The morphology of the cibarial armature and sensilla of Mansonia titillans , Psorophora cingulata , Coquillettidia arribalzagae , Culex coronator and Limatus durhamii ( Diptera : Culicidae )

A detailed description of the cibarial armature of the Neotropical mosquitoes Mansonia titillans, Psorophora cingulata, Coquillettidia arribalzagae, Culex coronator and Limatus durhamii, is presented. A sample of 15 specimens of each species was taken from the collections of two mosquito ecological projects located at Santa Clara, San Carlos, Alajuela and from La Selva, Sarapiquí, Heredia, Costa Rica. Each specimen, preserved in alcohol, was cleared, put into a mounting medium, head separated from body and eyes pinched to expose the cibarial armature and sense organs; finally a coverslip was added for a permanent slide. The bodies of all the mosquitoes were also mounted onto slides. The descriptions of the cibarial armatures were based on the characteristics of the dome, body, transversal bar, lateral flanges and cibarial teeth. Also the number, distribution and type of the sense organs are given. From the analysis, and comparison with known descriptions of other neotropical species, we conclude that the five species studied show enough characteristics for species recognition purposes. Rev. Biol. Trop. 54 (3): 815-820. Epub 2006 Sept. 29.

The study of mosquitoes of human and veterinary importance must be a basic approach in an integrated management of vector control, especially in the neotropics.The taxonomy of adult culicids is still based mostly in external characters, size, genitalia and scale patterns.This is especially true for females.However, some collecting techniques, preservation methods and time, result in deterioration of important characters employed in taxonomic keys.For such reasons the classical study of the external and internal morphology is still needed in the recognition of the disease vectors.
The use of internal structures in insect taxonomy is not new.In some groups of dipterans the cibarium shows valuable characteristics that serve to separate species (i.e.phlebotomines).The morphology of the cibarial armature (CA) is useful not only for taxonomic purposes but for the interpretation of possible affinities among genera and also for host-parasite relationships of epidemiological value (McGreevy et al.1978).
In mosquitoes the use of the CA in taxonomy has been limited to a few studies, basically those of Sinton and Covell (1927), Barraud and Covell (1928), Lane (1953), Valencia (1973), Lee (1974), Sirivanakarn (1978), and Lee and Craig (1983).Few authors, such as Lane (1953), Valencia (1973), Sirivanakarn (1978), have described or figured the CA of neotropical culicine species reported from Costa Rica.Lane (1953) described and figured the CA (which he called bucco-pharyngeal) armature of Culex (Lu.) bigoti, Culex (Cx.) pipiens fatigans and Culex (Car.)urichii.Valencia (1973) made a revision of the subgenus Carrollia of Culex.This author included figures of the Costa Rican species Culex (Car.)bihaicolus, Cx. metempsytus, Cx. urichii, Cx. secundus, Cx. babahoyensis, and Cx. antunesi. Sirivanakarn (1978) made an attempt to classify species on the basis of similarity in the CA.For example, for the subgenus Melanoconion he recognized five different types and five subtypes based on the number of the cibarial teeth and their shape and size.Also he followed the same criteria to consider three types and two subtypes of CA in Microculex.The author concluded that in the subgenera Aedinus, Anoedioporpa, Belkinomyia, Carrollia, Micraedes, Tinolestes and in the majority of species of Microculex, the CA is very characteristic and provides an important character at subgeneric level.
In his comparative study of New World subgenera of Culex, Sirivanakarn included the following species from Costa Rica: Culex (Mel.)bastagarius, Cx. conspirator, Cx. educator, Cx. elevator, Cx. erraticus, Cx. inhibitator, Cx. iolambdis, Cx. pilosus Lee and Craig (1983) made a detailed study of the cibarial sense organs: palatal papillae (pp), campaniform sensilla (cs), dorsal papillae (dp), trichoid sensilla (trs) and ventral papillae (vp).These authors showed that in the 37 species studied, representing nine genera, the number of campaniform sensilla and dorsal papillae is constant (two).Also four ventral papillae are present for all species except for one with two and another without such papillae.
The number of trichoid sensillae ranged from two to ten.An interesting fact is that the palatal sensilla divided species into two groups, one with four and the other with six.In regards to the cibarial teeth, the author found that such structures were not present in the genera Culiseta, Armigeres, Aedes, Psorophora, Coquillettidia and in some species of Anopheles.
The specimens were placed separately into small plates with Nesbitt's solution and kept for two days for complete clearing.After clearing, each specimen was placed on a microscope slide in a drop of Hoyer's mounting medium.The head was separated from the body and then placed onto another slide in a drop of Hoyer's for dissection of the mouth parts, antennae, and palps.Finally the compound eyes were pinched with minuten needles in order to expose the CA located immediately behind the clypeus.The dissected parts (head and body) of each specimen were covered with round coverslips, kept at 37 °C for a week and sealed and identified with a corresponding code.
The morphological comparative study of the five mentioned species was based on the following structures: dome, cibarial body, transversal bar, lateral flanges, cibarial teeth and sensilla.The measurements made were the length of the cibarial body, maximal width of the cibarial body, length of the lateral flanges and distance between the lateral flanges.

DISCUSSION
Based on the structure of the CA, the five species of mosquitoes we have studied from Costa Rica (Mansonia titillans, Psorophora cingulata, Coquillettidia arribalzagae, Culex coronator and Limatus durhamii) might be distinguished by the following characters: The CA in Mansonia species has not been studied previously.Ma. titillans does not have cibarial teeth, but the sensory organs, their number, type and distribution are typical (Fig. 1).The CA in Psorophora is described for two species, Ps. (Jan.)ferox and Ps.(Jan.)varipes (Lee and Craig 1983), both of which have the sense organ formula 4 pp, 2 cs, 2 dp, 8 and 6-8 str, 4 vv and both lack cibarial teeth.In contrast, Ps. cingulata (Fig. 2) has the formula 4 pp, 2 cs, 2 dp, 10 trs, 4 vv, and the cibarial teeth are distributed in two groups, a character that separates this species from ferox and varipes.
The CA of the genus Coquillettidia has been described only for Coquillettidia perturbans (Lee and Craig, 1983).These authors give the following sense organ formula: 6 pp, 2 cs, 2 dp, 6 trs, 4 vp and no cibarial teeth.In contrast, Coq.arribalzagae (Fig. 3) has the sense organ formula: 6 pp, 2 cs, 2 dp, 4 str, 0 vp and the cibarial teeth (contrary to the statement of Lane and Craig, 1983) distributed in a pattern of 2+2 basals, 1+1 towards the median line and with a central promontory with teeth ending in multiple points.
The CA of Culex (Cx.) coronator is included by Sirivanakarn (1978) as one of the species studied by him, but it is not described nor figured.The author only mentioned that in the subgenus Culex the dome is small, poorly sclerotised, the transversal bar is broad and the cibarial teeth vary from 20 to 30; these teeth are short or moderately long, deeply rooted with abruptly pointed apices.In Cx. (Cx.) coronator (Fig. 4) the dome is flat, with a central monticle.The cibarial body shows sclerotised borders.The anterior hard palate is slender, with four spines and the posterior is irregular.The transversal bar includes 24 very small teeth.The sense organ formula is: 2+2 pp,1+1 cs, 1+1 dp, 2+2 str, 2+2 vp.The measurements might be of value to separate this species from others of this subgenus.This aspect needs future comparative studies.
We could find no description of the CA for any Limatus species (Fig. 5) in the literature.Future descriptions of other species will be necessary to determine comparative differences of these structures.
Of the 208 species of mosquitoes recorded in Costa Rica by Vargas (1998) the CA has been described or figured for about 33.To these we add the CA of five more CA for neotropical female mosquitoes not previously described.
We consider that the CA, as shown by Sirivanakarn (1948), is important for the study of taxonomy, evolutionary relationships and disease epidemiology among mosquitoes, and stress the necessity of increasing this field of research to provide a better understanding of the biology of these disease vectors.

Fig. 1 )
Dome: very reduced.With microsetae ending in small points.Cibarial body: with very sclerotised margins.Anterior hard palate: Dark brown, elongated, with irregular margins.About 90 x 36 μm.Posterior hard palate: Dark brown.Elongated.About 90 x 30 μm.Lateral flanges: Very sclerotised.Strong and with a sub-distal inner salient and two small spicules.Transversal bar: Inner margin smooth.Cibarial teeth: Not present.Sensilla: With 1+1 dorsal papillae (dp), 2+2 ventral papillae (vp), 3+3 sensilla trichoides (str), 1+1 campaniform sensilla (cs), 2+2 palatal papillae (pp).Measurements: Length of cibarial body, 260 μm.Width of cibarial body: 130 μm.Length of lateral flanges: 80 μm.Distance between the lateral flanges: 160 μm.Psorophora cingulata (Fig. 2) Dome: Very reduced.Cibarial body: With moderately sclerotised margins.Anterior hard palate: Somewhat rectangular.Strongly corrugated.Posterior hard palate: Short.Elongated.Lateral flanges: Sclerotised.Very short.Strong.Recurved and ending in an expanded wing not sclerotised.Transversal bar: Anterior border smooth, convex and strongly sclerotised.Cibarial teeth: There are two types of teeth distributed in two groups, placed in a very sclerotised area.One group is placed laterally, very numerous, conical, with a wide base and hollows looking as very strong spines ending in several points.The second group is located medially and forms a part of the bar and is closely packed.Sensilla: 1+1 dp, 2+2 vp, 5+5 str, 1+1 cs, 2+2 pp.Measurements: Length of cibarial body: 300 μm.Width of cibarial body: 160 μm.Length of lateral flanges: 60 μm.Distance between lateral flanges: 160 μm.Coquillettidia arribalzagae (Fig. 3) Dome: Well developed.With triangular denticles.Slightly flattened.Cibarial body: Very strongly sclerotised, especially towards the lateral flanges.Anterior hard palate: With posterior and squamous and half-moon shaped.Posterior hard palate: Not very well defined except at the border of the bar that shows a series of small excrescences.Lateral flanges: Dilated at the distal end, forming a plate and with a medial concavity that serves to allocate the cibarial teeth.Tranversal bar: Anterior border almost straight.Cibarial teeth: Laterally placed in a concavity of the lateral flanges.Teeth of different sizes and shapes.A peculiar distribution of the teeth: 2+2 basal, 1+1 towards the medial line, distal teeth with multiple points or brush-tipped, a central