Economic injury levels for the scarabaeid Maladera matrida infesting peanut fields in Israel

Control of Maladera matrida Argaman (Coleoptera: Scarabaeidae) in peanut fi elds in the Negev region, Israel, relies on the 'rule of thumb' use of inse cticides. The aim of this study was to develop an economic injury level (EI L) for a more judicious application of insecticides. Field studies were con ducted from 1991 to 1993 to determine the relationship between the cumulati ve number of different immature stages and the damage of peanuts (Arachis h ypogaea L.). Observed damage to peanut yield was found to relate best to se cond- and third-instars (white grubs). This was supported by grub infestati on experiments on potted peanut plants. Three different EIL levels For seco nd- and third-instars of M. matrida were established in connection with the peanut plant developmental stages as follows: an average of 13 grubs per s oil sample (25 by 25 by 60 cm) taken during the first 3 weeks of nut develo pment, of 4 grubs per soil sample during week 4 to 6, and of 1.5 grubs per soil sample from week 7 until harvest.