Sex ratios in field populations of two parasitoids (Hymenoptera: Chalcidoidea) of Coccus hesperidum L. (Homoptera: Coccidae)

Abstract

We tested several assumptions and predictions of host-quality-dependent sex allocation theory (Charnov et al. 1981) with data obtained for the parasitoid Metaphycus stanleyi Compere on its host, brown soft scale (Coccus hesperidum L.), in a California citrus grove and in the laboratory. Scales ceased growing after parasitization by M. stanleyi. Thus, M. stanleyi may gauge host quality (=size) at oviposition. Host size positively influenced adult parasitoid size, and parasitoid size in turn influenced adult longevity of M. stanleyi. However, parasitoid fitness gains with host size and adult size were similar in males versus females. Sex allocation to individual hosts by M. stanleyi depended on host size; females consistently emerged from larger hosts than males. Host size was important in a relative sense; the mean host sizes of females versus males, and of solitary versus gregarious parasitoids varied with the available host size distribution. The offspring sex ratio of M. stanleyi reflected the available host size distribution; the sex ratio of emerging parasitoids varied with the available host size distribution. We did not detect a "critical host size" below which males emerged, and above which females emerged; rather, only females emerged from hosts in the upper size range, and a variable ratio of males and females emerged from hosts in the lower size range. We conclude that the sex ratio of field populations of M. stanleyi is driven largely by the available size distribution of C. hesperidum. In addition, we tested predictions resulting from theoretical analyses of sex allocation in autoparasitoids with data obtained on Coccophagus semicircularis (Förster) parasitizing brown soft scale in the field. The sex ratio of C. semicircularis was consistently and strongly female biased (ca. 90% females). Based on available theoretical analyses, we suggest that this sex ratio pattern may have resulted from a very low encounter rate of secondary hosts coupled with a strong time limitation in C. semicircularis females. This explanation was the most plausible given constraints stemming from the detection of secondary hosts, their variable location within primary hosts, and their handling times. Finally, the size of hosts which yielded single versus multiple parasitoids, and the sizes of these parasitoids, were compared. These comparisons suggested that: (1) M. stanleyi females gauge host sizes precisely, and in terms of female offspring; thus a fitness penalty is not incurred by females which share a host, while males benefit from sharing a host, and; (2) instances where multiple C. semicircularis emerged from a single host were probably the result of parasitism by different females, or during different encounters by a single female.

Augmentative Releases of <I>Metaphycus</I> sp. nr <I>flavus</I> Against Citricola Scale on Oranges in the San Joaquin Valley of California: Are Early Releases Better Than Late Ones?

“…5) as hosts, as proposed by Bernal et al (1999a), albeit only for male offspring production. This is consistent with the results of Lampson et al (1996) and Bernal et al (1998Bernal et al ( , 1999b, which suggested that Metaphycus spp. use hosts of marginal size mostly for male offspring production.…”

Host influences on sex ratio, longevity, and egg load of two Metaphycus species parasitic on soft scales: implications for insectary rearing

“…It is not currently established in California although it has been previously imported and released in the state (Kennett et al, 1995;Bernal, unpubl. Metaphycus stanleyi is also an internal parasitoid of various soft scales, including brown soft, citricola, and black scales (Annecke, 1964;Bernal et al, 1998). Metaphycus stanleyi is also an internal parasitoid of various soft scales, including brown soft, citricola, and black scales (Annecke, 1964;Bernal et al, 1998).…”

“…data). It was imported to California from South Africa in 1937 for release against black scale (Bartlett, 1978), and is currently widely distributed within the state (Bartlett, 1953;Lampson & Morse, 1992;Bernal et al, 1998). It was imported to California from South Africa in 1937 for release against black scale (Bartlett, 1978), and is currently widely distributed within the state (Bartlett, 1953;Lampson & Morse, 1992;Bernal et al, 1998).…”

“…data; H. Schweizer, unpubl. (Bernal et al, 1998). Also, M. flavus is currently being colonized for permanent establishment in California.…”

Lethal and sub-lethal effects of insecticides on natural enemies of citrus scale pests

“…A. melinus is considered the main biotic mortality factor of A. aurantii in Italy (Lizzio et al 1998) and it is currently used in biological control programs by means of augmentative releases (Tumminelli et al 2000;Mazzeo et al 2004;Zappalà et al 2008); C. lycimnia and other species of the same genus are among the most common parasitoids of soft scales of economic importance all over the Mediterranean basin (Walter 1988;Bernal et al 1998); L. dactylopii is the most widely used parasitoid of the Citrus mealybug by means of inoculative releases.…”