Winter mortality and spring emergence of corn stalkborers (Lepidoptera: Pyralidae) in subtropical Mexico

Winter survival and spring emergence of the crambine stalkborers Diatraea lineolata (Walker), D. saccharalis (F.), and Eoreuma loftini (Dyar) were studied in the corn agroecosystem of northern Tamaulipas, Mexico, from 1985 to 1992. Laboratory experiments to evaluate the effect of cold on survival of stalkborer larvae complemented the field studies. Numbers of stalkborers throughout the winter decreased linearly ,and resulting regression slopes differed among species. Overall, 50% of larvae remained 42, 64, and 66 d after corn physiological maturation for E. loftini, D. saccharalis, and D. lineolata, respectively. Larval disappearance was a result of mortality and development to pupae. Low temperatures caused significant mortality (45-100%) only during the winter of 1989-1990 when temperatures decreased to -8 degrees C, very unusual for northern Tamaulipas. Laboratory studies showed stalkborer populations were significantly reduced only if exposed for several hours at temperatures below -5 degrees C, which has only occurred during two winters in this region during the fast 28 yr. Borer mortality attributed to low temperatures was lower in stacked corn than in field corn. Percentage of survivorship from full grown larvae to adulthood in emergence cages averaged 4.1, 11.0, and 21.8% for D. saccharalis, D. linealata, and E. loftini, respectively. Although cumulative moth emergence of the Diaeraea species was sigmoid, that of E. loftini was linear. Fifty percent of cumulative emergence occurred during late February, mid-March, and early April for E. loftini, D. saccharalis, and D. lineolata, respectively.