Competition, resource partitioning and coexistence of an endoparasitoid Encarsia perniciosi and an ectoparasitoid Aphytis melinus of the California red scale

Abstract

Abstract. 1. Laboratory experiments and field studies were conducted to explain the coexistence of an endoparasitoid, Encarsia perniciosi Tower, and an ectoparasitoid, Aphytis melinus DeBach, both of which were introduced into California to control the California red scale, Aonidiella aurantii (Mask.). 2. Encarsia parasitized all scale stages but it preferred first and second instar scales. This is in contrast to Aphytis melinus, in which previous studies have shown that it parasitizes second and third instar females and second instar males but prefers third instar female scales. Encarsia developed most rapidly when it parasitized an early second instar and slowest when it parasitized the mature female scale. However, on early second instar scales it was about 80% as fecund as a wasp that emerged from a mature female scale. 3. Second instar scales parasitized by Encarsia were accepted by Aphytis as readily as unparasitized scales. 4. Encarsia did not distinguish between unparasitized hosts and those previously parasitized by Aphytis. 5. Encarsia always outcompeted by Aphytis when both species parasitize the same host. 6. Encarsia prefers scale on stems whereas Aphytis prefers those on leaves and fruits. This, too, may be a result of interspecific competition with Aphytis. 7. The partitioning of the scale resource by the two species explains why they coexist in coastal southern California but it does not explain why Encarsia disappeared from citrus groves in the inland valleys coincident with the introduction of Aphytis melinus into southern California.

Coexistence in a Competitive Parasitoid-host System

“…Similar results are reported by Yu, et al (1990) for A. melinus and Encarsia perniciosi, two competing parasitoids of the California red scale. They attributed coexistence to differences in host utilization (resource partitioning).…”

“…A consistent advantage by one species has been reported and it is based on the biology of competitors, for example, heteronomous and telytokous parasitoids (Bogra´n et al, 2002, Yu et al, 1990. Also, Aphidus smithi is consistently an inferior competitor to A. ervi (Godfray, 1994).…”

Displacement of Aphytis chrysomphali by Aphytis melinus, parasitoids of the California red scale, in the Iberian Peninsula

“…We have shown that A. melinus and E. perniciosi are sympatric in groves of southern Spain, and that the latter shows a preference for twigs. This coincides with the situation on the California coasts described by Yu et al (1990), who stated that this resource partitioning could explain the coexistence of A. melinus and E. perniciosi. In this work CRS sampling was not conducted during the first CRS generation, May-June, when fruit is not present yet and therefore, A. melinus and E. perniciosi are forced to compete for the same resource.…”

“…Aphytis lingnanensis and E. perniciosi were also introduced in this region, but their establishment was not successful (Rodrigo et al, 1996;Pina et al, 2003;Sorribas et al, 2010). Parasitoids of CRS are usually found as species guilds that may vary in their composition at different sites and different substrates of the plant due to different environmental condition requirements as well as host stage preferences (Yu et al, 1990;Rodrigo et al, 1996). For their ecological success, parasitoids must adapt to a range of environmental conditions similar to the ones required by their host.…”

Lethal interference competition in the whitefly parasitoids Eretmocerus eremicus and Encarsia sophia

“…Other examples of host feeding on parasitised hosts exist, though they are few. Yu et al (1990) found that Aphytis melinus multiparasitised and host fed on scale insects previously parasitised by Encarsia perniciosi. In combination, host feeding and multiparasitism by A. melinus caused mortality of E. perniciosi, although as presented, the data do not separate the effects of the two phenomena.…”