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 south western corn borer, Diatraea grandiosella Dyar, and fall armyworm, Spo doptera frugiperda da (J. E. Smith), neonates has been developed and r eleased. Laboratory studies were conducted over 2 yr to determine if t his 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 resista nce and a recovery response by larvae of both species, depending on le af tissue feeding regime. Southwestern corn borer larvae fed susceptib le tissue for 3 or 7 d before switching to resistant tissue gained sig nificantly less weight after the switch than those fed on only suscept ible tissue. In contrast, southwestern corn borer larvae fed resistant tissue for 3 or 7 d before switching to susceptible tissue gained sig nificantly more weight after the switch than those fed resistant tissu e only. Similar results were observed for the fall armyworm. An intere sting response occurred with fall armyworm larvae fed resistant tissue after being initially fed susceptible tissue for 7 d. Although the la rvae 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 use ful information when considering using a mixture of resistant and susc eptible seed as an integrated pest management strategy.