The role of Juvenile Hormone III in phonotaxis, mating behavior and egg production of cricket females from Gryllus campestris, Gryllus bimaculatus, Teleogryllus commodus, and Acheta domesticus was investigated. 1. Phonotaxis of crickets was measured on a Kramer spherical treadmill by means of an infrared system which allowed free walking at any speed and direction. Crickets were allatectomized during the adult or last nymphal stage, and the controls sham-operated. On each cricket, 2 to 9 phonotactic tests were performed during a period of 12 to 51 days; the allatectomized nymphs were tested as adults. 2. All females deprived of their corpora allata during the adult stage continued to exhibit phonotaxis, whereas females operated as nymphs developed and maintained phonotaxis (Tables 1–4). Some of these females allatectomized or sham-operated during the adult or nymphal stage exhibited correct phonotactic behavior as well as undirected walking. 3. At the end of the test series, all allatectomized females were found to be devoid of Juvenile Hormone, whereas the controls varied according to age from 0.2 to 2.0 pmol/10 μl. The individual ecdysteroid levels differed unpredictably in allatectomized and control females (0.02 to 6.4 pmol/10 μl), and no correlation was found between the number of eggs produced by allatectomized females and their ecdysteroid titer. 4. All allatectomized females displayed sexual receptivity. 5. Adults allatectomized during the last nymphal instar were still able as adults to develop single eggs in G. campestris and G. bimaculatus, while females of T. commodus did produce and store moderate numbers. However, in A. domesticus no eggs were produced, and terminal oocytes had reached 0.5 to 0.7 mm in length, which is the previtellogenic size of terminal oocytes in normal females at the age of one to two days.