Studies On Succession, Distribution, and Phenology of Imported Parasites of Therioaphis Trifolii (Monell) In Southern California

Abstract

The three introduced hymenopterous parasites of Therioaphis trifolii (Monell) were intensively studied for six years in four major climatic regions of southern California. These regions were the Colorado Desert the south coastal plain (two subdivisions), the western Mojave Desert, and the southern San Joaquin Valley. The studies revealed a succession in predominance of Trioxys utilis Muesebeck over Praon palitans Muesebeck, which dominated in the years immediately following parasite introduction. The status of the three wasps varies from one climate area to another. Trioxys is essentially exclusive in the Colorado Desert valleys and strongly dominant elsewhere. Praon attains its greatest importance in the western Mojave Desert and southern San Joaquin Valley. The third wasp, Aphelinus, reaches its most important status on the south coastal plain and is also relatively important in the western Mojave Desert. Parasite phenologies vary. Trioxys has the ability to be intensively active during the several seasons of the year. Praon is most active in the spring and fall. Aphelinus is relatively most active during the cooler, more humid times of the year. The general importance of these several phenomena to biological control programs is discussed.

Predation on aphids in California's alfalfa fields

“…Over-all parasitization of the two aphid species never reached more than three aphids per 100 stems or 2.4 per cent as a monthly mean. By contrast, van den Bosch et al (1964) report SAA parasitization rates of up to 65 per cent by the recently introduced Trioxys complanatus Quilis, Praon exsoletum palitans Muesebeck (both Aphidiidae), and Aphelinus as y chis Walker (Eulophidae, Aphelininae) only 120 miles south of our fields. Aphidius smithi Sharma and Rao (Aphidiidae) which was released against the PA from 1958 onward (Hagen and Schlinger, 1960), reached parasitization rates of 40 to 60 per cent in the early 60's, exhibiting a clearly density-dependent response (van den Bosch et al, , 1967.…”

“…More recently four imported parasites have become very important for the regulation of the spotted alfalfa aphid and the pea aphid. Although the ecology of the imported parasites (van den Bosch et al, 1964) and of the coccinellids (Smith and Hagen, 1966) is well known, little information is avail-able as to the relationship between other predators and these aphids.…”

Parasitization of Acyrthosiphon Pisum by Aphidius Smithi, A Density‐Dependent Process in Nature. (Homoptera: Aphidae) (Hymenoptera: Aphidiidae)

“…Sampling was done with a De-Vac mechanical sampler (Dietrick 1961) and depending on the density of the aphids, either 2S, SO, or 100 square feet of alfalfa were sampled on each collecting date. The collected material was processed through a modified Berlese funnel system as described by van den Bosch et al (1964). At the time of sample analysis, pea aphids, Aphidius adults, spotted alfalfa aphids (Therioaphis trifolii (Monell)), spotted alfalfa aphid parasites, and several known aphid predators were counted and recorded.…”

Introduced Species, Impacts and Distribution of

“…For example, the yellow clover aphid (Therioaphis trifolii) is controlled in California by three parasitic wasps, Praon palitans, Trioxys utilis, and Aphelinus semiflavus (van den Bosch et al, 1964). For example, the yellow clover aphid (Therioaphis trifolii) is controlled in California by three parasitic wasps, Praon palitans, Trioxys utilis, and Aphelinus semiflavus (van den Bosch et al, 1964).…”