Growth responses of southwestern corn borer (Lepidoptera: Crambidae) and fall armyworm (Lepidoptera: Noctuidae) larvae fed combinations of whorl leaf tissue front a resistant and a susceptible maize hybrid

Maize, Zea mays L., germplasm with resistance to leaf feeding by southwestern corn borer, Diatraea grandiosella Dyar, and fall armyworm, Spodoptera frugiperda da (J. E. Smith), neonates has been developed and released. Laboratory studies were conducted over 2 yr to determine if this resistance extends to older larvae initially fed susceptible leaf tissue and if larvae initially fed resistant leaf tissue recover when switched to similar susceptible tissue. Our results indicate a resistance and a recovery response by larvae of both species, depending on leaf tissue feeding regime. Southwestern corn borer larvae fed susceptible tissue for 3 or 7 d before switching to resistant tissue gained significantly less weight after the switch than those fed on only susceptible tissue. In contrast, southwestern corn borer larvae fed resistant tissue for 3 or 7 d before switching to susceptible tissue gained significantly more weight after the switch than those fed resistant tissue only. Similar results were observed for the fall armyworm. An interesting response occurred with fall armyworm larvae fed resistant tissue after being initially fed susceptible tissue for 7 d. Although the larvae gained less weight after the tissue switch than those reared only on susceptible tissue, the number of days to pupation did not differ. However, the resulting pupae weighed only 138.5 mg compared with 182.1 mg for those reared on only susceptible tissue. Our findings provide evidence that resistance to later instars does occur in maize and useful information when considering using a mixture of resistant and susceptible seed as an integrated pest management strategy.