Emergence Under Natural and Manipulated Conditions of Tetrastichus julis , an Introduced Larval Parasite of the Cereal Leaf Beetle, with Reference to Regional Population Management

The developmental threshold for Tetrastichus julis (Walker), a larval parasite of Oulema melanopus (L.), was determined to be 48°F (8.89°C). This threshold can be used to determine emergence rates under field conditions. However, soil surface cover significantly influences soil temperature and was found to be a controllable factor in manipulating spring emergence. The relationship between soil temperature and air temperature is sufficiently correlated to allow emergence rate predictions for T. julis from standard air temperature measurements. This prediction is critical to a control program which would allow for pesticide control of the cereal leaf beetle while having minimal effect on the T. julis population. Emergence of the overwintering generation of T. julis is well synchronized with the presence of susceptible hosts in the spring. The summer generation of the parasite is poorly sychronized and many hosts have pupated before the parasites emerge. These late hosts are critical since they are the means by which T. julis overwinters.