A numerical taxonomic study of variation in populations of Typhlodromus caudiglans Schuster (Acarina: Phytoseiidae)

Variation in morphological characters between Canadian populations of Typhlodromus caudiglans Schuster (Acarina: Phytoseiidae) was examined by the methods of numerical taxonomy. Western populations are separated from the other populations when multivariate tests are used. Two subspecies are proposed, and Typhlodromella nodosus De Leon is synonymized with Typhlodromus caudiglans. Morphological variations between northern and eastern populations are correlated with climatic variables and with host plants.

REPLACEMENT OF TYPHLODROMUS OCCIDENTALIS BY T. CAUDIGLANS AND T. PYRI (ACARINA: PHYTOSEIIDAE) AFTER CESSATION OF SPRAYS ON APPLE TREES

Organophosphorus sprays were applied during 1968 and 1969 to an unsprayed but otherwise well cared for apple orchard to destroy the resident phytoseiid predators, Typhlodromus caudiglans Schuster and T. pyri Scheuten. The phytoseiid commonly found in commercial orchards in British Columbia, T. occidentalis Nesbitt, was then released into the orchard.The population density of T. occidentalis increased greatly during 1970 but in the absence of sprays the resident predators reappeared. By the end of the 1971 season, T. caudiglans and T. pyri were once again the main phytoseiid predators and T. occidentalis was relegated to an insignificant role.

Toxicity of Some Pesticides to Predacious Arthropods in Ontario Peach Orchards

DDT, parathion, and carbaryl experimentally applied in peach orchards were highly toxic to most insect and arachnid predators, including those most effective in controlling orchard mites. Azinphos-methyl appeared to be as toxic as parathion to predators in grower-sprayed orchards. Larvae of the chrysopid Chrysopa carnea Stephens and the syrphid Toxomerus geminatus (Say) were remarkably tolerant of DDT. The phytoseiid mite Typhlodromus caudiglans Schuster appeared to have developed a high degree of resistance to DDT in one orchard. Sulphur was appreciably toxic only to phytoseiids and the erythraeid Balaustium sp., and captan had little or no effect on any predator. Chemical and biological control of phytophagous mites in peach orchards cannot be integrated while the presently used insecticides are needed for the control of the oriental fruit moth, Grapholitha molesta (Busck).

Relations between Typhlodromus caudiglans Schuster (Acarina: Phytoseiidae) and Phytophagous Mites in Ontario Peach Orchards

In peach orchards undisturbed by pesticides and where phytophagous mites were at endemic densities, spring populations of Typhlodromus caudiglans were small and remained so during early summer until phytophagous mites, especially Aculus cornutus, began to increase. T. caudiglans reached maximal densities in September. In such orchards T. caudiglans appears to be an important factor in maintaining Panonychus ulmi at low density levels. On trees where DDT applied the previous year had caused P. ulmi to build up and which could be repopulated by T. caudiglans from neighbouring trees, the predator increased very rapidly but appeared to reach an upper limit of density fixed by intrinsic factors, possibly cannibalism. Under these conditions T. caudiglans could not bring P. ulmi to endemic densities in one season, though it appeared to slow the mite’s rate of increase and to reduce its maximal seasonal density.