ENTOMOLOGIST'S MONTHLY MAGAZINE 27

TAXONOMX DISTRIBI/TION AND NESTING BIOLOGY OFWSPA AFFINIS (L.) AND WSPA MOCSARYANA DU BUYSSON

(HYM., VESPTNAE)

BY MICHAEL E. ARCHER

Vespa ffinis (Linnaeus, L764) and 14 mocsaryana du Buysson, L905are hornets of the mainland and islands of south east Asia. In a cladisticstudy of Vespa Archer (1994) found that these two species formed aholophyletic group (Mayr & Ashlock, 1991). This paper reports on thetaxonomic, distributional and nesting biology of V. ffinis and V.mocsaryana, reviews the colour subspecies of 14 affinis, and proposesinformal names for the colour subspecies of 14 ffinis.

'TAXONOMY AND DISTRIBUTION

V. affinis and 14 mocsaryana are united by the female derived characterstate of an elongated first gastral tergum which is half as long or longerthan wide. This character state also has been evolved in parallel by the 14

tropica group (Archer, t991), from which it can be separated by thesemicircular shape of the lateral apical margin of the clypeus (fig. 1A). Inthe V. tropica group the lateral apical margin of the clypeus has atriangular shape.

PNC

Fig. 1. - Vespa ffinislmocsaryarut. A, apical margin of female's clypeus; B, ventralview of the sixth (6) and seventh (7) gastral sterna of the male; C, lateral view of pronotum(PNC = pronotal carina, PTC = pretegular carina).

The males of 14 ffinis and 14 mocsaryana can be separated from theother species of Vespa by the following combination of characters:L, apical margin of the seventh gastral sternum with one emargination(fig. 1B); 2, apical margin of the sixth sternum with a deep emargination,semicircular in shape (fig. 1B); 3, pretegular carina complete (fig. 1C);4, pronotal carina much interrupted by the pronotal pit (fig. 1C).

V. ffinis and 14 mocsaryana may be separated from each other asfollows:

27th March, 1997 Vol. 133 (1997)

28 ENTOMOLOGIST'S MONTHLY MAGAZINE

1. Mesoscutal punctures small and clearly separted from each other, the distances betweenpunctures greater than the puncture diameter. Shaft of the aedeagus not bulbous(fig. 28) V. mocsaryana du Buysson

- Mesoscutal punctures large and often touching each other, the distances between

i1*::'::'::i'::: i:1":::: 1':TT: ::::: :: :i: ::i":::: ::1o"" (o'

i!)m,* rf j

Fig. 2. - Dorsal view of the male genitalia (SA = shaft of aedeagus): A, Vespa affinis;B, Vespa mocsaryana.

Taxonomy and distribution of 14 ffinisThe taxonomy of V. ffinis has been largely determined by Bequaert

(1936) and van der Vecht (1957). Bequaert (1936) showed that duBuysson (1904, 1905) confused two species under V. cincta Fabricius,1775, viz.: V. tropica (Linnaeus, 1758) and 14 ffinis. Bequaert (1936)included within V. ffinis the following colour varieties: nominate ffinis,indosinensrs Perez, I9"l.O, alduini Gu6rin, 1831, and picea du Buysson,1905. Bequaert also described the new colour varieties hainanensls andcontinentalis. Van der Vecht (1957) added the new subspecies:nigriventris, rufonigrans, moluccana, archboldi and alticincta. V. affinis,as understood through its eleven subspecies, would seem to be one speciesand not several species as was found for V. tropica, a similarly widespreadhomet (Archer, 1991).

The distribution of V. affinis (fig. 3,A.) is as follows: Ceylon, India(Kerala, Tamil Nardu, Karnataka, Maharashtra, Bihar, West Bengal),Sikkim, Assam, China (Hubei, Shanghai, Fujian, Guangdong, Hunan,Hainan Island), Hong Kong, Taiwan, Japan (Ryukyu Islands), Burma,Thailand, Laos, Vietnam, Sumatra, west Java, Philippines (Palawan),Papua New Guinea including New Britain and New Ireland, Indonesia(Irian Jaya, Moluccas, Sulawesi, Kalimanton), and Malaysia (Peninsular,Sabah, Sarawak).

ENTOMOLOGIST'S MONTHLY MAGAZINE 29

0

(/.

Fig. 3. - Distribution maps of; A, Vespa affinis;8, Vespa mocsaryarul

The colour forms of V. ffinis can be separated by variation in thecolour of the vertex, clypeus, and the first, second and third gastral terga(Table 1,). Specimens showing intermediate colours between several of the

TABLE 1. - THE COLOUR VARIATIONS OF THE SUBSPECIES OF VESPAAFFINIS.

ColourForm

Vertex Clypeus FirstGastralTergum

Second ThirdGastral GastralTergum Tergum

affinis

continentalis

lninanensis

indosinensis

rufonigrans

nigriventris

alduini

moluccana

archboldi

picea

alticincta

Red todark redRed to

dark redRed to

dark redRed &black

Dark red

Black

Dark red& black

Red

Red

Black

Red

Red

Red

Red &blackBlack

Red &blackBlack

Black

Black

Red

Black

Black

Orange& red

Dark redto blackOrange& red

Orange& red

Orange& red

Orange& blackBlack

Dark red& blackOrange& red

Dark red& blackRed &

dark red

Orange

Orange

Orange& blackOrange& blackOrange

Dark red& blackRed &

dark red

Black

Black

Black

BIack

Black

Black

BIack

Orange Black& orange

Orange Black

Orange Black

Orange Black

'\\ ^(/ (

\IJffi,ar \--\_lor.a, e,

30 ENTOMOLOGIST,S MONTHLY MAGAZINE

colour subspecies of tr4 ffinis have been found. Intermediates betweenV.

ffinis ffinis and 14 ffinis continentalis in the Bombay region, betweenV. affinis ffinis and V. ffinis indosinensrs in northern Burma, andbetween V. ffinis rufonigrans and V. ffinis archboldi in western NewGuinea have been seen. V. ffinis moluccana would seem to be an inter-mediate colour form between V. ffinis rufonigrans and V. ffinis alduini.The colour subspecies V ffinis archboldi falls within the variablenominate colour subspecies V. ffinis ffinis. Because of these colourforms it is suggested the subspecies nomenclature be replaced by"informal names" (Table 2) following the arguments of Wilson & Brown(1es3).

TABLE 2. - THE INFORMALAND FORMAL (SUBSPECIES) COLOUR FORMNAMES FOR YESPA AFFINIS.

Informal Name Subspecies

India & ChinaSouthern IndiaHainan IslandIndo-Malaya & SumatraBorneo to western New GuineaPalawanBuru IslandCeram & Aru IslancisNorthern New GuineaSouthern New GuineaNew Britain

affiniscontinentalishainanensisindosinensisrufonigransnigriventrisalduinimoluccannarchboldipiceaalticincta

Taxonomy and distribution of 14 mocsaryanaThe distribution of. V. mocsaryana (fig.38) is as follows: Sikkim,

Assam, China (Sichuan, Anhui, Fujian), Thailand, Laos, north Vietnam,Peninsular Malaysia, Burma (Tenasserim), Sumatra. The Chinese recordsfrom Sichuan and Anhui are from an unpublished map of van der Vecht(pers. comm., 1981).

No colour subspecies of 14 mocsaryana have been proposed, but van

der Vecht (1959) noted an increase in the presence of yellow on the gaster

on specimens from Tenasserim and Peninsular Malaysia. On these

specimens, tergum one has a complete apical yellow band and tergUm twoan interrupted yellow band with both bands widened laterally. Sterna twoto four ea-ch has a yellow band, but on sterna three and four the yellowband is more-or-less reduced in the middle. Sternum five has a trace of ayellow band. I have found a similar yellow development on a specimen

irom north Vietnam, with a yellow band on terga one to three and sterna

two to four, although this yellow did not exist in the middle on tergum twoand the sterna. The yellow apical bands became more extensive on aspecimen from Laoi: on the gastral terga the apical yellow bands

graduatly become more extensive from terga one to six so that the sixth

iergum is entirely yellow. Similarly development of the-yellow occurs on

the sterna so that the sixth sternum is nearly entirely yellow.

ENTOMOLOGIST'S MONTHLY MAGAZINE 3INESTING BIOLOGY OF V. MOCSARYANA

Very little is known of the nesting biology of V. mocsaryana other thanthat it is restricted to mountain forests (Matsuura, 1990).

NESTING BIOLOGY OF V. AFFINIS

The nesting biology of V affinis has been studied in the lowland{opics: Silgapore (1'20N) (Chan, 1972, Martin, 1993, pers. comm.),Bangkok, Thailand (13"45N) (seeley & Seeley, 1981, Gnmukayakul,I287),--Sumatra (0"555) (Matsuura, L983, 1990), New Guinea 15"ZlS1(spradbern 1986) and the Philippines (9"25N) (starr & Jacobson,'1990)

9_._d subtropics: Calcutta (22'35N) (Chopra, 1,925), Taiwan (24'N)

(Matsuura, L973, Yamane, 1977, Kuo, 1984) and the Ryukyu Iilandgsouthern Jgpan (26"30N) (Martin, r99za, L99zb, r99ic, 1992, pers.comm., 1993,1993, pers. comm.).

This paper will investigate the nesting biology differences betweentropical and sub-tropical populations of V. affinis.

Nesting SitesTropical and subtropical nesting sites are usually aerial: on trees and

shrubs, but sometimes on the outsides of buildings or in attics. In southemJapan from r34 nest sites found, r23 (gl.s%) were attached to acylindrical structure such as a twig or plant stem. The remaining elevennests were attached to the mid-ribs of leaves. Nests attached to stems lessthan 2.5 mm in diameter usually failed, either because the increasingweight of the nest bent the stem until the nest reached the ground, or th6nest became detached in bad weather during the spring. Most nests werewithin 1 m of the ground although some were at a height of lz.4 m. Nestsless than 12 cm above the ground failed to rear sexuals as nest expansionstopped when the nest reached the soil surface. The workers did nbt seemable to excavate a cavity in the soil. High level nests were usually in densebushes or well sheltered from the monsoon rains and strong winds.Exposed nests were easily destroyed by such severe weather.

In Sumatra,2r4 nests were all aerial with 197 (9z.lvo) in open sites (6gon shrubs , r22 on trees, 7 on buildings) and L7 in the enclosed space'ofattics. The height above the ground ranged from 0.5 m to 30 m.

In Taiwan, Kuo recorded nests on trees, shrubs, bamboo, under eaves,and in roof spaces of houses.

In New Guinea, nests were recorded most frequently on trees but alsoon the roofs of houses, under eaves of buildings, attached to vine-coveredwalls, and inside sheds and outbuildings.

In the Philippines, 20 nests were recorded on trees and shrubs and from1 m to 16 m above the ground but usually 2-3 m above the ground. Nestswere attached to a single branch, except in dense vegetation when severalbranches passed through the nests. Nests attached to slender, flexiblevegetation swayed on windy days.

In Singapore, chan recorded 316 nests, mostly found on trees and

32 ENToMoLoGIST's MoNTHLY MAGAZINE

shrubs (69.9Vo) but also on buildings, including 1o_ofs and vegetated

fences. Nests were found from ground level up to 26 m but most were

below 17 m.

Colonial life history characteristics - SubtropicsIn southern Japan during the autumn newly-emerged quee-ns remain in

the colony for a6out LTI4 days during which.time their body weight

increases ty about 4OVo due mainly to fat deposition. The males remain inthe colony for 8-LL days with a 38% increase of body weight. DuringNovembei and December the sexuals leave the colonies, and after matingthe males die and the queens enter over-wintering sites, e.g- lmong 9ty'dead wood piles. Queeni remain in the over-wintering sites for four to five

months living off their fat stores. They emerge during mid-April and by

the end otafrit nest initiation by a single queen starts. The queen colony

lasts for abolt 34 days with the adult workers appearing from the begin-

ning of June. Large iell building starts from the end of_August, with the

firsi adult males -and queens emerging at the end of September. Adult

sexual production t"a"h"s a peak during the first half of November. The

colonyLnds during Decembel. The length of colonial life is from April to

December, eight months or about 240 days.In Taiwan and Calcutta the length of colonial life is also about eight

months.

Colonial life history characteristics - TropicsThe duration oi tropical colonies is longer by about_ two- to three

months, but colonies are still annual. In Singapore, Martin found colonies

in all months of the year, but peak activity during September.- In New

Guinea, queens initiited colonies from AugUst until November, and

colonies *"t" found producing workers from October until December,

although some queen iolonies *ere found up to December. Production ofthe sexuals was delayed until the rainy season started in December.

Colonies reached p"uk development during the following_Jule and July.

In Sumatra, Matsuura (in Ross-& Matthews, I99l) found, during the rainy

season (mid-Novembei), that of 35 colonies, eleven we-re guegl colonies,

fS tnoird only adult-worker production, and nine had adult sexuals

emerging.

Queen usurpation in the subtropicsIn southern Japan evidence of intra-specific usurpation between queens

was found at L6 out of 55 colonies. Usurpation evidence was the presence

of dead queens under the colonies, and in one caseactual fighting between

the queens was observed. Fourteen of the usurped colonies failed to rear

,r*rrilt, but two developed normally. Usurpation occurred during June

when the worker population was smail, indeed at the time of, or just after,

the emerg"n". of tht first workers. From a sample of seven, the resident

qrrc.t wJn the fight on four occasions and the invader on three occasions.

ENTOMOLOGIST'S MONTHLY MAGAZINE 33

Larger queens were not more likely to win the fight and the presence ofworkers did not always help the resident queen in winning the fight.

In Taiwan, Kuo observed queen usurpation fights. In one fight in earlyJune when a few workers were present both the resident and invaderqueens died from their injuries so the colony was orphaned. Later anotherinvader queen was rejected by the workers. The colony expandednormally but as worker-laid eggs are unfertilized, so maturing as males,the colony ended in July.

Polygynous colonies in the tropicsIn the tropics, a colony usually has more than one egg-laying queen

(polygyny). Polygynous colonies may be founded by several queens(pleometrosis and primary polygyny). If one queen initiates a colony(haplometrosis) but is later joined by other egg-laying queens, thepolygyny is secondary.

In Sumatra, L30 colonies were collected from 1981 until 1984. Of 52queen colonies 4l (78.8Vo) were polygynous with a mean of 3.9 queens(range 1-10) per colony. In eight of these colonies from 198L, all thequeens were inseminated but only one queen (occasionally two) had fullydeveloped ovaries and was laying eggs. In42 colonies with adult workers,38 (90.5Vo) were polygynous with a mean of.4.4 queens (range I-12) percolony. Of 36 colonies with adult sexuals, 33 (9I.7Vo) were polygynous,with a mean of 4.6 queens (range L-I4) per colony. In the colonies from1981" with adult sexuals, all the queens were inseminated and with fullydeveloped ovaries and able to lay eggs. No marked dominance behaviourwas observed between the queens. It was not known if a colony wasinitiated by u single queen and then quickly joined by other queens orwhether pleometrosis was shown. In two queen colonies, a larger workerwith worn wings was present which could not have been reared in thecurrent colony. In these cases the worker had initiated the colony with oneor several queens.

In New Guinea, of seven queen colonies, five were polygynous with a

mean of 3.1 queens (range L*6) per colony. Of eight colonies with adultworkers, seven were polygynous with a mean of 4.5 queens (range 1-15)per colony. Of four colonies with adult sexuals, three were polygynouswith a mean of 3.0 queens (range 1-5) per colony. Thus 15 (78.9Vo) of theL9 colonies were polygynous. Except for the colony with 15 queens, allthe queens were inseminated, with fully developed ovaries, and capable oflaying eggs. In the colony with 15 queens, l3 were inseminated, of whicheleven had fully developed ovaries. It was considered that these colonieshad been initiated by several queens (pleometrosis).

In Singapore, Martin found two colonies from a sample of five thatwere polygynous.

Queen colonies - SubtropicsIn southern Japan, Martin observed 27 queen colonies, eight for more

34 ENTOMOLOGIST,S MONTHLY MAGAZINE

than one week and one for 27 days, until the emergence of the first worker.The queen nest consisted of a single comb attached to the vegetation by a

thick petiole coated in a shiny secretion. The secretion is produced by thesixth and seventh gastral sternal glands and acts as a barrier to ants. Thecomb was surrounded by an envelope which was bell-shaped with an

elongated entrance or vestibule. The vestibule varied in length fromL-5 cm (mean 3.1 cm, n = 15).The vestibule delayed the entrance of smallants onto the comb and probably prevented large ants from entering thenest. The vestibule is removed when the first workers emerge, when theworkers readily deter ants from getting onto the combs.

In southern Japan, the egg stage lasted for 6.8 (range 6.5:7.5) days, thelarval stage eighf to more than22 days but mostly for L2-t6 days, and thesealed brood stage for I7.3 (range 16-18) days). The developmentalperiod is therefore usually 3HO days. During the first ten days, the cellbuitding rate was I.2-1,.5 cells per day but later this rate dropped to0.75-0.85 cells per day. During the early stages of the queen colony, thequeen lays L-2 eggs per day. On the emergence of the first worker thequeen nest typically consisted of 28 (four egg, 13 larval, eight sealed

brood, and three empty) cells. On emergence the workers remain in thenest for two days before starting to forage.

In Taiwan, Kuo found queen colonies varied from ten to 30 cells witha development period of 4U41. days (egg 6 days, larva 15 days, sealed

brood L9-2O days).

Queen colonies - TropicsIn New Guinea, Spradbery found that the cell building rate in one

monogynous colony (0.3 cell per day) was lower than one polygynouscolony (0.7 cell per day). Generally there was a significant positive linearrelationship between the number of foundress queens and the number ofcells in a colony.

In Sumatra, Matsuura recorded polygynous colonies with 2249 cells.In Bangkok, Tonmukayakul recorded a worker developmental period

of 38 days (egg and larval stages L9 days, sealed brood stage 19 days) ina colony in which the first workers had recently emerged.

Nest development and size - SubtropicsIn southern Japan, Martin divided his sample of nests into two

subsamples. The first subsample (51 colonies) consisted of large nests

reaching mean mature size of about 4000 cells in the latter part of October.The second subsample (55 colonies) consisted of small nests reaching a

mean mature size of about 2500 cells in the latter part of November. Bothlarge and small colonies were successful in rearing sexuals. Nest growthstarted with a period of slow growth reaching about 500 cells in largecolonies by early August, and in small colonies by early September. Bothlarge and small colonies then showed rapid growth to maximum size, bymid-October for large colonies and by the latter part of November for

ENTOMOLOGIST'S MONTHLY MAGAZINE 35

small colonies. Cell building rates were estimated to start at about0.45 cells per worker per day in large colonies, and about 0.23 cells perworker per day in small colonies. Cell building rates per worker per daygradually decreased during the development of the colony.

Normally, a nest consisted of from six to ten combs althoughsometimes more combs were present. The small cells occupied the uppercombs and the large cells the lower combs. Each small cell could be usedto rear more than one individual. Matsuura & Yamane (1990) recordedthat mature nests in Japan usually had four to five combs and 800-1500cells.

In Taiwan, Matsuura recorded one large nest of 6178 cells.

Nest development and size - TropicsMature nest size has been recorded as follows: in Sumatra 12,058 cells

(9 combs), 9877 cells (8 combs); in New Guinea 9732 cells (5 combs),12,580 cells (8 combs), and 45,065 cells (L2 combs); Martin in SingaporeL0,927 cells; in the Philippines 12,000 cells (9 combs); and Seeley &Seeley in Thailand 9600 cells (6 combs). These eight nests give a mean"1.5,230 cells (or 10,968 cells if the very large nest of 45,065 cells isexcluded) on 8 combs.

Immature brood - SubtropicsIn southern Japan, the faster development of the large colonies was

reflected in the characteristics of the immature brood. The egg laying rateper day peaked at about 55 eggs during late September in large coloniesand at about 30 eggs during early October in small colonies. The numberof eggs peaked at about 430 during late September, and larvae peaked atabout 930 during early October in large colonies. In small colonies, thenumber of eggs peaked about 240 during early October and the number oflarvae at about 460 during mid-October.

In large colonies worker sealed brood peaked at about 450 during mid-September, male sealed brood at about 430 during early October andq.reen sealed brood at about 210 during late October. In

-small colonies

worker sealed brood peaked at about 130 at the end of September, malesealed brood at about 22O durine early November, and queen sealed broodat about 120 during mid-November. The lowest larval/worker ratio wasbetween two to four larvae per worker for both small and large colonies.The ovarian index (which is a measure of egg laying rate) was higher inqueens from larger colonies than in queens from smaller colonies.Towards the end of the colony development workers were often seenremoving withered or neglected larvae from the nest.

In southern Japan, the worker developmental period was 35-39 days(egg stage 7 days, larval stage 12-16 days, sealed brood stage 16 days).

Immature brood - TropicsIn New Guinea, the number of immature stages for each colony rearing

36 ENToMoLoGIST's MoNTHLY MAGAZINE

sexuals was higher than in the sub-tropics: eggs from 77VI709, larvaefrom 205f3103, and sealed brood from I57V3096. The larval/workerratio was 0.8-1.1 larvae per worker.

Martin, in Singapore, showed that in two polygynous colonies the

number of eggs present in a colony was less than the number predictedfrom an examination of the ovarian index of the queens. However the

number of eggs present in a colony was in excess of the predicted layingpower of a single queen so several queens must have contributed to the

"ggr present. In one monogynous colony the number and predicted

number of eggs were very similar.

Workers - SubtropicsIn southern Japan, the number of workers gradually increased to about

80 during early August. Afterwards there was an accelerating increase toabout 740 workers by early October in large colonies, and about 300workers just before mid-October in small colonies. The acceleration wasfollowedby a rapid decline in worker numbers, which was more abrupt inlarge colonies. It was estimated that the total number of workers reared

wai about t20O in large colonies, and 540 in small colonies. The workerlength of life was usuaily Iar-IS days but varied from 7-28 days.

In Taiwan, Kuo recorded a more rapid increase compared with southernJapan: to 7f80 workers by early July, 20f300 workers by early August,with a peak of 60O-L000 workers by early September. Worker length o!life varied from I0-l25 days. Also from Taiwan, Matsuura recorded 1095

workers from a large colony with an estimated 2I0O workers having been

reared.

Workers - TropicsFrom New Guinea much larger worker populations in a colony were

found, from about 2700 to over 5000.

Queens and MalesLittte information is known about the development of queens and

males and then only from the subtropics. However adult queens and

workers can be cleaily separated by a size difference in the tropics and

subtropics.In iouthern Japan, in large colonies adult males peaked at about 300

after mid-Octobei and adult (ueens at about 250 during mid-November. Insmall colonies adult males peaked at about 200 and adult queens at about

85 during mid-November.InTaiivan, Yamane found higher peaks with 500 or more males and 400

or more queens.In southern Japan, Martin estimated the

males and 540 queens and small coloniesqueens.

large colonies produced 1440produced 540 males and L20

ENTOMOLOGIST'S MONTHLY MAGAZINE 37

DISCUSSION

Subtropical colonies have a shorter life cycle (say 240 days) and reacha smaller mature nest size (usually up to 4000 cells) compared with thelonger life cycle (say 320 days) and larger mature nest size (in excess ofL0,000 cells) of tropical colonies. The development of subtropicalcolonies is synchronised by the need for the queens to overwinter. Tropicalcolonies, without this need, are not synchronised, although the occurrenceof a wet season can lead to the synchronisation of rearing sexual brood.Subtropical colonies show haplometrosis and monogyny, iuith the queensfighting between themselves for nest ownership (usurpation). Tropicalcolonies are usually polygynous (either showing haplometrosis withsecondary polygyny or pleometrosis with primary polygyny), andusurpation has not been recorded.

The larger size of tropical colonies must ultimately be linked to theavailability of food for a longer time each year due to more favourableweather conditions, so that the life cycle can be extended. The larger sizeof tropical colonies is not a consequence of a reduced length of workerdevelopmental period, which is very similar in tropical and subtropicalcolonies. These similar developmental lengths of workers are probablydue to the good colonial temperature regulation. With such favourableweather conditions why do tropical colonies remain annual colonies,rather than become perennial, as is shown by some of the paravespulidwasp species which have expanded their ranges into warmer climates(Ross & Matthews, 1991)? If Vespa evolved from a temperate, over-wintering, species thenVespa could be carrying a phylogenetic constraintof annual development. The queens of the tropical species, V.philippinensis de Saussure, L854 still build up fat bodies after emergence(Starr, L987), which in temperate species are used as an overwinteringfood store. These fat stores could be a relic from an evolutionary past, orthe food stores could have acquired an unknown new function. Theretention of an annual cycle also could be used to inhibit the build up ofpathogenic or parasitic attack.

The larger size of tropical colonies could be a consequence of polygynywith several egg layers. Previously it was recorded that polygynouscolonies show a quicker development of the queen colony. However, laterduring the worker rearing phase, cell building rate limits egg laying rate,and, compared with subtropical colonies, sexual production is delayed.When sexual production begins the larva worker ratio is more favourablein tropical colonies and the cell building rate is probably not limiting, sothe sexual production can be greatly increased.

Polygyny could also have evolved as a defence of the queen and earlyworker colonies against parasites and predators such as birds, ants andother hornet species since polygynous colonies are left unattended forshorter periods of time: (I7Vo) compared with monogynous colonies(50Vo) (Martin, 1993, pers. comm.). Such colonies seem to have gooddefences against ants, and Martin in Singapore reported that Dr N.S. Nling

38 ENTOMOLOGIST,S MONTHLY MAGAZINE

observed that the queens of a queen colony successfully repelled an attackby a single worker of V tropica.

Polygyny could also have evolved as a defence against queenusurpation and a more rapid rebuilding of the nest after its destruction ordamage. Certainly usurpation has not been recorded in polygynouscolonies.

ACKNOWLEDGEMENTS

I am grateful to Dr S. Martin and his wife Yuko for translating theChinese paper by Kuo.

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October 26th, L994.