Entomophaga

, Volume 38, Issue 1, pp 69–77 | Cite as

Effects of host age and cocoon position on attack rate by the hyperparasitoid,Eurytoma sp. [Hym.: Eurytomidae], on cocoons of the parasitoid,Cotesia (=Apanteles) glomerata [Hym.: Braconidae]

  • J. Tagawa
  • H. Fukushima
Article

Abstract

Host age preference of the hyperparasitoid,Eurytoma sp., attacking the cocoons of the gregarious parasitoid wasp,Cotesia (=Apanteles) glomerata L., was investigated in the field and laboratory. Under laboratory conditions of 20°C and L16D8 photoperiod.Eurytoma sp. parasitized cocoons of all ages, laying 7 to 10 eggs per cluster during a 24 h period. Field-collected cocoons also indicated that the host was parasitized regardless of its developmental stage. However, the mortality ofEurytoma sp. laid in cocoons on the day before host emergence was as high as 60%. Furthermore, progeny sex ratio (proportion males) reached 0.708 in eggs laid in the oldest cocoon clusters, whereas that for younger cocoons was strongly female-biased. Together, these facts suggest that older hosts are less suitable forEurytoma sp. than are younger ones, even though there was no significant decreasing tendency in the number of parasitized cocoons per cluster. In addition, the effect of cocoon position within a cluster was apparent, outer cocoons being more easily parasitized than inner ones. TheEurytoma sp. female oviposited at random on the free surface ofC. glomerata cocoons.

Key-Words

hyperparasitoid host age sex ratio cocoon position 

Résumé

Le rôle de l'âge de l'hôte dans les attaques de cocons du parasitoïde grégaireCotesia glomerata par l'hyperparasitoïdeEurytoma sp. a été étudié en conditions de laboratoire et en conditions naturelles. En laboratoire (température de 20° et photopériode L16/D8),Eurytoma parasite des cocons de tous âges et pond 7 à 10 œufs par agrégat en 24 h. Les cocons prélevés sur le terrain montrent également que l'hôte est parasité indépendamment de son stade de développement. Néanmoins la mortalité des œufs d'Eurytoma pondus dans les cocons la veille de l'émergence de l'hôte atteignait 60%.

En outre, le sex ratio de la descendance (proportion des mâles) s'élevait à 0,708 dans les œufs pondus dans les agrégats les plus âgés alors qu'il était nettement en faveur des femelles dans les cocons les plus jeunes. L'ensemble de ces observations semblent indiquer que les hôtes les plus âgés conviennent moins bien àEurytoma sp. que les plus jeunes, même s'il n'y a pas de tendance significative à une diminution du nombre de cocons parasités par agrégat.

Enfin l'effet de la position du cocon dans l'agrégat a été démontré, les cocons situés à l'extérieur étant plus facilement parasités que les autres. La femelle d'Eurytoma sp. pond au hasard sur les surfaces accessibles des cocons deC. glomerata.

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Copyright information

© Lavoisier Abonnements 1993

Authors and Affiliations

  • J. Tagawa
    • 1
  • H. Fukushima
    • 1
  1. 1.Faculty of Liberal Arts and ScienceOkayama University of ScienceOkayamaJapan

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