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

Control of Maladera matrida Argaman (Coleoptera: Scarabaeidae) in peanut fields in the Negev region, Israel, relies on the `rule of thumb' use of insecticides. The aim of this study was to develop an economic injury level (EIL) for a more judicious application of insecticides. Field studies were conducted from 1991 to 1993 to determine the relationship between the cumulative number of different immature stages and the damage of peanuts (Arachis hypogaea L.). Observed damage to peanut yield was found to relate best to second- and third-instars (white grubs). This was supported by grub infestation experiments on potted peanut plants. Three different EIL levels for second- and third-instars of M. matrida were established in connection with the peanut plant developmental stages as follows: an average of 13 grubs per soil sample (25 by 25 by 60 cm) taken during the first 3 weeks of nut development, of 4 grubs per soil sample during week 4 to 6, and of 1.5 grubs per soil sample from week 7 until harvest.