An Ecological Survey of Anopheles Albimanus Larval Habitats in Colombia
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An Ecological Survey of Anopheles albimanus Larval Habitats in Colombia 1 2 3 Gerald G. Marten , Marco F. Suarez , and Rodrigo Astaeza Servicio Nacional de Erradicaci6n de Malaria, Bogota, Colombia lSchool ofPolicy Studies, Kwansei Gakuin University, Sanda, Hyogo 669-13, Japan 2Instituto de Inmunolog{a del Valle, Universidad del Valle, Apartado aereo 25360, Cali, Colombia 3Floramerica, Calle 93 No. 19-25, Santafe de Bogota, Colombia Journal o/Vector Ecology Society for Vector Ecology Vol. 21, No.2: 122-131, December, 1996 I Journal ofVector Ecology 21(2): 122-131 An Ecological Survey of Anopheles albimanus Larval Habitats in Colombia 2 Gerald G. Marten}, Marco F. Suarez , and Rodrigo Astaeza3 Servicio Nacional de Erradicacion de Malaria, Bogota, Colombia lSchool ofPolicy Studies, Kwansei Gakuin University, Sanda, Hyogo 669-13, Japan 2Instituto de Inmunolog{a del Valle, Universidad del Valle, Apartado aereo 25360, Cali, Colombia 3Floramerica, Calle 93 No. 19-25, Santafe de Bogota, Colombia Received 13 December 1994; Accepted 20 March 1996 ABSTRACT: The flora and fauna of 69 aquatic sites in Colombia were surveyed to identify ecological conditions that favor production of Anopheles albimanus. Anopheles albimanus larvae were most numerous at sun-exposed sites with abundant Culex larvae and grass at the edge of the water. Only 29% ofthe sites with An. albimanus larvae contained pupae, suggesting that poor larval survival prevented the production ofadultmosquitoes atmany sites. In the Atlantic region, An. albimanus production was highest from large ponds with an abundant and varied aquatic insect fauna, including many kinds ofpredators of An. albimanus larvae. Although productive sites were often covered with water hyacinth, aquatic vegetation was generally not a reliable indicator ofAn. albimanus production. In the Pacific region, An. albimanus production was highest from small water bodies with few aquatic macrophytes and an abundance ofcladocera, reflecting an abundance ofmicroalgal food for mosquito larvae. In bothregions, An. albimanus production was negatively associated with a complete cover ofLemna, fish, hydrometrid nymphs, large species of cyclopoid copepods, and dragonfly or mayfly nymphs. Anopheles albimanus production was also negatively associated with dytiscid beetle larvae in the Pacific region. Keyword Index: Mosquito, ecology, habitat, larvae, biological community. INTRODUCTION Anopheles albimanus larvae are generally found at sites that are well exposed to sunlight (Breeland 1972). Anopheles albimanus Wiedemann is a common One way to expand and refine this characterization is to and widely-distributed neotropical mosquito species look for discemable communities of aquatic flora and that breeds in a variety of aquatic habitats (Breeland fauna. Plants and animalsthatshare aquatic ecosystems 1972): ditches, temporary pools, ponds of all sizes, withAn. albimanus larvae shouldhave profoundimpacts lakes, streams, and estuaries. Source reduction for such on the larvae as food, shelter, predators, or competitors. extensive larval habitat would appear to be an over Savage et ale (1990), Rejmankova et al. (1991, whelming task. 1992), and Rodriguez et ale (1993) surveyed aquatic The prospects for source reduction might be habitats on the Pacific coastal plain ofsouthernMexico, improvedifecological common denominators could be where An. albimanus larvae were associated with identifiedthatcutacross theapparentdiversityofhabitats. emergent aquatic plants, planktonic algae, pasture Such information might provide ecological indicators grasses, or waterhyacinth. In Belize, Rejmankovaetal. for recognizing sites that are most important for An. (1993) observed An. albimanus larvae to be associated albimanus production, sothatlarvicidingorotherforms withcyanobacterial matsand submergedplants covered of source reduction could be focused on those sites. with periphyton. Ecological infonnation might also help to identify key Anopheles albimanus is common throughout the characteristics of An. albimanus larval habitats that coastal zone of Colombia (Quinones et ale 1987) (Fig. could be modified to render the habitats unsuitable for 1). We conducted a field survey of aquatic habitats in An. albimanus production. Colombia to identify ecological conditions that support I December, 1996 Journal o/Vector Ecology 123 theproductionofAn. albimanus. Weparticularly wanted Aquaticfauna, includingmosquitolarvaeandpupae, to know if the habitat associations were the same in were collected with a plankton net (120 Jl1l1 mesh). The Colombia's Pacific and Atlantic regions. The survey mouth ofthe net was attached to a square frame, 20 cm emphasized aquatic flora and fauna, their organization on a side, which was dragged with a pole through water into biotic communities, and their associations withAn. up to 50 cm in depth. The total distance sampled by the albimanus larvae and pupae. net at each site varied from 10mto 50 m, depending on the size ofthe body ofwater. Whereverpossible, the net MATERIALS AND METHODS was dragged along a transect from one side ofthe water to the other, butitwas necessary to drag the netonly near The survey was designed to cover the full range of the shore if the water was too deep in the middle. aquatic habitats that might produce An. albimanus on Sampling at the largest sites was at intervals along the the Pacific and Atlantic coasts of Colombia. Twenty shore. seven sites were sampled on the Pacific coast from Animalscollectedin'the planktonnetwerepreserved October 1986 to April 1987 in the vicinity of Tumaco in formalin for identification and counting in the (Fig. 1) and extending 50 kIn inland along the highway laboratory. Counts were by taxonomic groups (TABLE east ofTumaco. Mangroves dominate the coastal part 2); subsamples were counted when animal numbers ofthe area surveyed, while farther inland the landscape were large. Mosquito larvae were counted by instar. is dominated by small-scale agriculture (coconut and The large numbers ofanimals collected by the plankton palm plantations, sugar cane, and subsistence crops). net provided quantitatively reliable samples of most The rainy season on the Pacific coast extends from kindsofanimalspresentateachsite,includingsubstantial Septemberto June with peaks inJanuary, February, and numbers of mosquito pupae (if present), which we May. Small bodies of water are numerous because consideredtoreflecttheproductionofadultmosquitoes. much ofthelandisonly slightly above sealevel, rainfall Allanimalcounts, includingmosquitolarvaeandpupae, is plentiful, and the water table is high. Sample sites on were expressed as numbers per meter dragged by the the Pacific coast included borrow pits, stream plankton net. A log (X+1) transformation was applied impoundments, roadside ditches, and temporary pools. to animal counts to bring them closer to a nonnal distri Forty-two sites were sampled on the Atlantic coast bution before including them in the statistical analysis. (from May 1987 to October 1987) in the vicinity ofLas GutcontentsofAn. albimanuslarvaewereexamined Flores, Santa Catalina, and Cannen de Bolivar (Fig. 1). underthemicroscopetoassessthequantityofmicroalgae, Cattle ranches dominate the Atlantic landscape along bacteria, detritus, and mineral particles. Gut content withsmall-scaleagriculture. Therearetworainyseasons data were not included in the statistical analyses. on the Atlantic coast-September to November and Two kinds ofcorrelations werecalculatedbetween May to June-with distinct dry seasons between them. the 56 quantitative variables (physical, chemical, floral, Small bodies ofwater are unusual on the Atlantic coast. andfaunal): conventionallinearcorrelationcoefficients Large cattle ponds and impoundments to storewaterfor and nonparametric Spearman rank-order correlation household use are common. coefficients. A positive correlation between two kinds A total of seven physicaVchemical factors, ten ofplants or animals reflected a tendency for both to be categories of terrestrial or aquatic plants, and 39 abundant at the same site, as well as scarce or absent at categories of aquatic animals (five stages of An. the same sites. A negative correlation reflected a albimanus plus34otherkinds ofanimals)wereassessed tendency to be present or abundant at different sites. at each site (TABLE 1, TABLE 2). Physicalandchem The rank: correlations were helpful for identifying ical properties ofthe water at each site were measured associations that were not apparent from conventional between lOAM and 2 PM. The pH was measured with correlations because the associations were not linear. colorimetric paper. Temperature, salinity, and Factor analysis with varimax rotation was applied conductivity were measured with a YSI meter (Yellow to the 1,540 conventional correlation coefficients SpringsInstrumentCo.,YellowSprings,Ohio). Oxygen between all physical/chemical, floral, and faunal was measured by the Winkler method (Ruttner 1963). variables to identify intercorrelatedgroups ofvariables. Terrestrial vegetation was assessed visually as Factorswitheigenvalues>2 wereconsideredsignificant. percent groundcoveroftrees, bushes, flowering plants, A variablewasconsideredto bepartoftheintercorrelated orgrasseswithin onemeterofthewater'sedge. Aquatic group represented by a particular factor if its factor vegetation was assessed visually as percent cover of loading exceeded 0.3. submersed, emergent, or floating macrophytes overthe The factor analysis was repeated with a single entire body of water.