguous cells form acluster, the roofs of eachcell merge to form acommon tube connectingthe entrances of all thecells, becoming also ashelter for the adultindividuals of the colony.Nests in some cases canbe covered by algae andthey can contain up to 60cells, even though activenests were found onlywithin the range of 3-39cells (see Table). Activenests can be quite closeto each other in somecases.Construction material isformed by (sometimesglossy) pieces of vegetaland mineral origin, partsof insects, fungal hyphaekept together by silkthreads secreted by thewasps’ abdominal glands.Cells are clearly re-usedand nests can persist fora long time as shown byvarious abandoned nestsand by the coat of byalgae covering someactive nests.RESULTSNest sites. Nests of Spilomena sp. were mainlyfound on the vertical walls of buildings and, inparticular, along the grooves of white pillars ofcement recreational gazeboes scattered along theroads of the resort.Nest cluster on the walls of a forest gazeboA nest covered with algae with a female on it. Thelength of the wasp is about half a centimeterA nest formed by rows of cells connected by anupper tube

Nest architecture and colony composition of a Malaysian sphecid wasp

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Nest architecture and colony composition of a Malaysian sphecid wasp

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