Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2014
Publication Date: 4/8/2015
Citation: Harris-Shultz, K.R., Ni, X., Wang, H., Knoll, J.E., Anderson, W.F. 2015. Use of benzimidazole agar plates to assess fall armyworm (Lepidoptera: Noctuidae) feeding on excised maize and sorghum leaves. Florida Entomologist. 98(1):394-397.
Interpretive Summary: The fall armyworm is an economically important pest of sorghum and corn as it feeds on the growing leaves and the ear/seed head. To screen sorghum and corn plants for resistance to fall armyworm feeding, field, greenhouse, or laboratory bioassays are often used individually or in combination. Laboratory bioassays are best for insect confinement but as the number of replications and entries increase, a large amount of time each day is spent by the experimenter replenishing leaf tissue, adding water, and cleaning the experimental system. A previous study had used agar plates containing benzimidizole, a chemical that prevents leaf dying, to assess the Russian wheat aphid feeding on barley. We sought to determine if agar plates containing benzimidizol could be used to assess fall armyworm feeding in sorghum and corn. We found this method accurately identified resistant and susceptible maize lines and was able to be used for sorghum. Furthermore this method requires no labor by the experimenter until 7 days after the experimental setup, preserved sorghum and corn leaf tissue, and minimal fungal and bacterial contamination was seen. 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 plants with resistance to fall armyworm feeding.
Technical Abstract: The fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) is an economically significant pest of sorghum and maize. To screen sorghum and maize germplasm for resistance to fall armyworm feeding, field, greenhouse, or lab bioassays are often utilized individually or in combination. 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 supplemented with benzimidazole can be used to assess fall armyworm feeding in maize and sorghum. We conducted two trials consisting of three cultivars of maize with known resistance or susceptibility to fall armyworm feeding, and four cultivars of sorghum that are parents of existing mapping populations. The top two (or whorl) leaves were removed from 36-37 day old plants, leaves were excised, and placed on benzimidazole agar plates. One larva per plate was placed on the leaf tissue, the plate was sealed with Parafilm and placed in an incubator for seven days. Average larval weights for Trial 1 were significantly different than Trial 2 after seven 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 four sorghum lines except for those larvae fed ‘Collier’ in Trial 2 which had weights significantly greater than larvae fed the other three 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 armyworms.