Oviposition Patterns by Several Lepidopterous Pests on Processing Tomatoes in California’ F. G. ZALOM. L. T. WILSON.’ AND R. SMITH’ IPM implementation Group. University of California. Davis. Califomia 95616 Environ. Entomol. I?: 1133-1 137 (1983) ABSTRACT Oviposition pattems of Heliothis mi. Mandi4c.u spp., Spodopterci exigiia, and Tricho- plusiu ni were studied in processing-tomato fields of northem Califomia. The initiation of egg laying appears to be related to flower formation, with peak egg deposition occurring in relation to the peak number of open flowers per plant for H. zea. S. e.rigctu, and T. ni. Oviposition by Munditca spp. increases as the season progresses. All species deposit most of their eggs on leaves of the terminal halt of the branch. The majority of eggs are located on the ventral leaf surface, within one leaf of the inflorescence. From these data, it is possible to estimate the number of plants that would have to be sampled to find an egg of one species at a given egg density. Insects may affect processing tomatoes directly by reducing yields and indirectly by altering quality stan- dards through contaminating the product with insect pests, cast skins, excreta, or eggs. The key pests of processing tomatoes in northern California are tomato fruitworm, Heliothis zea (Boddie), and beet armyworm, Spodoptera exigua (Hubner), both of which bore directly into the fruit (Lange and Kishiyama 1978). Other Lepidoptera in this region which are considered to be of occasional importance include tobacco and tomato hornworms, Manducn spp., and cabbage looper, Trichoplusia ni (Hubner), (Okumura 1974). Few implementable monitoring programs have been suggested for any of the lepidopterous pests on process- ing tomatoes (Lange and Bronson 198i). Quantitative monitoring procedures currently require sampling dam- aged fruit (Zalom et al. 1983) which does not provide a measure of pest population levels for predicting crop loss. Sampling a life stage such as eggs would permit a quantitative estimate of pest populations; however, monitoring costs must be minimized. Wilson et al. (1980, 1982) have shown that monitoring costs can be reduced without sacrificing reliability by subsampling a plant only in the area where a pest would most likely be found. This requires basic understanding of pest distribution on plants in the field. Of the lepidopterous pests of processing tomatoes, oviposition pattems are best known for H. Zen; little is known about oviposition by the other species relative to plant parts. Wilcox et al. (1956) found that most H. zea eggs were laid on the outer periphery of the plant, with few or none on the fruit. Harcharau and Gurwattan ( 1977) have observed oviposition by H. armigera on both fruit and flowers. Snodderly and Lambdin (1982) reported the preferred oviposition site of H. zea on fresh-market tomatoes to be the foliage of the middle plant rcgion. Alvarado-Rodriguez et al. (1982) found a relationship of H. zeo to blooms in a field cage study. Some authors have suggested that female moths oviposit in response IRrceived for publicntion 13 October 19x2: acccpied 2 Frbrurary -Dept. of Eniomology. University ol’California. Davis. CA 9Shlh. 19x3; to volatile compounds emmitted from certain tissues of the plant host (Thomas and Dunnam 1931, Fletcher 1941). This study was initiated to determine the relationship of eggs to specific plant parts for H. zea. S. e.uiguo, Manduca spp., and T. ni. and to quantify the frequency distribution of each. Materials and Methods Three commercial fields were sampled weekly begin- ning with the initiation of flowering. In each field, two plants were uprooted at each of 36 predetermined sites on all sampling dates. The first plants were sampled before flowering (early July). Sampling terminated the week before harvest (late September). Foliage and other plant parts were examined for eggs in the field by using a IO X hand lens. The location of eggs was recorded by plant part, location on the plant part, and leaf in relation to terminal, fruit, and open flowers. Fields were located in Sutter and Yolo Counties and were monitored as part of an integrated pest management (IPM) program aimed at bringing about more judicious pesticide use. The cul- tivars were ‘Murietta’ and ‘Early Castle Peel,’ and were planted in late May. Results of this study would likely not be applicable to fresh-market cultivars. The process- ing cultivars used were grown prostrate and have more determinate fruiting patterns in accordance with normal cultural practice in Califomia. A fourth field planted in late May on the Davis Cam- pus was also sampled weekly beginning with the initi - ation of flowering. On the first five sampling dates, 63 plants were removed. and plant growth information and oviposition patterns were recorded. Plant growth para- meters included number of open flowers and number of fruit larger than 0.25 in. in diameter. Egg locations were recorded as in the commercial fields. The number of samples was reduced to 21 plants on the last six sam- pling dates. Results and Discussion Oripositioii in Reltrtion to Frirititig Parsons ( 1940) found that maximum oviposition by H. cirtniXcvw on cotton occurred at pcak bloom. with both oviposition and bloom curves closely synchro- 1133 This article is the copyright property of the Entomological Society of America and may not be used for any commercial or other private purpose without specific written permission of the Entomological Society of America.