Field Observations of Irbisia Pacifica (Hemiptera: Miridae): Feeding Behavior and Effects on Host Plant Growth

Great Basin Naturalist

Volume 48 Number 1 Article 11

1-31-1988

Field observations of Irbisia pacifica (Hemiptera: Miridae): feeding behavior and effects on host plant growth

James D. Hansen Utah State University

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Recommended Citation Hansen, James D. (1988) "Field observations of Irbisia pacifica (Hemiptera: Miridae): feeding behavior and effects on host plant growth," Great Basin Naturalist: Vol. 48 : No. 1 , Article 11. Available at: https://scholarsarchive.byu.edu/gbn/vol48/iss1/11

This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. FIELD OBSERVATIONS OF IRBISIA PACIFICA (HEMIPTERA: MIRIDAE): FEEDING BEHAVIOR AND EFFECTS ON HOST PLANT GROWTH"

James D. Hansen

Abstract. —The interaction between a grass-feeding mirid, Irhisia pacifica (Uhler), and plant growth of intermediate wheatgrass, TJunopynim intcnncchttm (Host) Barkw. ik D. R. Dewey, was examined on a field site in northern Utah in 1985. With egg hatch beginning in April, the bug completed its life c\ cle within two months. 0\ arian development was completed by 1 1 June, a week after all bugs had become adidts. The proportion of feeding damage per leaf (35. 1%) peaked on the se\enth week of the twelve-week study (IS July). Green leaf area per tiller decreased initialh' from bug feeding and then continued to decrease because of seasonal aging. All plants senesced within three months. Grass bugs predominantly attacked the second and third yoimgest leaves. AnaKses of age-specific leaf cohorts demonstrated that the major effect of bug feeding was the loss of green leaf area and potential foliage production over time. Bug feeding may also exacerbate other physiological stresses on the host plants.

The grass bug, Irhisia pacifica (Uhler) riim intermedium (Host) Barkw. & D. R. (Hemiptera: Miridae), has the widest distri- Dewey, and to obtain biological information bution among all species within the genus on the development and population changes

(Schwartz 1984). In this univoltine species, all in /. pacifica. five nymphal instars and the adult stage feed on an assortment of native and introduced Materials and Methods grasses (Schwartz 1984, Hansen 1986). At times this insect is a pest of forage grasses in The stud)' was conducted during the spring the Intermountain West (Knowlton 1951, growing season of 1985 at an ungrazed pasture 1967). that contained a monoculture of intermediate In spite of its economic importance, very wheatgrass. This site, ca 3 km NE North Lo- little is known about the interaction between gan, Utah, was selected because of its history feeding by /. pacifica and its impact on host of high populations of/, pacifica. plants. Hansen and Nowak (1985) observed Along a fence row, 25 grass tillers (or plants) that although chlorophyll concentration in 50 cm apart were identified by colored wire leaves of crested wheatgrass, A^iropyron rings. The plants were examined weekh from desertorum (Fisch. ex Link) Schult., de- the time the insects became acti\e (8 May) to creased as feeding by /. pacifica intensified, full plant senescence (24 July). For every ob- specific leaf mass remained about the same. servation, all leaves on each marked plant They also suggested that a compensatory re- were measured for length, width, condition, sponse occurred with this feeding. Hansen height from ground, and location on the plant.

(1987) showed that adult /. pacifica prefer the The amount (expressed as a proportion) of second and third youngest leaves and that bug-feeding damage for each leaf was visually feeding was greatest near the leaf tip. How- estimated as described b\ Hansen and Nowak ever, these studies did not examine the im- (1985). Relatixc bug population densities pact of feeding on plant growth and sur\ i\ al in were obtained b> taking 10 full .sweeps with a the field. standard (38-cm-diameter) net in the pasture. The objectives of the present study were to Adult females were dissected to determine determine in the field tlie effect of feeding by reproductixc condition b\ using the tech-

/. pacifica during its life cycle on spring nic^ue of Kanun and Ritcher (1972). growth of intermediate wheatgrass, Thinopij- Total leaf area was estimated 1)\ multipK ing

111,- > 'This paper presents thrr.-MiltsotioDp.TatnciiiM'sli.u.itioiiM.irS I )\-\US .111.1 I l.ili \m i, nllui.il l\p,-Miiii-iilISl.itinii. l,oi;.ni, l't,iliS|:i22 Approved as journal Paper No. .3.311.

"Mention of aeonimercial or proprietary product does not constitute endorsement by tlie I'.S. Department of Agriculture "USDA-ARS, Crops Research Laboratory. Utah State University. Logan. Utah 84322. Present address; USDA-ARS, Tropical Kruil and \ egctablc R.scmk Uboratorv, Box 44.59. Hilo, ll.ivvaii 96720.

68 January 1988 HANSEN: IRBISIA FEEDING BEHAVIOR 69

2 — o X

(0 r —

70 Great Basin Naturalist Vol. 48, No. 1

1982 ed., p. 527). Linear correlation and Stu- dent's t-tests were conducted with a Hewlett- Packard HP-llC calculator. 30- Results

Early instar nymphs of/, pacifica were al- 20- ready present when the field study began on 8 May (Fig. 1). Adults appeared in the third week (21 May), and metamorphosis was com- 10- H pleted by the fifth week (4 June). The largest weekly collection was in the fourth week.

Weekly adult sex ratios llivored females, I I I I I I I ex- -I—————TT—I———r— cept for the collection during the third week 1 23456789 1011 12 when males outnumbered females by 63.6%. In the seventh week females exceeded males by 700%, and no bugs were found after this ^40- B collection. E <30- No eggs were found in the first dissection of adult females (week 3). By the fifth week, ^20- 87.3% of the adult females contained eggs, <10- and females collected the next week had the o

greatest proportion of eggs (90.0%). In the last I I ° -I I I I I r-i I I I i —— —— — week that females were collected, the fecun- 1 23456789 1011 12 dity level remained high (78.6% with eggs). IT Although some grass bugs were present at 330- the start of the study, grass plants appeared uninjured (Fig. 2). The proportion of feeding |25- damage on green leaves was initially low 520- (7. 1%) but increased very rapidly between the < third and fourth weeks. After culminating on z the seventh week (35.1%), the proportion of III 510- feeding damage steadily declined, thus indi- 5- cating some form of recovery. Only one plant o^ ^ survived to the twelfth week, a factor that 8 1 I ~r- —i—T—I I I I——I I I resulted in erratic values. Total GLA per tiller 1 2 3 4 5 6 7 8 9 1011 12 increased during the first few weeks of the study and then dropped consistently from the 25-1 third week to the eleventh. The correlation D between average per leaf GLA and week of |20- collection was highlv significant (r" .893, slope ~ -2.36, <'.01). il5- P Total leaf area per UJ UJ tiller peaked a week after maximum GLA. 5l0- Most of the grass plants endured to the tenth O week, then senesced or died within the re- 5 5- maining two weeks. Seed head production I I I I I I I I —I— ———I I I was first observed in the se\(Mith week and 1 23456789 1011 12 continued irregularK during the rest of the WEEK OF STUDY

I I I 1I—I I I I—rn—rn study. Only 44% of the plants grew seed 128 134 141 148 1SS 162 169 176 183 190 197 204 DAY OF YEAR heads.

Initially, all plants had at least three green I'itl. 2. SuiHTiKiiA ol weekly iiKMSiirciiKMits ol iiitfiiiU'- (liatf uhcattirass attacked 1)\ Irhisia pacifica: \, percent leaves. In the second obserxation fi\e i^lants iet'cliiiu (laniat^e/leaf" of green leaves; B. total leiif area had five green leaves, and in the fourth week (iin")/tiller; C, total green leaf area (enr)/tiller; I), nuin- one plant had six green leaves. Yet after the her of green plants. —

January 1988 HANSEN: iKBISIA FEEDING BEHAVIOR 71

LEAF AREA

• NO. LEAVES 15t A

10-

: H^ -fH r25 -20 -15 -10 -5 ^0 I I I I I I I T I I I I E 1 23456789 1011 12 o <1 O•

72 Great Basin Natuflxlist Vol. 48, No. 1

100n O— COHORT A A--r:\ COHORTS •— COHORT C 80- — COHORT D UJ O l60 Q O 40-

20-

1 I I I I I I I I I I T 1 23456789 1011 12 WEEK OF STUDY

1 I 1 1 \ \ \ \ \ 1 \ ] 128 134 141 148 155 162 169 176 183 190 197 204 DAY OF YEAR

Fig. 4. Weekly percentage of feeding damage of lour age-specifie cohorts o( intermediate wheatgrass.

eration oflrbisia pacifica occuis in late spring after the adult molt for o\ arian development. and early summer. At the study site, develop- The oviposition period seemed short, peaking ment of all nymphal stages was rapidly com- about a week after maximinn female popula- pleted in about a month. Schwartz (1984) esti- tion level (28 May). Since most males were mated the duration of nymphal development gone by the seventh week, mating pre- in Irhisia sp. from western Oregon to he four sumably occiured early. weeks. The population (Fig. 1) increased until The amount of GLA is physiologically im- peaking at the fourth week. More likely, how- portant to the plant. GLA is a good indicator of ever, this apparent increase resulted because the potential for plant growth and mainte- either adults were more easily collected than nance. A leaf in good condition has a large nymphs or adults moved from the middle to (iLA relati\c to its total size. GLA is also the the periphery of the pasture. primary food source lor /. pacifica.

Female adults of/, pacifica generally out- When GLA is compared to total leaf area, mmibered males (Fig. I). Females also out- plant damage from different origins can be lived males. These observations were similar demonstrated. The greatest proportion of to those of Schwartz (1984) for the genus Ir- bug-feeding damage occurred between the hisia. Total adult life span at the study site was third and fourth weeks, which coincided with less than six weeks, but it may differ else- the decline of GLA (Fig. 2). However, total where. These insects appear higliK sensitive area peaked one week later, suggesting that to increased temperatures (Hansen 1987), and the grass bugs caused a premature drop in a cool summer may conceivably prolong life. GLA. The percent of feeding damage per leaf Females apparently required about a week declined after the seventh week because the January 1988 HANSEN: Irbisia Feedinc; Behavior 73

grass bugs were no longer present. Yet, the reduced by another grass-feeding mirid,

total GLA per tiller also deelined, indieating Lahops hcspcriu.s Uhler (Malecheck et al. that other physiologieal factors, such as 1977). drought stress, were also causing senescence. This study suggests several areas for future Other grass-feeding mirids and early instar research with Irhisia pacifica. First, the nutri- nymphs of grasshoppers were on the study tional (|uality of the host plants, particularly site during this time, but there were too few of the nitrogenous compounds, should be exam- these insects to be the primary cause of late- ined to determine their effect on insect devel- season decline of GLA. Senescence is a com- opment and egg production (McNeill 1971, of wheatgrass mon characteristic intermediate 1973). Does /. pacifica complete its life cycle during dry periods. The decline in plant pop- before grass senescence because of an intrin- ulation after the tenth week was not directly sic mechanism, or is it due to nutrition? If due to bug feeding, but feeding damage may nutrition is important, how can intermediate contributed to plant mortality that oc- have wheatgrass be developed as a good forage crop curred earlier in the growing season. without encouraging /. pacifica population feeding differed with leaf posi- Grass bug growth? How do grazing practices interact tion. Irhisio clearly preferred the sec- pacifica with growth of plants attacked by grass bugs? ond and third youngest leaves. This feeding If monocultural stands of intermediate wheat- preference verified an earlier study on 1. grass increase /. pacifica populations, what pacifica feeding-site selection on leaves of other forage species can be interspersed to field-collected intermediate wheatgrass and reduce bug-feeding damage? Finally, the ef- other grass species (Hansen 1987). Reasons fect of I. pacifica feeding on growth of other for this preference are still unknown. host plants needs to be examined. The interrelationship between the host plants and grass bug feeding was best illus- trated by the cohort data (Figs. 3, 4). Cohort Acknowledgments A, which had mature leaves at the start of the Appreciation is extended to Scott F. Parker study, was relatively unharmed by /. pacifica. and Lew D. Kelso for assistance in the field, As the season progressed and the grass bugs K. L. Bartz for support in data analysis, and developed, the other cohorts were affected the many reviewers of this manuscript, partic- more. The leaves of Cohorts B, C, and D all ularly Robert S. Nowak (University of Nevada had an opportunity to expand successfully be- at Reno) and Michael D. Schwartz (American cause the youngest leaves present on a tiller Museum of Natural History), for their perti- are less preferred (Hansen 1987). Cohort B nent comments. had less damage than Cohort C because more of the grass bugs were immature at the time of attack. The rapid increase in percent feeding Literature Cited damage for Cohorts B, C, and D between the Hansen. 1986. Differential feeding on range grass third and fifth weeks occurred when the bugs J. D seedlings by Irbisia pacifica (Hemiptera: Miri- became adults. All cohorts exhibited a reduc- dae). J. Kansas Entomol. Soc. 59; 199-203. tion in GLA and eventual death due to normal 1987. Feeding site selection by Irbisia pacifica aging. Yet, the greatly reduced GLA in the (Hemiptera: Miridae) on four cool-season western

later cohorts (Cohorts C and D) suggested that range grasses. J. Kansas Entomol. Soc. 60: meaningful damage from bug feeding reduced 316-323.

Hansen. D , andR. S. Nowak. 1985. Evaluating damage biomass production. J. by grass bug feeding on crested wheatgrass. In summary, grass bug feeding resulted Southwestern Entomol. 10: 89-94. in less both GLA and in less potential foliage. Kamm. J A., and P O. Ritcher. 1972. Rapid dissection of Feeding may also cause presenescent stress insects to determine ovarial development. Ann. 271-274. that may weaken the grass plant physiologi- Entomol. Soc. Amer. 65: Knovvlton, G F 1951. Bugs damage grass in Utah. Bull. cally. Although we did not examine it in this Brooklyn Entomol. Soc. 46: 74-75. study, other researchers found that seed head 1967. Grass bugs: a serious range problem in 1966. production in intermediate wheatgrass was Utah Acad. Sci., Arts, Letters 43: 20-21. Naturalist Vol. 48, No. 1 -74 Great Basin

low doloJ.rata ^" ^^^ infested by black'grass bugs at ^^^'^^^^^^^^^^^^ wh"s Annual Ecol. 42. 495 dU7. Manage. 30: k)od resources. J. nonulation densities. J. Range ^oTA SCHWARTY.M.D. 1984. A revision of the black grass bug ^' 1971. The energetics of a population of L.p- MCNEILS. ¥". ^"orXm"'"'^"'19.3-,306. An- ^""VfNew York Lntomol.""'"^SSoc. 92: topf.rn« rfo/o/;rflf« (Heteroptera: Miridae). J.