BIOLOGICAL CONTROLÐPARASITOIDS AND PREDATORS Impact of Rag1 Resistant Soybeans on communis (: ), a Parasitoid of Soybean Aphid (Hemiptera: Aphididae)

KIRAN GHISING,1 JASON P. HARMON,1 PATRICK B. BEAUZAY,1 DEIRDRE A. PRISCHMANN-VOLDSETH,1 TED C. HELMS,2 PAUL J. ODE,3 1,4 AND JANET J. KNODEL Downloaded from https://academic.oup.com/ee/article/41/2/282/483303 by guest on 27 September 2021

Environ. Entomol. 41(2): 282Ð288 (2012); DOI: http://dx.doi.org/10.1603/EN11196 ABSTRACT Multiple strategies are being developed for pest management of the soybean aphid, Aphis glycines Matsumura; however, there has been little published research thus far to determine how such strategies may inßuence each other, thereby complicating their potential effectiveness. A susceptible soybean (Glycine max L.) variety without the Rag1 gene and a near isogenic resistant soybean variety with the Rag1 gene were evaluated in the laboratory for their effects on the Þtness of the soybean aphid parasitoid, (Gahan). The presence or absence of the Rag1 gene was veriÞed by quantifying soybean aphid growth. To test for Þtness effects, parasitoids were allowed to attack soybean on either a susceptible or resistant plant for 24 h and then aphids were kept on the same plant throughout parasitoid development. Parasitoid Þtness was measured by mummy and adult parasitoid production, adult parasitoid emergence, development time, and adult size. Parasitoids that attacked soybean aphids on susceptible plants produced more mummies, more adult parasitoids, and had a higher emergence rate compared with those on resistant plants. Adult parasitoids that emerged from resistant plants took 1 d longer and were smaller compared with those from susceptible plants. This study suggests that biological control by B. communis may be compro- mised when host plant resistance is widely used for pest management of soybean aphids.

KEY WORDS soybean, Aphis glycines, host-plant resistance, Binodoxys communis, biological control

A primary concept underlying integrated pest man- fecting the quantity and quality of the herbivores that agement (IPM) is the use of multiple pest control natural enemies rely on to reproduce (Ode 2006). strategies (Allen and Rajotte 1990, Kogan 1998). Two Parasitoids may be particularly susceptible, as host common strategies are deploying host plants resistant plant resistance can affect host quality, which in turn to herbivores and promoting biological control agents impacts the survival of immature parasitoids, devel- that can also help control herbivores (Smith 2005). opment time, and ultimately adult Þtness (Barbosa et Combining these two strategies can result in enhanced al. 1982, Duffey and Bloem 1986, van Emden 1995). herbivore suppression compared with using either Moreover, parasitoid foraging behavior can be inßu- method alone; however, in some cases one strategy enced by morphological and chemical attributes of can negatively inßuence the other (Beddington et al. resistant plants, ultimately undermining their ability 1978, Auclair 1989, Harrewijn and Minks 1989, Bottrell to control herbivore populations (Gould et al. 1991, et al. 1998, Dogramaci et al. 2005). Turlings and Benrey 1998, Hare 1992, Ode 2006). Resistant plants often have chemicals and morpho- Since its Þrst detection in North America in 2000, logical characteristics that make them less attractive to the soybean aphid, Aphis glycines Matsumura herbivorous (antixenosis, nonpreference) or (Hemiptera: Aphididae), has spread throughout soy- negatively inßuence pest fecundity, survival, or de- bean-growing regions in the north central United velopment time (antibiosis) (Painter 1958, Smith States and some Canadian provinces where it is con- 2005). However, these same attributes can directly or sidered one of the most economically important pests indirectly impact higher trophic levels, often by af- of soybean (Alleman et al. 2002, Venette and Ragsdale 2004). Besides causing direct damage to plants, soy- 1 Department of Entomology, North Dakota State University, bean aphids can vector several viral diseases and ex- Fargo, ND 58108. crete honeydew, promoting a fungus known as sooty 2 Department of Plant Sciences, North Dakota State University, mold that disrupts photosynthesis (Guo and Zhang Fargo, ND 58108. 1989, Clark and Perry 2002). Insecticide applications 3 Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO 80523. are a common and effective method of soybean aphid 4 Corresponding author, e-mail: [email protected]. control, although drawbacks associated with broad-

0046-225X/12/0282Ð0288$04.00/0 ᭧ 2012 Entomological Society of America April 2012 GHISING ET AL.: IMPACT OF Rag1 APHID RESISTANT SOYBEANS ON B. communis 283 spectrum pesticide use, such as insecticide resistance, Soybean aphid colonies were reared and maintained nontarget effects, and environmental contamination on the susceptible soybean variety, RG607RR. All col- make alternative management strategies desirable onies and experiments were held at 25 Ϯ 5ЊC, 60Ð80% (ffrench-Constant et al. 2004, Heimpel et al. 2004, RH, and 16L:8D photoperiod. Ragsdale et al. 2007). Classical biological control and The B. communis colony (Harbin strain) was initi- host plant resistance are two nonchemical approaches ated in winter 2009 and maintained for several gen- that are currently being explored for soybean aphid erations in the laboratory from the soybean aphid management (Heimpel et al. 2004, Hill et al. 2004b, colony. The colony was started from 30 mummies Wyckhuys et al. 2009). obtained from Dr. George E. Heimpel, University of Classical biological control using parasitoids from Minnesota, St. Paul, MN. This parasitoid colony was Asia is believed to be an important option for man- originally established from 7 males and 33 females of agement of soybean aphids for two reasons. First, parasitized A. glycines near Harbin and Suihua county

soybean aphids are kept below economically damag- of Heilongjiang province, China in late August 2002 Downloaded from https://academic.oup.com/ee/article/41/2/282/483303 by guest on 27 September 2021 ing population levels in Asia through natural control (Wyckhuys et al. 2007a). Specimens of soybean aphids with both predators and parasitoids (Wu et al. and B. communis were deposited in the North Dakota 2004). Second, parasitism levels in Asia are often Insect Reference Collection at North Dakota State Ͼ10%, while in North America they are typically be- University in Fargo. low 1% (Heimpel et al. 2010, Lui et al. 2004). Binodoxys Experiments were performed with young, naõ¨ve fe- communis (Gahan) (Hymenoptera: Braconidae) is a male parasitoids from the colony. To obtain each of monophagous aphid parasitoid that has been these parasitoids, one B. communis mummy from the collected from eastern Asia, and recently released in colony was kept in a clear gelatin capsule (size 0) the United States on a limited scale for experimental nested within a 1.5 ml micro centrifuge tube until adult purposes (Wyckhuys et al. 2007b). Because of its high emergence. Once adults emerged, pairs of male and prey speciÞcity, B. communis is thought to be more female adults were isolated in separate glass vials with effective than other biocontrol agents at maintaining plaster of Paris at the bottom to maintain moisture. A soybean aphid populations at low levels (Desneux et mixture of honey and water (4:1) was soaked in cotton al. 2009, Wyckhuys et al. 2007b). balls (size 5) as a feeding supplement. Parasitoids were Plant resistance to the soybean aphid has been ad- given the opportunity to mate for 24 h and then fe- vanced with the discovery of resistance in cultivars males were transferred to an experimental plant. Fe- like ÔDowlingÕ and ÔJackson,Õ which show resistance to male parasitoids in the experiment were naõ¨ve with the soybean aphid (Hill et al. 2004a). Resistance in respect to hosts, and were Ϸ1Ð2 d old at the start of the Dowling is conferred by a single dominant gene, Rag1, experiment. which limits soybean aphid colonization and nega- Plant Varieties. Two soybean varieties were used as tively affects their fecundity, survival, longevity, and treatments: a susceptible variety without the Rag1 development (Li et al. 2004, Hill et al. 2006). Rag1 is gene, RG607RR, and a near isogenic resistant variety currently being bred into commercial soybean lines. with the Rag1 gene (provided by T. Helms, North Despite the potential associated with each of these Dakota State University, Fargo, ND). The source control strategies, there has been little work investi- of the Rag1 gene used for the experiment was gating their effects on each other. LDXG04018Ð3 (provided by B. Diers, University of Our overall research objective was to evaluate the Illinois, Urbana-Champaign, IL), which was devel- development and Þtness of B. communis when exposed oped by crossing Dwight X (Loda X Dowling) (T. to soybean aphids on a near isogenic resistant soybean Helms, personal communication). The resistant line is variety with the Rag1 gene compared with a suscep- a BC3F3-derived line (using RG607RR as the recur- tible soybean variety without the Rag1 gene. We Þrst rent parent) that carries the Rag1 gene. For our ex- conÞrmed that our experimental varieties differed in periment, the presence of the Rag1 gene in the resis- their resistance to soybean aphid by measuring the tant soybean variety was conÞrmed by performing an growth rate of aphid populations reared on resistant aphid growth rate experiment (see Aphid Growth). In and susceptible soybean plant varieties and by assay- addition, individual plants used in the experiment ing for the Rag1 gene. We then assessed effects of the were tested for the allelic state of the Rag1 gene using Rag1 gene on the parasitoid by allowing parasitoids to the simple sequence repeat marker Satt435 and elec- attack and develop on soybean aphids reared on either trophoresis of the polymerase chain reaction (PCR) the resistant or susceptible plants. We measured para- product according to the methods of Kim and Diers sitoid Þtness by determining the total number of (2009). Electrophoresis of the PCR products from aphids and mummies, emergence rates, parasitoid de- individual resistant and susceptible plants showed that velopment time, and adult parasitoid size. resistant plants had the dominant Rag1 gene and sus- ceptible plants did not (Ghising 2011). Aphid Growth. Susceptible and resistant plants Materials and Methods were used to assess the effect of the Rag1 gene on Insect Colonies. Laboratory colonies of soybean soybean aphid populations reared on individual aphids were established from aphids collected in soy- plants. The experiment was repeated twice for a total bean plots at the Prosper Agricultural Experimental sample size of 20 plants per variety. Each experimental Station Farm near Prosper, ND, in the summer of 2008. plant was covered with a clear plastic cage (50 cm 284 ENVIRONMENTAL ENTOMOLOGY Vol. 41, no. 2 high ϫ 10 cm diameter) with a Þne nylon mesh at the adult was collected using an aspirator and stored in a top of the cage to allow for air ßow, and the plant glass vial with 95% ethanol labeled with treatment, location was randomized. Four days after the devel- date, time, and sex. Development time from attack to opment of the Þrst set of trifoliate leaves, a mixture of mummy formation and from mummy to adult emer- Þve nymphs (approximately third instar) and Þve gence was recorded. We also measured parasitoid apterous adult aphids were transferred to the upper body size and the length of their right and left metati- surface of each experimental plant leaf using a Þne biae using a microscope stage micrometer accurate to paint brush to avoid injury (Hodgson et al. 2005). This one micron. Body size was measured from the anterior mixture of aphids was used because different life tip of the frons to the posterior tip of the abdomen. stages are differentially susceptible to the parasitoid Body size and hind metatibiae are often used for de- (Wyckhuys et al. 2008), and could be differentially termination of parasitoid Þtness, including fecundity affected by resistant soybean plants as well. Aphids and male mating ability (Ode and Strand 1995, Sagarra

were counted on each plant 24 h after initial inocu- et al. 2001, Lampert et al. 2011). Downloaded from https://academic.oup.com/ee/article/41/2/282/483303 by guest on 27 September 2021 lation and then every other day for 14 d. To compare the performance of parasitoids on re- To examine treatment effects on aphid establish- sistant and susceptible soybean plants, we determined ment and reproduction, we compared the total num- the total number of mummies produced, proportion of ber of aphids 24 h after inoculation, size of the aphid aphids parasitized (number of mummies found on a population after 14 d, and per capita growth rate (log plant/number of aphids available to parasitize), pro- [aphids at day 14/aphids after day 1]). The number of portion of adult parasitoid emergence (number of aphids observed 24 h after inoculation included aphids successfully emerged adults from a plant/number of that successfully established on a plant and any mummies found on that plant), days to mummiÞca- nymphs born during the Þrst 24 h. In the second block tion, days from mummiÞcation to adult emergence, of the experiment, we differentiated established total development time for male and female parasi- aphids from new nymphs. Potential heterogeneous toids, offspring mean body size (mm), and offspring growing conditions in the greenhouse were accounted mean hind metatibiae length (mm). Count data were for by placing one resistant plant next to a susceptible analyzed using a two-way ANOVA (SAS Institute Inc.; plant within the tray and then each tray tested as a JMP Statistics 2000) with a treatment factor (suscep- nested blocking variable within each experiment. Be- tible vs. resistant plants) and a blocking factor to cause we found no effect of individual trays, we used account for the two different runs of the experiment. the repeated experiments (2) as the only blocking The proportional results were analyzed using logistic variable. Data were analyzed using two-way analysis regression (SAS Institute Inc.; JMP Statistics 2000) of variance (ANOVA) (SAS Institute Inc. 1989Ð1999, with the original counts that produced the propor- Cary, NC; JMP Statistics 2000). Soybean aphid den- tions. The logistic regression model tested the same sities at the end of the experiment were log-trans- terms as the ANOVA, but also requires an additional formed and the total number of aphids after 24 h was term to account for each plant nested within treat- square-root transformed for normality and homoge- ments, thereby giving the proper degrees of freedom. neity of variance to meet assumptions of parametric All data were checked to meet the assumptions of statistical tests. ANOVA and transformations were made as necessary Parasitoid Experiment. Single plants of each treat- to data that were not normally distributed. In addition, ment (susceptible or resistant soybean variety) at the likelihood ratio tests (adjusted G-tests) were used Þrst trifoliate leaf stage were each infested with 10 when comparing count data (number of plants pro- soybean aphid nymphs (approximately third instar) ducing mummies vs. not producing mummies in sus- and 10 apterous adults to the upper leaf surface using ceptible and resistant plants; number of adults pro- the same technique as described previously. There ducing mummies vs. not in susceptible and resistant were 12 replications per treatment per block in each plants; and number of males vs. females produced experiment. Each experiment was repeated twice. across all susceptible and resistant plants). A paired Soybean aphids were allowed to establish for 24 h after t-test was used to compare development time of males which their densities were assessed. Each plant was and females from the same plant in the susceptible caged in a clear plastic cage as mentioned earlier. plant treatment. Then, a single newly mated female parasitoid (see Insect Colonies) was released into each caged plant Results for 24 h and then removed using an aspirator. The experiment was conducted at normal room tempera- Aphid Growth. After 14 d across both replicates, ture (25 Ϯ 5ЊC, 60Ð80% RH, and 16L:8D photope- aphid populations were over 30 times greater on sus- riod). Starting 3 d after parasitoids were removed, ceptible soybean plants than on resistant plants (F ϭ caged plants were inspected daily until day 15, and 139.6; df ϭ 1, 37; P Ͻ 0.0001; Table 1). Susceptible newly formed parasitized aphids (mummies) were plants also had signiÞcantly more aphids 24 h after collected using a spatula and placed individually into inoculation than on resistant plants (F ϭ 15.5; df ϭ 1, clear gelatin capsules (size 0) that were then placed 37; P ϭ 0.0004; Table 1). When we differentiated inside 1.5 ml micro-centrifuge tubes and maintained at established aphids versus reproduction in the second room temperature. Mummies were examined twice run of the experiment, more aphids successfully es- daily for adult parasitoid emergence. When found the tablished after 24 h on susceptible plants than on April 2012 GHISING ET AL.: IMPACT OF Rag1 APHID RESISTANT SOYBEANS ON B. communis 285

Table 1. Effect of plant resistance on soybean aphid popula- produced on resistant plants (F ϭ 34.8; df ϭ 1, 45; P Ͻ tions 0.0001; Table 2). Most susceptible plants produced at least one adult parasitoid whereas only a quarter of No. of aphids No. of aphids Per capita Treatment 24 h after initial resistant plants did (20/24 susceptible plants vs. 6/24 after 14 d growth ratea inoculation resistant plants; Gadj ϭ 17.1; df ϭ 1, 46; P Ͻ 0.0001), Susceptible 19.5 Ϯ 2*** 634.7 Ϯ 68.0*** 1.42 Ϯ 0.1*** and no resistant plants produced more than two adults. Resistant 10.7 Ϯ 1.4 19.5 Ϯ 2.8 0.2 Ϯ 0.1 In addition to susceptible plants having more mum- mies, the proportion of mummies that developed into Data shown as means Ϯ SEM. Means within a column are signiÞcant adult parasitoids was higher on susceptible plants Ͻ when followed by ***P 0.001. compared with resistant plants (␹2 ϭ 4.70; P ϭ 0.030; a Average per capita change in aphid pop 24 h after inoculation to 1 the end of the exp. Data were log-transformed to meet normality Table 2). Controlling for initial differences in aphid assumptions. density, the number of adult parasitoid produced per

aphid was over 10 times greater on susceptible plants Downloaded from https://academic.oup.com/ee/article/41/2/282/483303 by guest on 27 September 2021 Ϯ Ϯ resistant ones (mean Ϯ SEM; 9.9 Ϯ 0.7 vs. 4.4 Ϯ 0.6; t ϭ compared with resistant ones (0.17 0.03 vs. 0.01 ␹2 ϭ Ͻ 5.4; df ϭ 1, 18; P Ͻ 0.0001), and more newly born 0.005; 1 98.2; P 0.0001). aphids were found on susceptible plants than on re- The development time for attacked aphids to be- sistant plants (susceptible plant 7.9 Ϯ 1 vs. resistant come mummies was signiÞcantly longer on resistant ϭ ϭ ϭ plant 4.8 Ϯ 0.7; t ϭ 2.6; df ϭ 1, 18; P ϭ 0.019). To versus susceptible plants (F 10.7; df 1, 36; P account for the difference in the number of aphids 0.002; Table 3). Removing those plants that had mum- after 24 h, we determined the growth rate of aphid mies but no emerged adults, soybean plant treatment populations from 24 h after inoculation through the did not have any effect on the time it took for adults ϭ ϭ ϭ end of the experiment. The susceptible soybean plant to develop from mummies (F 0.6; df 1, 24; P 0.45; had a signiÞcantly higher per capita aphid growth rate Table 3). However, adults on susceptible plants com- than on the resistant plant (F ϭ 102.0; df ϭ 1, 37; P Ͻ pleted their entire development (attack to adult) 0.0001; Table 1). about 1 d faster than those from resistant plants (F ϭ Parasitoid Experiment. Almost 10 times as many 13.2; df ϭ 1, 24; P ϭ 0.001; Table 3). mummies were produced on susceptible plants com- Development time of male parasitoid was the pared with resistant plants (F ϭ 78.6; df ϭ 1, 45; P Ͻ same as the development time of female parasitoid 0.0001; Table 2). The difference in mummy produc- wasps reared from susceptible plants (males 11.2 Ϯ tion was because of both a difference in the number 0.13 d vs. females 11.0 Ϯ 0.19 d; paired t-test t ϭ 0.75; of plants that successfully produced at least one df ϭ 1, 15; P ϭ 0.46). We could not compare males and mummy (23/24 susceptible plants vs. 17/24 resistant females on resistant plants as only one plant produced plants; Gadj ϭ 5.60, df ϭ 1, 46; P ϭ 0.018) and the both males and females and that plant only produced average number of mummies produced on plants that one adult of each sex. Overall, there were more male produced at least one mummy (susceptible plant wasps produced on susceptible plants compared with 22.0 Ϯ 1.5 vs. resistant plant 2.8 Ϯ 1.8; F ϭ 64.99; df ϭ female wasps (86 vs. 55), but the average proportion 1, 37; P Ͻ 0.0001). of males produced on each plant was not different This difference in mummy production could have than 0.5 when looking across susceptible plants been inßuenced by the number of aphids available for (0.59 Ϯ 0.06; t ϭ 1.50; df ϭ 1, 8; P ϭ 0.15). There was the parasitoid to attack. Despite starting all plants with no difference in the numbers of males and females the same number of aphids, 24 h after infestation there produced from resistant plants (resistant plants: 4 were 50% more aphids available on susceptible plants males and 5 females; Gadj ϭ 0.89, df ϭ 1, 48; P ϭ 0.35). than on resistant plants (F ϭ 34.2; df ϭ 1, 45; P Ͻ Body length (mm) and length of the left and right 0.0001; Table 2). However, when we account for these metatibiae (mm) of adult parasitoids were measured differences in aphids available to parasitize by calcu- as indicators of Þtness. The average body size of adult lating proportion parasitism (total number of mum- parasitoids was similar for susceptible and resistant mies from a plant/total number of aphids available to plants (F ϭ 1.5; df ϭ 1, 24; P ϭ 0.22; Table 3). In parasitize), susceptible plants still produced signiÞ- contrast, parasitoids reared from susceptible plants ␹2 ϭ cantly more mummies than resistant plants ( 1 had larger metatibiae compared with parasitoids 403.2; P Ͻ 0.0001; Table 2). reared from resistant plants (left hind metatibia: F ϭ The total number of adults produced on susceptible 4.7; df ϭ 1, 24; P ϭ 0.04, and right metatibia: F ϭ 11.6; plants was almost 20 times greater than the number df ϭ 1, 24; P ϭ 0.002; Table 3).

Table 2. Parasitism rates of adult B. communis on soybean aphids reared from susceptible and resistant soybean plants

No. of No. of aphids available Proportion No. of adult Proportion of mummies Treatment mummies prior to parasitoid inoculation parasitisma parasitoids emerged emerged into adult parasitoids Susceptible 21.2 Ϯ 2.1*** 36.2 Ϯ 1.1*** 0.6 Ϯ 0.05*** 5.8 Ϯ 0.9*** 0.3 Ϯ 0.04* Resistant 2 Ϯ 0.5 24.5 Ϯ 1.7 0.1 Ϯ 0.02 0.3 Ϯ 0.1 0.2 Ϯ 0.1

Data shown as means Ϯ SEM. Means within a column are signiÞcant when followed by *P Ͻ 0.05, ***P Ͻ 0.001. a Proportion parasitism equals the total no. of mummies from a plant divided by the total no. of aphids available to parasitize. 286 ENVIRONMENTAL ENTOMOLOGY Vol. 41, no. 2

Table 3. Effect of Rag1 on the development and fitness of the soybean aphid parasitoid, B. communis (Hymenoptera: Braconidae)

Metatibiae length of Aphids to Mummies to adult Parasitoid adult Mean body adult parasitoids (mm) Treatment mummies parasitoids development size of adult (days) (days) time (days) parasitoids (mm) Left Right metatibiae length metatibiae length Susceptible 7.5 Ϯ 0.14** 3.6 Ϯ 0.16NS 11.1 Ϯ 0.17*** 1.2 Ϯ 0.02NS 0.322 Ϯ 0.004* 0.321 Ϯ 0.004** (n ϭ 23) (n ϭ 20) (n ϭ 20) (n ϭ 20) (n ϭ 20) (n ϭ 20) Resistant 8.7 Ϯ 0.3 3.5 Ϯ 0.15 12.4 Ϯ 0.31 1.15 Ϯ 0.02 0.297 Ϯ 0.005 0.282 Ϯ 0.006 (n ϭ 17) (n ϭ 7) (n ϭ 7) (n ϭ 6) (n ϭ 6) (n ϭ 6)

Data shown as means Ϯ SEM. Means within a column are signiÞcant when followed by *P Ͻ 0.05, **P Ͻ 0.01, ***P Ͻ 0.001; NS, not signiÞcant. ÔnÕ denotes the sample size of resistant plants used for the calculation.

Discussion mortality rate of soybean aphids on resistant plants. Downloaded from https://academic.oup.com/ee/article/41/2/282/483303 by guest on 27 September 2021 Because we were primarily interested in the net Soybean aphid resistant plants with the Rag1 gene change in aphid populations, we cannot disentangle were shown to negatively affect the performance and whether higher aphid populations on susceptible Þtness of the parasitoid, B. communis, compared with plants were because of aphids living longer or higher near isogenic susceptible plants. Fewer mummies and a lower emergence rate of adult parasitoids were ob- reproductive rates. However, we do know that estab- served on resistant soybean plants compared with lishment rates of aphids were much higher on suscep- susceptible soybeans. The few adult parasitoids that tible plants (almost 100% establishment) than on re- did emerge from resistant plants took longer to de- sistant plants (under 50% establishment), which is velop and had shorter metatibiae compared with consistent with higher mortality on resistant plants. adults from susceptible soybean plants. A number of Further evidence is provided by Li et al. (2004) who other studies have shown that parasitoids from her- found that soybean aphid longevity decreased on re- bivores on resistant plants can have similarly reduced sistant plants with the Rag1 gene. We speculate that Þtness, for example longer development and smaller aphids parasitized by B. communis were more likely to sized adults (Bottrell et al. 1998, Ode 2006). die before the parasitoid completed development Speculating about the mechanisms producing this when the aphid was on a resistant plant compared with negative effect of resistant plants on parasitoids is a susceptible plant. This mechanism would go a long potentially useful for hypothesizing when this type of way in explaining our biggest effect, lower proportion effect may occur and how it could ultimately affect parasitism on resistant plants. soybean aphid control. In general, resistant host plants A third indirect mechanism is that soybean aphids can affect parasitoids through a variety of indirect and are a poorer host for parasitoids when they feed on direct mechanisms. Host plant resistance can indi- resistant plants. Feeding on resistant plants may make rectly inßuence a natural enemy by altering the her- aphids smaller, less nutritious, or even potentially toxic bivoreÕs population size, its growth (or death) rate, (Li et al. 2004, Diaz-Montano et al. 2007). All of these and the quality of an individual herbivore as a host or factors could result in lower Þtness for the parasitoid prey for the natural enemy that depends on them developing in that aphid and potentially help make it (Bottrell et al. 1998). more likely that a parasitized aphid will perish before One of the largest negative effects that resistant the parasitoid completes its development (Kaufman plants are likely to have on parasitoids in the Þeld is a and Flanders 1985, Werren et al. 1992, Ode 2006). substantial reduction in the number of potential hosts All of the mechanisms mentioned thus far work available. We tried to control for this variable by start- indirectly against the parasitoid by altering the aphid, ing all plants with the same number of aphids. Leaving yet it is also possible that resistant plants have a direct the aphids to establish, however, resulted in a 50% negative effect on parasitoids as well. Lundgren et al. difference in the number of aphids available on plants (2009) discovered a direct effect of reduced adult of each treatment. We chose to maintain this differ- longevity for a key predator, Harmonia axyridis (Pa- ence rather than manipulating the situation in a way las), when it was exposed to resistant soybean varieties that may have further confounded the treatments. containing the Rag1 gene. More generally, some re- Thus, it is possible that the lower density of aphids on sistant plant characteristics directly inßuence natural resistant plants resulted in the large observed differ- enemy host searching behavior, host accessibility, and ence in parasitoid performance. However, it is un- aphid dropping/falling behavior where the aphid falls likely that density itself was entirely responsible for from the plant (Grevstad and Klepetka 1992, Hare our results because most experimental studies at this 1992, Bottrell et al. 1998). Mechanisms that govern spatial and temporal scale Þnd that proportion para- such effects may be because of morphological fea- sitism decreases when more aphids are available tures, such as glandular trichomes or plant chemistry (Walde and Murdoch 1988), yet we found a drastic (Kauffman and Kennedy 1989, van Lanteren and de increase in the proportion parasitism on the suscep- Ponti 1991). Another explanation is that sensory cues tible plants that had more aphids. required to locate its host are modiÞed on resistant A more likely explanation for the large difference in plants, thereby altering the parasitoidÕs effectiveness mummy and parasitoid production is related to the (Wa¨ckers and Lewis 1994). April 2012 GHISING ET AL.: IMPACT OF Rag1 APHID RESISTANT SOYBEANS ON B. communis 287

In summary, B. communis was able to successfully iÞcation: a realistic strategy? Annu. Rev. Entomol. 43: reproduce and survive on soybean aphids on resistant 347Ð367. soybeans; however, parasitoid production and Þtness Clark, A. J., and K. L. Perry. 2002. Transmissibility of Þeld were negatively affected by the Rag1 aphid resistant isolates of soybean viruses by Aphis glycines. Plant Dis. 86: plants. Establishment and success of B. communis as an 1219Ð1222. effective biological control agent of soybean aphid Desneux, N., P. Stary, C. J. Delebecque, T. D. Gariepy, and may be more problematic if resistant plants become R. J. Barta. 2009. Cryptic species of parasitoids attacking the soybean aphid, Aphis glycines Matsumura Hemiptera: widely grown in the Þeld. These negative effects may Aphididae), in Asia: Binodoxys communis Gahan and be even stronger if we account for an overall lower Binodoxys koreanus Stary sp. n. (Hymenoptera: Braconi- population of soybean aphids caused by resistant dae: ). Ann. Entomol. Soc. Am. 102: 925Ð936. plants. This means that in all likelihood, the combi- Diaz-Montano, J., J. C. Reese, J. Louis, L. R. Campbell, and nation of resistant plants and biological control by B. W. T. Schapaugh. 2007. Feeding behavior by the soy-

communis will be less effective than one would expect bean aphid (Hemiptera: Aphididae) on resistant and sus- Downloaded from https://academic.oup.com/ee/article/41/2/282/483303 by guest on 27 September 2021 given their individual performance. However, our re- ceptible soybean genotypes. J. Econ. Entomol. 100: 984Ð sults alone cannot fully evaluate whether greater soy- 989. bean aphid control will be achieved by using both Dogramaci, M., Z. B. Mayo, R. J. Wright, and J. C. Reese. strategies as opposed to just using one. The parasitoidÕs 2005. Tritrophic interaction of parasitoid Lysiphlebus tes- relative Þtness and reproductive output as well as the taceipes (Hymenoptera: Aphididae), greenbug, Schiza- availability of suitable hosts from refuges or resistant phis graminum (Homoptera: Aphididae), and greenbug- resistant sorghum hybrids. J. Econ. Entomol. 98: 202Ð209. biotypes could all play important roles in ultimately Duffey, S. S., and K. A. Bloem. 1986. Plant defense, herbi- determining the compatibility and utility of using both vore/parasite interactions and biological control, pp. 135Ð B. communis and resistant soybean plants for soybean 183. In M. Kogan (eds.), Proceedings, Ecological Theory aphid control. Research on refuges with plants that and Integrated Pest Management. Wiley, New York. provide food, shelter or alternative hosts for beneÞcial ffrench-Constant, R. H., P. J. Daborn, and G. Le Goff. 2004. have illustrated that habitat management The genetics and genomics of insecticide resistance. for beneÞcial arthropods is important for maximizing Trends Genet. 20: 163Ð170. their valuable services in agricultural landscapes Ghising, K. 2011. Impact of Rag1 aphid resistant soybeans (Landis et al. 2000, Isaacs et al. 2009). on Binodoxys communis (Gahan) (Hymenoptera: Bra- conidae), a parasitoid of soybean aphid Aphis glycines (Hemiptera: Aphididae). M.S. thesis, North Dakota State Acknowledgments University, Fargo, ND. Gould, F., G. G. Kennedy, and M. T. Johnson. 1991. Effects We thank B. Diers (University of Illinois) who provided of natural enemies on the rate of herbivore adaptation to the seeds with the source of Rag1 gene for these experiments; resistant host plants. Entomol. Exp. Appl. 58: 1Ð14. G. Schmidt for help in rearing soybean aphid and B. com- Grevstad, F. S., and B. W. Klepetka. 1992. The inßuence of munis colonies; and J. Hochhalter for providing her screening data on different Rag1 aphid resistant lines. This work was plant architecture on the foraging efÞciencies of a suite funded by grants from the North Dakota Soybean Council of ladybird beetles feeding on aphids. Oecologia 92: 399Ð and the North Central Soybean Research Program to the 404. Department of Entomology at North Dakota State Univer- Guo, J. Q., and M. H. Zhang. 1989. Study on the important sity. vectors of soybean mosaic virus and their transmission efÞciency. Soybean Sci. 8: 55Ð63. Hare, J. D. 1992. 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