Distribution of Lygus hesperus (Knight) (Miridae: Hemiptera) on Cotton L. T. WILSON,’ T. F. LEIGH,l D. GONZALEZ,* AND c. FORISTIERE3 University of California J. Econ. Entomol. 77: 131.3-1319 (1984) ABSTRACT Lygus hesperus (Knight) on cotton in the field were, on the average, distrib- uted on the fifth through seventh nodes from the terminal. Most nymphs were located on squares, while the majority of adults were found on bolls In comparison, adults 011 glasshouse plants were located predominantly in the upper four mainstem nodes; most were found on leaves. In the glasshouse, L. hesperus that were on fruit structures were almost entirely on squares. The difference in distribution between L. hesperus populations in the field and glasshouse appeared to be largely due to different plant growth patterns. Glasshouse plants were spindly, with a simple canopy characterized by short branches, few fruits, and rela- tively little vegetation. Plants in the field developed a full canop) , larger and more branches, and more fruit per branch, thus providing more habitat turther down the plant for L. hesperus to feed. These results suggest that glasshouse experiments provide biased infor- mation on L. hesperus distribution and, possibly, feeding behavior. Lygus hesperus (Knight) is a pest of cotton in Cal- periments involving confinement or habitat mod- ifornia’s San Joaquin Valley. Feeding is reported ification, such as using a cage or rearing in a to occur primarily in fruiting structures in the up- glasshouse or growth chamber, however, has been per terminal area of the plant (Jubb and Carruth limited (Latson 1972). 1971, Tugwell et al. 1976, Gutierrez et al. 1977, Here we report the results of a study done to Mauney and Henneberry 1979); young squares examine how the distribution of L. hesperus on (flower buds) are preferred (Mauney and Henne- cotton is affected by fruit availability and by insect berry 1979, Pack and Tugwell 1976). Tugwell et activity, and to compare results obtained in the al. (1976) estimated for two cultivars that about field and the glasshouse. 10 and 1%of the potential yield in their field trials was lost due to Lygus spp. damage to bolls. The actual amount of feeding on bolls was possibly less Methods and Materials and that on squares greater since, when older Field and glasshouse experiments were con- squares are damaged by Lygus bugs, development ducted with the cotton cv. Acala SJ-2. of the fruit often continues but results in a dam- In 1974, insect distribution on all plants within aged boll (Pack and Tugwell 1976). The amount 24 rows 1 m long (embedded within 0.5 ha of of damage to bolls is also likely to depend on the cotton) was mapped from 0800 to 1400 hours at relative phenologies of the crop and the Lygus five time periods through the season near Shafter, spp. Large early season populations probably cause Calif. On two additional sample dates, plants from more damage to squares, while populations devel- a commercial field were mapped near Bakersfield, oping later probably damage more bolls. Since bolls Calif. The information recorded included the fol- are located further from the plant terminal than lowing for each observed L. hesperus adult and are squares, the distribution of Lygus bugs on the nymph: mainstem node location (MSN)-for these plant may affect the relative availability of squares analyses, the first partially unfurled mainstem leaf and bolls as feeding sites. in the terminal equals position 1; branch node lo- Lygus adults are flighty; for this reason, most cation (BSN), and whether the L. hesperus were detailed studies of feeding behavior and damage on primary sympodial and mainstem node leaves have concentrated on nymphs (Tugwell et al. 1976) or on monopodial branches-the mainstem node or on caged nymphs or adults (Gutierrez et al. leaf equals 0,the first sympodial position equals 1; 1977, Jubb and Carruth 1971, Mauney and Hen- structural location-structures are considered as neberry 1979). The validation of results from ex- fruit (square, flower, or boll), stem, branch, or leaf (top or bottom surface). Mainstem nodes are produced successively as ’ Dept. of Entomology, Univ. of California, Davis, CA 95616. the plant grows and a single MSN leaf (position 0 * Div. of Biological Control. Dept. of Entomology, Univ. of for each branch) is produced at each node. Mono- California, Riverside, CA 92521. Previously Univ. of California, Kearney Hortic. Field Stn., podial (or vegetative) branches, which produce Parlier, CA 93648. secondary sympodial (or fruiting) branches, are 1313 1314 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 77, no. 5 ber and December 1981 to obtain data on the feeding behavior of adult L. hesperus and their distribution on the plant. Those bugs were collect- ed from alfalfa at the University of California, Kearney Agricultural Center. To avoid cage ef- fects on L. hesperus behavior, experiments were conducted to test methods to prevent bugs from flying from plant to plant within the glasshouse. In the first test, a small dot of Testors paint was applied to the cuneus area of the wings (Benedict 1975). The bugs spent most of their time grooming L and ca. 67% had freed their wings within 24 hours. In a second test, the cuneus was clipped from the hemelytra with surgical scissors (Wilson et al. 1983a). This method worked quite satisfactorily. Care had to be taken during removal of the cu- neus, however, to ensure that the posterior end of the abdomen was not inadvertently removed. Two Fig. 1. Branching pattern of cotton. (1) Mainstem; trials were then conducted using the cuneus-re- (2) mainstem node leaf locations (position 0, represented moval technique. In each trial, 25 adult L. hes- by petioles); (3) monopodial or vegetative branch; (4) perus females were placed, one per plant, on plants sympodial branch node leaf (at position 1);and (5) fruit with no fruiting structures older than squares, and structure positions, either retained (-), or abscised on 25 plants having a full complement of fruiting (- - -). structures including full-size green bolls. The cot- ton was grown, one plant per 6-liter pot, in a mix- ture of peat and sandy loam soil. Water was ap- often formed at the lower mainstem nodes, and plied as often as every day and the temperature primary sympodial branches are usually produced in the glasshouse was maintained between 29 and higher up the plant (Fig. 1). Tharp (1960) and 35°C. Hoagland’s solution (Hoagland and Arnon Mauney (1984) present detailed descriptions of the 1950) was added in the water once a week. morphology of the cotton plant. For the first trial, observations were made once Glasshouse experiments were done in Novem- or twice per day for a total of 7 days. For the Table 1. Mean number of mainstem nodes through the season and the average number of nodes, distant from the terminal, where Lygus hesperus nymphs and adults were distributed Sampling period 18-28 8-12 26-29 17-20 6-1 1 June July July Aug. Sept. Nymphs Nonvegetal ivd ab 2.92 4.57 4.91 5.60 3.50 SD 3.35 3.14 3.25 3.56 2.97 n 13 138 139 37 12 All data f 4.63 5.36 5.83 7.21 8.24 SD 4.79 3.92 4.58 5.48 8.17 n 19 154 169 614 17 Adults Nonvegetative f - 4.25 5.16 3.60 - SD - 2.30 3.10 2.07 - - n - 12 19 5 All data f - 4.25 6.09 3.60 - SD - 2.30 3.94 2.07 - n - 12 22 5 - Mainstem nodes f 11 14.77 17.84 21.33 22.88 a Primary sympodial branches plus mainstem node leaves. The first node is identified as having any part of its upper surface visible. October 1984 WILSON ET AL.: DISTRIBUTION OF L. hesperus ON COTTON 1315 Table 2. Cumulative proportional distribution of Lygus hesperus from the first partially unfurled leaf in the Cotton terminal; field data summed for all sampling dates Nymph9 Adultsb Mainstem node NonvegetativeC Vegetative Nonvegetative Vegetative Total branches branches branches branches Total 1 0.16 0.08 0.15 0.12 0.13 0.12 2 0.24 0.11 0.22 0.18 0.13 0.18 3 0.32 0.14 0.30 0.26 0.13 0.24- -. 4 0.43 0.14 0.39 0.38 0.13 0.35 5 0.53 0.15 0.48 0.53 0.13 0.49 6 0.63 0.17 0.57 0.61 0.13 0.55 7 0.72 0.20 0.65 0.74 0.13 0.68 8 0.80 0.24 0.73 0.79 0.13 0.72 9 0.87 0.28 0.79 0.88 0.25 0.81 10 0.92 0.30 0.84 0.91 0.25 0.84 11 0.94 0.34 0.86 0.95 0.25 0.88 12 0.96 0.41 0.89 0.97 0.37 0.91 13 0.97 0.45 0.91 0.98 0.37 0.92 14 0.98 0.50 0.92 0.98 0.50 0.93 15 0.99 0.64 0.94 0.98 0.75 0.96 16 0.99 0.70 0.95 1.0 0.75 0.97 17 -1.0 0.81 0.97 1.0 1.0 18 -1.0 0.85 0.98 19 1.0 0.89 0.98 20 0.92 0.99 21 0.96 0.99 22 0.98 -1.0 23 0.99 -1.0 24 0.99 -1.0 25 1.0 1.0 For nymphs 775; 675 on nonvegetative branches.