BEHAVIOR Postmating Behavior of Female Dogwood Borer (Lepidoptera: Sesiidae) in Apple Orchards

1,2 3 1 D. L. FRANK, T. C. LESKEY, AND J. C. BERGH

Environ. Entomol. 38(4): 1219Ð1225 (2009) ABSTRACT The postmating behavior of female dogwood borer, Synanthedon scitula (Harris) (Lep- idoptera: Sesiidae), was examined in a young apple orchard planted on size-controlling rootstock in Virginia. All female dogwood borers captured while exhibiting casting ßight near the base of trees were mated, based on the presence of a spermatophore. Surveys of female activity within orchards were conducted at regular intervals throughout the daylight hours, showing a diel periodicity that peaked between 1700 and 1900 hours, with most females located below the graft union of trees. A transition matrix based on 1,108 behavioral sequences exhibited by 66 females was used to produce a Þrst-order Markov chain of behavioral events that occurred signiÞcantly more often than expected by chance. Casting ßight, probing with ovipositor, and oviposition were the most frequent behaviors observed, representing 31.7, 30.0, and 18.1% of all behaviors recorded, respectively. Our observations showed that 88, 99, and 99% of casting ßight, probing with the ovipositor, and oviposition, respectively, occurred below the graft union. Observed behaviors considered not directly related to oviposition site selection or oviposition included antennal grooming, noncasting ßight, and resting, representing 1.3, 8.3, and 10.6% of all behaviors recorded, respectively. Mated females spent signiÞcantly more time resting than in other behaviors and signiÞcantly more time in that state within the apple tree canopy than on other parts of the tree. Results are discussed in relation to the inßuence of insectÐhost plant interactions on oviposition site selection by female dogwood borer.

KEY WORDS Synanthedon scitula, dogwood borer, Sesiidae, behavior, apple

The dogwood borer, Synanthedon scitula (Harris), at- tissue and the surrounding cambium can result in the tacks a broad range of ornamental, fruit, and nut trees decline of tree health and vigor, or in severe cases throughout eastern North America (Eichlin and cause tree death from girdling (Weires 1986, Howitt Duckworth 1988, Johnson and Lyon 1991). Histori- 1993). cally recognized as an important pest of dogwood, Oviposition by many Synanthedon species occurs Cornus florida L. (Underhill 1935, Wallace 1945, Pless near wound sites on the host surface (Solomon 1995). and Stanley 1967), it has become increasingly prob- Increased susceptibility to infestation caused by me- lematic in apple orchards since the 1980s, coinciding chanical injury or pruning scars were documented for with the adoption of size-controlling rootstocks (Riedl several species including S. tipuliformis (Clerck) et al. 1985, Kain and Straub 2001, Leskey and Bergh (Hardy 1982), S. novaroensis (Hy. Edwards) (Johnson 2005). A common characteristic of these rootstocks is 1993), and S. sequoiae (Hy. Edwards) (Koehler et al. the development of adventitious root initials, or burr 1983). Rocchini et al. (1999) suggested that the pres- knots, below the graft union or on the scion of trees ence of fungal-induced cankers and galls in lodgepole (Rom 1970, 1973; Marini et al. 2003). The presence of pine inßuenced the susceptibility of trees to attack by burr knot tissue on host trees increases the likelihood S. novaroensis. In peach, S. pictipes (Grote and Rob- of dogwood borer infestation (Riedl et al. 1985, inson) were shown to deposit signiÞcantly more eggs Warner and Hay 1985, Kain and Straub 2001, Leskey in response to stimuli associated with canker wounds and Bergh 2005). In newly established apple orchards, (Swift 1986, Reed et al. 1988, Cottrell et al. 2008) and the quantity of available burr knot tissue has the great- mechanically damaged bark (Cottrell et al. 2008) com- est inßuence on the initiation, persistence, and extent pared with nondamaged bark. Furthermore, volatile of infestations (Leskey and Bergh 2005). Consecutive compounds emanating from the gum and frass of in- seasons of infestation and larval feeding on burr knot fested peach trees were shown to stimulate oviposi- tion by both S. pictipes (Reed et al. 1988, Cottrell et al. 1 Virginia Polytechnic Institute and State University, Alson H. 2008) and S. exitiosa (Say) (Gentry and Wells 1982, Smith, Jr. Agricultural Research and Extension Center, Winchester, Derksen et al. 2007). VA 22602. Numerous early studies suggested that dogwood 2 Corresponding author, e-mail: [email protected]. 3 USDAÐARS, Appalachian Fruit Research Station, 2217 Wiltshire borer infestation was associated with wounded host Road, Kearneysville, WV 25430. plant tissue (reviewed in Bergh and Leskey 2003).

0046-225X/09/1219Ð1225$04.00/0 ᭧ 2009 Entomological Society of America 1220 ENVIRONMENTAL ENTOMOLOGY Vol. 38, no. 4

Potter and Timmons (1981) conÞrmed that increases Table 1. Behaviors observed by mated female dogwood borer in the severity of mechanical wounding signiÞcantly in an apple orchard increased the probability of dogwood borer attack in Observed behavioral categories of females alighted on apple trees ßowering dogwoods, and Pless and Stanley (1967) Resting Body motionless with abdomen noted that previously infested dogwood trees were parallel to resting surface highly prone to subsequent infestation by dogwood Probing Lateral movement of the borer. Bergh et al. (2009) captured signiÞcantly more abdomen including brief periods (Ͻ1 s) of direct dogwood borer males in pheromone traps deployed in contact of extruded ovipositor apple orchards than in urban or forest environments. tip with host tissue The proximate and ultimate reasons for higher den- Grooming Female grasps an antennae with sities of dogwood borer in orchards remain speculative tibia of foreleg and scraped the antennae in an anterior but may be associated with aspects of the insectÐplant direction (sometimes relationship, including host preference or attraction repeatedly) and enhanced Þtness. Ovipositing Female abdomen slightly ßexed Electrophysiological studies have shown that both towards substrate surface with extruded ovipositor tip virgin and mated female dogwood borer respond to contacting host tissue for volatile compounds collected from apple burr knot periods Ͻ1s tissue (Frank et al. 2007), and we are exploring the Observed ßight patterns of mated females within the apple orchard ecological role of these stimuli, including their use in Noncasting Observed ßight that does not include casting ßight patterns host plant location and oviposition site selection by Casting Female executes a rapid series mated female dogwood borer. An important Þrst step of counterturning ßight in the interpretation of their responses to these patterns in the horizontal sources of stimuli is to observe and quantify their plane directed toward, and Ͼ20 cm away from, the host behavior under Þeld conditions. Although Bergh et al. tissue (including burr knot (2006) characterized premating behaviors of male and tissue, cracks in bark, or female dogwood borer, previous attempts to measure wound sites) the postmating behaviors of female dogwood borer have failed. For example, observations of postmating behavior of females in cages containing potted dog- sisting of 60 trees in three rows with 6.1 m between wood trees (Wallace 1945, Pless and Stanley 1967) or rows and 2.4 m between trees. Trees were Ϸ2.7 m tall blueberry plants (Ayers 1966) or in heavily infested by 2.4 m wide with an average trunk diameter of 6.5 dogwood nurseries (Pless and Stanley 1967) were un- cm directly above the graft union. Orchard drive rows successful. were mowed frequently throughout the study, and Here we report the results from Þeld studies that 1.75-m-wide weed-free strips were maintained be- used quantitative descriptions of behaviors and tran- neath trees with herbicides. Disease management in sition matrices to characterize the behavioral reper- the orchard was based on recommended guidelines toire of mated female dogwood borer within apple for commercial fruit growers in the mid-Atlantic states orchards under natural conditions and the periodicity (Anonymous 2007). In 2006, insecticide evaluation with which those behaviors occurred. trials conducted in the orchard included foliar sprays to 20% of the Idared trees through late April and to 33.3% of the Gala trees through mid-August. In 2007, Materials and Methods a standard management program for other apple pests Sex and Mating Status of Adults Orienting to Apple used only foliar sprays from mid-April through late Trees Under Field Conditions. To determine whether August. None of the products used would be expected casting ßight (Table 1) toward apple trees was unique to reduce the infestation of dogwood borer at the base to mated female dogwood borer, 25 moths orienting to of trees. the base of young apple trees on size-controlling root- Temporal Survey of Female Activity. A survey of stock in four orchards in Frederick Co., VA, were the temporal patterns of female dogwood borer ac- collected using a sweep net from June to August in tivity in the orchard involved two observers walking 2006 and 2007 during the afternoon. Moths were dis- abreast on opposite sides of each orchard row while sected under a ϫ10 stereomicroscope (SZ40; Olym- recording the presence and location of female dog- pus, Center Valley, PA) to conÞrm their sex and to wood borer on each tree. The number of female sight- determine their mating status, based on the presence ings was recorded at 2-h intervals in noninclement or absence of a spermatophore within the bursa copu- weather from 0900 until 1900 hours in 2006 (11 sur- latrix. veys) and from 0800 until 2000 hours in 2007 (10 Orchard Site for Temporal and Behavior Studies. surveys) from July to September. Temperature, rela- Behavioral studies were conducted in a 0.65-ha re- tive humidity, wind speed, barometric pressure, and search apple orchard containing 5-yr-old ÔBuckeye solar radiation data for each 2-h period were collected GalaÕ and ÔIdaredÕ apple trees on M.26 rootstock at the from a weather station at the AHS-AREC. Alson H. Smith Jr. Agricultural Research and Exten- Characterization of Mated Behaviors. Orientation sion Center (AHS-AREC), near Winchester, VA. Tree and oviposition site selection behaviors exhibited by varieties occurred in two adjacent blocks, each con- 28 female dogwood borer in 2006 and 38 females in August 2009 FRANK ET AL.: POSTMATING BEHAVIOR OF FEMALE S. scitula 1221

2007 were characterized within the orchard described above. Observations were recorded by a single ob- server during peak periods of activity determined from results generated by our temporal survey. Ob- servations of individual females lasted for a minimum of 1 min and a maximum of 60 min with a mean duration of 15.2 Ϯ 12.8 (SE) min. SpeciÞc behaviors recorded included resting, grooming, probing with the ovipositor, oviposition, casting ßight, and noncasting ßight (Table 1). The location of all females observed was also recorded, based on the following categories: (1) within the canopy, (2) above the graft union (i.e., between graft union and lower scaffold limb), (3) below the graft union, and (4) on the ground. A behavioral ethogram was developed and pro- grammed into The Observer (Version 3.0; Noldus In- formation Technology, Leesburg, VA). Behaviors were recorded using a portable cassette recorder and subsequently transcribed into the The Observer for calculation of the frequency and duration of each behavior observed and the location at which it oc- curred. After recording the behavior of a female, the observer moved to a different area of the orchard Fig. 1. Mean Ϯ SE proportion of female dogwood borer (minimum distance of 15 m away from the previous sightings at 2-h intervals in (a) 2006 and (b) 2007. observation site) to minimize the possibility of re- cording the same individual a second time. Statistical Analysis. The number of female sightings more sightings occurred at 1900 and 1800 hours, re- during surveys at each 2-h interval in 2006 and 2007 spectively, compared with all other intervals. There were converted to proportions, transformed using arc- was no signiÞcant difference in the number of sight- sine square-root to stabilize variance, and compared ings in ÔBuckeye GalaÕ and ÔIdaredÕ cultivars in 2006 using analysis of variance (ANOVA) and Fisher least (F ϭ 0.58; df ϭ 1,129; P ϭ 0.4487) or 2007 (F ϭ 1.21; signiÞcant difference (LSD) test (SAS Institute 2003). df ϭ 1,139; P ϭ 0.2726). Combined data from both The inßuence of abiotic factors on the numbers of years showed nonrandom distribution of females female sightings was analyzed using stepwise regres- among tree locations: 89.7% of females were observed sion (SAS Institute 2003). A transition matrix was near the graft union of trees compared with 8.6% constructed by transferring behavioral data from The within the canopy and 1.7% ßying away. There was a Observer into a matrix of preceding and succeeding signiÞcant inverse relationship between solar radia- behaviors. To examine whether transitional behaviors tion and the number of sightings in 2006 (F ϭ 9.23; df ϭ were more likely to occur than expected by chance, a 1,64; P ϭ 0.0035), although this relationship explained ␹2 test was applied to all transitions with a frequency only 13% of the variation and was not signiÞcant in Ͼ1% of the total. Data from the transition matrix were 2007. No signiÞcant effects were detected among all used to construct a Þrst-order Markov chain (Gottman other environmental factors measured. and Roy 1990, Bishir et al. 2004) depicting the prob- Characterization of Mated Behaviors. The se- abilities of transitions between behavioral activities. quence of behaviors established by analysis of a tran- The duration of each behavior was analyzed using sition matrix (Table 2) was used to produce a Þrst- ANOVA (SAS Institute 2003) with means separated order Markov chain of behavioral events that occurred using Fisher LSD. Results from all tests were consid- signiÞcantly more often than expected by chance ered statistically different at P Ͻ 0.05. (Fig. 2). The sequence, or chains, of behaviors are represented as arrows and the relative frequency of a speciÞc behavioral pattern as bounding boxes. Casting Results ßight was the behavior most frequently observed and Sex and Mating Status of Adults Orienting to Apple began as a loop that was followed by probing with the Trees under Field Conditions. Dissection of 25 moths ovipositor and oviposition, representing 31.7, 30.0, and captured while exhibiting casting ßight at the base of 18.1% of all behaviors recorded, respectively. When apple trees conÞrmed that all were mated females, exiting this loop, females transitioned into noncasting based on the presence of a spermatophore in the bursa ßight from which they again entered the loop or pro- copulatrix. ceeded to the resting state, followed by grooming, Temporal Survey of Female Activity. Time of day representing 8.3, 10.6, and 1.3% of all behaviors re- had a signiÞcant effect on the number of female sight- corded, respectively. Although the frequency of cast- ings recorded at 2-h intervals in 2006 (F ϭ 7.18; df ϭ ing, probing, and oviposition represented 80% of total 5,129; P Ͻ 0.0001) and 2007 (F ϭ 5.91; df ϭ 6,139; P Ͻ occurrences, dogwood borer females spent a signiÞ- 0.0001; Fig. 1a and b). In 2006 and 2007, signiÞcantly cantly greater percentage of time resting (Table 3) 1222 ENVIRONMENTAL ENTOMOLOGY Vol. 38, no. 4

Table 2. Transition matrix summarizing the frequency with which a behavior (column) was succeeded by another behavior (row)

Resting Probing Grooming Ovipositing Noncasting Casting ͚ Resting Ñ 22 15 1 41 38 117 Probing 22 Ñ 0 200 7 104 333 Grooming 15 0Ñ 0 0 015 Ovipositing 22 89 0Ñ 683 200 Noncasting 35 00 0 Ñ 57 92 Casting 23 218 00110 Ñ 351 ⌺ 117 329 15 201 164 282 1,108

Transitions that occurred signiÞcantly more often than expected by chance (P Ͻ 0.05, ␹2 test) are shown in bold. compared with all other behavioral activities. Fifty ing the late afternoon and evening, conforming with percent of resting occurrences were recorded below the results of laboratory studies of S. pictipes showing the graft union compared with 32.3% in the canopy, that the mean rate of oviposition by this species 15.3% on the ground, and 2.4% above the graft union peaked during the late afternoon and ceased during (Fig. 3). However, the average duration of a resting scotophase (GreenÞeld and Karandinos 1976) and bout was signiÞcantly greater within the canopy com- with Þeld observations of other sesiid species showing pared with on the ground or above and below the graft that peak oviposition occurred mainly from mid- to union (F ϭ 6.94; df ϭ 3,122; P ϭ 0.0005). Although late afternoon (Solomon 1975, Barry and Nielsen females engaged in behaviors directly involved with 1984). Because it was very difÞcult to track between- oviposition site selection (i.e., casting ßight, probing tree movements of individual females, our observa- with the ovipositor, and ovipositing) above and below tions were conÞned to the periods during which each the graft union, the frequency of casting, probing, and female remained at a particular tree; inter-tree move- oviposition occurrences below the graft union was 88, ments of females were observed but not recorded. The 99, and 99% of the total for each behavioral category, duration of observing and recording the behavior of respectively (Fig. 3). each female was as short as 1 min, but we also observed individual females repeatedly searching for oviposi- tion sites on a single tree for up to 60 min. We did not Discussion attempt to record the number of eggs on host tissues Mated female dogwood borer were easily recog- of trees on which females were observed, because it nized in the Þeld, based on their characteristic casting would not have been possible to differentiate between ßight directed toward apple trees, enabling us to de- eggs laid by females observed and those laid previ- termine their daily period of activity and to quantify ously. However, some females exhibited what we in- speciÞc behaviors in an apple orchard. Mated female terpreted to be repeated instances of oviposition on an dogwood borer were recorded more frequently dur- individual tree. The sequences of casting ßight, prob- ing, and ovipositing were interspersed with relatively long periods of resting behavior within the canopy, as has been observed for other Synanthedon species (Bobb 1959, Barry and Nielsen 1984). Relative to other major sesiid pests, little is known about the stimuli responsible for host location or ovi- position site selection by female dogwood borer. Gen- try and Wells (1982) showed that volatiles from S. exitiosa cocoons and peach tree bark, and gum-frass mixtures obtained from wounds on peach trees, con- tained substances that stimulated oviposition by

Table 3. Mean ؎ SEM duration of behaviors exhibited by mated female dogwood borer and the percentage of total time engaged in each

Percent of Behavior Mean Ϯ SEM (s) total time Fig. 2. First-order Markov chain analysis of a transition Resting 160.90 Ϯ 30.77a 65.76 Ϯ matrix constructed from 1,108 behavior patterns exhibited by Probing 15.25 0.77b 16.79 Grooming 11.96 Ϯ 1.81b 0.59 66 mated female dogwood borers. The size of bounding boxes Ovipositing 5.29 Ϯ 0.26b 3.49 is proportional to the frequency of a behavioral pattern. Noncasting 6.14 Ϯ 0.25b 3.81 Sequences of behaviors are represented as arrows when Casting 7.21 Ϯ 0.25b 9.56 transitions occur signiÞcantly more often than predicted by 2 chance (P ϭ 0.05, ␹ test). The size of arrows show the degree Means followed by the same letter are not signiÞcantly different to which a speciÞc transition is over-represented. (P ϭ 0.05, LSD test), F ϭ 33.05; df ϭ 5, 70; P Ͻ 0.0001. August 2009 FRANK ET AL.: POSTMATING BEHAVIOR OF FEMALE S. scitula 1223

Fig. 3. Percentage of the total number of occurrences of each behavior exhibited by mated female dogwood borer at selected locations on apple hosts. gravid females. Electrophysiological bioassays con- ence of previously infested or infested burr knots, or ducted by Derksen et al. (2007) showed 21 com- other factors that might have inßuenced their re- pounds from gum-frass mixtures that elicited antennal sponse to individual trees, an increasing body of evi- responses by male and female S. exitiosa. Synthetic dence supports the hypothesis that females respond to blends containing all 21 compounds, and synthetic volatile stimuli associated with these plant features. blends containing all compounds except three ace- Leskey and Bergh (2005) showed that greater tates, stimulated signiÞcantly higher rates of oviposi- amounts of burr knot tissue on newly established apple tion compared with unbaited controls. Cottrell et al. trees resulted in higher dogwood borer infestation (2008) showed that surrogate peach branches that rates. Furthermore, Frank et al. (2007) reported that were mechanically wounded, actively infested with several volatile compounds collected from infested larvae, or that possessed fungal-induced wounds were burr knot tissue evoked a strong and repeatable elec- more attractive to gravid females than undamaged trophysiological response by dogwood borer females. branches or decoys. Similarly, Reed et al. (1988) Although we have yet to determine whether the showed that natural and chemically fractionated electrophysiologically active compounds are plant or peach wood volatiles and hosts possessing cankers as insect derived, or a combination of the two, or well as nonhosts treated with canker-bark extracts whether these compounds elicit attraction and orien- stimulated oviposition by S. pictipes females even tation to apple burr knots, this tissue seems to be an when blinded. Although chemosensory stimuli were important resource for dogwood borer. Burr knots are strongly implicated for stimulating oviposition, Þeld- rather soft and spongy compared with apple bark and cage studies showed that size and texture of host often possess many small crevices associated with root surfaces were also signiÞcant factors and that mech- primordia. Female dogwood borer provided burr knot anoreceptors located on the ovipositor may further aid tissue commonly deposit their eggs tightly within oviposition site selection. these crevices and neonate larvae quickly enter and Previous studies examining dogwood borer infesta- tion in apple and other hosts have suggested that begin feeding on the tissue (D.L.F., unpublished mated females preferentially oviposit near areas asso- data). In Europe, Dickler (1976) showed that larvae of ciated with pruning cuts (Herrick 1904, Pierce and the congeneric species, Synanthedon myopaeformis Nickels 1941), mechanical wounds (Potter and Tim- (Borkhausen), developed more quickly on apple burr mons 1981, Rogers and Grant 1990), insect-induced knot tissue than on other apple tissues and our pre- galls (Eliason and Potter 2000), apple burr knot tissue liminary evidence (T.C.L., unpublished data) has sug- (Riedl et al. 1985, Warner and Hay 1985, Kain and gested a shortened developmental duration of dog- Straub 2001, Kain et al. 2004, Leskey and Bergh 2005), wood borer larvae on this tissue as well. as well as insect- and disease-induced injuries to the By observing individual female dogwood borers, we exterior of trees (Pless and Stanley 1967). Our obser- showed distinct behavioral patterns common to mated vations showed that mated female dogwood borer females in nature. Further studies are needed to fully most frequently engaged in casting ßight, probing with understand the chemical ecology and insectÐhost the ovipositor, and oviposition below the graft union plant interactions of female dogwood borer in apple. of trees. The orchard used for these studies contained A complete understanding of the mechanisms in- trees with cracks and crevices below the graft union volved with oviposition site selection and acceptance and also burr knots below the union that were either will create opportunities to assess female responses to previously infested or actively infested by dogwood manipulated stimuli toward the development of mon- borer larvae. Although we did not attempt to relate the itoring or management programs that speciÞcally tar- searching behavior of mated females with the pres- get female dogwood borer. 1224 ENVIRONMENTAL ENTOMOLOGY Vol. 38, no. 4

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