An allometric study was conducted on the boxelder bug, Boisea trivittata, to confirm the number ofinstars and to identify characteristics most useful for rapid instar identification of field samples. Analysis of field populations collected throughout the 1990-92 seasons indicated that there were five instars, clearly defined on the basis of size and the presence of wing pads. This finding is in contrast with the only other published study on stages of the boxelder bug, which claims there are six nymphal instars.
Size data gathered from field populations were substantiated by laboratory growth studies. Head width and/or second antennal segment length were identified as the most useful parameters for instar identification

Bouldrey, Scott M

Grimnes, Karin A

English

Valparaiso University

The Great Lakes Entomologist Volume 28 Numbers 3 & 4 -- Fall/Winter 1995 Numbers 3 & 4 -- Fall/Winter 1995 Article 3 January 1995 An Allometric Study of the Boxelder Bug, Boisea Trivittata (Heteroptera: Rhopalidae) Scott M. Bouldrey Alma College Karin A. Grimnes Alma College Follow this and additional works at: https://scholar.valpo.edu/tgle Part of the Entomology Commons Recommended Citation Bouldrey, Scott M. and Grimnes, Karin A. 1995. "An Allometric Study of the Boxelder Bug, Boisea Trivittata (Heteroptera: Rhopalidae)," The Great Lakes Entomologist, vol 28 (3) Available at: https://scholar.valpo.edu/tgle/vol28/iss3/3 This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. THE GREAT lAKES ENTOMOLOGIST1995 207 AN ALLOMETRIC STUDY OF THE BOXELDER BUG, BO/SEA TRIV/TTATA (HETEROPTERA: RHOPALIDAE) Scott M. Bouldrey and Karin A. Grimnes 1 ABSTRACT An allometric study was conducted on the boxelder bug, Boisea trivittata, to confirm the number ofinstars and to identify characteristics most useful for rapid instar identification of field samples. Analysis of field populations col­lected throughout the 1990-92 seasons indicated that there were five instars, clearly defined on the basis of size and the presence of wing pads. This rmd­ing is in contrast with e only other published study on stages of the boxelder bug, which claims there are six nymphal instars. Size data gathered from field populations were substantiated by labora­tory growth studies. Head width and/or second ant nnal segment length were identified as the most useful parameters for insta identification. Boisea trivittata (Say), the boxelder bug, is a pest closely associated with the pistillate boxelder tree (Acer negundo) throughout much of their shared range (Slater and Schaefer 1963). During hot, dry summers, the number of boxelder bugs can reach epidemic proportions, as evidenced by a long history of scattered reports in the literature (see the revi w in Wheeler 1982). Al­though they rarely cause economic damage, boxelder bugs ar considered a significant household nuisance. A recurring outbreak site in Gratiot County, Michigan, was discovered in the spring of 1990. As we be~an population studies, we realized that the only detailed report on this insect s life history identifies six nymphal instars after hatching (Smith and S epherd 1937). According to these authors, minute wing pads did not appear until the fourth instar, and the authors did not iden­tify any exuvia left in the egg after hatching (an egg-bound molt). The gen­eral rule for hemipteran species appears to be five nymphal instars before the adult ecdysis, not counting any egg-bound molt left after hatching (Slater ndBaranowski 1978). Subsequent investigators of this insect either avoided a direct challenge of the instar number (Tinker 1952) or divided the population into only adults and nymphs (Yoder and Robinson 1990). We became inter­ested in the question of instar number for the boxelder bug because our pre­liminary studies of field populations showed only five clearly discernable in­stars that were not easily reconciled with results of Smith and Shepherd (1937). As a result, we began a detailed growth study and allome ric analysis of our population f B. trivittata for use in subsequent seasonal studies. 1 Author to whom reprint requests should be sent: Department of Biology, Alma College, Alma, MI 48801. 1Bouldrey and Grimnes: An Allometric Study of the Boxelder Bug, Boisea TrivittataPublished by ValpoScholar, 1995-208 THE GREAT lAKES ENTOMOLOGIST Vol. 28, No.3 & 4 MATERIALS AND METHODS Insects were collected at Lang's Veterinary Clinic west of Alma in Gratiot County, Michigan, biweekly from March emergence to October hi nation during 1990-1992. The site contains numerous taminate and pistillate box­elder trees (Acer negundo) close to the residence. Insects were swept into 70% ethanol with a small brush from the sa e stretch of south-facing wall and west-facing fence on each collecting date. Samples were separated into five nymphal instars or adults on the basis of body size, presence and degree of wing pad growth, and head width. All measurements were made under a dissecting microscope with an ocular mi­crometer. Body par s (see Tables 1 and 2) were measured at their maximum point with the exception of antennal segments (1-4) where only the melanized portions were measured. For each instar, and for adult males and females, thirty-five individuals were measured. Mated females were allowed to oviposit in the laboratory on filter paper in 100 mm petr dishes. Because mortality of individually raised animals was high, first instars were kept in groups of five in etri dishes containing moist­ened filter paper. Maple syrup (5% v/v) was loaded into cotton-plugged tub­ing and placed in the dish for food. The dishes were exposed to a 16:8 LD pho­toperiod and maintained at 24°C ± 1°C in an incubator. Animals were observed daily. molts were recorded, an the newly molted a imals were moved to new dishes (in groups of five if possible). Head widths and second antennal segment lengths were recorded for recently molted individuals. Means between morphological characteristics of male and female adults, and between field and laboratory-raised nimals, were compared with stu­dent's t-test. Growth curves were fit using linear regression techniques. RESULTS Size of nymphs is ighly correlated with age for all parameters measured in this study (Table 1). When growth data for the five instars were analyzed with simple linear regression, no parameter had an r2 value less than 0.90.Head width was most highly correlated to instar number, as was length ofthe second antennal segment. For pronotallength and width, visual inspection of the data indicated that a logarithmic curve might better describe the growth relationship. Subsequent analysis of the logarithmic dat produced an r2 value of 0.96 (pronotum length) a d 0.97 (pronotum width). All correlations reported in this study are somewhat time independent because the regression analysis is against instar number (which assumes equal duration of each stage) and not against actual growth in days. Adult females were significantly larger than adult males for all parame­ters measured (Table 2). Difference in body length was easily discernable in the field. No attempt was made to sex fifth instars in th s preliminary study, so some of the variation in fifth instar measurements could result from sex­related growth differences. Although head width classically is u ed as an indicator of growth for many insect species, we noticed that the length of the second antennal segment was equally predictive of nstar number in B. trivittata (Table 1). This observation led us to compare growth ra es (using instar number, and not actual time) of the four antennal segments (Fig 1). Clearly, the first segmen changes little as the animal grows, but all other segments lengthen noticeably with instar. The second segment is the second shortest at hatching, yet by the f fth instar, 2The Great Lakes Entomologist, Vol. 28, No. 3 [1995], Art. 3https://scholar.valpo.edu/tgle/vol28/iss3/3'" ~Table 1. Measurements of nymphs of Boisea trivittata· (Say). Values are mean mm ± SE, n=35 (based on field collected individuals). Character 1st Instar 2nd Instar 8rd Instar 4th Instar 5th Instar r2 slope --t:c: m Body length Head width 2.91 ± 0.04 0.68 ± 0.01 3.80:!: 0.06 0.92:!: 0.01 5.11:!: 0.06 1.17 :!: 0.01 7.01 :!: 0.09 1.51 :!: 0.01 9.60:!: 0.11 1.89 ± 0.02 0.93 0.97 1.67 0.30 Q ;><:> m ~ Interocular dist. Pronotallength Pronotal width Antennal length Segment 1 Segment 2 0.50:!: 0.01 0.29:!: 0.01 0.80 ± 0.01 0.23:!: 0.01 0.45:!: 0.01 0.63:!: 0.01 0.38:!: 0.01 1.O1:!: 0.01 0.28:!: 0.01 0.68:!: 0.01 0.80:!: 0.01 0.57:!: 0.01 1.30:!: 0.01 0.37:!: 0.01 0.93 ± 0.01 1.04:!: 0.01 0.76:!: 0.01 1.69:!: 0.02 0.49:!: 0.01 1.23 :!: 0.01 1.28:!: 0.01 1.51 ± 0.01 2.51:!: 0.03 0.64 ± 0.01 1.70:!: 0.01 0.96 0.91 0.90 0.93 0.97 0.20 0.21 0.41 0.10 0.31 ~ A m Vl m Z --t 0 ~ 0 r­0 Q Qj Segment 3 0.46:!: 0.01 6 ± 0.01 0.81 ± 0.01 1.07 ± 0.01 1.44:!: 0.01 0.95 0.24 Segment 4 0.65:!: 0.01 0.85:l: 0.01 1.05 ± 0.01 1.28 ± 0.01 1.64:l: 0.01 0.95 0.24 N ~ 3Bouldrey and Grimnes: An Allometric Study of the Boxelder Bug, Boisea TrivittataPublished by ValpoScholar, 1995210 THE GREAT tAKES ENTOMOLOGIST Vol. 28, No.3 & 4 Table 2. Measurements of adults ofBoisea trivittata. Values are mean mm :!: SE, n=35 (field collected individuals). Adult Adult Character females males p valuesB Body length 12.1 :!: 0.10 10.3 ± 0.08 <0.0001 Head width 2.14 ± 0.01 1.96 ± 0.02 <0.0001 Interocular dis. 1.34:!: 0.01 1.19 :!: 0.02 <0.0001 Pro notal length 1.93:!: 0.04 1.73 ± 0 02 <0.0001 Pronotal width 3.70 ± 0.03 3.09 ± 0.02 <0.0001 Antenna! length Segment 1 0.64:!: 0.01 0.62:!: 0.01 <0.01 Segment 2 2.09:!: 0.02 1.90 :!: 0.01 <0.0001 Segment 3 1.80 :!: 0.02 1.70:!: 0.02 <0.0001 Segment 4 1.90:!: 0.02 1.73 ± 0.02 <0.0001 a student's t-test. 2.5 E g 2.0E (]) E Ol (]) 1.5 en tilc: c: (]) 1.0 E til 15 0.5.s:: t5lc: .!!! "'-0--' antenna I seg 1 --II-antennal seg II -'--!r" antennal seg 111 ----0---anlennal seg IV ...0...... .....::~:::~ .8···· ........ 01' ..."' .. ...K··· .0,,- ", .-_••••­•••••• • ••• -l!: c-oooooo_oooo::::::ooooC-oooo--ooooc-ooooo--ooo<>ooooooooooo insler 1 instar 2 inslar 3 inslar 4 inslar 5 adull Age Figure 1. Mean length of antennal segments (mean ± SE) of field-collected Boisea tnvittata specimens. Thirty-five measurements were averaged for each nymphal data point; values for adults were obtained by averaging male and female means from Table 2. it is the longest. In the regression analysis, the predictive growth line for thesecond antennal segment has the greatest slope (Table 1, Fig. 1). Growth studies in the laboratory w re carried out on animals reared in groups of five, wherever possible. Animals reared as individuals perished quickly; only eight of 58 (13.8%) molted to the secon instar, and none ofthose animals survived to the third instar. In contrast, 43.1% (148/343) of animals 4The Great Lakes Entomologist, Vol. 28, No. 3 [1995], Art. 3https://scholar.valpo.edu/tgle/vol28/iss3/31995 211THE GREAT LAKES ENTOMOLOGIST raised in groups offour or five survived to the secondinstar, and 17.0% (8/47) survived to the third instar. Mass rearing (even in groups of as few as five) increases the risk of death from cannibalism, a phenome on reported first by Abbott (1948). In our study, cannibalism appeared to be rare. It was observed only in the absence of a water source and only whe an animal emerged un­usually helpless and unable to move away from the probosci of its fellow hatchlings. We found no evidence of egg-bound exuvia after first instars hatched from the egg. Under our laboratory conditions, the first stadium averaged 5.5±0.2 days (n=148) and first instars had a mean head width ofO.64±0.01 mm (n=25) and a mean second antennal segment length of 0.42±0.01 mm (n=25). The second instars had a mean head width of 0.88±0.01 mm (n=20) and a mean second antennal segment length of 0.66±0.01 mm (n=20), while the mean in­star duration was 6.5±0.8 days (n=8). For the third instars, the mean head width was 1.09±0.01 mm (n=6), while the mean length of the second anten­nal segment was 0.92±0.01 mm (n=6). All third instar nymphs possessed wing pads, in contrast to the study of Smith and Shepherd (1937) where wing pads were not observed until the fourth instar. Although the mean values of all parameters measured were slightly smaller for insects raised in the labo­ratory, neither head widths nor second antennal segment lengths were signif­icantly different from field-caught instars (stud 's t-test). Unfortunately, all laboratory-reared animals were lost because of an incubator malfunction just before the majority of insects reached the third instar, resulting in a low num­ber of data points (n=6) for measurements of that instar. Nevertheless, the presence of wing pads in lab-reared third instars clearly was established. DISCUSSION There has not been a detailed growth analysis of the boxelder bug previ­ous to the present study. Smith and Shepherd (1937) reported head width and body length data, but included only mean and range values. Also, as previ­ously mentioned, they identified six, rather than five, instars for this insect. We believe we have clearly established the presence of five, and only five, in­stars in B. trivittata, not only through our identification of discrete size classes for the parameters measured in field animals, but through the insects that were reared into the third instar. Although Smith and S epherd report duration data for six instars, their sample numbers suggest that the same in­dividuals were not followed throughout their entire life cycle. All of the third instars raised in our study possessed wing pads ( ften con­sidered "the rule" for hemipteran species) gives the first clue toward explain­ing the differences between our data and those of Smith and Shepherd (1937). Comparing mean head widths for our third instar (1.17 mm) to their four h(1.17 mm), our fourth instar (1.51 mm) to their fifth (1.51 mm), and our fifth instar (1.89 mm) to their sixth (1.83 mm) makes it clear that the discrepancy in instar identification must lie prior to our third ins tar. Also, me n head width for our second i star sample (0.92 mm) matches their third instar (0.90 mm), and if we average their values for first (0.64 mm) and second instars (0.78 mm), the head width of 0.71 mm compares nicely with our first instar value of 0.68 mm. No statistical differences were seen between our field and laboratory-reared populations for either head width or for length of the sec­ond antennal segment for instars 1 - 3, further substantiating our proposed instar identification of field-caught an mals. Based on these data, we believe that Smith and Shepherd may have inadvertently subdivided a highly vari­able first instar population into smaller than average (instar 1) and larger 5Bouldrey and Grimnes: An Allometric Study of the Boxelder Bug, Boisea TrivittataPublished by ValpoScholar, 1995212 THE GREAT LAKES ENTOMOLOGIST Vol. 28, No.3 &4 than average (instar 2) samples and labelled them accordingly. We observed that slightly desiccated eggs may result in hatchlings t do not expand be­fore sclerotization to the same extent as nondesiccated animals; thus, desic­cation results in animals with smaller head widths and a wider variation in hatchling size. The values we report for adult head width, pronotum length and width, and length of the four antennal segments agree fairly well with the values presented by Schaefer (1975) for six populations of B. trivittata collected across the United States. His samples of adults were not identified b;V sex: slight differences in mean values, therefore, may r present variation In the sex ratios of his samples. Both male and female adu ts observed by Smith and erd (1937) possessed slightly larger dimensions for head width, body , and pronotal width than the adults in this study. ACKNOWLEDGMENTS We thank Christina Krupp, University of Vermont, for editorial advice and Angie Williams, Alma College, for additional measurement data. This work was partially supported by a g ant from the Kellogg Foundation enti­tled: The Science Teacher Pr paration Project. LITERATURE CITED Abbott, C.E. 1948. Cannibalism in Leptocoris trivittatus Say. Bull. Brooklyn Entomol. Soc. 43:112-113. Schaefer, C.W 1975. A re-assessment of North American Leptocoris (Hemiptera-Het­eroptera:Rhopalidae). Ann. Entomol. Soc. Am. 68:537-541. Slater, J.A. and RM. Baranowski. 1978. How to know the true bugs. Wm. C. Brown: Dubuque, Iowa. 256 pp. Slater, J.A and C.W Schaefer. 1963. Leptocoris trivittatus (Say) and Coriomeris humilis Uhl. in New England (Hemiptera: Coreidae). Bull. Brooklyn Entomol. Soc. 58:114-117. Smith, RC. and B.L. Shepherd. 1937. The life history and control of the boxelder bug in Kansas. Trans. Kansas Acad. Sci. 40:143-159. Tinker, M.E. 1952. The seasonal behavior and ecology of the boxelder bug Leptocoris trivittatus in Minnesota. Ecology 33:407-414. Wheeler, AG. 1982. Bed bugs an other bugs. pp. 313-345, in: A Mallis, ed. Handbook of Pest Control. Franzak and Foster Co., Cleveland, Ohio. Yoder, K.M. and WH. Robinson. 1990. Seasonal abundance nd habits of the boxelder bug, Boisea trivittata (Say), in an urban environment. Proc. Entomol. Soc. Wash. 92:802-807. 6The Great Lakes Entomologist, Vol. 28, No. 3 [1995], Art. 3https://scholar.valpo.edu/tgle/vol28/iss3/3

An Allometric Study of the Boxelder Bug, \u3ci\u3eBoisea Trivittata\u3c/i\u3e (Heteroptera: Rhopalidae)

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An Allometric Study of the Boxelder Bug, \u3ci\u3eBoisea Trivittata\u3c/i\u3e (Heteroptera: Rhopalidae)

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