The occurrence of the bedbugs Cimex hemipterus and Cimex lectularius in northern Natal and KwaZulu, South Africa

TR,+NSACXONSOF THE ROYAL.SOCIETYOF TROPICALMEDICINE AND HYGIENE (1987) 81, 431-433

431

The occurrence of the bedbugs Cimex hemipterus and Cimex lectularius in northern Natal and KwaZulu, South Africa K. NEWBERRY, E. J. JANSEN AND G. R. THIBAUD National Institute for Tropical Diseases, Private Bag X508, E&owe 3815, Republic of South Afica

Abstract

Two species of anthropophilic bedbugs, Cimex bctulariw and C. hemipter+ infest dwellings in KwaZulu, the known range of the latter extending to 28”15’S. C. hemiptencs1sthe more commop speciesin KwaZulu north of 27”15’. The pattern of distribution of C. hemiperus in South Africa 1s consistent with the species requiring a tropical climate, being a more recent invader than C. Zedarius, and being able to thrive sympatrically with the latter species. Introduction MELLANBY (1935) showed that South Africa is part

of the range of Cimex lecnrlarius, the common bedbug, but not of C. hemiprerus, the tropical bedbug. USINGER (1966) similarly recorded C. lectulatius as widespread in South Africa, but also showed C. liemipterus on his map somewhere in the Natal/ KwaZulu area, the details of the location not being given. Recent collections in the northern Transvaal (JuPP~~ al., 1978, 1983)found only C. lectularius. The present work was undertaken to determine the prevalence of C. hemiptems in northern Natal and KwaZulu, where bedbugs present a problem to malaria control programmes (NEWBERRY et al., 1984) and a potential health hazard concerning mfective hepatitis causedby hepatitis B virus (JUPPet al., 1983; OGSTON & LONDON, 1980). Materials and Methods All but 2 of the areas sampled lay between the Mgambique border with South Africa (26”45’S) and the NkundusiI Mfekayi regions (28”lS’S) east of 32”E (Fig. 1). The remaining 2 collections were made along the Nkwaleni valley (28”45’S, 31”30’ to 40’E) and near Lake Cubhu (28”5O’S, 31”57’E). With the exception of the sample from near Lake Cubhu, all bedbugs were found in areaswhere buildings are currently sprayed annually with DDT as part of an anti-malaria programme, and where DDT or BHC have been used for up to 40 years (DE MEILLON et al., 1977; SMITH et al., 1977). Collections of bedbugs from farm labourers’ quarters in the Nkwaleni vallev, Natal. were from brick-walled buildings. All other coll&tions w&e made in KwaZulu and, with very few exceptions, were from mud-walled huts with thatched or corrugated iron roofs. Bedbugs were found in dwellings by visual search of likely harbourages in beds, other furniture and cracks in walls, or by insecticidal knockdown. For the latter procedure, white spray sheets were spread on floors to catch bugs killed by various insecticidal treatments. Bedbugs in the third or later nymphal stage and adults were identified to species using morphological criteria (USINGER,1966), especially the width and shape of the pronotum and the degree of develo ment of the eyes. 11 huts which on visual search were Pound to contain both species of bug were resampled some months later. Results Our collections revealed a sympatric distribution of C. lectularius and C. hemipterus as far south as

NkundusilMfekayi at 28”lS’S. Within this sympatric distribution, C. lectularius and C. hemipterusseparate-

ly infested 196 (60.5%) and 96 (29.6%) huts respectively, with another 32 (9.9%) huts containing both species. From the northern limit of the study area, moving south at 15’ intervals on the map (Fig. l), C. hemipterus was found respectively in 94.3%; 70.6%;

39.4%; 89%; 8.3%; and 32.2% of infested huts. No. C. hemiptetuswere found in the Nkwaleni valley or near Lake Cubhu. Spatial variation in relative abundance of bedbug specieswas also found on a smaller scalein Nkundusti Mfekayi where an area about 20 km long was studied intensively (Fig. 2). C. hemiptetuswas found in 38.1% of infested huts along the main road (section D) and in 68.6% of infested huts in a busy area including the

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Fig. 1. Map of northern Natal and KwaZulu divided into 15’ squares. Numbers adjacent to circles denote numbers of huts in each square that were infested with C. lectularius (black circles), C. hcmiptms (white circles), and both species(black and white circles). Position of July 18°C isotherm from POYNTON(1964).

432

OCCURRENCE

0F Cimex

spp.

IN NATAL

AND

KWAZULU

Table l-Collections of bedbugs during 1984 from huts which on a first visual search yielded both C. Zecruhiusand C. hemiptem Hut A

B

.$1 ...:..... s\.. Fig. 2. Map of NkundusiIMfekayi won of KwaZulushowing numbers of infested huts io each of four areas. Black circles represent C. &I&V&S, white circles denote C. hemipterw, and mixed infestations are indicated by black and white circles. local clinic and secondary school (section C). Further along the minor dirt road terminating at False Bay, C. lectuZuriuswas by far the most common species, C. hemipterusbeing found in only 105% and 5.2% of infested huts in sections B and A respectively. In 3 huts (B to D, Table 1) where infestations with both species of bedbug had been found by visual search, collections at a later date revealed only C. hemipterus in each hut. In another hut (A) C. hemi~teruswere relatively much more plentiful in the second sample. 6 of the 7 other huts sampled twice (E to K) gave low numbers of C. hemi~terus in one or both collections with (except for hut I) appreciable numbers of C. lecculurius in both samples. Discussion

C. lectularius and C. hemipterus were sympatric in the present study area north of 28”15’S (Fig. l), and samples from 10% of infestations in this area con-

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Numbers of C. hemipterus 2

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mined both species. As samples were by no means exhaustive, the actual percentage of infested huts will be higher. These results contrast with those of MEKURIA (1967), who never found the two speciesin the same locality in Ethiopia, and of LEWIS(1949), who “seldom found” both speciesin one house in the Sudan. The question arises whether C. hmipterus is restricted to northern NatahKwaZulu by climatic factors, or whether it is in the process of invading South Africa from Mgambique. Although C. hernip terushas now been found well south of the tropics in the present study, its known distribution in South Africa lies within the July 18°C isotherm (Fig. 1). As POYNTON (1964) remarked, the July 18°Cisotherm is an indicator of a variety of climatic conditions which together constitute a tropical climate. MELLANBY (1935) did not demonstrate any aspects of the physiology of C. hemipremsthat would preclude it from living in temperate countries. However., until the tropical bedbug is found thriving well outstde the limits of tropical climate, the possibility that climatic factors limit its distribution cannot be ruled out. C. hemipterus is most abundant relative to C. lectuhius in the part of the study area north of 27”30’ (Fig. l), where mean daily temperatures are higher for part of the year (THORRINGTON-SMITHet al., 1978). However, the relative scarcity of C. hemipterus further south would also be expected if C. hemipterus were in the process of expanding its range from Mofambique. Opportunities for passive dispersal were very important in determining the distribution of C. lectularius and C. kemi~terus in the Sudan (LEWIS, 1949)?and MELLANBY (1935) explained the world-wide distribution of these species largely in terms of dispersal opportunities. From the present study there is reason to believe that C. hemipterushas

K.

NEWBERRY

not yet dispersed throughout the whole range in South Africa which is suitable for it. For example, in the NkundusVMfekayi area (Fig. 2), C. hemipterus was common in huts along the main road and around a school and clinic, but &ely found away from the main flow of human traffic. Bv contrast. C. lectularius was ubiquitous in the area &d commbnlv found in huts in iess frequented places. MELLANBY (193% concluded that C. lectularius is better able to‘wi&tand starvation and desiccation than C. hemiprerus, breeds faster at temperatures below 3O”C, and should thrive at least as well as C. /zenzipterusin a tropical climate. It is therefore surprising that 3 huts initially containing appreciable numbers of C. lectularius as well as C. hemipterus yielded only the latter species some months later (Table 1). If replacement of C. lectulmius by C. hemipterus did occur, a mechanism which could explain it was mentioned by USINGER (1966), who related that transfer of sperm during mating between male C. hemipterus and female C. lectularius had fatal consequencesfor the latter, and that this phenomenon has been suggestedas the reason for the absenceof C. lectularius from some areas of the tropics. Male bedbugs certainly can be very unselectiie in their matine behaviour in the laboratorv (USINGER. 1966). but d&ect evidence from the field is ieeded to co& that interspecific mating actually occurs in nature frequently enough to exterminate C. lectularius infestations. The annual spraying of dwelling places with DDT may have facilitated the spread of bedbugs by the removal or reduction in numbers of their predators (NEWBERRY et al., 1984). It is not known whether there are differences between the two speciesin levels of resistance to DDT which may affect distribution. Acknowledgements We thank the following for their helpful ideas and criticisms of this work: M. Coetzee, C. F. Hansford, E. K. Hartwig, R. H. Hunt, P. G. Jupp, J. A. Ledger, G. Newlands and D. Walpole. Permission to publish was granted by the Director General, Health and Population Planning, Pretoria.

433

et al.

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fm publication

8 April

1986