Author
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Castle, Steven |
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Submitted to: Bemisia International Workshop Proceedings
Publication Type: Abstract Only Publication Acceptance Date: 12/3/2006 Publication Date: 12/8/2006 Citation: Castle, S.J. 2006. Fertility of Bemisia tabaci and Sex Ratio Determination According to Male Availability. Bemisia International Workshop Proceedings, December 3-8, Key West, FL, 8:4 p. 34. http://www.insectscience.org/8.04/ref/abstract19.html Interpretive Summary: Technical Abstract: The expression of biotic potential in Bemisia tabaci populations is recognized worldwide by numerous historical outbreaks and a propensity to routinely attain high density infestations in various crop environments. Fertility rates of females are a crucial aspect of population growth and an important component of the pest potential of herbivorous insects. Based on mean lifetime eggs laid per female, past studies have provided variable estimates of fecundity ranging from <50 to >300. In the present study, per capita reproduction was measured by collecting F1 progeny adults from individual parental pairs, thus providing a measure of fertility. In addition, sex ratios of F1 progeny were determined for both paired and unpaired parental females, thereby allowing the role of male availability to be revealed. Experiments were carried out under natural light conditions in a clean greenhouse to avoid extraneous whiteflies and natural enemies. To obtain wild-type virgin adults, outdoor-grown eggplant leaves with late fourth instar nymphs were collected from the field one day prior to adult emergence. Virgin adults were collected as they emerged from their nymphal exuviae and held in gelatin capsules, then sorted into male and female groups using a microscope. Single males and females were then randomly paired within an 8 cm2 clip cage attached to whitefly-free cantaloupe plants. In the initial study, a cohort of 36 pairs were followed over a 24 day period. Serial tranfers of the parental pairs were carried out on six different leaves per pair. Once attached, clip cages remained in position on leaves through courtship and copulation, egg laying and hatching, immature development and emergence of the progeny adults. Collection of emerged adults were made each day over a 30 day emergence period and daily proportions of sons and daughters were determined under a microscope for each parental female. In a follow-up study, access to males was experimentally manipulated using five different treatments involving period and duration of exposure to males over the course of female lifetimes. Of the initial 36 pairs started in the first experiment, 11 pairs remained intact for the 24 day duration. Eight of the 11 pairs produced total brood female proportions ranging from 0.59 to 0.77, while the other three pairs produced sex ratios near parity. Five of the eleven pairs produced total adult progeny that exceeded 500, and all but one pair had total adult progeny in excess of 400. The highest number of progeny produced was 608; mean progeny for all 11 pairs was 439. Of the remaining pairs of the original 36, surviving females that lost mates soon began laying unfertilized eggs based on records of subsequent adult emergence. The decline of female progeny was quite rapid and usually complete within three days following loss of the male. These observations were substantiated in the second experiment in treatments that involved isolation of females following a period of coupling with a male. In contrast, females initially isolated from males produced only male progeny until being paired with a mate, then began producing female progeny within one day of being paired; only male progeny were produced by females that remained unpaired for the duration of the experiment. These results demonstrate that males must be available for repeated copulations throughout the lifetime of females for egg fertilization to occur. Rapid shifts in sex ratio in both greenhouse colonies and field infestations may occur according to the availability of males for mating. |
