Biology of the hop cyst nematode Heterodera humuli

In an intensively sampled English hop garden, cysts of Heterodera humuli were found in every sample taken. Most occurred in the top 15 cm of soil, decreasing in number by half with every 15 cm in depth. Numbers of second-stage juveniles fluctuated during the vegetative period in a pattern which indicated that more than one generation, possibly two to three, were produced. The generation time was about 1.5 months. In pot experiments under controlled conditions (20°C; 16 h light/day) the life cycle lasted 40 days. The optimal temperature was 20°C for the development of H. humuli in the roots of its host Humulus lupulus. Most H. humuli juveniles invaded hop roots at 15°C, but egg hatch was greatest at 20°C. In moist soil, second-stage juveniles survived for at least 54 days and thereafter invaded roots and reproduced.