Distinguishing the two forms of Egyptian Aedes (Ochlerotatus) caspius Palias species (Diptera: Culicidae) by ultra structure micrographs of eggs.

Ultrastructure of the two forms autogenous and anautogenous eggs of Aedes (Ochlerotatus) caspius of Egypt are described using Scanning Electron Microscope (SEM). The eggs of the two forms are slightly boat shape with quite difference in width. Chorionic cells of the ventral surface are ultimately different in both forms in shape, width of reticulum, number and size of tubercles. The chorionic cells of the autogenous form's egg are elongate, narrow and almost curved with unusually wide, outer reticulum contain 2 - 13 large tubercles along with a few number in small size. However, the anautogenous form's egg, the chorionic cells of the ventral surface fairly distinct, very regular in outline with thin reticulum and usually hexagonal, each cell contain one or two large tubercles with many small scattered peripheral tubercles. Fine structure micrographic work of eggs of the Egyptian Ae. caspius provides new morphological evidence that both autogenous and unautogenous forms are certainly different and suggests that those forms are two distinct species.

A description and morphometric comparison of eggs of species of the Anopheles gambiae complex.

Eggs of the 6 named species of the Anopheles gambiae complex are described from scanning electron micrographs of specimens obtained from laboratory colonies or wild-caught females. Morphometric measurements of eggs from 5 sources of Anopheles arabiensis, 2 of Anopheles gambiae, one of Anopheles quadriannulatus, 2 of Anopheles bwambae, 2 of Anopheles merus, and one of Anopheles melas are compared, and relationships are analyzed by multivariate statistics. No morphologic characters were species-diagnostic, although tendencies of the saltwater species An. merus and An. melas to have wider decks and shorter floats were confirmed. Species and populations overlapped considerably in principal components and discriminant function analyses based on 10 attributes of eggs. Nevertheless, discriminant functions revealed similarities in eggs of species believed to be most closely related, namely, An. gambiae and An. arabiensis, An. merus and An. melas, and An. quadriannulatus and An. bwambae.

Egg structures of Anopheles fluminensis and Anopheles shannoni

Eggs of two species belonging to the Arribalzagia Series of the Laticorn Section of Anopheles (Anopheles) collected in Brazil are described from scanning electron micrographs. The An. fluminensis egg is long with shallow floats displaced far dorsally. The narrow deck region is overlain by a frill modified into prominent ridges that are nearly continuous to both ends of the egg. Slightly opened decks at both poles contain an average of four lobed tubercles. Polygonal, plastron-type chorionic cells cover the lateral and dorsal surfaces. The egg of An. shannoni is unique in possessing 22-27 fingerlike filaments that project with regular spacing from each of its massive floats. These filaments and their bases are highly perforated and are believed to trap air and support flotation of the egg with the dorsal surface up, contrary to the usual orientation for anophelines. The eggs are compared with those of related species bearing similar structures, notably An. fluminensis with An. mediopunctatus s.s. and An. shannoni with An. peryassui.

Comparative egg morphology of six species of the Albimanus section of Anopheles (Nyssorhynchus) (Diptera:Culicidae).

Scanning electron micrographs were used to describe and compare structures of eggs obtained from wild-caught females of 6 species of the Albimanus section of Anopheles (Nyssorhynchus) from South America, which includes important regional vectors of human malaria. Among species from the Oswaldoi Complex, eggs of Anopheles oswaldoi (Peryassu) were not differentiated from those of its sibling Anopheles konderi Galvão & Damasceno, and eggs of the former species from Brazil, Ecuador, and Suriname showed no regionally distinguishing characteristics. Eggs of Anopheles dunhami Causey were recognized by the reticulate beadwork of outer chorion on the dorsal plastron, 1 of several egg characters separating this species from the related Anopheles trinkae Faran and Anophels nuneztovari Gabaldón. In both species examined from the Strodei Complex, Anopheles strodei Root and Anopheles benarrochi Gabaldón, Cova Garcia & Lopez, the anterior frill forms a distinctive ventral crown separated from the floats. Anopheles triannulatus (Neiva & Pinto), collected from 4 geographic sites, differed in the occurrence of perforated mounds on the dorsal plastron, but these chorionic structures and the extent of overlap of floats varied among eggs from single females. Changes among related species in the structure of the anterior frill and dorsal plastron are described for phylogenetic and developmental inferences.

SEM examination of the eggs of five British Aedes species.

Ultrastructure descriptions are given of the eggs of five British Aedes species, namely Aedes (Aedes) cinereus Meigen, Aedes (Ochlerotatus) cantans (Meigen), Aedes (Ochlerotatus) punctor (Kirby), Aedes (Ochlerotatus) detritus (Haliday), and Aedes (Ochlerotatus) rusticus (Rossi). Eggs of the first 4 species are broadly cigar/boat-shaped, with those of Ae. cinereus being characteristically long and narrow, in contrast to the overall shape of Ae. rusticus, which is quite distinct, being in profile almost subtriangular with rounded corners, and is completely species-diagnostic. In Ae. cantans, Ae. punctor, and Ae. rusticus there is usually a single large tubercle in each chorionic cell and there is little, if any, difference in the sculpturing of the ventral and dorsal surfaces, whereas in Ae. detritus each cell contains more than 20 tubercles, and in Ae. cinereus there are usually 6 tubercles per cell ventrally, but dorsally there are no tubercles or distinct cells but numerous cone-shaped papillae. All 5 species can be separated from each other by SEM examination of their chorionic patterns.

Ultrastructure of the eggs of Culicoides circumscriptus, Culicoides gejgelensis, and Culicoides imicola (Diptera:Ceratopogonidae).

The eggs of Culicoides circumscriptus Kieffer, Culicoides gejgelensis Dzhafarov, and Culicoides imicola Kieffer collected in Israel are described and illustrated by scanning electron micrographs. Eggs of all 3 species were morphologically similar, generally sausage- or cigar-shaped, with slight dorsal-ventral curvature and longitudinal rows of tubercle pillars covered with a thin adhesive layer. Tubercle pillars were scarce on C. circumscriptus and C. imicola eggs, but were common on C. gejgelensis eggs, forming longitudinal plastrons with an associated hydrofuge meshwork. All 3 species had micropyle domes and associated aeropyles at the anterior end of their eggs.

A description and morphometric comparison of eggs from eight geographic populations of the South American malaria vector Anopheles (Nyssorhynchus) nuneztovari (Diptera:Culicidae).

The egg of Anopheles nuneztovari is described from scanning electron micrographs of specimens collected from western Venezuela. Morphometric measurements of egg samples from 3 localities in Venezuela, one in Suriname, and 4 in Brazil are compared and relationships analyzed by multivariate statistics. Morphological characters were similar in 2 geographical groups, one Venezuelan and the other Amazonian, that were distinguishable on the basis of differences in size and density of tubercles in the anterior deck region and area of pores in the dorsal plastron. Eggs from western Brazil did not cluster with other Amazonian collections. The distinction of Venezuelan from Amazonian eggs of An. nuneztovari is consistent with chromosomal, ecologic, and molecular evidence for regional genetic differentiation in this species.

Description of the egg of Aedeomyia squamipennis (Diptera: Culicidae).

The egg of Aedeomyia squamipennis (Lynch Arribalzaga) is described with the aid of scanning electron micrographs. This study allows separation of the eggs of Ad. squamipennis from the eggs of other mosquitoes inhabiting similar aquatic vegetation.

Behavior on approach to surface prey by larvae of Toxorhynchites amboinensis and T. brevipalpis (Diptera: Culicidae).

Behavior of Toxorhynchites amboinensis (Doleschall) and Toxorhynchites brevipalpis (Theobald) larvae (starved 48 h) as they approach and capture surface prey is described quantitatively from videotaped records. Of 106 T. amboinensis and 82 T. brevipalpis larvae observed, 84.9 and 97.6%, respectively, responded to the presence of surface prey within 2 min (most < 20 s). Once they detected prey, larvae executed initial backward swims if prey was rearwardly positioned, then approached it in a series of undulatory forward swims with progressive adjustments of body angle so that the final movements were directly toward the prey. Swims consisted of an active phase, during which propulsive bodily flexions were made and a passive one of continued inertial drift after active motion had ceased. Quantitative changes in the nature of the swims in terms of interval separating active phases and also distances, times, and speeds throughout the approach sequence were analyzed from the video tapes. T. brevipalpis responded to the presence of prey more rapidly, captured prey in less time, and approached prey more rapidly, with shorter rest periods between active swim phases than T. amboinensis. The behavior indicated that Toxorhynchites larvae are able to assess both the angle to surface prey and its distance and that they interpolate this information to optimize the approach path. The degree of refinement in this behavior indicates that it is well adapted to take advantage of the important surface food source in nature. In this phase of their feeding, Toxorhynchites larvae are active hunters and are not entirely the passive ambush predators they have seemed to be from many studies that have used other mosquito larvae as (subsurface) prey.

Ultrastructure of the eggs of seven flea species (Siphonaptera).

Eggs of seven flea species representing five families, Ctenocephalides felis (Bouché) (Pulicidae), Orchopeas leucopus (Baker) and Aetheca wagneri (Baker) (Ceratophyllidae), Conorhinopsylla stanfordi Stewart and Epitedia faceta (Rothschild) (Hystrichopsyllidae), Sternopsylla distincta texana (C. Fox) (Ischnopsyllidae), and Craneopsylla minerva (Rothschild) (Stephanocircidae), were examined with a scanning electron microscope and are described from the resulting micrographs. In the Pulicidae and Ceratophyllidae the individual outer chorionic cells are not visible; the egg surfaces are covered uniformly with small, nodular tubercles. In contrast, the Hystrichopsyllidae and Ischnopsyllidae have a prominent, raised reticulum, very heavily constructed in the latter, delineating the chorionic cells. The single representative of the Stephanocircidae has only a faintly embossed chorionic reticulum. All of the species examined except E. faceta and C. minerva (both with a single micropylar opening) have multiple micropyles at the posterior end. C. felis, O. leucopus, A. wagneri, and C. stanfordi also have multiple aeropyles at the anterior end (these are lacking in S. d. texana). Lateral aeropyles, consisting of small groups of pores often associated with small mounds in the chorion, are present (maximum of two seen on any one egg) in all species except E. faceta, C. stanfordi, and C. minerva.

Fecundity and proportions of gravid females in populations of the bluetongue vector Culicoides imicola (Diptera: Ceratopogonidae) and several other species in Israel.

The gravid proportions of five Culicoides spp. in Israel were determined based on a suction light trap placed above calves in a cowshed and on two similar traps hung in a Eucalyptus tree at elevations of 1.4 and 26 m. In the cowshed, the proportion of gravid Culicoides distinctipennis Austen showed no significant variation between seasons; C. imicola Kieffer (the dominant species) was caught in significantly smaller proportions in winter; C. schultzei gp (second most dominant) showed no significant seasonal variation. In the Eucalyptus tree, a significantly smaller percentage was gravid in winter at the lower trap, but at the higher trap there was no significant variation between seasons. Culicoides circumscriptus Kieffer showed no significant seasonal variation at either height. C. distinctipennis was present with a significantly higher proportion gravid at the lower level in spring, but no significant variation between seasons was observed in the higher level trap. In C. imicola, gravids were proportionately more numerous in the lower trap in summer and autumn, but, in the higher trap, there was no significant variation between seasons. A significantly greater proportion of gravid C. schultzei gp females occurred at the higher level trap in spring, whereas no significant variation occurred in the lower level trap. Counts of eggs were made for C. cataneii, C. circumscriptus, C. distinctipennis, C. imicola, C. newsteadi Austen, C. obsoletus Meigen, C. saevanicus Dzhafarov, C. schultzei gp, and C. univittatus Vimmer. Counts for all four seasons were made only for C. circumscriptus and C. imicola, and only C. imicola showed significant variation between seasons (fecundity lower in autmn and winter).

Morphology of long- and short-day eggs of Aedes atropalpus and A. epactius (Diptera: Culicidae).

Scanning electron micrographs are used to document differences in the shape and fine structure of long-day (16:8 [L:D] h) and short-day (8:16 [L:D] h) eggs of Aedes atropalpus (Coquillett) and Aedes epactius Dyar & Knab from Illinois. Both shape and structural detail differed much more in A. atropalpus than in A. epactius. Long-day eggs of A. atropalpus were significantly longer and narrower; their outer chorionic cells on both the ventral (upper) and lateral surfaces were significantly smaller in area, with fewer small tubercles, and the detailed structure, shown in a comprehensive series of micrographs, was distinctly different than those of the short-day eggs. Dimensional differences of the whole egg were much less apparent in A. epactius; only width was significantly greater in short-day eggs. However, the ventral and lateral chorionic cells in the 2-d length groups showed the same highly significant differences in area and numbers of small tubercles as in A. atropalpus. Fine structural differences also were much less apparent in the eggs of A. epactius.

Natural food and feeding behavior of Culicoides furens larvae (Diptera: Ceratopogonidae).

The gut contents of Culicoides furens (Poey) larvae were compared with the relative abundance of potential food items in the natural larval habitat. Additional experiments examined the predatory behavior of the larvae by means of video recordings. Gut analyses indicated that filamentous green algae were the most frequently consumed food items. Diatoms, despite their high density in the soil, were not a major food source and many may have been ingested accidentally with algae. Gut content and video recording analyses indicated that nematodes, although occasionally eaten, probably were not the major dietary item. Moreover, fourth instars seemed to feed on nematodes more frequently during the day than during the night, possibly related to diel, small-scale vertical migrations of larvae in response to changes in light. When starved, larvae seemed to ingest nematodes more readily, as indicated by the absence of other items when nematodes were present in the gut. Overall, the results indicated that C. furens larvae are trophic generalists rather than solely predators.

Effect of light trap height on catch of Culicoides (Diptera: Ceratopogonidae) in Israel.

Vertical suction light trapping was conducted in 1981 at two dairy farms, Bet Dagan (traps at 1.4 and 26 m above ground) and Bet Alfa (traps at 1.5 and 20 m). Of the nine Culicoides species caught in both localities, only C. circumscriptus Kieffer and C. cataneii Clastrier showed a significant difference in abundance related to trap height; C. imicola Kieffer and C. schultzei sp. gp. also demonstrated a height preference, but catch sizes did not differ statistically. C. circumscriptus and C. cataneii, both avian feeders, and C. imicola, a mammalian feeder, were caught in greater numbers in the higher than in the lower traps. In contrast, more C. schultzei sp. gp. females were caught in lower than higher traps. Species collected more frequently in higher traps may be more prone to carriage for long distances by air currents and therefore are more likely to be important as dispersal vectors.

Activity of Culicoides furens larvae (Diptera: Ceratopogonidae) as related to light and nutritional state.

The diel activity of fourth-instar Culicoides furens (Poey) was studied in the laboratory by means of video recordings. Larvae in 0.5% agar under a photoperiod of 12:12 (L:D) h were observed under three nutritional states: starved 24 h before and during observation; fed (with nematodes) 24 h before, but starved during, observation; and fed both before and during observation. Starved larvae displayed considerably reduced activity compared with those that were better fed, both in terms of speed and type of movement (the proportion of time spent in continuous rather than intermittent motion). Under all nutritional states, larvae were more active during dark than light hours; 3-hourly observations of speed plotted for four periods of 24 h strongly indicated a diel cycle of activity, which may, in the field, be accompanied by vertical migration in the soil. Overall, our observations indicated that during development, C. furens larvae rove constantly through the substrate, at speeds of approximately 2 m/h (and up to 4 m/h), and that this movement is maintained even in the presence of abundant food.

Search behavior associated with egg cannibalism in Toxorhynchites amboinensis and Toxorhynchites rutilus rutilus (Diptera: Culicidae).

Observations based on time-lapse video recordings were used to study behavior associated with egg cannibalism in fourth-instar Toxorhynchites amboinensis (Doleschall) and Tx. r. rutilus (Coquillett). Analysis indicated that, once triggered by finding of the first egg, larvae of both species engaged in a systematic search of the water surface in an attempt to find additional eggs, which were often seized and eaten. Seven behavioral elements were identified in the search repertoire, and their relationships studied by analysis of a matrix of preceding and succeeding behaviors. The pivotal behavior was "sweep-adjust," which accounted for 87.2% of the time budget in Tx. amboinensis and 73.3% in Tx. r. rutilus. Activity in sweep-adjust consisted predominantly of side-to-side sweeps of the head, held just below the surface, punctuated by small forward adjustments of position. Quantitative aspects of the sweep arcs, in terms of angular and linear velocity, were determined for the two species. Eggs encountered during search probably were detected by mechanoreception, only within a very limited, kidney-shaped zone (area approximately 9.8 mm2) centered at the anterior margin of the head. Eggs were seized with the lateral palatal brushes but without head extension as seen in strikes at subsurface prey.

Effects of ultra-low volume and thermal fog malathion, Scourge and naled applied against caged adult Culicoides furens and Culex quinquefasciatus in open and vegetated terrain.

The adulticidal effect of ULV and thermal fog malathion, Scourge and naled was tested at 2x label dosage (1.42, 0.22, 0.39 oz/acre, respectively) against caged Culicoides furens and Culex quinquefasciatus in open and vegetated (orange grove) terrain. Cages were at 122 cm elevation and positioned at 15.2, 45.7, 76.2, 106.7, 137.2 and 167.6 m from the line of insecticide release. Ultra-low volume applications of all 3 insecticides were markedly more effective than thermal fog under all conditions, especially in vegetated terrain. Of the 3 insecticides, malathion performed the poorest, especially against Cx. quinquefasciatus (in which there was some resistance) and particularly when applied as thermal fog. Scourge and naled were about equally effective. The best adulticide against C. furens was naled, which was clearly superior applied as ULV. It yielded 75% mortality out to 283 m in the open, and to 38 m in the presence of dense vegetation.

Fine structure of the eggs of Haemagogus equinus and Hg. janthinomys (Diptera: Culicidae).

The eggs of Haemagogus equinus Theobald and Hg. janthinomys Dyar, the first of this genus to be examined with a scanning electron microscope, are described from material collected in Trinidad, West Indies. All surfaces of the eggs are described, including both dorsal and ventral surfaces at the anterior and posterior ends as well as the micropyle and associated apparatus. The dorsal surface, normally attached to the substrate, consists of a dense, hairlike mat of filaments formed from numerous, greatly elongated outer chorionic tubercles. These filaments possibly serve to improve anchorage of the egg as a protection against flushing by rain water or physical removal by predators. The outer chorionic cells on the ventral (upper) surfaces are extremely similar to those of two species of the subgenus Finlaya of Aedes, Ae. albolateralis (Theobald) and Ae. melanopterus (Giles), both collected in Taiwan.

Fine structure of the egg of Trichoprosopon digitatum (Diptera: Culicidae) and its relationship to egg raft formation.

Eggs of Trichoprosopon digitatum (Rondani) occur in rafts; the anterior poles are submerged, and the posterior two-thirds float above the water surface. Each egg is approximately 1,060 microns long and 270 microns wide. The hydrophilic end is more curved dorsally than ventrally and is covered with flattened, anteriorly pointed, scalelike tubercles except for a small area around the micropyle. The hydrophobic portion is clad in a layer of closely arrayed, small, round tubercles among which are positioned much larger, flattened, anteriorly directed tubercles with deeply fissured surfaces. At three positions equidistant around the periphery of the egg, narrow, tongue-shaped extensions (the embrasures) from the anterior hydrophilic region project posteriorly into the hydrophobic region. Along these embrasures, progressing posteriorly, the tubercles change in form from flattened and bladelike to finely tapered, then, at the extension's posterior two-thirds, to long filaments with well-developed terminal hooks. Eggs in rafts are maintained in polygonal rosettes by the interlocking of these filaments and hooks and the surface tension of menisci between contiguous embrasures.

Comparative fine structure of the eggs of Aedes albopictus, Ae. aegypti, and Ae. bahamensis (Diptera: Culicidae).

Complete descriptions, including details of the micropylar apparatus and outer chorion at the anterior and posterior poles and on the dorsal surface, are given for the eggs of Aedes (Stegomyia) albopictus Skuse and Ae. (S.) aegypti (L.). The egg of Ae. (Howardina) bahamensis Berlin, the first of this subgenus to be examined with the electron microscope, is described for the first time. Certain characters may be useful for differentiating eggs of these three species under a stereomicroscope. The substantially greater egg length in Ae. bahamensis alone separates it from the other two species, at least in the laboratory populations studied. The micropylar collar in Ae. aegypti clearly differentiates it from the other two. Further examination of mixed groups of eggs is needed to determine whether fine structural differences in the outer chorion can be correlated with consistent differences in the stereomicroscopic image.