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Mortality Factors Affecting Cotton Insects: I. Resistance of Smooth and Nectariless Characters in Acala Cottons to Heliothis zea, Pectinophora gossypiella, and Trichoplusia ni¹

ABSTRACT

Host plant resistance to insects has become a major breeding objective in cotton (Gossypium hirsutum L.), since significant increases in resistance may result simultaneously in yield increases and reduced usage of insecticides. Nectariless ‘Acala’ cotton strains with reduced pubescence are being developed in an attempt to gain significant host plant resistance against harmful Lepidoptera. Extensive studies were undertaken to evaluate the first-order effects that the nectariless and reduced pubescence plant modifications would have upon oviposition behavior of three key insects. Cage trials with pink bollworms (Pectinophora gossypiella) have been difficult to manage and results are inconclusive. It was found that cabbage loopers (Trichoplusia ni) showed a slight increase in oviposition on nectariless cottons with reduced pubescence. The increase was so small as to be of doubtful economic importance. Paired isolation cage studies conducted over a 4-year period showed that similar numbers of Heliothis zea moths laid only 45% as many eggs on nectariless Acala strains as on their normally hairy, nectaried companion lines. There was a disturbing reversal in form in certain tests, due to variables not yet clearly understood. However, there was a clear trend indicating that the suppression of oviposition is greatest when environmental conditions are most favorable for a bollworm epidemic. This large reduction of egg numbers at peak oviposition is the strongest confirmation of the value of developing nectariless cottons to minimize Heliothis damage.

Key Words: glabrous cotton • insect cages • insect oviposition

¹ Contribution from the Agricultural Experiment Station, New Mexico State Univ., Las Cruces, New Mexico 88003. Journal Article No. 459. This research was partially supported by PL 89-106 funds administered by the Cooperative State Research Service, USDA. The authors appreciate the cooperation of M. J. Lukefahr, USDA Entomology Research Division, Brownsville, Texas, and are indebted to William and James Lukefahr for compiling the Brownsville data.

² Associate Professor, Department of Agronomy, Associate Professor and Research Assistant, Department of Botany and Entomology, respectively.

Received for publication January 26, 1973.