Use of Benzimidazole Agar Plates to Assess Fall Armyworm (Lepidoptera: Noctuidae) Feeding on Excised Maize and Sorghum Leaves

Abstract

The fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) is an economically significant pest of sorghum and maize. Laboratory bioassays are often conducted for convenience and for fall armyworm confinement but as the number of entries and replications increase, the replenishing of fresh tissue daily and the cleaning of insect diet cups or petri dishes becomes laborious. The current study was conducted to determine if agar plates, used to retain leaf moisture, supplemented with benzimidazole, a fungicide that delays leaf senescence and retards fungicide growth, can be used to assess fall armyworm feeding on fresh maize and sorghum leaf tissue with minimal labor. We conducted 2 trials consisting of 3 cultivars of maize with known resistance or susceptibility to fall armyworm feeding, and 4 cultivars of sorghum that are parents of existing mapping populations. The top 2 (whorl) leaves were removed from 36–37-day old plants, 7.6 cm long pieces of leaf were excised, and each piece was placed on a benzimidazole agar plate. One larva per plate was placed on the leaf tissue; the plate was sealed with Parafilm and placed in an incubator for 7 days. Average larval weights for Trial 1 were significantly different than Trial 2 after 7 days, and thus each trial was analyzed separately. For both trials, the larvae that were fed susceptible maize line ‘AB24E’ had weights that were significantly greater than larvae fed resistant maize lines ‘Mp708’ and ‘FAW1430’. No significant differences in weight were observed for fall armyworm larvae fed on the 4 sorghum lines except for those larvae fed ‘Collier’ in Trial 2, which had weights significantly greater than larvae fed the other 3 sorghum cultivars (Entry 22, ‘Honey Drip’, ‘AN109’). Thus, the benzimidazole agar plate method is an easy and effective method for assessing fall armyworm feeding on maize and sorghum, and thus can be used to identify maize and sorghum germplasm lines with resistance to fall armyworm.