Some Factors of Foliage Condition Limiting Population Growth of Oligonychus punicae (Acarina: Tetranychidae)

The population growth and age distribution of Oligonychus punicae (Hirst) were studied on seedlings of Persea indica Spreng in the greenhouse. Starting with 20 ♀,10 ♀, and 5 ♀ per plant, the populations increased about 1000-, 2000-, and 4000-fold, respectively, in 7-8 weeks, and then declined rapidly as leaves became severely bronzed. The proportion of females decreased and that of males increased with time, until males finally comprisedthe highest percent of the active stages. When heavily bronzed leaves were washed to remove webbing, cast skins and other debris, and then reinfested with O. Punicae, the mite populations reached a peak more than 6 times higher than those on bronzed leaves which were reinfested but not washed. Adult females taken from declining populations on heavily bronzed leaves and transferred to excised unbronzed leaves in the laboratory had a low reproductive rate at first, but after 2-3 days arapid rate was resumed. Laboratory experiments confining adult female mites on excised leaves indicated a lower rate of reproduction of the females and slower development of their progeny on bronzed leaves, on the undersides of mature leaves, and on the upper sides of immature leaves, compared with that of the controls onthe upper sides of mature unbronzed leaves. Adverse leaf condition did not appear to affect the sex ratio of the F1 progeny.