Consistent pattern in the placement of taste sensilla on the labellar lobes of Aedes aegypti Sharon R. Hill, J.J. Berry Smith* Department of Zoology, University of Toronto, Toronto, Ontario, Canada M5S 3G5 Received 6 December 1998; received in revised form 4 June 1999; accepted 18 August 1999 Abstract The long sensilla on the labellar lobes of Aedes aegypti were studied using scanning electron microscopy. The surface of the labella is populated by 3 hair-like structures: long sensilla (female 33.5 mm, SD 3.81 n = 114; male 32.0 mm, SD 2.69 n = 20), short sensilla (female 4.27 mm, SD 0.550 n = 15; male 4.52 mm, SD 0.609 n = 15), and microtrichia (female 5.00 mm, SD 0.656 n = 55; male 5.27 mm, SD 0.376 n = 53). This current study is concerned with the long sensilla. The ventral surface of the labella is consistently populated with 10 long sensilla. The dorsal surface is populated by 5 long sensilla. We assigned the base of each sensillum Cartesian co-ordinates describing its relationship to the other sensilla on the ventral and dorsal surfaces of each individual. These Cartesian co-ordinates were pooled and a stringent form of cluster analysis was used to determine if these sensilla could be identi®ed by location on the labella. Sensilla from dierent individuals are more closely related by position than sensilla on the same individual, suggesting that these sensilla are located in a consistent pattern over the labellar surface. Sensilla were labeled V1±V10 and D1±D5 on the ventral and dorsal surfaces respectively. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Aedes aegypti; Yellow fever mosquito; Chemosensory sensilla; Labella; Cluster analysis 1. Introduction The female mosquito Aedes aegypti transmits dis- eases such as Dengue fever and yellow fever through bloodfeeding. Many factors aect bloodfeeding beha- vior. For example sugar feeding has a profound aect on the short and long term propensity of a mosquito to take a blood meal (Jones and Madhukar, 1976). The conditions and regularity of sugar feeding in females, however, are not yet fully understood (Edman et al., 1992; Van Handel et al., 1992, 1994). Ingestion of sugar, in the form of nectar or honey- dew, probably depends on stimulation of labellar che- moreceptive sensilla, which in the mosquito Culiseta inornata were shown to be sugar-sensitive (Pappas & Larsen, 1978; Friend et al., 1988). Similar terminal pore sensilla on the labellum have been well character- ized in other Dipteran species (e.g. Neobellaria (=Sar- cophaga ) bullata, Calliphora spp., and Phormia regina ) and have been shown to contain dendrites sensitive to sugars, salts, water, and mechanical stimulation (Owen, 1963; Dethier, 1976). The labellar hairs of these calyptrate ¯ies show variation in both mor- phology (Wilczek, 1967) and function (Albert et al., 1991). A. aegypti has only 15 ``long'' (>5 mm) labellar chemoreceptive sensilla compared to the more than 120 reported by Wilczek (1967) for Phormia regina. To casual inspection these 15 sensilla appear morphologi- cally similar, however, preliminary neurophysiological recordings of sensillar sensitivity to sugars suggested a division into functional subclasses within them. To determine whether such functional subclasses, if they exist, are associated with particular sensilla or represent random variation within a population of like sensilla, we needed to determine if the sensilla occur in International Journal of Insect Morphology and Embryology 28 (1999) 281±290 0020-7322/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S0020-7322(99)00031-8 www.elsevier.com/locate/ijinsectme * Corresponding author. E-mail address: berry@zoo.utoronto.ca (J.J. Berry Smith).