Sex identification of eggs of a dryinid parasitoid, Haplogonatopus atratus, based on oviposition behaviour

Autor: Yoshihiro Y. Yamada, Megumi Kawamura
Rok vydání: 1999
Předmět:
Zdroj: Entomologia Experimentalis et Applicata. 93:319-322
ISSN: 1570-7458
0013-8703
Popis: Sex ratio in Hymenoptera shows wide variation between different species as well as within the same species under different conditions (King, 1987; Godfray, 1994). This observation has recently attracted many researchers with an interest in the development of sex-allocation theories (see Charnov, 1982). Researchers have often measured sex ratio at the time of emergence to test sex-allocation theories, but for more accurate testing, it is necessary to sex eggs as well as emerging adults. The sex ratio is often different in eggs and emerging adults due to differential mortality between the sexes (see King, 1987). However, sex identification of insect eggs is not easy because they have the same appearance irrespective of their sex. Two methods are currently available to determine the sex of hymenopteran eggs. One method is to determine the number of chromosomes at the egg stage (van Dijken, 1991; Ueno & Tanaka, 1997): this method relies on the fact that hymenopteran sex is determined by haplodiploidy, so that males are haploid and females are diploid. The other method is to detect and measure behavioural differences between male-egg oviposition and female-egg oviposition. This method relies on the fact that a pause phase is seen during femaleegg oviposition; i.e., during female-egg oviposition there is a period of little or no rhythmic movement of the whole abdomen or the abdominal tip including the ovipositor and valvifers (Gerber & Klostermeyer, 1970; Cole, 1981; Suzuki et al., 1984; van Dijken & Waage, 1987; Strand, 1989; Ueno, 1995), or such a period is longer during female-egg oviposition than during male-egg oviposition (van Baaren et al. 1995). The chromosome-checking method is exact, but is usually time-consuming and sometimes requires special techniques. In addition, eggs are killed by the procedure, making further experimentation impossible. On the other hand, the behaviour-observational method is very efficient, but may not provide precise identification (van Baaren et al., 1995; Ueno, 1995). In this study, videotape was used to document the oviposition of Haplogonatopus atratus Esaki and Hashimoto (Hymenoptera: Dryinidae), a solitary parasitoid host-specific to the small brown planthopper, Laodelphax striatellus Fallen (Hemiptera: Delphacidae). The details of sexing eggs based on oviposition behaviour are shown, and furthermore, the difference in oviposition behaviour between mated and unmated females is clarified.
Databáze: OpenAIRE
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