The period 1875–1925 was remarkable in the history of parasitology partly because of the number of significant discoveries made, especially the elucidation of important life cycles, and partly because of the achievements of the clinicians and scientists who made these discoveries. What is remarkable is that so many of these individuals were Scots. Preeminent in this pantheon was Patrick Manson, who not only discovered the mosquito transmission of filarial worms but was instrumental in directly encouraging others to make significant discoveries in the fields of malaria, Guinea worm disease (dracunculiasis), onchocerciasis, loiasis and schistosomiasis and, indirectly, sleeping sickness and leishmaniasis. This chapter describes and discusses the contributions made by Douglas Argyll-Robertson, Donald Blacklock, David Bruce, David Cunningham, Robert Leiper, William Leishman, George Low, Patrick Manson, Muriel Robertson and Ronald Ross together with short biographical notes.

Anti-Wolbachia therapy delivers safe macrofilaricidal activity with superior therapeutic outcomes compared to all standard anti-filarial treatments, with the added benefit of substantial improvements in clinical pathology. These outcomes can be achieved, in principle, with existing registered drugs, e.g. doxycycline, that are affordable, available to endemic communities and have well known, albeit population-limiting, safety profiles. The key barriers to using doxycycline as an mass drug administration (MDA) strategy for widespread community-based control are the logistics of a relatively lengthy course of treatment (4–6 weeks) and contraindications in children under eight years and pregnancy. Therefore, the primary goal of the anti-Wolbachia (A·WOL) consortium is to find drugs and regimens that reduce the period of treatment from weeks to days (7 days or less), and to find drugs which would be safe in excluded target populations (pregnancy and children). A secondary goal is to refine regimens of existing antibiotics suitable for a more restricted use, prior to the availability of a regimen that is compatible with MDA usage. For example, for use in the event of the emergence of drug-resistance, in individuals with high loiasis co-infection and at risk of severe adverse events (SAE) to ivermectin, or in post-MDA ‘endgame scenarios’, where test and treat strategies become more cost effective and deliverable.

Introduction. Several reports indicate high prevalences of both onchocerciasis and epilepsy in some regions of Africa. This raises the question of whether these diseases are associated. We therefore investigated people with epilepsy and/or onchocerciasis living in an area in Tanzania endemic for Onchocerca volvulus (O. volvulus). Methods. We collected clinical information, skin snips, and blood from 300 individuals, and cerebrospinal fluid (CSF) from 197. Participants were allocated to 4 groups consisting of people with epilepsy and onchocerciasis (n=135), those with either epilepsy (n=61) or onchocerciasis only (n=35), and healthy individuals (n=69). Samples were evaluated for microfilaria, IgG4 antibodies against O. volvulus, O. volvulus antibody index (CSF/serum), and CSF routine parameters. Polymerase chain reaction (PCR) was performed on skin snips and CSF. Results. No difference was found in microfilarial density between participants with and without epilepsy (P=0·498). The antibody index was raised in 2 participants. CSF PCR was negative in all samples tested. Discussion. Our results do not give evidence of a relationship between O. volvulus and epilepsy. Despite the fact that 2 participants had raised antibody index, the existence of cerebral onchocerciasis caused by migration of microfilariae into the CSF appears unlikely. However, to date unexplored reactions to the infestation with O. volvulus causing epilepsy cannot be excluded.

Detection of Onchocerca volvulus larvae in vector populations is of prime importance in the assessment of the effectiveness of onchocerciasis control programmes. Traditionally, detection of larvae is attained by the dissection of flies, but this time-consuming method cannot easily discriminate between species of Onchocerca. The genome of all Onchocerca species has a unique 150 bp repeat, which can be amplified by PCR, and O. volvulus-specific DNA probes can detect these products by Southern blot (SB). This study optimizes a PCR/SB assay, and compares it with fly dissection to estimate the prevalence (p) and intensity of infection (m) in the local vector population of a Mexican community that has become hypoendemic as a result of 7 years of treatment with ivermectin and nodulectomy. The PCR detected 1 infected fly in a pool of 99 uninfected flies, but the optimal pool size was 50 flies. At the community level, 1 out of 10550 flies was positive (p=0·0095%, 95% confidence intervals CI=0·00024–07·05280%; m=0·00027 larvae/parous fly, CI=−0·00026–0·00081) by PCR, and 4 out of 10772 flies (p=0·0371%, CI=0·01012–0.09505%; m=0·00107 larvae/parous fly, 95% CI=0·00002–0·00212) by dissection (observed m=0·0005). Both methods produce statistically similar estimates of the prevalence and intensity, indicating that pool screening is a viable alternative for entomological surveillance in areas where the intensity of transmission is becoming extremely low as a result of control interventions.

Vector-borne nematodes of the Order Filarioidea produce chronic, debilitating human infections which are usually non-fatal but are associated with a high degree of severe morbidity. Weight loss often accompanies infection and is probably a consequence of the increased energy cost associated with filarial fever, lymphangitis and lymphadenitis. In onchocerciasis, weight loss is associated with heavy worm loads as assessed by abundant nodules and large numbers of skin microfilariae. Experimental infections using rodent filariae have confirmed these observations and have also shown that low protein diets render hosts more susceptible to infection; nevertheless, parasite growth and embryogenesis is retarded in stunted female worms from protein deficient animals. In the absence of appropriate evidence, studies of experimental filariasis suggest that human protein-energy malnutrition may delay the development of stage-specific acquired immunity with a corresponding prolongation of patency. Epidemiological and experimental evidence shows that filarial nematodes acquire certain nutrients directly from their hosts. Of major importance in this respect is vitamin A which is taken up preferentially by human and rodent filariae; in humans, symptoms of hypovitaminosis A often accompany infection and could be an aggravating factor in onchocerciasis. Filariae also appear to require other specific nutrients such as iodine, thiamine and pyridoxine; dietary levels of these nutrients affect the host-parasite relationships in filariasis and pyridoxine seems to be of particular importance in this respect. Filarial parasites obviously compete with their hosts for available nutrients and, in the real world, human filariasis is often associated with a deterioration in the plane of nutrition of infected individuals.

Onchocerca ochengi is a common parasite of cattle in savanna areas of West Africa and its adult stages inhabit intradermal nodules. We have exploited the accessibility of the macrofilariae to examine quantitative and qualitative differences in both the macro- and microfilariae (mff) in relation to age in naturally infected cattle. Autochthonous cattle at a site on the Adamawa plateau, North Cameroon, situated near a perennial Simulium damnosum s.l. breeding site, were examined in three age groups (1·5–2·5, n = 34; 3–5, n = 39 and ≥ 8 years old, n = 21). Skin mff densities were assessed from ventral skin biopsies, total body counts of nodules were done by palpation and 1–4 nodules were excised from positive animals, collagenase digested and the numbers and condition of macrofilariae determined. Embryogenesis profiles (embryograms) were done on a representative number of female worms in each age group. The overall prevalence of infection in the study population was 71% for mff and 85% for nodules. Nodule prevalence increased significantly from the 1·5–2·5 to 3–5 years old groups, but no other inter-age prevalences were significantly different. While the mean number of nodules per animal increased with age, geometric means (gm) 3·7, 15·5 and 23·1, the skin mff density maximized in the middle age group and decreased significantly in the old animals (gm 15·8, 44·7 and 11·4 mff/g, difference between latter two parameters significant, P < 0·05). Moreover, there was a significant correlation (P < 0·01) between individual nodule counts and skin mff densities in the mid-aged group but not in the oldest group. Examination of nodules showed that nodule counts equated to numbers of female worms, since almost all of 133 nodules examined contained only 1 live female worm. Although the proportion of old female (and male) worms increased with the age groups – 2 (0), 30 (28) and 54 (32)% – the proportion of gravid females (52·8, 48·8 and 58·0%) and the mean number of viable embryos in these females (82·5 × 103, 76·0 × 103 and 102·1 × 103) did not change with age. Thus, due to the higher nodule counts, a calculated productivity index reflecting the potential mff production per animal was 8 times higher in the ≥ 8-year-old animals than in the youngest and 3 times higher than in the middle group, which sharply contrasts with the decline in skin mff density. Although further research is required, these findings may indicate acquired immunity directed against microfilariae. They demonstrate the potential of O. ochengi infections in cattle to investigate a number of aspects of the host–parasite relationship which may have relevance to human onchocerciasis.

The exact taxonomic identity of members of the Simulium damnosum Theobald complex in Ethiopia was not known until recently. A cytotaxonomic analysis of larval chromosomes from the Kulfo River area in southern Ethiopia, from where the ‘Kulfo’ form was reported, and from the Awash River at Sodere in central Ethiopia has revealed the existence of two newly recognized species, namely Simulium kulfoense and Simulium soderense. Although three fixed and 11 floating inversions in the chromosomes of the ‘Kulfo’ form were described in an idiogram, in the present study four fixed and 17 floating inversions were observed, out of which only seven floating inversions were the same as Dunbar's, indicating that the remaining 10 inversions were either missed or misinterpreted. Though both species share many inversions, S. kulfoense sp. nov. has a diagnostic inversion on chromosome II, IIL-E6, with no sex-linked chromosomal arrangement, while S. soderense sp. nov. has a sex-linked inversion, IIS-3, which warrants it as a distinct species. Both of these new species also share many inversions with the recently described new species from south-western Ethiopia, Simulium kaffaense, including the fixed inversions IIL-E1 and E3. Since both the study sites are known to be free of onchocerciasis, and the flies are not anthropophilic, both the species are not presumed to be vectors of human onchocerciasis. The presence of IS-1 and a complex inversion possibly involving IL-3 strongly indicates that the two species belong to the ‘Nile’ phylogenetic group of S. damnosum s.l.

There is no published account which allows the morphological discrimination of microfilariae of Onchocerca volvulus and M. ozzardi from each other. However, they occur together in parts of Brazil and Venezuela, and presumably there is always the possibility that migration could establish new sympatric populations in the future. The objective of this study was to evaluate simple morphological characters that might be used for species-diagnosis of microfilariae. The conclusions were that the location of microfilariae in the blood or skin, the body size and the nucleation of the nerve ring are expected to be useful first indications of species identity, but cannot be used for confident diagnosis. The structure of the cephalic armature (stained with alcian blue) seems to be species specific, but is of limited application because it is often difficult to see. However, the pattern of nucleation of the tail (as expressed by the ratio of the length of the terminal nucleus compared with the length of the tail space) is distinctive and is expected to be diagnostic.

The standard assay for onchocerciasis diagnosis is microscopical detection of microfilariae in skin snips. Skin snipping is painful, requires appropriate sterilization of equipment, and may fail to diagnose light infections. Two alternatives are a polymerase chain reaction (PCR) test which detects parasite DNA in pieces or scrapings of skin and a test based on allergic reactions to topical application of diethylcarbamazine (DEC). We compared these 2 diagnostics with standard skin snip microscopy in 313 individuals from 2 villages in Guinea, with low prevalence after over 10 years of control by the Onchocerciasis Control Programme. Lower and upper bounds on sensitivities and specificities of these 3 tests were estimated. In addition, these parameters were estimated using 5 different statistical models. Where prevalence was low, PCR and the DEC patch test appeared to be more sensitive than skin snipping which has low sensitivity. As the DEC test is non-invasive, simple and cheap, it may provide a good alternative to skin snipping alone for surveillance in low prevalence areas.

This paper describes, for the human onchocerciasis focus of southern Venezuela, the age profiles of Onchocerca volvulus microfilarial (mf) and nodule prevalence, mf intensity, and mf aggregation for the whole examined population (836 Yanomami people) living in 20 villages, and for these communities classified according to endemicity levels (hypoendemic: [les ] 20%; mesoendemic: 21–59%; hyperendemic: [ges ] 60% infected). Mf prevalence and intensity increased with age, particularly in the hyperendemic areas, and there were no marked differences between the sexes. The prevalence of nodules followed the same age pattern. Fifty percent mf prevalence was reached in the 15–19 year age-class when the population was taken as a whole; nearly in the 10 to 14-year-olds for the hyperendemic level, in those aged 20–29 years in mesoendemic areas, and not reached at all in hypoendemic villages. The degree of mf aggregation was measured by the k value of the negative binomial distribution and by the variance to mean ratio (VMR). The relationship between the standard deviation (S.D.) of mf counts and the mean mf density was also explored. These 3 indices (k, VMR, and S.D.) showed a tendency to increase with both mean mf load and host age. Since infection intensity and host age were themselves positively related, it was not possible to draw definite conclusions about age-specific changes of parasite aggregation. There was not a significant decrease of mf intensity after an earlier peak neither was there a shift towards younger ages of the maximum no. of mf/mg reached as the endemicity level increased. These results are discussed in relation to detection of density dependence in the human host, selection of an indicator age-group for rapid epidemiological assessment (REA) methods, and strategies of ivermectin distribution in the Amazonian focus. It is recommended that, for the Amazonian onchocerciasis focus, the indicator group for REA consists of all those aged 15 years and over.

In the previous paper it was concluded that those aged [ges ] 15 years of both sexes could comprise the indicator group for rapid epidemiological assessment (REA) of onchocerciasis in the Amazonian focus. This paper explores relationships between community microfilarial (mf) prevalence, intensity, and nodule prevalence in 20 Yanomami communities, that would allow identification of REA methods in the region. The mean nodule ratio (prevalence of nodules/prevalence of mf) was 0·54 when onchocercomata in the indicator group were considered. The Spearman correlation coefficient between mf and nodule prevalence was 0·686 (P = 0·001). Palpation of nodules had 92% specificity and 32% sensitivity when compared to skin-snipping for the diagnosis of onchocerciasis. The predictive value positive increased from 75% to 81% when the indicator group was used. A microfilarial prevalence > 75% in this group would be indicative of hyperendemic status in the village, between 30 and 75% of mesoendemicity, and < 30% of hypoendemicity. For the assessment of infection intensity, biopsies may be taken from the iliac crest for all endemicity levels. Five of the hyperendemic villages surveyed in this work had a community microfilarial load (CMFL) greater than 10 mf/skin snip; the remaining 5 had a CMFL between 5 and 9. These levels of infection merit high priority ivermectin treatment. In Latin America, communities at both moderate and severe risk are included in mass chemotherapy programmes (i.e. when mf prevalence is over 20%). Roughly, a nodule prevalence in the indicator group > 10% would suggest a community mf prevalence > 20% with a sensitivity of 85% and a specificity of 71%. A multiple linear regression model of the arc-sine transformed mf prevalence in the village (all ages) on nodule prevalence in those aged [ges ] 15 years and altitude of the village explained 72% of the variance. The model combining nodule and altitudinal information had a sensitivity of 92% and a specificity of 71% in comparison to an estimated mf prevalence of 21% or more. It is suggested that the usefulness of the REA methods proposed be assessed in other areas of the Amazonian onchocerciasis focus.

The bovine parasite Onchocerca ochengi is a nodule-dwelling filarial nematode, closely related to O. volvulus, the causal agent of human River Blindness, and, sharing with it, the same vector. This brief review, based on a presentation at the BSP Autumn Symposium 1999, describes recent work supported by the WHO Drug Development Research Macrofil programme and the Edna McConnell Clark Foundation vaccine development programme, to research the chemotherapy and immunology of onchocerciasis utilising this model system, with experimental infections in Liverpool and field infections in northern Cameroon. In a series of chemotherapeutic trials involving 10 compounds in 20 treatment regimes, the comparability of drug efficacy against O. ochengi with that described against O. volvulus has been demonstrated. Repeated, long-term treatment with oxytetracycline has been shown to be macrofilaricidal and the effect is hypothesized to be related to action on Wolbachia endobacteria, abundant in O. ochengi. Avermectins/milbemycins are not macrofilaricidal (even in high and repeated long-term treatments) but induce sustained abrogation of embryogenesis. In prospective, field exposure experiments with naive calves, prophylactic treatments with ivermectin and moxidectin prevented the development of adult worm infection, raising the possibility that drug-attenuated larval challenge infections may induce immunity. Putatively immune adult cattle exist in endemically exposed populations, and these have been shown to be significantly less susceptible to challenge than age-matched naive controls, whereas radically drug-cured, previously patently-infected cattle were not. Experimental infections with O. ochengi have revealed the kinetics of the immune response in relation to parasite development and demonstrate analogous responses to those reported in O. volvulus infection in humans and chimpanzees. In an immunization experiment with irradiated L3 larvae, cattle were significantly protected against experimental challenge – the first such demonstration of the experimental induction of immunity in a natural Onchocerca host–parasite system. Taken collectively, these studies not only demonstrate the similarity between the host–parasite relationships of O. ochengi in cattle and O. volvulus in humans, but promise to advance options for the control of human onchocerciasis.

Onchocerciasis is a widespread disease in intertropical Africa, which, ultimately, causes irreversible blindness. The disease is transmitted by a small blackfly, Simulium damnosum (Diptera), which has aquatic larval and pupal stages. The breeding sites of the blackflies are riffles. These river reaches are the targets of the control campaign of the Onchocerciasis Control Programme in West Africa (OCP). An aquatic monitoring network covering the totality of the area exposed to the insecticide was set up to evaluate environmental impact. In this paper, we present results from the OCP 20-year period of monitoring of the ichthyofauna regularly exposed to larvicides. We do not record any measurable effects of pesticides on the CPUE, abundance of species, trophic structure, community structure or fish health. However, we detect the emergence of a number of medium-term tendencies. These tendencies may relate to climatic conditions that have a consequent effect on hydrology. Thus, we note a constant decrease in the CPUE from the beginning of the monitoring until 1995. The rivers were treated during that time until 1990 or 1993, depending on the station. But even after the treatments ended, the number of catches continued to decrease. As a result, we consider other factors to be the cause of that decline. The average level of annual discharges in this region has been decreasing regularly from the beginning of the 1970s. The production of fish fluctuates in all the rivers according to the flood rate. Important floods inundate larger areas, making greater quantities of food available, and thus improving the conditions for reproduction. The determining factor of the ichthyological stock abundance seems to depend both on the extent and the duration of the flood. In our catches, the observed effect was not immediately evident but appeared a few years later as a cumulative effect of poor hydrological conditions. An increase in the CPUE since 1996 has been related to improved hydrological conditions. In these last few years, we have observed an intensification of the basic flow leading to a ground water renewal. Furthermore, on three of the stations investigated, it appeared that the impediment of rivers (dams) could induce different and/or antagonistic effects. In some cases, we have observed that in spite of unfavourable hydrological conditions, certain species appear to be favoured by the presence of the dam. But, the damming of the river has a negative effect on other species, particularly on the coefficient of condition of migratory fishes. The impact of these factors is enhanced by the fact they exist conjointly.

Onchocerciasis (‘River Blindness’), caused by the filarial nematode Onchocerca volvulus is of major public health importance in West Africa. Ivermectin, a drug originally developed for veterinary use, is now being incorporated in control strategies but whilst it has potent efficacy against L1 larvae (microfilariae), ivermectin is not lethal to adult (L5) O. volvulus, nor to adults of the related cattle parasite O. ochengi. We have exploited this model to determine if ivermectin has prophylactic activity against naturally transmitted, O. ochengi infections in a controlled, prospective study in northern Cameroon. Calves were treated monthly with ivermectin at either 200 μg/kg or 500 μg/kg for 21 months. None of 15 treated calves developed adult worm infection, whereas 5/6 untreated controls became infected (P<0·001) with a total of 54 O. ochengi nodules, and all 5 developed patent microfilaridermia. These results have significant implications for the use of ivermectin in humans, and suggest that strategic chemotherapy at times of maximal transmission will confer prophylactic as well as therapeutic benefits.

In order to assess the prevalence of the cattle filaria Onchocerca ochengi in onchocerciasis vectors (Simulium damnosum s.l.) in North Cameroon, we searched for a means to morphologically identify its developing larvae, which closely resemble those of O. volvulus. To this end microfilariae of the 2 Onchocerca species were isolated from slaughter cattle in Ngaoundéré and injected into neonate Simulium species. Whereas the early developmental stages (sausage stage, L2 and pre-infective larva) were indistinguishable, the infective larvae (L3) of O. ochengi were longer (median: 740 μm), more slender (diameter = 19·3 μm = 2·6% of body length) and had a relatively shorter tail (4·9% of body length) than those of O. volvulus (680 μm, 20·5 μm, 3·0% and 5·8% respectively). The tail of O. ochengi L3 was thick and rounded, whereas it was slightly tapering in O. volvulus L3. O. ochengi L3 produced by feeding flies on infected cattle in a different area in North Cameroon (Sora Mboum) showed the same features as intrathoracically produced O. ochengi L3 from Ngaoundéré, but were even longer (785 μm). On the basis of the differences in length, relative diameter, length of the tail and shape of the tail, a simple key for the separation of O. volvulus and O. ochengi L3 was elaborated, and 248 L3 found in wild S. damnosum s.l. were separated into ‘O. ochengi’ (160 L3) and ‘O. volvulus’ (88 L3) following this key. Sequential dot blot hybridization of each of the 248 larvae with a DNA probe which reacts with O. ochengi and O. volvulus but not with other Onchocerca species (pOo5/1) and with an O. volvulus-specific DNA probe (pOv12) revealed that the morphological identification had been correct in 86–91% of the cases. Only a small proportion (6–9%) of the dot blots did not react with either probe. Since this proportion was equal in experiments using experimentally produced L3 and in experiments using wild L3, the non-hybridization was certainly due to a loss of L3 during washing of the filters and not due to the presence of other unknown L3 species resembling O. volvulus and O. ochengi. Our study shows that in Cameroon it is possible to identify O. volvulus and O. ochengi infective larvae during routine fly dissections by morphology alone.

In the savanna areas of tropical Africa, cattle are frequently infected with the filaria Onchocerca ochengi. This parasite is closely related to Onchocerca volvulus, the causative agent of human onchocerciasis (river blindness), and is capable of developing in the same vector, Simulium damnosum s.l. In North Cameroon, where both O. ochengi and O. volvulus are endemic, we carried out a field study (reported in this and 2 following papers) to examine to which extent the transmission of the 2 parasite species overlap and what influence this has on the epidemiology of human onchocerciasis. In this paper we report our experiments to determine which of the S. damnosum species in North Cameroon act as vectors of O. ochengi, how efficiently they do so and whether other Simulium species play a vector role. To this end, infected cattle were exposed near 5 rivers in different geographical areas. Among 14 Simulium species identified as aquatic and/or adult stages at these rivers, only 6 (S. squamosum, S. damnosum s.s., S. sirbanum, S. bovis, S. wellmanni and S. hargreavesi) were found to bite cattle in important numbers in at least 1 of the sites. The 3 species of the S. damnosum complex were all capable of ingesting microfilariae (mf) of O. ochengi and developing a proportion of them to infective larvae (L3). Whereas S. squamosum and S. damnosum s.s., the prevailing vectors in the Guinea and Sudan savanna respectively, showed a high vector competence (17% of ingested mf developed to L3), S. sirbanum, which was much rarer in both areas, appeared to have a much lower susceptibility (2%). Other boophilic Simulium species were only seen in certain sites and seasons, being either incapable of ingesting important numbers of O. ochengi mf from body regions where these mf were abundant (S. bovis, S. hargreavesi); not able to support the development of ingested mf to L3 (S. wellmanni), or bit cattle preferentially in the ears, where O. ochengi mf do not occur (S. hargreavesi). We conclude that in North Cameroon members of the S. damnosum complex are the only important vectors of O. ochengi, with S. squamosum and S. damnosum s.s. being the main vectors.

The effects of climate on the diurnal biting pattern of Simulium damnosum s.s. were measured at Jos Plateau, Nigeria. Rain in the hours prior to the catch inhibited morning activity by lowering the temperature and light intensity, and raising the humidity. Under shade there were no remarkable fluctuations in the light intensity, and no obvious peaks in activity; in sunny places, activity was bimodal, with a small morning peak and a pronounced afternoon one. The fastest changing climatic factor relative to an increase in the biting activity of flies was light intensity; followed by temperature.

Electrophoretic studies of Guatemalan blackflies, Simulium ochraceum, the main vector of Central American onchocerciasis, were performed using isozyme patterns. A total of six larval and adult populations originating from four localities (a non-endemic area, Finca La Ruda, a low-endemic area, Finca Rincon, and two high-endemic areas, Finca Brote and Finca Recreo) were analyzed. The enzymes examined were adenylate kinase (AK), alkaline phosphatase (ALP), glucose phosphate isomerase (GPI), hexokinase (HK), isocitrate dehydrogenase (IDH), leucine aminopeptidase (LAP), malic enzyme (ME), and phosphoglucomutase (PGM). Of these, six enzymes, AK, ALP, HK, IDH, LAP, and ME showed no variation either within or among populations. GPI and PGM were found to be highly polymorphic in all of the six populations. χ2-test for fit to Hardy-Weinberg equilibrium (HWE) revealed that the distribution of the phenotypes of the two polymorphic enzymes was not significantly out of the HWE. A verages of values of proportion of polymorphic loci (P) and heterozygosity per individual (H) of the six populations were 0.234 and 0.084, respectively, each of which was similar to the values reported for different groups of organisms (Nei, 1975). Genetic diversity among populations was measured by FST and GST and both parameters showed that the non-endemic population from the Finca La Ruda (Dl) was greatly differentiated genetically from the other five populations. Estimates of genetic distance (Nei, 1975) showed that the Dl population was furthest from the other populations.