Competition between two parasites of the Florida red scale in Israel

Abstract

1. During the last decade, the endoparasitic wasp Pteroptrix smithi (Compere) has gradually replaced the ectoparasitic wasp Aphytis holoxanthus DeBach on the Florida red scale, Chrysomphalus aonidum (L.), on citrus in Israel. The studies reported herein were aimed at elucidating some of the mechanisms of this process.2. Aphytis adults detected, and were attracted to hosts containing eggs of Pteroptrix, whereas adults of Pteroptrix did not detect hosts containing eggs of Aphytis. In this extrinsic aspect of host discrimination, Aphytis is superior to its competitor. Neither species responded to hosts containing heterospecific first-instar larvae, and both tended to avoid hosts containing more advanced developmental stages of the other species.3. Aphytis outcompeted Pteroptrix in most cases of multiple parasitism, as observed under both controlled and field conditions. 4. Aphytis was superior in mixed-species cultures; however, its dominance was affected by the availability of adult food.5. Aphytis adults were found to be more sensitive (X4.11) to the insecticide malathion as compared to adults of Pteroptrix. This finding provides a possible explanation to the displacement of Aphytis by Pteroptrix in the citrus groves along the coastal plain of Israel.

The population dynamics of the white peach scale and its parasitoids in a mulberry orchard in Campania, Italy

“…tend to be more vulnerable to pesticides because they develop externally. In the parasitoid complex of Florida red scale in Israel, A. holoxanthus was generally more abundant than Pteroptrix smithi (Compere), but the relative abundance was reversed when malathion was applied (Steinberg et al, 1987). Encarsia berlesei may also be more vulnerable to pesticides than P. orientalis because its peak emergence period in June and July coincides with a period of frequent pesticide treatment.…”

“…Aphytis proclia was the probable victor in these contests (PAP, unpublished data), and therefore caused mortality of E. berlesei. All species of Aphytis are ectoparasitoids, and are often competitively superior to endoparasitoids in the same complex (Kennett et al, 1966;Steinberg et al, 1987).…”

Two Competing Parasitoid Species Coexist in Sympatry

“…It is also argued now (Bakker et al 1985, van Alphen and Visser 1990) that intraspecific discrimination is not always an advantageous strategy. The detection by parasitoids of competitors within a host generally appears to require host necrosis provoked by the first infection (Strand 1986, Steinberg et al 1987.…”

Interspecific discrimination and larval competition amongMicroplitis croceipes, Microplitis demolitor, Cotesia kazak (Hym.: Braconidae), andHyposoter didymator (Hym.: Ichneumonidae), parasitoids ofHeliothis virescens (Lep.: Noctuidae)

“…Interspecific host discrimination is relatively rarely reported, and in studies where rejection of hosts parasitized by another parasitoid species has been shown, this discrimination is time-dependent (Steinberg et al, 1987 ;Strand, 1986 ;Vinson, 1972 ;Wylie, 1970Wylie, , 1971 ; van Aiphen & van Strien-van Liempt, unpubl, data). Other endoparasitoids of H. virescens have been reported not to discriminate interspecifically.…”

“…In cases where rejection of hosts parasitized by another parasitoid species has been shown, this rejection is more likely to be due to a severely changed physiological condition of the host, rather than to the recognition of a specific mark (Steinberg et al, 1987 ;Strand, 1986;Vinson, 1972;Wylie, 1970Wylie, , 1971; van Alpben & van Strien-van Liempt, in preparation). An exception was reported by Vet et al (1984) who determined that Asobara tabida (Nees) and Asobara rufescens (Foerster) were capable of discriminating against hosts recently parasitized by females of the other species.…”