Pupal-adult parasitism of the coconut hispine beetle by the koinobiont pupal parasitoid Tetrastichus brontispae

Pupal parasitoids are considered to be idiobionts. However, some pupal parasitoids do not seem to kill or paralyze hosts at oviposition, including Tetrastichus brontispae, an endo-pupal parasitoid of Brontispa longissima. We conducted laboratory experiments to determine if T. brontispae parasitizes pupal hosts with a koinobiont developmental strategy. For this to be the case, its immatures would have to develop during the host transition from pupa to adult and in adulthood. With 0-d-old to 5-d-old pupal hosts, the T. brontispae females stung hosts of all ages with over 80% frequency. When the pupal hosts were parasitized, there were two modes of parasitism: pupal parasitism and pupal-adult parasitism. For pupal hosts that were parasitized, the majority showed a typical pupal parasitism, involving first the mummification of parasitized pupae and then the development of the parasitoid immatures within and emergence from these mummified pupae. However, the parasitized pupae that did not become mummified developed to host adults in which the parasitoid immatures developed, indicating pupal-adult parasitism. When parasitized pupal hosts were mummified, the 0-d-old to 3-d-old pupae were more likely than the older pupae to be mummified and had a greater number of parasitoid adults produced per host. The pupal-adult parasitism was not as successful. The parasitoid adults only successfully emerged from two host adults, which were parasitized as 2-d-old pupae, and one host adult parasitized as a 3-d-old pupa. The parasitoid eggs laid in 4-d-old and 5-d-old pupae continued to develop during and after the host transition from the pupa to adult. However, when the host adults died within 10 days after emergence, all the parasitoids died without completing their development. These results suggest that T. brontispae is a koinobiont parasitoid that successfully parasitizes young pupal hosts mainly through host mummification and rarely through pupal-adult parasitism. The fact that many parasitized 4-d-old or 5-d-old pupae died at the pupal or adult stage without producing any parasitoids, may also suggest that, under natural conditions, the pupal and adult mortality of B. longissima resulting from parasitism by T. brontispae is significant.