Age and suitability of Amorbia cuneana (Lepidoptera : Tortricidae) and Sabulodes aegrotata (Lepidoptera : Geometridae) eggs for Trichogramma platneri(Hymenoptera : Trichogrammatidae)

The relationship between different ages of Amorbia cuneana (Lepidoptera: To rtricidae) Walsingham and Sabulodes aegrotata (Guenee) (Lepidoptera: Geomet ridae) eggs and parasitism by Trichogramma platneri Nagarkatti platneri (Hy menoptera: Trichogrammatidae) was studied in the laboratory. T. platneri ma nifested low rates of larval mortality, high numbers of emerging adults per egg mass, and highly female-biased sex ratios, when T platneri parasitized A cuneana egg masses that were 1, 5, or 7 days old. No parasitoid larvae e merged when T platneri parasitized 9-day-old egg masses. When T. platneri p arasitized S. aegrotata eggs in an egg cluster, it had low rates of larval mortality and a highly female-biased sex ratio, but it only parasitized a f ew of the eggs in a 1- or 3-day-old egg cluster. No parasitoids emerged fro m the eggs in a 5-day-old egg cluster. In both species, embryos in the olde st eggs tested had well-developed head capsules. A few parasitoids emerged from singly laid, 9-day-old A. cuneana eggs, but those that emerged were sm aller and less fecund than their counterparts from 1-, 5-, and 7-day-old eg g masses. Acceptance of S. aegrotata eggs also depended on their physical p roperties. The thick chorion of S. aegrotata eggs and the sticky coating on recently laid eggs leads to fewer of the eggs being parasitized. These fac tors when coupled with the shorter developmental time of S. aegrotata eggs appear to explain the less frequent parasitism of S. aegrotata eggs when co mpared to those of A cuneana. Acceptance of these eggs as hosts was also re flected in the percentage of the parasitoid's egg load retained after expos ure to the hosts. Using this criterion, A cuneana eggs were more readily ac cepted than those of S. aegrotata. (C) 2000 Academic Press.