Impact of Seed Predators on the Herb Baptisia Lanceolata (Fabales: Fabaceae)
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398 Florida Entomologist 87(3) September 2004 IMPACT OF SEED PREDATORS ON THE HERB BAPTISIA LANCEOLATA (FABALES: FABACEAE) Scorn HORN AND JAMES L. HANULA USDA Forest Service, 320 Green Street, Athens, GA 30602 The reproductive success of plants is a complex South Carolina were commonly infested byA. ros- interaction among beneficial organisms such as trum. Therefore, the objectives of this study were pollinators, and destructive ones such as defolia- to determine the extent ofA. rostrum seed preda- tors or seed predators that eat plant tissue. Many tion on B. lanceolata and the efficacy of an insec- insects that consume reproductive tissue destroy ticide to limit damage to B. lanceolata seed much of a plant’s reproductive output (Breedlove & production. Insecticides could provide managers Ehrlich 1968; Janzen 1971; Evans et al. 1989). In with an additional tool to use in efforts to increase particular, the predation of seeds serves as a major local populations. selective force affecting plant abundance, distribu- The study was conducted during the spring tion, and evolution (Harper et al. 1970; Moore and summer of 2003 at the Savannah River Site 1978; Duggan 1985). Seed predation (destruction (SRS) near Aiken, South Carolina. The SRS is prior to dispersal) often accounts for a large por- owned and operated by the Department of Energy tion of a plant population’s mortality (Janzen 1969; (DOE), and the land is managed as a National Louda 1978; Norambuena & Piper 2000). Environmental Research Park. Baptisia lan- Lance-leaf wild indigo, Baptisia lanceolata ceolata is only found at a few scattered localities (Walter) Elliott (Fabaceae), is a member of a large in the southwestern corner of the SRS where it is group of plants containing several alkaloids mainly associated with pine forests (Knox & (Cranmer & Turner 1967) that deter some herbi- Sharitz 1990). This species blooms from April to vores (Frost 1945). In particular, Baptisia spp. May, with seed pods being present from June to contain alkaloids called quinolizidines that are November. We were unsure when seed predators toxic to herbivores (Gibbons et al. 1990). Baptisia began oviposition on plants in our study area so lanceolata occurs sporadically on sandhills, in we started insecticide applications early to in- open woods, and along roadsides in Alabama, crease the likelihood of protecting seeds. We se- Georgia, South Carolina, and northern Florida. lected 37 plants as untreated controls and 33 The plant is considered rare in South Carolina be- plants that were treated with insecticide at two cause it is found in only two counties (Knox & locations on the SRS. Plants were sprayed with Sharitz 1990). Because this species is of special permethrin (1% AI) until runoff. The first applica- concern to the state of South Carolina, research tion occurred on 29 April at the time several of the on its life history is needed to identify factors af- plants started to bloom. Plants were treated three fecting populations and to aid efforts to maintain more times (9 May, 21 May, and 18 June) through- and increase B. lanceolata populations. out the blooming and fruiting period. Seed pods Leguminous seeds are a concentrated source of were collected on 17 July and examined for num- nutrition (Brashier 2000). In a nutrient-poor habi- ber of seeds produced and the presence of insect tat, these seeds are important resources for many seed predators. A t-test was used to compare of the animal species residing there. Several insect treated and control plants statistically. predators are known to feed on Baptisia seeds. Plants treated with insecticide experienced One such insect isApion rostrum Say (Coleoptera: greater reproductive output (Table 1). The num- Curculionidae), a weevil that feeds on seeds of sev- ber of damaged seeds per plant was significantly eral wild indigo species. Females lay eggs in devel- lower on insecticide-treated plants (P = 0.046) re- oping seed pods where the larvae eat the seeds. sulting in an increase of 5 seeds/plant. In addition, Haddock & Chaplin (1982) found that A. rostrum percent success (no. pods formed I no. original consumed as much as 5% of the yearly seed crop of flowers) was significantly higher on treated plants B. leucantha in the tallgrass prairies of Missouri. (P = 0.010) probably due to reduced weevil attacks Peterson (1989) examined the relationship be- in the early stages of pod development. Studies tween these same two species in an Illinois have suggested that A. rostrum may be responsi- tallgrass prairie and found that limiting seed pred- ble for premature pod abortion (Peterson 1989; ator access to plants with a sticky barrier in- Peterson & Sleboda 1994; Peterson et al. 1998). creased seeds per pod and pods per plant. Thus, it appears insecticides effectively lowered Similarly, a study on two Haplopappus spp. (Aster- initial damage by ovipositing females. Insecticide aceae) in California showed that insecticides were applications resulted in a net increase of 15 un- effective in reducing seed predation (Louda 1982). damaged seeds per plant. Because treated and Little is known about the life history and fac- control plants had similar numbers of seeds per tors influencing survival of B. lanceolata. In pre- pod and seeds per plant, the increased seed yield liminary examinations, B. lanceolata seed pods in resulted from reduced propagule damage. Scientific Notes 399 TABLE 1. MEAN + SE OF SELECTED FLOWER AND SEED YIELD PARAMETERS FROM CONTROL AND INSECTICIDE TREATED BAPTISIAOWCEOLATA PLANTS. Control (n = 37) Treated (n = 33) Blooms/plant 43.0 zt 5.68 36.7 ziz 5.76 Pods/plant 7.78 i 1.82 10.6 i 2.23 % success (no.pods/no.flowers)* 16.5 i 3.03 29.1 f 4.08 Seeds/plant (damaged + viable) 42.7 + 8.09 52.9 f: 9.88 Damaged Seeds/plant* 7.10 i 2.07 2.20 f 1.11 % of seeds damaged 14.0 + 2.81 4.30 * 1.62 A. rostrumlplant 0.49 f 0.15 0.79 f 0.41 Tortricid larvae/plant* 0.49 f 0.15 0.00 i 0.00 *denotes a significant difference G’ < 0.05). Peterson & Sleboda (1994) stated that A. ros- ties occur in South Carolina that feed on wild in- trum was the only known predator impacting digo (Scott 1986) and all six may occur at the Buptisia spp. in their study area in Illinois. Like- Savannah River Site. These include Colias eury- wise, A. rostrum was the only seed predator en- theme (Lepidoptera: Pieridae), Colias philodice countered at SRS during preliminary seed counts (Lepidoptera: Pieridae), Callophrys irus (Lepidop- in 2002. However, when pods were collected for tera: Lycaenidae), Everes comyntas (Lepidoptera: analysis during summer 2003, A. rostrum ap- Lycaenidae), Achalarus lyciades (Lepidoptera: peared to be less common than the year before Hesperiidae), and Erynnis baptisiae (Lepidoptera: and another seed predator was found. Hesperiidae). These species are closely associated The latter was an unidentified caterpillar in with wild indigo and may require it for survival, so the family Tortricidae found on almost half of the it may be appropriate to survey plants targeted for plants sampled. Previous authors found tortricid insecticide application to ensure that larvae are larvae to be prevalent on plants in Missouri (Had- not present. However, this may not be necessary dock & Chaplin 1982) and Kansas (Evans et al. since most of these butterfly species can survive on 1989). It is unclear whether this caterpillar was any plants in the genus Baptisia. Areas containing overlooked the previous year or was not present. plants of other more common Buptisia species Unlike A. rostrum, the caterpillar seemed to con- such as B. alba or B. australis are likely to have sume almost all of the seeds within a pod. Infested sufficient host plants to lessen the impacts of in- pods contained frass and silk similar to that ob- secticide application to B. lanceolata on butterfly served by Haddock & Chaplin (1982). Although populations. In addition to insecticide applica- we were able to collect several specimens, many tions, other methods such as fire, fertilization, or larvae apparently exited the pods before 17 July planting may be useful for increasing local popula- We found no evidence of pupation in the pods. Our tions of B. lanceolata. insecticide treatments were especially effective in Future work should investigate how seed pre- reducing tortricid numbers. None of the 18 larvae dation is affected by biotic and abiotic factors and collected from seed pods were from treated plants. how it changes over time; how to time sprays bet- The insecticide effectively protected seeds from ter so less insecticide is needed; and whether tortricid larvae, but weevils and their damage other insecticides may be better at controlling were still evident, despite four applications. Al- certain seed predators. Insecticides may be a sim- though the treatments only reduced damaged ple, inexpensive, and effective means of increas- seeds from 7.1 to 2.2, it is likely that they would ing seed yields of other rare plants. have increased yields more if weevil populations We thank D. Dyer and M. Ulyshen for techni- were higher. For example, Peterson (1989) found a cal assistance during this project and T. Kuntz for sticky barrier increased yields by 0.4 and 2.6 seeds helping locate plants for the study We also thank per pod in 1985 and 1988, respectively. Even Theresa Pitts-Singer for helpful comments on the though our treatments resulted in an increase of manuscript. Assistance was provided by the U.S. only 15 viable seeds per plant, this would be an in- Forest Service-Savannah River under the Depart- put of 600 additional seeds in a 40-plant popula- ment of Energy Savannah River Operations Of- tion. More research is needed to determine if fice through Interagency Agreement DE-AlOS- increasing seed yield within a plant population is OOSR22188.