Behavior Associated with the Larval Diapause of the Southwestern Corn Borer, Diatraea grandiosella: Probable Involvement of Juvenile Hormone1,2

Abstract

The elaborate behavior of pre-diapausing larvae of the southwestern corn borer, Diatraea grandiosella Dyar, and the probable involvement of juvenile hormone (JH) in its control is described. At the end of their feeding period, pre-diapausing larvae descend to the root zone, excavate a cell in the stalk crown, prepare a plugged exit hole for the emergence of the adult, and molt from a spotted to an immaculate morph. They may also girdle the host plant just above ground level. In contrast to last stage non-diapausing larvae, last stage pre-diapausing larvae were found to retain a high JH titer in their hemolymph. The Galleria wax test showed that at the time pre-diapause behavior is initiated the hemolymph contains a mean JH titer of about 2600 Galleria Units/ml, and retains a mean JH titer of > 1230 GU/ml throughout the immediate pre-diapause period. In addition, the treatment of non-diapausing larvae with JH mimic induced some of the behavioral traits shown by pre-diapausing larvae. These findings suggest that JH potentiates the pre-diapause behavior. Prediapause behavior appears to be regulated by environmental cues (short days, low temperatures, senescence of host plant) linked to diapause determination, and operating through the neuroendocrine system.