Occurrence of Goldenrod Galls: Study of Insect Ovipositing Behavior
How-To-Do-It
Occurrence of Goldenrod Galls: study of Insect Ovipositing Behavior
Sandra J. Newell
Goldenrod galls are a valuable re- terminateher ovipositionbehavior, (2) Eurosta gall may occur on one stem,
source for use in biology labs (Peard punctureonly the outer bud leavesand but they do not say how frequently Downloaded from http://online.ucpress.edu/abt/article-pdf/56/1/51/46455/4449743.pdf by guest on 29 September 2021 1992). Goldenrods and the associated rejectthe bud,or (3) continueher oviposi- multiple galls occur. It is unknown gall-forming insects are often abun- tionalprobe through additional bud leaves whether an ovipositing female can rec- dant in early stages of old-field succes- whichfrequently, but not always, results ognize that another female's egg has sion. In addition, these old-field habi- in the injectionof an egg into the bud. already been deposited in a particular tats can be accessible to groups of stem. students. The laboratory exercise de- Abrahamson et al. (1989) were able A second species of gall-maker scribed here takes advantage of this to demonstrate that E. solidaginis which is relatively common is Gnori- resource to explore a question con- exhibits a preference for Solidago moschemagallaesolidaginis, a goldenrod cerning the behavior of the female altissima, although S. canadensis, S. moth. Gnorimoschemaproduces an el- gall-forming insects as they lay eggs gigantea and S. rugosa support liptical swelling, approximately 2.5- on the goldenrod plant. populations of E. solidaginis in some 5 cm long, on the stem of the golden- The most common gall-makers on areas. Abrahamson et al. (1989) sug- rod. As in the spherical gall, the ellip- goldenrods are Eurosta solidaginis gest that the preference exhibited by tical gall contains one larva. The moth (Diptera: Tephritidae), Gnorimoschema the fly is based on both tactile and larva pupates in late-July, and the gallaesolidaginis (Lepidoptera: Gelechi- chemical information gained by the adult emerges in August or September idae), and Rhopalomyia solidaginis female while she is on the bud. In (Leiby 1922; Abrahamson & McCrea (Diptera:Cecidomyiidae). The golden- addition, Anderson et al. (1989) dem- 1986). After mating, the female ovi- rod gall fly, Eurosta solidaginis, pro- onstrated that E. solidaginis is able to posits on the lower leaves and stems duces a sphericalswelling (ball gall) on distinguish between susceptible and of goldenrod, and the eggs overwinter the upper stem of goldenrods, about resistant genotypes of S. altissima and in the leaf litter at the soil surface. 2.5 cm in diameter and containing a generally chooses the susceptible ge- Each Gnorimoschema female deposits single fly larva (Milne 1940). The larva notypes for oviposition. They were about 60 eggs (Leiby 1922). The larva pupates in early spring, emerging unable to specify a mechanism for this hatches in May, climbs up a new stem from the gall in April or May. Adult discriminatory ability, but susceptible of S. altissima to the apical meristem, flies mate, and females begin laying plants tend to be the faster growing and bores into the bud. It remains in eggs by late May (Miller 1959). Ovipo- plants. the bud, feeding for several days, then sition, the laying of an egg by the Females typically lay 70-75 eggs undergoes a molt (Leiby 1922). The female, was described in detail by (Milne 1940). Consequently, infesta- second instar burrows through the Abrahamson et al. (1989): tion rates tend to be high. For exam- apical meristem and down about 5- Prior to oviposition,an E. solidaginis ple, Milne (1940) collected 1000 gold- 8 cm into the stem (Leiby 1922; Abra- femaletypically climbs to the apex of the enrod stems and 264 stems had ball hamson & McCrea 1986). How the goldenrodbud and rapidlyrubs the apex galls. The egg of the goldenrod gall fly larva recognizes a goldenrod plant is with herforelegs, occasionally pulling the hatches soon after being deposited, unknown. Leiby (1922) says that the budtip to hermouth parts. If not discour- and the larva burrows through the larva "crawls aimlessly about until it aged by the informationthese activities apical meristem to produce the gall in comes in contact with a new golden- elicit, thefly walksdown to the baseof the the stem of the goldenrod. The gall rod shoot whereupon it crawls up the budand walksaround the basesearching appears by mid-June and grows in stem to the unfolding bud." Occasion- for a suitableplace to oviposit.If shefinds diameter until mid-July (Weis & Abra- ally, two Gnorimoschemagalls exist on a suitableoviposition site, she archesher hamson 1985; McCrea & Abrahamson one stem (Leiby 1922). It is unknown thoraxand abdomeninto ovipositionpos- 1987). The larva feeds on the gall tis- whether the larva can recognize the ture. With the ovipositortouching the sue through the summer, burrowing presence of another of its own species surfaceof the bud leaves, the fly can (1) an exit tunnel up to the epidermis of on the stem. Also, the larva burrows the stem (McCrea & Abrahamson into the apical bud at about the same 1987). In October the larva enters dia- time that the Eurosta females are ovi- Sandra J. Newell, Ph.D.,teaches biology pause, a resting stage in which the positing on the apex; and it is un- at Indiana Universityof Pennsylvania, In- larva overwinters (Weis & Abraham- known whether the two species can diana, PA 15705. son 1985). Cane and Kurczewski recognize that a stem is already inhab- (1976) indicate that more than one ited by the other species.
OVIPOSITINGBEHAVIOR 51 Goldenrod Galls - Sample Data Sheet Transect# 1 StudySite # Date 10-1-91 X = gall present
Stem # ballgall elpseall bunchgall Stem# ball ellipse gall bunchgall 1 X 351 X
2 __--______36 X 3 -} l } x 37 4 ___ X 38 r 5 ___ X 39 1X 6 x x 401 ______7 r___ 41 T _1 Downloaded from http://online.ucpress.edu/abt/article-pdf/56/1/51/46455/4449743.pdf by guest on 29 September 2021 8
10 x______11 _ 1 ______
12 _ _ _ _ _ X ______
14 1 X 1 _ I_I_I
______15 7__ 1 16 ______1 _ 1 7 1 _1_1 17 ---
18 _ -_ _ _ _ X ______
19 1 1 I . 1_1_._I___ 20
21 _ 22 23 T _ I _T___1_1_ 24 T_1 - _-- X T ______
25 _ _ _ _ _
26 X___ _
27 __ _ _ 28 _ -- X ______29 _ T ----1 __T_1--_1_1 30 _ 7_ ____1____ 31 _ _ Xx I ______32 _ _ _ _ X _ r ___ __ 33 ______34 I T 1 ______r_ Figure 1. Sample data sheet for collecting data on the presence or absence of galls on individual stems of goldenrods. Students are instructed to place an X in the appropriatecolumn when a gall is present and leave all columns blank for a stem with no galls.
52 THEAMERICAN BIOLOGY TEACHER, VOLUME 56, NO. 1, JANUARY'1994 Table 1. Data from transects recording the number of goldenrod stems in each category. Ball & Ball & Bud & Study No Ball Bunch Ellipse Bud Bunch Bud Bunch Total Site Galls Gall Gall Gall Gall Galls Galls Galls Stems 1 698 2 128 1 1 0 0 0 830 2 337 3 14 0 2 0 0 0 356 3 312 11 77 1 6 1 1 2 411
A third species of gall-makeris Rho- ing insects on goldenrods tend to goldenrod? Or, would you expect to palomyiasolidaginis, a gall midge. This avoid each other, ignore each other, or find stems with only one kind of gall?" is one of several midges that produces attracteach other?As a group, discuss Similarly, "If the different species of different types of galls on goldenrods the ways one could answer this ques- gall insects attracted each other, (Felt 1940). Rhopalomyiasolidaginis pro- tion, including direct observations of would you expect to find stems with duces a rosette or bunch gall. In other ovipositing insects. The students then several kinds of galls?" Based on this words, leaves are bunched together at must try to find a way to answer this discussion, students realize they must the top of the plant, as if the stem question given the following con- survey goldenrod stems to find out failed to elongate but continued to straints: what kind and how many galls exist Downloaded from http://online.ucpress.edu/abt/article-pdf/56/1/51/46455/4449743.pdf by guest on 29 September 2021 on individual stems. produce new leaves. Little is known 1. The question should be answer- At the field site, the students are about the naturalhistory of this partic- able within the 3-hour time span ular insect. Hartnettand Abrahamson faced with two problems: 1. how to of one laboratoryperiod. (1979) found rosette galls to be rela- identify the goldenrod species and 2. If the time of year is fall or win- and 2. tively abundant in central Pennsylva- ter, only galls are available. galls, how to sample the stems. nia (0-3.97 gall/m2);and Maddox and Goldenrods are difficult to identify; Root (1987) indicate that Rhopalomyia Often, the students have a difficult they have tremendous variability in solidaginisis restricted to feeding on time with this task and might need to appearance within species. The in- Solidagospecies. be prompted with leading questions. structormust choose carefullythe field After the students have a back- For example, "If the different species site for the exercise. Newcomb (1977) ground in goldenrods and gall insects, of gall insects tended to avoid each can help in the identification of gold- ask them to consider the following other, would you expect to find differ- enrods. One must not rely on one or question: Do the species of gall-form- ent kinds of galls on a single stem of two individual plants to make the identifications. The study site I use contains three species of goldenrods which are fairly easy for a student to Ball Gall & Bunch Gall-Test of Independence identify (Solidagoaltissima, S. rugosa,S. Bunch Gall graminifolia).Students take samples of these species to use for comparison Ball Gall present absent total purposes during their survey. Solidago present 1 12 13 altissimawas the only species used in the survey because some gall insects absent 79 319 398 exhibita preferencefor this species. In addition, samples of galls can be used total 80 331 411 to learn the different types. After students are confident they can differentiateamong the goldenrod 1. f In f for cell frequencies species and the gall types, I introduce = 1 In 1 + 12 In 12 + 79 In 79 + 319 In 319 them to transect sampling. A transect = 0 + 29.819 + 345.186 + 1839.096 length of 5 meters is often appropriate. = 2214.101 If the goldenrods are sparse, a longer 2. l: f In f for totals transect may be needed. Students = 80 In 80 + 331 ln 331 + 13 In 13 + 398 In 398 working in small groups were able to = 350.562 + 1920.501 + 33.344 + 2382.608 tally all goldenrod stems within 10 cm = 4687.015 on either side of the 5-meter transect 3. n In n for grand total line for a total of 47 transectslocated at = 411 In 411 = 2473.642 3 differentold-fields. Data sheets were 4. G = 2 [2214.101 - 4687.015 + 2473.642] provided to the students (Figure 1), = 1.456 although students might benefit from X2 05[1] = 3.841 developing their own data sheets if G is less than the critical X2 value of 3.841, therefore ball and bunch galls are time allows. independent. In other words, the two gall-forming insects ignore each other in As with most research, data collec- ovipositing on goldenrod stems. tion by my students produced some surprises (Table 1). The published lit- Figure 2. Example of analysis of data using a 2 x 2 test of independence with a erature on goldenrod galls is not en- G-statistic. If one of the categories has the value of zero, add one to values in all tirely reflective of what one finds in categories (Sokal & Rohlf 1981). the field. In this case, the ball gall was unusually rare. Also, we found a bud
OVIPOSITINGBEHAVIOR 53 gall to be more abundant than ex- ment, technical problems may arise Anderson, S.S. (1989). Host prefer- pected. Even though the data sheet that make it difficult to answer the ence and recognition by the golden- was preparedwithout a space for bud question. For example, the ball galls rod ball galimaker Eurosta solidaginis galls, we improvised and kept trackof turned out to be unusually rare in our (Diptera: Tephritidae). American the bud galls. study sites, and two of the three study Midland Naturalist, 121, 322-330. Students then must analyze the data sites yielded data that could not be Anderson, S.S., McCrea, K.D., Abra- to answer the originalquestion: Do the analyzed in the intended way. Finally, hamson, W.G. & Hartzel, L.M. species of gall-forminginsects on gold- there are questions that remain after (1989). Host genotype choice by the enrods tend to avoid each other, ig- the project is completed. Is the lack of ball gallmaker Eurosta solidaginis nore each other or attracteach other? interaction among ovipositing gall in- (Diptera: Tephritidae). Ecology, 70, This question is asking whether or not sects due to the low population size of 1048-1054. the gall insects are acting indepen- the ball gall insects? Would the results Cane, J.H. & Kurczewski, F.E. (1976). dently of each other when they lay be different if there were large num- Mortality factors affecting Eurosta eggs. The appropriateanalysis is a test bers of ball and bunch galls? What solidaginis (Diptera: Tephritidae). of independence using a G-statistic accounts for the low population size of Journal of the New York Entomological (Sokal & Rohlf 1981). This test calcu- ball gall insects? Is the large number of Society, 84, 275-282. lates a G-value that is compared to a bunch galls a cause for the low num- Felt, E.P. (1940). Plant galls and gall critical A2 value. If the G-value is ber of ball galls, or is the reduced ball makers. Ithaca, NY: Comstock Pub- an greater than the critical x2 value, the gall number due to abiotic factor lishing Co., Inc.
such as very wet weather during the Downloaded from http://online.ucpress.edu/abt/article-pdf/56/1/51/46455/4449743.pdf by guest on 29 September 2021 two factors being tested are signifi- Hartnett, D.C. & Abrahamson, W.G. cantly associated. One then inspects time of ovipositing? Students should (1979). The effects of stem gall insects the data to determine the form of the be guided to understand possible in- on life history patterns in Solidago association (e.g. too many stems with terpretations of the results. Different canadensis.Ecology, 60, 910-917. 0 or 2 galls and too few stems with ways of looking at the results should only 1 gall of either type, or vice ver- lead the students to think of other Leiby, R.W. (1922). Biology of the sa). In the data collected by my stu- designs that help to clarify what is goldenrod gall-maker Gnorimo- dents, study sites #1 and #2 had happening in nature. schema gallaesolidaginis Riley. Journal predominantlyone kind of gall, while Finally, one advantage of this exer- of the New York EntomologicalSociety, study site #3 had ball, bunch and bud cise is that there is no obvious right 30, 81-95. galls. Since the original question in- answer to the original question. So Maddox, G.D. & Root, R.B. (1987). volves interactionamong two or more many lab exercises are designed to Resistance to 16 diverse species of species, only data from site #3 were illustrate a known biological fact that herbivorous insects within a popu- analyzed using the test of indepen- students are trained to look for "the lation of goldenrod, Solidago al- dence. For students, it is easiest to right answer." When students obtain tissima: Genetic variation and herita- consider the gall insects in pairs, test- unexpected results in a lab, they im- bility. Oecologia, 72, 8-14. ing to see if any two insect species act mediately make excuses and search for McCrea, K.D., & Abrahamson, W.G. independently of each other (i.e. a 2 x errors. Consequently, students fail to (1987). Variation in herbivore infes- 2 test of independence). This analysis explain data; they even fail to look tation: Historical vs. genetic factors. is illustratedwith ball and bunch galls carefully at data. In this exercise, stu- Ecology, 68, 822-827. (Figure2). The results indicate that the dents simply consider what the data Miller, W.E. (1959). Natural history G-value is not significant. Conse- are telling them, without preconceived notes on the goldenrod ball gall fly, quently, the ball and bunch galls occur ideas of what is the "correct answer." Eurosta solidaginis (Fitch), and on independently of each other. One can its parasites Eurytoma obtusiventris conclude that at least in this particular Gahan and E. gigantea Walsh. Jour- field the bunch gall insect and the ball Acknowledgments nal of the TennesseeAcademy of Science, gall insect are ignoring each other. 34, 246-251. Each insect is laying its eggs on the Thanks go to the students of my Milne, L.J. (1940). Autecology of the goldenrod independently of the other General Ecology course who forced goldenrod gall fly. Ecology, 21, 101- species. [Note: If one of the categories me to be clear and concise. Also, R. 105. or cells in the analysis has the value of Silverstein and T. Peard made valu- Newcomb, L. (1977). Newcomb's wild- zero, add 1 to values in all categories able contributions in their reviews of flower guide. Boston: Little, Brown (Sokal & Rohlf 1981.)] the lab exercise and this manuscript. and Co. The student should learn several Peard, T.L. (1992). Using goldenrod lessons from this exercise beyond the galls to teach science process skills. simple conclusion from the test of in- References The American Biology Teacher, 56(1), dependence. Although the students 47-50. are initially provided with a question, Abrahamson, W.G. & McCrea, K.D. Sokal, R.R. & Rohlf, F.J. (1981). Biom- they must explore together the ways (1986). Nutrient and biomass alloca- etry (2nd ed.). New York: W.H. to try to answer this question. In other tion in Solidago altissima: Effects of Freeman and Co. words, they must think about experi- two stem gallmakers, fertilization, Weis, A.E. & Abrahamson, W.G. mental designs that could allow them and ramet isolation. Oecologia, 68, (1985). Potential selective pressures to answer the question. Also, students 174-180. by parasitoids on a plant-herbivore learn that after designing an experi- Abrahamson, W.G., McCrea, K.D. & interaction. Ecology, 66, 1261-1269.
54 THEAMERICAN BIOLOGY TEACHER, VOLUME 56, NO. 1, JANUARY1994