Morphology of Leaf Surface Trichomes and Its Influence on Egglaying by Heliothis virescens

Structure, color, growth habit, and pubescence of plants, in addition to chemical characteristics, affect acceptability of plants as potential food, refuge, or oviposition sites for insects; however, the impact of physical characteristics of plants on egglaying by the tobacco budworm moth, Heliothis virescens (F.), is poorly understood. This study was undertaken to determine the physical attributes, especially trichome types and growth habit, that may influence oviposition by gravid H. virescens females on several species of plants. The types and densities of trichomes found on the leaves of eight plant species, pigeonpea [ Cajanus cajan (L.) Huth], crimson clover ( Trifolium incarnatum L.), Texas bluebonnet ( Lupinus texensis Hooker), cotton ( Gossypium hirsutum L.), velvetleaf ( Abutilon theophrasti Medikus), rose‐scented geranium ( Pelargonium graveolens L'Her.), tobacco ( Nicotiana tabacum L.), and groundcherry ( Physalis angulata L.) were investigated using light and scanning electron microscopy. Simple or branched, hairlike (nonglandular) trichomes and capitate or club‐shaped (glandular) trichomes were found. Greater densities of trichomes occur on the abaxial surfaces than adaxial surfaces of leaves of most species. Heliothis virescens laid more eggs on the under surfaces of leaves, although the difference in oviposition rate was significant only for tobacco. Trichome type did not influence oviposition. In choice tests in laboratory and field cages, moths preferred to oviposit on tobacco and velvetleaf. In field cages, plants with erect growthabit were more acceptable to females than plants with procumbent growth habit.