20 August 1977

J. Med. Entomol. Vol. 14, no. 1: 121-127

THE INFLUENCE OF CARBOHYDRATE-FEEDING AND INSEMINATION ON OVIPOSITION OF AN INDIANA STRAIN OF AEDES VEXANS (DIPTERA: CULICIDAE)1 By D. A. Shroyer 23 a n d D. P. Sanders 24 insemination (Craig 1967, Fuchs et al. 1969, Gwadz & Craig 1970, Gwadz et al. 1971). Matrone is also responsible for stimulation of oviposition in several mosquito species (Leahy & Craig 1965, Hiss & Fuchs 1972). Aedes vexans (Meigen) is one of the most common and locally abundant mosquitoes in the midwestern U.S.A., and the species is of considerable medical importance aside from its notoriety as a nuisance mosquito. Yet the poor qualities of Ae. vexans as a laboratory animal have contributed to a paucity of experimental investigations into its reproductive biology. Ae. vexans has not been studied with regard to the effects of insemination or carbohydrateingestion on oviposition behavior, and this became the objective of the present study. Indeed, the interaction of these 2 factors has not been previously examined within a single species of mosquito. MATERIALS AND METHODS

Mosquitoes of both sexes ingest carbohydrates from floral and extrafloral nectaries and from other sources such as fallen fruit. In most species, carbohydrate food is necessary for survival of females to a reproductive age, and it is customary to provide colonized mosquitoes a sugar source to maximize

The TIPPECANOE strain of Ae. vexans utilized in this study originated from larval and pupal collections made in 1973 at a vernal woodland depression habitat in Tippecanoe County, Indiana. The results reported herein were obtained from the 3rd and 4th laboratory generations. survival. However, in Culex pipiens quinquefasciatus Larvae were reared in incubators providing a Say and Aedes atropalpus Coquillett it has been noted water temperature of 25.0 ± 1.0 °C in the open that prolonged exposure to a sugar source leads to rearing trays. Pupae and adults were maintained inhibition of oviposition despite otherwise favorable at 25.0 ± 0.5 °C and 85 ± 1 0 % RH. Postembryonic conditions (de Meillon et al. 1967, Hudson 1970). development and adulthood occurred under a It has become apparent that insemination in 15-hr incandescent photophase, without "dawn" the Culicidae has important functions other than and "dusk" periods. the obvious one of sperm transfer. Matrone, a Eggs were hatched in deionized water by deoxypheromone produced by the male accessory gland genation with nitrogen. Larvae were reared in and transferred to the female during copulation, deionized water at a maximum density of 100 per renders the female mosquito refractory to further 1.2 liters, and were fed finely powdered Tetramin 4 in 1® fish food deposited as a slurry below the 'Journal Paper No. 6217 of the Purdue University Agricultural water surface. Larval mortality was generally Experiment Station. Part of a thesis submitted by the senior author in partial fulfillment of the requirements for the degree 1-2%. Pupae were transferred to gallon-capacity of Master of Science at Purdue University. (3.8-liter) emergence cages, and mortality in this 'Department of Entomology, Purdue University, West stage was rare. Lafayette, Indiana 47907, U.S.A. Adults were routinely provided a 10% (wt/vol.) 'Present address: Vector Biology Laboratory, Department of Biology, University of Notre Dame, Notre Dame, Indiana solution of sucrose (commercial cane sugar) prior 46556, U.S.A. to the single blood meal. Feeding was restricted 4 Present address: Department of Entomology, Texas Tech to a single human host to eliminate any possible University, Lubbock, Texas 79409, U.S.A.

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Abstract: The oviposition behavior of an Indiana strain of Aedes vexans (Meigen) was studied in relation to the effects of rarbohydrate-feeding and insemination. Oviposition of inseminated and virgin Ae. vexans was compared at 2 levels of availability of a 10% sucrose solution. Both insemination and frequency of carbohydrate-feeding markedly influenced oviposition, as measured by several parameters. Inseminated females oviposited on 4 or 5 different days during the first 17 after a single human blood meal, whereas virgins averaged only 3 ovipositions. Virgins commenced oviposition 1-2 days later than inseminated females. Carbohydrate-starved females deposited about 49 eggs per oviposition. Females allowed to ingest sucrose during the gonotrophic cycle deposited approximately 22 eggs per oviposition. When sucrose was continuously available, virgins and inseminated females deposited 35% and 61%, respectively, of the eggs developed. Carbohydrate-starved mosquitoes laid 87-90% of their eggs regardless of mating condition. The effects of sucrose ingestion and insemination were also reflected in the proportion of females failing to oviposit. Ingestion of a honey solution inhibited oviposition in a manner similar to that of sucrose. Virginity and ingestion of carbohydrate enhanced survival of Ae. vexans, but carbohydrate diet and insemination had no influence on the number of eggs developed by the females.

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ment were completed, involving a total of 216 individuals. Within each replicate, individuals were siblings of identical age. Females of the "inseminated" category were force-copulated, while "virgins" were etherized for 15 s. to avoid confounding of the effects of insemination and the etherization procedure. Experimental manipulations were performed 1-3 hr after the blood meal (4-6 days postemergence). Egg counts for each female were made daily between 0600 hr and 1200 hr. Each replication ran a minimum of 17 days following the single blood meal. All females were dissected to determine by spermathecal examination the success of forced copulation, and to count any Stage V ova retained in the ovaries. Data from force-copulated females later found to have empty spermathecae were discarded. Parameters of oviposition response evaluated included (1) percentage of females ovipositing, (2) number of days ovipositing, (3) number of eggs laid per day of oviposition, (4) number of days to 1st oviposition, and (5) the oviposition index. Use of the oviposition index was first proposed by Hiss & Fuchs (1972), and as used in this study it represents the proportion of all mature eggs deposited by a female by a specified time after the blood meal. Oviposition index = number of eggs laid/ (number of eggs laid + number of eggs retained), calculated for a specified period of time after the blood meal. An index of 0.000 represents retention of all eggs in the ovaries, while an index of 1.000 indicates complete oviposition. RESULTS

The mean number of eggs produced per female (eggs retained -f eggs deposited) was determined for each experimental group (TABLE l). Most

TABLE 1. Fecundity and survival of inseminated and virgin Aedes vexans under conditions of limited and unlimited availability of 10% sucrose.* No. EXPERIMENTAL GROUP

OF

$$

MEAN NO. OF EGGS DEVELOPED**

MEAN NO. OF DAYS SURVIVING***

Inseminated $°. Sucrose before and 58 149.3 ± 4.5 16.1 ± 0.3 after blood meal Sucrose before blood 57 meal only 147.8 ± 4.8 13.3 ± 0.3 Virgin ?? Sucrose before and 50 after blood meal 137.7 ± 4.6 17.0 ± 0.0 Sucrose before blood 51 meal only 141.1 ± 4.2 14.0 ± 0.4 •The number of days surviving in the first 17 following the blood meal was determined. **Mean ± standard error. Means are not significantly different. ***Mean ± standard error. All means are significantly different at the 5% level (NewmanKuels Sequential Range Test).

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differences in blood sources. Blood-fed females to be inseminated by forced copulation were anesthetized by a 15- to 20-s. exposure to ethyl ether fumes. Females were mated to sibling males which had been chill-anesthetized prior to their decapitation, removal of their legs, and impalement by a minuten pin mounted in an applicator stick. Male preparations were discarded after copulation with 2 females. The forced copulation procedure induced no female mortality, and resulted in insemination of 90% of all females. Isolated Ae. vexans females were maintained in 18.5 cm3-capacity cages constructed from plastic zipper cases, and fresh carbohydrate food was supplied on alternate days by placing saturated pads of facial tissue over an access hole on the top of the cage. The oviposition substrate consisted of 8-layer cheesecloth strips in which a moisture gradient was maintained. Cages were positioned on the cheesecloth in a previously determined zone of preferential oviposition. This system was an alternative to a less desirable, water-saturated oviposition substrate. Eggs were removed from cheesecloth and filtered onto discs of paper towelling, on which they were counted under a stereo microscope with the aid of a 1-cm grid. A factorial experimental design was employed to determine the effects of carbohydrate-feeding and insemination on oviposition response of Ae. vexans. Four groups of females were required, as follows: (1) inseminated females having access to 10% sucrose prior to the single blood meal, and continuously thereafter, (2) inseminated females provided sucrose prior to the blood meal only, (3) virgin females having access to sucrose prior to the blood meal and continuously thereafter, and (4) virgin females having access to sucrose prior to the blood meal only. Four replications of the experi-

Vol. 14, no. 1

1977

Shroyer & Sanders:

Influences on oviposition of Ae. vexans

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TABLE 2. Duration of the preoviposition period and incidence of complete inhibition of oviposition in Aedes vexans. Females were either inseminated or virgin, and they were maintained under conditions of limited or unlimited availability of 10% sucrose. !¥ WHICH OVIPOSITED EXPERIMENTAL GROUP

% WHICH FAILED TO OVIPOSIT

No.

Mean no. of days to 1st oviposition*

females produced 140-150 eggs per human blood meal in the 1st gonotrophic cycle, though fecundity ranged from 15-208 eggs. Analysis of variance performed on these data indicated that neither insemination nor availability of sucrose significantly affected the number of eggs developed after a single blood meal. The carbohydrate diet X insemination interaction was also nonsignificant. However, fecundity differed significantly from one replication of the experiment to the next (P

The influence of carbohydrate-feeding and insemination on oviposition of an Indiana strain of Aedes vexans (Diptera: culicidae).

20 August 1977 J. Med. Entomol. Vol. 14, no. 1: 121-127 THE INFLUENCE OF CARBOHYDRATE-FEEDING AND INSEMINATION ON OVIPOSITION OF AN INDIANA STRAIN O...
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