Impact of phenology, brown midrib (BMR), seed treatment, and herbivory on epicuticular wax content and fall armyworm (Spodoptera frugiperda) feeding in sorghum-sudangrass (Sorghum x drummondii)

In crop production, management strategies have historically relied upon chemical control to mitigate insect pest pressures. As resistance to pesticides grows at an alarming rate, and as non-target effects are found more frequently, the search for sustainable, novel pest management strategies has become more important. Plants are equipped with diverse physical and chemical defenses against insect pests. Among these physical defenses, epicuticular waxes serve as an important first line of defense. Yet, how these chemical control methods such as seed treatment affects epicuticular waxes is underexplored. Brown midrib (BMR) is a host-plant trait from a recessive gene that affects the monolignol biosynthetic pathway, reducing lignin content, and presents as a gene of interest for evaluation as a form of pest management. Sorghum-sudangrass, Sorghum x drummondii, is an economically important forage crop with BMR; however, the effects of BMR have primarily been studied in animal agriculture and its effects on insects is largely unknown. In addition, how BMR affects epicuticular waxes is also unknown. This study aims to understand how the quantity of epicuticular wax in Sorghum x drummondii is affected by chemical control (seed treatments), BMR, phenological stages, and how wax affects a polyphagous, destructive pest, fall armyworm, Spodoptera frugiperda (FAW). Through wax quantification and FAW feeding induction and wax added artificial diet experiments, we show that while BMR and seed treatment does not affect wax content, plant phenology affects wax, and wax is induced by FAW feeding and has negative consequences for caterpillar growth.