SOME ASPECTS OF THE BIOLOGY AND A LABORATORY LIFE TABLE OF THE ACARINE PREDATOR ZETZELLIA MALI

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Abstract
A rearing technique was developed to study various aspects of the biology of Zetzellia mali (Ewing) in the laboratory. The rate of development of Z. mali feeding upon the phytophagous mite Aculus schlechtendali (Nalepa) was determined at 9°±1°C and 14°±1°C (56% R.H.), 19°±1°C (33%, 56%, 76%, and 97% R.H.), and 24°±1°C (51% R.H.). The average preovipositional and ovipositional periods for 16 female Z. mali were 1.5 and 9.4 days respectively and an average of 1.7 eggs per day were laid by these females. Z. mali was found to be arrhenotokous with unmated females producing only male offspring and mated females producing 2.6 females: 1 male offspring. Diapause in Z. mali was broken at 24°±1°C, 16L:8D) with egg deposition beginning after 11 days (51% and 76% R.H.) or 12 days (33% and 96% R.H.) when the adults feed upon the winter eggs of Panonychus ulmi (Koch).A life table was constructed for Z. mali and the intrinsic rate of increase (rm) was determined to be 0.109 female offspring/female/day. The mean generation time (T) was calculated to be 21.0 days and the net reproductive rate (R0) during this time was 10.04. The theoretical stable age distribution of the laboratory population of Z. mali at 19°±1°C, 56% R.H. was 59% eggs, 15% larvae, 7% protonymphs, 6% deutonymphs, and 13% adults.Comparison of the intrinsic rates of increase and prey consumption of Z. mali and other species of predaceous mites indicate that Z. mali is not as efficient a regulating agent of phytophagous mites as the phytoseiids.