Biological Control 48 (2009) 294–300
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Biological Control
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The interactions of tropical soda apple mosaic tobamovirus and Gratiana boliviana (Coleoptera: Chrysomelidae), an introduced biological control agent of tropical soda apple (Solanum viarum)
W.A. Overholt a,*, L. Markle a, E. Rosskopf b, V. Manrique a, J. Albano b, E. Cave a, S. Adkins b a Biological Control Research and Containment Laboratory, University of Florida, 2199 South Rock Road, Fort Pierce, FL 34945, USA b USDA-ARS Horticultural Research Laboratory, 2001 South Rock Road, Fort Pierce, FL 34945, USA article info abstract
Article history: Tropical soda apple (Solanum viarum Dunal (Solanaceae) is a South American invasive plant of rangelands, Received 5 September 2008 pastures and natural areas in Florida. A chrysomelid beetle from South America, Gratiana boliviana Spa- Accepted 29 October 2008 eth, has been released at >300 locations in Florida for biological control of tropical soda apple since 2003. Available online 6 November 2008 Tropical soda apple is a host of several plant viruses, including the newly described tropical soda apple mosaic virus (TSAMV). We investigated the influence of TSAMV infection of tropical soda apple plants Keywords: on developmental time, leaf tissue consumption, longevity, fecundity, and feeding preference of G. boliv- Biological control iana, and also tested transmission of the virus by the beetle. Developmental time was approximately 10% Gratiana boliviana slower, and adults consumed only about 50% as much leaf tissue, for beetles fed on infected plants com- Tropical soda apple Solanum viarum pared to uninfected plants. Longevity did not differ between females reared on infected and uninfected Tropical soda apple mosaic virus plants, but females fed on uninfected plants produced 71% more eggs than those fed on infected plants. TSAMV Adult G. boliviana preferentially fed on uninfected plants when given a choice. There was no evidence of Plant pathogen/insect herbivore TSAMV transmission by G. boliviana. The potential impacts of TSAMV infection on the effectiveness of G. interactions boliviana as a biological control agent are discussed. Ó 2008 Elsevier Inc. All rights reserved.
1. Introduction vidually on the upper or lower surfaces of leaves, and eclose after about 5 days at 25.5 °C. Larvae complete five instars in 15–18 days, Tropical soda apple, Solanum viarum Dunal (Solanaceae), is a and then pupate on the underside of leaves (Diaz et al., 2008). Fe- prickly, perennial weed from South America which was first re- males lay a mean ± SE of 132 ± 20 eggs during a 122 ± 15 day life ported in Florida in 1988 (Mullahey et al., 1993). It has spread span (Overholt, unpublished). The beetles enter a reproductive dia- throughout Florida and into several other states including Georgia, pause during the winter months from about November to April in North Carolina, Arkansas, Tennessee and Texas (The Plants Data- central Florida (Overholt, unpublished). Extensive host range stud- base, 2007). Tropical soda apple invades rangelands, improved pas- ies revealed that G. boliviana adults caused minor feeding damage tures, and natural areas with an estimated one million acres to a few non-target Solanum spp., and laid a few eggs on two non- infested in Florida (Mullahey, 1996). Although cattle do not con- target species; Solanum torvum Sw. and Solanum melongena L. sume tropical soda apple leaf tissue, they readily feed on the fruits, However, larvae could develop from neonates through to adult- and in doing so, transport seeds in their digestive tracks to new hood only on S. viarum (Gandolfo et al., 2007; Medal et al., 2002). geographic areas; the primary means of spread (Brown et al., The beetle was first released in Florida in 2003 (Medal et al., 1996). Cattle ranchers spend an estimated $6.5 to $16 million 2006), and has since been released at more than 300 locations in annually for chemical and mechanical control of tropical soda ap- Florida, Georgia, Alabama, and Texas (University of Florida, ple (Thomas, 2007). 2008). Establishment has been confirmed at several sites (Univer- Exploration for classical biological control agents of tropical sity of Florida, 2008), and the impact on tropical soda apple popu- soda apple was initiated in 1994 in South America, and one of lations is currently being evaluated. Initial results are promising the agents discovered in Argentina and Paraguay was Gratiana bol- with 20–100% defoliation of tropical soda apple at release sites in viana Spaeth (Coleoptera: Chrysomelidae) (Medal et al., 1996). Florida (Medal et al., 2006). Gratiana boliviana feeds as larvae and adults on foliage in the upper Tropical soda apple is a host for numerous plant viruses, some of third of the canopy of tropical soda apple plants. Eggs are laid indi- which cause disease in cultivated solanaceous plants, such as toma- toes and peppers (McGovern et al., 1994, 1996; Adkins et al., 2007a). Three tobamoviruses are known to infect tropical soda apple: tobac- * Corresponding author. Fax: +1 772 460 3673. E-mail address: billover@ufl.edu (W.A. Overholt). co mild green mosaic virus (TMGMV) (Charudattan and Hiebert,
1049-9644/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.biocontrol.2008.10.018 W.A. Overholt et al. / Biological Control 48 (2009) 294–300 295
2007), tropical soda apple mosaic virus (TSAMV) (Adkins et al., (150 mm  15 mm) in an incubator at 25 °C, 60–70% RH, 14:10 2007a) and Tomato mosaic virus (ToMV) (Adkins et al., 2007a; (L:D) until eclosion. Neonate G. boliviana were transferred individ- McGovern et al., 1994). TMGMV causes rapid mortality of tropical ually to Petri dishes (150 mm  15 mm) lined with moistened fil- soda apple, and is currently being commercialized as a bioherbicide ter paper and an excised whole young leaf from an infected (Charudattan et al., 2004). The recently characterized TSAMV (n = 50) or uninfected plant (n = 50), and held at the same condi- induces less severe symptoms, but is widespread. TSAMV was found tions as the eggs. Larvae were inspected every 2 days until adult in tropical soda apple at 42% of locations surveyed in peninsular emergence to record molting and survival. Leaves were replaced Florida; approximately one third of the TSAMV-infected tropical at every other inspection. Only leaves with obvious symptoms of soda apple plants were co-infected with ToMV (Adkins et al., 2007a). TSAMV infection (mosaic) were collected from the TSAMV-inocu- The effect of plant pathogen infection on insect herbivores has lated plants for use in these experiments. been investigated in a number of systems, but a common trend is not evident. In general, insects which vector plant pathogens 2.3. Leaf consumption by fifth instars and adult females have higher fitness when fed on plants infected by the pathogens they transmit, and this is often accompanied by a preference to Leaf disks were cut from infected and uninfected leaves using a feed or oviposit on infected plants (Belliure et al., 2005; Stout 2 cm cork borer, and placed individually in Petri dishes (9 cm et al., 2006). However, the effects of plant pathogen infection on diameter) containing a moist filter paper, one fifth-instar (8 repli- herbivores that are not disease vectors are difficult to predict. In cations) or one adult female (31 replications). Petri dishes were some cases, feeding on infected plants increases herbivore fitness, held in an incubator at 25 °C, 60–70% RH, 14L:10D. After 24 h, lar- while in others, the effects are detrimental or neutral (see Stout vae were removed, leaf disks were taped to a white sheet of paper et al., 2006 for a review). TSAMV is transmitted through plant and photocopied, and the copies scanned to the computer. Leaf wounds and surface contamination of seeds (Adkins et al., area consumed was calculated by subtracting the final area, mea- 2007a), but it is not known whether the virus can be transmitted sured using Image-J software, from the initial area (3.14 cm2) by chewing insects like G. boliviana. Although tobamoviruses are (Abramoff et al., 2004). generally not considered to be transmitted by insects (Fulton et al., 1987), there are scattered reports of beetle transmission of 2.4. Longevity and fecundity of adults tobamoviruses in the literature (Chant, 1959; Orlob, 1963; Rao and Varma, 1984). Gratiana boliviana pupae were collected from colony cages and The primary objective of our study was to determine the effects of held individually in Petri dishes at 25 °C, 60–70% RH, 14:10 (L:D) TSAMV infection of tropical soda apple plants on G. boliviana fitness, until adult emergence. Newly emerged adults were held together as measured by developmental time, fecundity, and longevity. We in cages (same type as previously described) on uninfected plants. also measured larval and adult consumption of infected and non-in- As soon as the sexes could be differentiated (8–13 days post-emer- fected leaf tissue, and examined whether beetles discriminated be- gence), pairs (one male, one female) were removed and placed on tween infected and uninfected plants when selecting a feeding infected (n = 20) and uninfected (n = 20) tropical soda apple leaf site. Finally, we investigated transmission of TSAMV by G. boliviana. bouquets. Bouquets consisted of a stem and associated leaves (5– 7) of the lateral meristem of either an infected or uninfected trop- ical soda apple. The stem was inserted into a florist water pick 2. Methods and materials (76 mm  16 mm) that had been glued to the base of a Petri dish (60 mm  15 mm). The Petri dish was then placed in a 1 l plastic 2.1. Plants and insects container (15 cm  11 cm), and closed with a lid which had the center removed and replaced with mesh netting to allow air ex- Mature tropical soda apple fruits were collected in the field in change. Eggs were counted and removed until the female died. St. Lucie Co., Florida, and the seeds were removed and dried. Prior Water was added to picks every 2 days to ensure that bouquets re- to planting, seeds were surface decontaminated to remove TSAMV mained fresh. Bouquets were replaced as needed (usually twice a and other tobamoviruses by treating with a saturated solution of week). As males died, they were replaced. trisodium phosphate as previously described (Adkins et al., 2007a). Seeds were then planted in trays (6 cm  27 cm  54 cm) 2.5. Dual choice adult preference in Fafard Superfine Germinating Mix. At the 5–7 true leaf stage (ca. 10 cm tall), seedlings were transferred to nursery pots Gratiana boliviana were reared from first instar to pupa on unin- (16 cm  19 cm) containing Fafard 3B potting soil. fected plants. Pupae were collected from cages and held collectively Tropical soda apple plants were inoculated with TSAMV 3–4 in a Petri dish until adult emergence. Adults were then placed indi- weeks prior to their use. Briefly, TSAMV-infected Nicotiana benth- vidually in Petri dishes until gender could be determined. Five vir- amiana leaves were homogenized in 20 mM sodium phosphate gin males and 5 virgin females were placed in an open Petri dish in buffer (pH 7.0) containing 1% (wt./vol.) Celite in a mortar and the center of a cage with one infected plant and one uninfected pestle at 1:5 (wt./vol.) leaves:buffer and the unfiltered homog- plant of approximately the same size (height: 55–60 cm, diameter enate was rubbed with cheesecloth onto tropical soda apple 45–50 cm). The number of adults on infected and uninfected plants leaves. was counted at 2, 4, 8, 24, and 52 h after release, as well as the num- Adult G. boliviana were collected from the field and placed in ber of mating couples on each plant. At the end of the experiment, cages (60 cm  60 cm  60 cm, BugDorm 2; Bioquip, Rancho plants were cut at the base, dried for 1 week at 70 °C and weighed. Dominguez, CA, USA) with 2–4 uninfected tropical soda apple Latex gloves and forceps were used and changed between replica- plants in nursery pots and held in a laboratory maintained at tions throughout the study to ensure that virus was not inadver- 24 ± 2 °C. Individuals were collected from cages as necessary. tently transmitted to uninfected tropical soda apple. There were six replications, with cages positioned such that three cages of each 2.2. Developmental time and survival of immatures treatment were on a table that was located in the eastern side of the greenhouse and three cages of each treatment were placed on a ta- Eggs of G. boliviana were harvested from the colony cages and ble in the western side of the greenhouse. The infected and unin- held in groups of 10–20 on moist filter paper inside Petri dishes fected plants were placed in cages in an alternating pattern to 296 W.A. Overholt et al. / Biological Control 48 (2009) 294–300 offset any possible directional bias. The greenhouse was main- time, adult fecundity, and leaf tissue consumption by fifth-instar tained at 27 ± 2 °C and RH fluctuated from 50% to 80%. larvae and adults were compared between treatments using a T-test (PROC TTEST). Immature survival was compared between 2.6. TSAMV transmission treatments using a {2 statistic (PROC FREQ). Differences in number of adults selecting infected and uninfected plants in Adult beetles (10) reared from first instar to adult on uninfected the dual choice test were compared with repeated measures plants were placed on infected plants (height: 55–60, diameter: analysis of covariance, with plant infection status the main fac- 45–50 cm) in cages for 48 h and then transferred to uninfected tor and dry weight of the plant at the end of the trial as the plants of the same size for 48 h. The experiment was replicated covariate (PROC GLM). The covariate was included as it was 30 times for a total of 300 beetles transferred from infected to apparent that virus-infected plants had less biomass after 52 h uninfected plants. After removal of the insects, target plants were than uninfected plants. Specific leaf area and leaf moisture con- monitored for 50 days for symptoms of TSAMV infection. After tent were analyzed using a two-way ANOVA with treatment and 50 days, two fully expanded leaves were collected from each plant leaf age as factors. Since significant interactions were obtained to test for the presence of TSAMV. A double-antibody sandwich- for both specific leaf area and leaf moisture content, T-tests were enzyme-linked immunosorbent assay (DAS-ELISA) and conditions used to determine differences between treatments for each leaf previously described (Adkins et al. 2007a) were used for initial age. TSAMV detection in the collected tropical soda apple leaves. Inoc- ulation of Nicotiana tabacum cv. Xanthi nc (a local lesion host for TSAMV) (Adkins et al., 2007a) with the collected tropical soda ap- 3. Results ple leaves homogenized in the phosphate buffer described above was used for confirmation of the DAS-ELISA results. The inoculated 3.1. Developmental time and survival of immatures N. tabacum cv. Xanthi nc leaves were examined 1 week post-inoc- ulation for the presence of necrotic local lesions. Developmental time from first instar to the adult stage was about 2.5 days faster when G. boliviana was reared on leaves from 2.7. Specific leaf area, leaf water content, and leaf nutrients uninfected plants compared to infected plants (Table 1). Immature survival was not different ({2 = 0.16, P = 0.70) between beetles fed The following parameters were measured on infected and unin- on uninfected (57.7%) and infected plants (53.8%). fected plants at 3 weeks after inoculation: (1) specific leaf area (leaf area/leaf dry weight), (2) percent leaf moisture content 3.2. Leaf consumption by fifth instars and adult females ((fresh-dried leaf weight)  100/fresh weight) and (3) leaf nutrient contents (C, Ca, K, Mg, N, P, B, Cu, Fe, Mn, Mo, and Zn). Specific leaf Fifth instars on uninfected leaves consumed about three times area and leaf moisture content were determined for one newly ex- as much tissue as those on infected leaves, whereas adult females panded leaf (second from top of the stem), one mature leaf (4th consumed approximately twice as much tissue of uninfected from top of the stem), and one old leaf (first from the base of the leaves compared to infected leaves (Table 1). stem) for each treatment plant. For nutrient analyses, leaves from each plant treatment were harvested, oven dried at 70 °C for 1 3.3. Longevity and fecundity of adults week and ground to pass a 20-mesh screen using a Wiley mill. Con- centrations of B, Ca, Cu, Fe, Cu, Fe, K, Mg, Mn, Mo, P, and Zn were The longevity and the number of eggs laid on infected and unin- determined by inductively coupled plasma-optical emission spec- fected plants were not different (longevity: T38 = 0.46, P = 0.065; troscopy (model Intrepid, ThermoScientific, Waltham, MA) accord- fecundity: T38 = 0.96, P = 0.34). However, there was one extreme ing to US EPA Method 6010B (1997a) following microwave- outlier female that laid 347 eggs in the infected treatment (com- assisted acid digestion according to US EPA method 3052 (1997b) pared to a mean of 74.5 ± 10.6 for all treatments). Dixon’s Q-test modified as follows: plant tissue (500 mg) was digested in 10 ml for outlier detection (Barnett and Lewis, 1984) indicated that this concentrated (15.8 N), trace-metal grade HNO3 for 10 min at observation statistically qualified as an outlier (Q = 0.49 compared 170 °C and 300 psi (internal digestion-vessel conditions). Dige- to a critical value of 0.34 at a = 0.05). Once the outlier was re- states were brought to volume (100 ml) with distilled-deionized moved, fecundity was different between treatments (T37 = 2.27, water and then gravity filtered (Whatman 541, Whatman Int. P = 0.03). Misidentification of gender is a possible explanation for Ltd., Maidstone, England) prior to analysis by ICP-OES. Total N the extraordinary fecundity of the outlier female. Two females and C analysis were performed on the dried, milled leaf by flash- may have initially been used in the replication, rather than one fe- combustion GC (model NC 2100, CE Elantech Inc., Lakewood, NJ). male and one male, or when one of the insects died, it was identi- fied as a male, but inadvertently replaced by a female. Data 2.8. Data analyses presented in Table 1 for longevity and fecundity are after removal of the outlier. In both treatments, most eggs were laid during the All statistical analyses were conducted using SAS (SAS Insti- first 20 days, and very few eggs were laid after about 45 days tute, 2001), with a significance level of a = 0.05. Developmental (Fig. 1).
Table 1 Developmental time, fecundity, longevity and leaf tissue consumption (means ± SE) of immature G. boliviana fed on TSAMV-infected and uninfected tropical soda apple plants.
Treatment Immature developmental Leaf tissue consumed by Leaf tissue consumed by Female longevity Fecundity time (days) fifth instars (cm2) adult females (cm2) (days) (eggs/female) Infected 26.2 ± 0.24 0.34 ± 0.09 0.14 ± 0.02 65.3 ± 7.2 49.3 ± 11.2 Uninfected 23.7 ± 0.52 1.04 ± 0.30 0.26 ± 0.05 63.4 ± 8.2 84.3 ± 10.8 T 4.39 2.23 2.10 0.17 2.27 Df 56 14 60 37 37 P <0.0001 0.04 0.04 0.87 0.03 W.A. Overholt et al. / Biological Control 48 (2009) 294–300 297
Table 2 Specific leaf area (means ± SE) (cm2/g) of different leaf ages for TSAMV-infected and uninfected tropical soda apple plants (df = 28 for all comparisons).
Treatment New leaves Mature leaves Old leaves Infected 123.65 ± 9.46 133.57 ± 4.08 180.95 ± 12.79 Uninfected 171.12 ± 18.33 144.55 ± 4.58 168.44 ± 9.42 T 2.30 1.79 0.79 P 0.03 0.08 0.44
Table 3 Percent leaf moisture content (means ± SE) of different leaf ages for TSAMV-infected and uninfected tropical soda apple plants (df = 28 for all comparisons).
Treatment New leaves Mature leaves Old leaves Infected 67.77 ± 2.55 71.04 ± 0.66 77.52 ± 1.27 Uninfected 72.81 ± 2.77 71.52 ± 0.95 73.23 ± 1.87 T 1.34 0.41 1.9 P 0.19 0.69 0.07
3.5. TSAMV transmission
None of the plants which received beetles from infected plants developed symptoms of TSAMV infection by 50 days after removal
Fig. 1. Daily per capita egg production (±SE) of G. boliviana females reared on of the beetles. All plants tested negative for TSAMV by DAS-ELISA TSAMV-infected and uninfected tropical soda apple plants. and by inoculation of N. tabacum cv. Xanthi nc.
3.6. Specific leaf area, leaf moisture content, and leaf nutrients
There was a significant interaction between treatment and leaf
age (F2,89 = 3.83, P = 0.02), and thus results were analyzed sepa- rately for each leaf age. New leaves of uninfected plants had higher specific leaf area compared to infected plants, but there were no differences for other leaf ages (Table 2). A significant interaction between treatment and leaf age was also obtained for leaf moisture
content (F2,89 = 3.16, P = 0.04), but no differences were found be- tween plant treatments for any leaf age (Table 3). The percentages of phosphorus and magnesium in infected leaves were higher than in uninfected leaves, but there were no differences between levels of other macronutrients (Table 4). Among the micronutrients, bor- on and copper levels were higher in infected leaves, while molyb- denum was lower in infected leaf tissue (Table 4).
Table 4 Macro (%) and micronutrient (lggÀ1) concentrations (means ± SE) in leaf tissue of Fig. 2. Number of adult G. boliviana on TSAMV-infected and uninfected plants at TSAMV-infected and uninfected tropical soda apple plants at 3 weeks after different times after release (mean ± SE). inoculation (df = 28 for all comparisons). Nutrient Source TP Infected Uninfected 3.4. Dual choice adult preference Macronutrient C 50.43 ± 1.05 51.32 ± 1.01 0.61 0.55 When given a choice, G. boliviana preferred to feed on unin- Ca 1.55 ± 0.04 1.52 ± 0.04 0.46 0.65 fected plants (F1,9 = 5.2, P = 0.048) (Fig. 2). Two hours after release, K 3.53 ± 0.12 3.59 ± 0.08 0.44 0.67 about one-half of the beetles had settled on a plant, by 4 h nearly Mg 0.35 ± 0.01 0.33 ± 0.01 2.09 0.05 90% had settled, and after 8 h, >95% of beetles had selected a plant. N 2.46 ± 0.12 2.27 ± 0.13 1.05 0.30 P 0.38 ± 0.02 0.34 ± 0.01 2.23 0.03 At 52 h, approximately twice as many beetles were found on unin- fected plants (6.7 ± 0.7) as compared to infected plants (3.1 ± 0.7). Micronutrient B 36.49 ± 1.42 21.78 ± 0.74 9.19 <0.0001 Gratiana boliviana has a pre-oviposition period of 9–12 d (Medal Cu 7.75 ± 0.86 4.40 ± 0.28 3.69 0.001 et al. 2007), so the experiment was not run sufficiently long to Fe 61.49 ± 3.11 61.86 ± 3.28 0.10 0.93 compare numbers of eggs laid between treatments. However, more Mn 46.93 ± 6.99 50.27 ± 4.66 0.40 0.69 couples were observed mating on uninfected plants (6) compared Mo 3.43 ± 0.51 5.38 ± 0.35 3.14 0.004 Zn 79.52 ± 11.89 56.72 ± 2.73 1.87 0.07 to infected plants (2). 298 W.A. Overholt et al. / Biological Control 48 (2009) 294–300
4. Discussion was negatively affected when fed leaves from soybean plants fertil- ized with boron in various combinations with zinc and iron. We Plants are often attacked simultaneously by insect herbivores examined nutrient levels in tropical soda apple only once, and rel- and pathogens, and these organisms may interact directly or indi- atively early in the infection cycle. Measurements of tropical soda rectly through the host plant. For insect vectors of plant pathogens, apple nutrient content during the entire TSAMV infection cycle are the herbivore often benefits from feeding on infected plants (Belli- in progress. ure et al., 2005; Stout et al. 2006). For example, Frankliniella occi- In addition to nutrient content, leaf toughness and water con- dentalis Pergande (Thysanoptera: Thripidae) had increased tent are important parameters of plant quality, in particular for survival and more rapid development on tomato plants infected chewing insects such as G. boliviana (Feeny, 1970; Raupp, 1985; with a pathogen it vectors, Tomato spotted wilt virus, than on Scriber, 1979; Wheeler and Center, 1996). Increased leaf toughness uninfected plants (Maris et al., 2004). However, other studies have may reduce herbivore feeding (Huberty and Denno, 2004; Wheeler shown negative or mixed effects in vectors fed on plants infected and Center, 1996). In this study, new leaves of tropical soda apple with the viruses they transmit. Mann et al. (2008) found that infected plants had lower specific leaf area, which translates into developmental time was shorter and egg viability higher for Bemi- thicker leaves and higher toughness. Thus, tougher leaves of in- sia tabaci (Gennadius) (Hemiptera: Aleyrodidae) fed cotton plants fected plants may have influenced the feeding of both larvae and infected with Cotton leaf curl virus compared to uninfected plants, adult G. boliviana. but fewer eggs were laid on infected plants, and adult longevity Infection by a plant pathogen induces plant defense responses was lower. For non-pathogen vectoring insects, there appears to that can affect host finding, feeding behavior and physiology of in- be no general trend, with positive, negative, and neutral effects sect herbivores (Walling, 2000). Highly specialized herbivores, to herbivores feeding on virus-infected plants. Colorado potato such as G. boliviana, are adapted to respond to specific secondary beetle (Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomeli- compounds, or blends of those compounds, associated with their dae) survival was higher on plants infected with tobacco mosaic host plants (Schoonhoven et al., 2005). The presence or quantity virus than on uninfected plants, and this effect was attributed in of secondary compounds involved in host plant finding and/or ini- part to a higher nitrogen content in infected plants (Hare and tiation and maintenance of feeding may be altered by pathogens Dodds, 1987). In contrast, Helicoverpa armigera Hubner (Lepidop- (Barbosa, 1993). Concentrations of feeding arrestants, stimulants tera: Noctuidae) growth and consumption rates were lower on to- or deterrents in tropical soda apple may have been altered by virus mato plants infected with ToMV than on uninfected plants (Lin infection, which could explain the low feeding rate of larvae and et al., 2008). Infection of Mimulus guttatus (Phrynaceae) by Cucum- adults on infected plants. ber mosaic virus had negative, positive or neutral effects on a spit- When given a choice, G. boliviana exhibited a clear preference tlebug, Philaenus spumarium (L.) (Hemiptera: Cercopidae), for uninfected plants. At 2 h, about one-half of the beetles had depending on plant genotype (Eubanks et al., 2005). Thus, it is dif- moved to the plants, but the number on infected and uninfected ficult to make predictions about the influence of feeding on virus- plants did not differ, suggesting that choice was not determined infected plants on the fitness of vector and non-vector herbivorous by olfactory or visual cues which could be perceived prior to con- insects. tacting a plant. The beetles apparently rejected plants only after In the system we investigated, G. boliviana did not transmit touching or tasting. The rejection of virus-infected plants has clear TSAMV, in agreement with current dogma that tobamoviruses advantages for adult beetles in terms of increased fecundity, and are generally not vectored by insects (Fulton et al., 1987). However, also progeny fitness. Gratiana boliviana larvae are not highly mo- feeding on infected plants did negatively influence the fitness of G. bile and do not migrate from the plant on which they are ovipos- boliviana. The lower fecundity on infected leaves is likely related to ited (Overholt, unpublished). Thus, host plant selection for the lower consumption of infected tissue by both larvae and oviposition by adults is critical to the development of immature adults—the beetles either did not accumulate sufficient nutrients stages. to produce a normal number of eggs or the females recognized Whether TSAMV and G. boliviana have an evolutionary history the lower quality of infected plants and in response, laid fewer that could explain the avoidance of virus-infected plants is un- eggs, as has been reported in other systems (Hopkins and Ekbom, known. TSAMV was first isolated in Florida from tropical soda ap- 1999). ple (Adkins et al., 2007a), and has recently been found in a closely The prolonged developmental time of G. boliviana on infected related plant (D’Arcy, 1991), Solanum capsicoides All. (Adkins et al., leaf tissue also suggests that infected plants may be nutritionally 2007b). The geographic origin of S. capsicoides is uncertain. Wun- inferior to uninfected plants. There are numerous examples of derlin and Hansen (2003) list this plant as a native species in Flor- sub-optimal plant nutritional quality, especially low levels of nitro- ida, whereas others believe it is native to the Caribbean (D’Arcy, gen, negatively affecting developmental times of insects (for re- 1974) or eastern Brazil (Wagner et al., 1999). It is certainly conceiv- views, see Altieri and Nicholls, 2003; Awmack and Leather, 2002; able that TSAMV was introduced into Florida along with tropical Scriber, 1984). However, we found no difference in nitrogen con- soda apple, or possibly S. capsicoides, particularly considering that tent of the infected and uninfected tropical soda apple leaves used the virus can be transmitted through contaminated seed. Alterna- in this study. Phosphorus and magnesium were significantly higher tively, TSAMV may be a native virus which is able to develop on in infected leaves, but the differences were relatively small (6–11% tropical soda apple and S. capsicoides. As far as we are aware, increase), and within or lower than typical ranges observed in TSAMV has not been reported in tropical soda apple in its native other solanaceaeous plants (Hochmuth and Carrijo, 1999; Wilkin- South American range, although at least one other virus has been son et al., 1990). Two micronutrients were higher (boron and cop- observed (Vicente et al., 1979). per) and one lower (molybdenum) in infected leaf tissue compared It is difficult to predict how the negative effects of virus infec- to uninfected tissue. The influence of micronutrients on insect tion on beetle fitness observed in the laboratory will translate into physiology has been less studied than that of macronutrients, population level effects in the field. Adkins et al. (2007a) found although several recent papers point to their importance, espe- TSAMV infection of tropical soda apple at 42% of the locations sur- cially their relative proportions (Beanland et al., 2003; Busch and veyed but in only 15% of plants. If the incidence of TSAMV remains Phelan, 1999; Popham and Shelby, 2006). For example, Beanland low, our data suggest that beetles will select uninfected plants for et al. (2003) reported that development of three insect species oviposition and feeding, and thus there would be little impact on W.A. Overholt et al. / Biological Control 48 (2009) 294–300 299 its biology, although increased energy may be expended in finding Feeny, P.P., 1970. Seasonal changes in oak leaf tannins and nutrients as a cause of virus-free plants. In this case, the combined effect of the virus and spring feeding by winter moth caterpillars. Ecology 51, 565–581. Fulton, J.P., Scott, H.A., Gamez, R., 1987. Beetles. In: Harris, K.F., Maramorosch, L. G. boliviana on tropical soda apple populations may be largely addi- (Eds.), Vectors of Plant Pathogens. Academic Press, New York, pp. 115–147. tive, which may increase overall suppression of the noxious weed. Gandolfo, D., McKay, F., Medal, J.C., Cuda, J.P., 2007. Open-field host specificity test However, if TSAMV becomes more widespread (as would be ex- of Gratiana boliviana (Coleoptera: Chrysomelidae), a biological control agent of tropical soda apple (Solanaceae) in the United States. Florida Entomologist 90, pected if the virus is a recent introduction), the beetles may have 223–228. to oviposit on infected plants, and population increase of G. boliv- Hare, D., Dodds, J.A., 1987. Survival of Colorado potato beetle on virus-infected iana will be negatively affected due to longer developmental peri- tomato in relation to plant nitrogen and alkaloid content. Entomologia Experimentalis et Applicata 44, 31–35. od and lower fecundity. Additionally, other viruses of tropical soda Hochmuth, G., Carrijo, O., 1999. Tomato yield and fruit size did not respond to P apple, such as ToMV, which was found in 9% of plants and 33% of fertilization on a sandy soil testing very high in Mehlick-1P. HortScience 34, locations surveyed in central Florida (Adkins et al., 2007a), may 653–656. Hopkins, R.J., Ekbom, B., 1999. The pollen beetle Meligethes aneus changes egg have similar effects on G. boliviana biology. Field studies are re- production rate to match host quality. Oecologia 120, 274–278. quired to evaluate the effect of virus infection of tropical soda ap- Huberty, A.F., Denno, R.F., 2004. Plant water stress and its consequences for ple by TSAMV and other viruses on the abundance and population herbivorous insects: a new synthesis. Ecology 85, 1383–1398. dynamics of G. boliviana. Lin, L., Shen, T.-C., Chen, Y.-H., Hwang, S.-Y., 2008. Responses of Helicoverpa armigera to tomato plants previously infected by ToMV or damaged by H. Armigera. Journal of Chemical Ecology 34, 353–361. Acknowledgments Mann, R.S., Sidhu, J.S., Butter, N.S., Sohi, A.S., Sekhon, P.S., 2008. Performance of Bemisia tabaci (Hemiptera: Aleyrodidae) on healthy and Cotton leaf curl virus infected cotton. Florida Entomologist 91, 249–255. The authors wish to thank Rodrigo Diaz, Jackie Markle, Ana Maris, P.C., Joosten, N.N., Goldbach, R.W., Peters, D., 2004. Tomato spotted wilt virus Clariza Samayoa, and Ben Anuforom at the University of Florida’s infection improves host suitability for its vector Frankliniella occidentalis. Biological Control Research and Containment Laboratory, and Phytopathology 94, 706–711. McGovern, R.J., Polston, J.E., Mullahey, J.J., 1994. Solanum viarum: weed reservoir of Carrie Vanderpool, Shannon Clark, Nicole Miller, Chris Lasser, Ryan plant viruses in Florida. International Journal of Pest Management 40, 270–273. Hamm, and Marcus Martinez, at the USDA/ARS Horticultural Re- McGovern, R.J., Polston, J.E., Mullahey, J.J., 1996. Tropical soda apple (Solanum search Laboratory for technical assistance in conducting laboratory viarum Dunal): host of tomato, pepper, and tobacco viruses in Florida. In: Mullahey, J.J. (Ed.), Proceedings of the Tropical Soda Apple Symposium, 9–10 experiments. This work was funded through a grant from the Flor- January. Bartow, Florida. University of Florida-IFAS. Gainesville, FL, pp. 31–34. ida Department of Agriculture and Consumer Services. Medal, J.C., Charudattan, R., Mullahey, J.J., Pitelli, R.A., 1996. An exploratory insect survey of tropical soda apple in Brazil and Paraguay. Florida Entomologist 79, 70–73. References Medal, J.C., Sudbrink, D., Gandolfo, D., Ohashi, D., Cuda, J.P., 2002. Gratiana boliviana, a potential biological control agent of Solanum viarum: quarantine host- Abramoff, M.D., Magelhaes, P.J., Ram, S.J., 2004. Image processing with Image-J. specificity testing in Florida and field surveys in South America. BioControl 47, Biophotonics International 11, 36–42. 445–461. Adkins, S., Kamenova, I., Rosskopf, E.N., Lewandowski, D.J., 2007a. Identification and Medal, J., Overholt, W., Stansly, P., Osborne, L., Roda, A., Chong, J., Gaskalla, R., Burns, characterization of a novel tobamovirus from tropical soda apple in Florida. E., Hibbard, K., Sellers, B., Gioeli, K., Munyan, S., Gandolfo, D., Hight, S., Cuda, J., Plant Disease 91, 287–293. 2006. Classical biological control of tropical soda apple in the USA. Entomology Adkins, S., McAvoy, G., Rosskopf, E.N., 2007b. Tropical soda apple mosaic virus and Nematology Department, Florida Cooperative Extension Service, Institute of identified in Solanum capsicoides in Florida. Plant Disease 91, 1204. Food and Agricultural Sciences, University of Florida. Available from:
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