FRUIT-BASED TOLERANCE TO DAMAGE BY BEET ARMYWORM (LEPIDOPTERA, NOCTUIDAE) IN TOMATO

Damage to fruit of eight accessions and cultivated varieties of tomato by natural infestations of beet armyworm, Spodoptera exigua (Hubner), in Southern California ranged from 0.1 to 10%. This field damage was significantly correlated with 9-d weight and survival of S. exigua lar vae reared to pupation from third instar in the laboratory on fruit of these tomato test entries. Two accessions of Lycopersicon esculentum variety cerasiforme and one small-fruited cultivated variety of L. esc ulentum sustained lowest damage in the field (1-50% of susceptible con trols). S. exigua larvae had reduced survival and reduced 9-d weight ( almost-equal-to 20% of susceptible controls). Time to pupation was als o increased on these three lines (30% greater than controls). The resi stant fruits had high concentrations of total glycoalkaloids in the fr uit tissue (5.4 to 25.4 mg/g dry weight versus 1.8 mg/g in a susceptib le fruit) and this may have been the basis of the antibiosis. Phytoste rol concentrations in the fruits were not sufficiently high to potenti ally alleviate glycoalkaloid toxicity. In binary choice tests between fruit and foliage of the most resistant line, L. esculentum variety ce rasiforme LA 1320, larvae of S. exigua fed on fruit 70% less than larv ae in choice tests between the fruit and foliage of susceptible 'VFN 7 718'. Larval nonpreference for fruit apparently contributes to resista nce in LA 1320. The resistance to S. exigua, of LA 1320 predicted by t his mechanism, is close to observed levels of resistance in the field.