Dynamique de la maturation des oeufs chez le parasitoïde Lixophaga diatraeae (Diptera, Tachinidae) élevé dans un hôte de substitution Alleria mellonella (Lepidoptera, Pyralidae).

Abstract

The content of the uterus and ovaries of L. diatraeae (an ovolarviparous tachinid fly) was studied by dissecting 121 females 0 to 25 days old. Several size classes of flies (p: small; m: medium; g: big) were used, weighing 10 to 12.5 mg, 12.5 to 13.5 mg, and 13.5 to 16 mg, respectively. The mean number of ovarioles per ovary, correlated to female size, was 12.1 for p as against 12.9 for m + g females. The total mean number of eggs and oocytes changed with female age and weight. For 0, 5, 10 and 15-day old females, this number was 56, 149, 158 and 202, respectively in g flies and 51, 128, 141 and 139, respectively, in p ones. To study egg maturation dynamics, we counted the total number of eggs + oocytes per p female (Y1), the eggs in the uterus (Y2), partially embryonated eggs (Y3), and entirely embryonated eggs (Y4). The experimental results were fitted to various age functions using a non-linear adjustment program. The models fitting each datum best were asymptotic functions of the form, Y = A [1-e-K(x-D)], where A is the asymptotic value, K a speed constant of the studied phenomenon and D age at the beginning of the phenomenon. At emergence time, each female contained a mean of 50 oocytes which passed into the uterus immediately after mating. Egg production continued for at least 10 days after emergence. The rate of embryogenesis seemed to be influenced by the number of eggs in the uterus and/or the age of the fly; it was high for the first eggs then decreased progressively. In our conditions, the first eggs with a planidium ready to hatch appeared at 10 days post-emergence. To obtain a maximum number of larvae in good health, it is better to dissect 12 to 18-day old females. The egg volume increases slightly during embryogenesis.