University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Entomology Papers from Other Sources Entomology Collections, Miscellaneous 1988 Feeding Damage by Irbisia pacifica (Hemiptera: Miridae): Effects of Feeding and Drought on Host Plant Growth James D. Hansen USDA-ARS, Crops Research Laboratory, Utah State University, Logan, Utah 84322 Robert S. Nowak Department of Range, Wildlife & Forestry, University of Nevada- Reno, Reno, Nevada Follow this and additional works at: https://digitalcommons.unl.edu/entomologyother Part of the Entomology Commons Hansen, James D. and Nowak, Robert S., "Feeding Damage by Irbisia pacifica (Hemiptera: Miridae): Effects of Feeding and Drought on Host Plant Growth" (1988). Entomology Papers from Other Sources. 78. https://digitalcommons.unl.edu/entomologyother/78 This Article is brought to you for free and open access by the Entomology Collections, Miscellaneous at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Entomology Papers from Other Sources by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Feeding Damage by Irbisia pacifica (Hemiptera: Miridae): Effects of Feeding and Drought on Host Plant Growth 1 JAMES D. HANSEN2,3 AND ROBERT S. NOWAK4 Ann. EntomoL Soc. Am. 81(4): 599-604 (1988) ABSTRACT The interaction of feeding by a grass bug, Ir"bisia pacifica (Uhler), and drought stress on growth of Great Basin wildrye, Leymus cinereus (Scrih. & Merr.) Love, and intermediate wheatgrass, Thinopyrum intermedium (Host) Barkw. & D. R. Dewey, was studied in the greenhouse. At peak production, control plants of Great Basin wildrye had more than twice as much green leaf area per tiller than bug-infested ones, and intermediate wheatgrass controls had three times as much as the bug-infested plants. Total leaf area of control plants also exceeded that of bug-infested plants. Watered plants of both species recovered very little after bugs were removed. Drought conditions augmented the reduction in green leaf area on previously bug-infested plants of Great Basin wildrye but not on previously infested intermediate wheatgrass plants. Thus, when plants were well watered, bug feeding affected growth of intermediate wheatgrass more than growth of Great Basin wildrye. However, when plants were subjected to bug feeding and drought stress, the vigor of Great Basin wildrye was reduced more than that of intermediate wheatgrass. For both species, the potential forage for livestock consumption was lost because of direct damage by bug feeding as well as indirect effects on the acquisition or allocation of plant resources to growth. KEY WORDS Insecta, grass bug, wheatgrass, wildrye A GRASS BUG, Irbisia pacifica (Uhler), is widely caused by moderately high feeding levels of I. pa­ distributed throughout the western United States cifica, and to examine postfeeding recovery in plants and occupies most ecoregions (Schwartz 1984). This under drought and watered conditions. insect attacks many types of grasses (Schwartz 1984, Hansen 1986). In the Great Basin and Intermoun­ tain Region, it can be economically damaging to Materials and Methods Great Basin wildrye, Leymus cinereus (Scrib. & i\lerr.) Love (Knowlton 1951, Lauderdale & Knight The research was conducted in the greenhouse 1982). The grass bug also attacks pastures of in­ from May to July 1985, at the USDA-ARS Crops termediate wheatgrass, Thinopyrum intermedium Research Laboratory, Logan, Utah. The host plants (Host) Barkw. & D. R. Dewey (Hansen 1988). were Great Basin wild rye and intermediate wheat­ Previous studies on feeding behavior of I. pa­ grass. All plants were grown in the greenhouse and cifica evaluated the effects of feeding damage on initially had more than one tiller. A single tiller chlorophyll concentration and specific leaf mass in with at least three leaves was selected as represen­ crested wheatgrass, Agropyrum desertorum (Fisch. tative of each plant, and the remaining tillers were ex Link) Schultes (Hansen & Nowak 1985) and removed. Plants of the same species were arranged feeding site selection among and within leaves in two rows of four plants each within a cage with (Hansen 1987). Field observations concerning the Plexiglas sides (25 by 28 by 47 cm) and a plastic relationship between feeding and growth in inter­ screen top. For each grass species, three cages were mediate wheatgrass were reported by Hansen used as controls and three other cages were stocked (1988). Nevertheless, the degree of growth reduc­ with adults of I. pacifica (100 bugs per cage). The tion caused by I. pacifica feeding had not been bugs were collected from a field of intermediate determined. Also unknown is how I. pacifica feed­ wheatgrass about 3 km NE of North Logan, Utah. ing interacts with other stresses, particularly All bugs were replaced each week at the same drought, on host plant growth. Summer drought initial stocking rate during the feeding phase of commonly follows spring feeding by grass bugs. the study. Our objectives in this study were to measure the The drought-stress phase began after the field reduction in growth of two common host plants population of I. pacifica declined (week 5, mid­ June). All bugs were removed from cages to pre­ vent further feeding damage, then half the plants : :\lention of a commercial or proprietary product does not constitute endorsement bv the USDA, of each treatment for each species were separated 2 USDA-ARS, Crops R~search Laboratory, Utah State Univer­ and not watered to promote drought stress. The sit y. Logan, Utah 84322. others were watered as usual. This phase ended J Current address: USDA-ARS, Tropical Fruit & Vegetable Re­ when the drought-stressed plants approached se­ search Laboratorv, P.O. Box 4459, Hilo, Hawaii 96720. 4 Department ~f Range, Wildlife & Forestry, University of Ne­ nescence. Although no attempt was made to sim­ vada-Reno, Reno, ::\ev. 89512. ulate exactly the development of water stress under 600 ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA Vol. 81, no. 4 Leymus cinereus 50 ,---------------------------------, Results N A E Initially, average TLA per tiller was similar be­ ~40 L tween control and bug-infested plants within both ev species (Fig. lA and 2A). However, by the fourth : 30 week, average TLA per tiller of controls was about ev a. 40-50% more than that of bug-infested plants. Af­ o ter the fourth week, average TLA per tiller of all ~ 20 plants declined. At the end of the study, average o TLA per tiller in drought-stressed plants of inter­ -o mediate wheatgrass was lower than that of watered ~ 10 plants (Fig. 2A), whereas in Great Basin wild rye, .8 o average TLA per tiller of drought-stressed plants ~ tended to exceed that of watered plants (Fig. lA). o ~--~--~--~--~--~----~--~--~ A second indicator of plant growth, average green 50 ~------------------------------~ leaf area (GLA) per tiller, represented the available N B E photosynthetic leaf tissue. Controls of both plant (J species grew well during the first month of the "'-" 40 Control. watered l,I Lev study (Fig. IB and 2B). Peak growth (maximal T/ .,ontrol. GLA) for controls of Great Basin wildrye (x ± SE = • ~ drought L 30 39.9 ± 4.0 cm2) and intermediate wheatgrass (x ± ev T / • SE = 37.3 ± 3.1 cm2) occurred during the fourth a. ~, o . week. Bug-infested Great Basin wild rye showed ev T ~ 20 T __ ·-" TO.'~T some growth (Fig. IB), whereas average GLA per • ~. T .... .1. ' o tiller of bug-infested intermediate wheatgrass re­ -ev ~Bug. watered -." \ , mained about the same (Fig. 2B). Average GLA c 10 .X per tiller from control plants was significantly ev ev greater than that from bug-infested plants at the L Bug. drought '0 '-' second week for both Great Basin wild rye (t = o ~--~--~--~--~--~----~--~--~ o 2 4 6 8 2.74; df = 46; P < 0.01) and intermediate wheat­ Week grass (t = 7.83; df = 46; P < 0.01). This significant Fig. 1. Effects of feeding by I. pacifica on leaf pro­ difference persisted at least as long as bugs were duction in Great Basin wild rye under watered and on the plants. By the fourth week, average GLA drought conditions. Circles, controls; squares, bug-in­ per tiller of bug-infested Great Basin wild rye (x ± fested treatments; closed symbols and solid lines, water SE = 17.0 ± 2.0 cm2) was 57% less than peak GLA treatment; open symbols and dashed lines, drought treat­ of the control, and average GLA per tiller of bug­ ment. (A) x ± SE for total leaf area (cm2) per tiller; (B) infested intermediate wheatgrass (x ± SE = 12.2 ± x ± SE for green leaf area (cm2) per tiller. 1.3 cm2) was 67% less than maximal GLA of the control. field conditions, the drought-stress treatment in the In the drought phase of the study, which began greenhouse paralleled that to be expected under after the bugs were removed, Great Basin wildrye natural conditions. was more severely affected than intermediate All leaves were measured weekly for length, wheatgrass. The Great Basin wildrye plants were width, condition, and location on each tiller (or without water for 2 wk before the study was ter­ plant). Bug feeding, expressed as "% damage," was minated because of imminent mortality. The visually evaluated for all leaves, a procedure rou­ drought-stressed intermediate wheatgrass plants tinely used to estimate damage caused by grass persisted for 5 wk. Average GLA per tiller in Great feeding mirids (Hansen et al. 1985a,b). Total leaf Basin wildrye dropped dramatically in the drought­ area (TLA) was estimated by multiplying length stressed plants; the greatest decline occurred in by width, then the undamaged green leaf area previously bug-infested plants (Fig. IB). Average (GLA) was calculated by subtracting the amount GLA per tiller in intermediate wheatgrass also de­ of leaf area damaged by feeding from total leaf clined for drought-stressed plants. To assess the area. interaction between aridity and preceding insect Data were analyzed at the USDA Washington feeding, ratios of the average GLA of drought­ Computer Center using the Statistical Analysis Sys­ stressed plants to watered plants were compared tem with the MEANS procedure (SAS Institute between control and bug-infested treatments.