Rose, tomato, apple and bean-leaf discs 40-48 mm. in diam., their edges streaked with tanglefoot, are floated in water or 2% sucrose soln. in Petri dishes. Five female mites are introduced onto each disc and the resulting progeny counted. Dishes can be refrigerated and mites counted when convenient. Balanced lighting providing 300 foot-candles over a photoperiod of 16 hours is sufficient for maintaining the culture; temp. is kept at 26[degree]C[plus or minus] 1[degree].