Lantana lace bug, Teleonemia scrupulosa Stål, (Hemiptera: Tingidae) is a primary insect pest of lantana, a landscape plant commonly grown across the southern United States. Twenty-eight cultivars of lantana were evaluated for resistance to lantana lace bug in replicated field plantings. Natural infestations of lantana lace bugs developed in mid-Jul, and were dispersed across all the replicates within 30 d in Dallas, TX. Populations of nymphs and adults were sampled bi-weekly from Sep-Nov 1996. Highest mean populations were present on ‘Patriot Desert Sunset’ (40.3 nymphs and adults/3-leaf sample/plant), ‘Pink Frolic’ (20.6) and ‘Patriot Sunburst’ (19.4). Nineteen of the cultivars exceeded 4 lace bugs per 3-leaf sample. Lace bugs were never detected on 3 cultivars, ‘Weeping White’, ‘White Lightning’ and ‘Weeping Lavender’ during the test period, and ‘Imperial Purple’, ‘Patriot Rainbow’ and ‘Denholm Dwarf White’ had seasonal means of only 0.1 total lace bugs per sample. Cultivars of L. montevidensis (K. Spreng.) Briq. (mean of 0.02 lace bugs/3 leaf sample) were highly resistant, whereas many cultivars of L. camara L. and L. hybrida hort (6.73 and 9.54 lace bugs/3 leaf sample, respectively) were susceptible. Cultivars with gold, red, purple, and white flowers had far fewer lace bugs than did cultivars with either orange/red, yellow, or bicolors of yellow with another color. These results indicate that within most flower colors or bicolors, there exists a range of resistance among the cultivars and usually at least 1 cultivar per color form with resistance to the lantana lace bug.
Many cultivars of lantana (Verbenaceae) are used as annuals or as herbaceous perennials in containers and hanging baskets, or as a low hedge or as foundation shrubs in urban landscapes. Most cultivated species are native to tropical or subtropical North and South America, but some are native to warmer regions of the Old World. As a landscape plant, lantana is valued for its profuse show of color throughout a long season, often every month of the year in frost-free areas, its drought, heat and salt tolerance, aromatic foliage, and attractiveness to butterflies (Arnold 1999; Everett 1981; Welch 1989). Two species are commonly used by the landscape industry. Lantana camara L. is a robust, more or less prickly shrub that is native to the southern United States and tropical America, whereas L. montevidensis (K. Spreng.) Briq. is a trailing or weeping lantana with slender pubescent stems up to 90 cm long or longer (Staff, L. H. Bailey Hortorium 1976; Everett 1981). Lantana hybrida hort cultivars is considered to be a hybrid between South American, Mexican, and West Indian species, but some are probably hybrids between the former two species (Everett 1981). Lantana hybrida hort cultivars exhibits characteristics of L. camara but is far more compact and seldom exceeds 30 cm in height.
Much of the literature on lantana centers on its introduction around the world as an ornamental and its unfortunate escape to become a noxious weed. It has been reported as a weed in 47 countries competing with 14 crops and infesting millions of hectares (Holm et al. 1977). Lantana lace bug, Teleonemia scrupulosa Stål (Hemiptera: Tingidae), has been introduced for biocontrol of lantana in over 20 countries, including Australia, India, many countries in Africa, Hawaii, and many island nations around the world (Harley and Kassulke 1971; Julien 1987). Most of the literature (other than taxonomic) on lantana lace bug relates to its introduction and use for biological control.
Across the southern United States, lantana lace bug is a late summer and fall annual pest of lantana cultivated in ornamental plantings. In Texas, as summer temperatures begin to rise and most plants begin to suffer from water stress, lantana plants thrive and flower profusely except where they are under attack by the lantana lace bug. The insect’s behavior has been studied in Fiji (Simmonds 1929), India (Kahn 1946; Roonwall 1952) and Australia (Fyfe 1937). The nymphs develop on the underside of the leaves first causing a yellow spotting of the foliage, followed by silver to white bronzing with the leaves eventually browning and dropping from the plant. During nymphal feeding, large patches of black varnish-like droplets of excrement are deposited on the underside of the leaves and the molted skins of nymphs frequently remain attached. Adults are found on the leaves but also feed heavily on the flowers and cause a marked reduction in flowering and seed set (Wilson 1960). The objective of the present study was to evaluate 28 cultivars of lantana that are used in the nursery trade for their resistance or susceptibility to the lantana lace bug.
Materials and Methods
Lantana plants cultivated in 10 × 10 cm pots were planted ≈1 m apart in a series of raised field beds in a randomized complete block design with 6 replications of 1 plant per replicate. Only 3 replicates of several of the cultivars were evaluated (Table 1) due to a shortage of plant material. The highly alkaline (∼8.0 pH), poorly aerated clay soil in the beds was amended by thoroughly incorporating a 5.1-cm-thick layer of sphagnum peat. Beds were mulched with a layer (7.5 cm thick) of cottonseed hulls and plants were irrigated thoroughly with soaker hoses every 7-10 d. A 21-7-14 (N-P-K) fertilizer, in which half of the N was formulated for slow-release, was incorporated into the soil mix prior to planting at a rate of 907.2 g / 9.3 m2. A second application at the same rate of nutrients was applied as a side dressing to the plants in mid-Jul, ca. 8 wk later.
Most of the lantana cultivars were planted on either 15 or 16 May 1996. Due to unavailability of plant material on these dates, ‘Patriot Dove Wing’ and ‘Patriot Honeylove’ were not planted until 2 Aug 1996. Cultivars were chosen because of their popularity with growers across Texas and the southwestern United States. Only a few of these cultivars are listed by Howard (1969) in his checklist of lantana cultivars at the Harvard University Arboretum, but many of the cultivars evaluated are recommended for Texas and the Southwest (Brenzel 1997; Perry 1992; Sperry 1991).
Population counts for lantana lace bug were taken every 2 wk beginning 11-12 Sep through 11 Nov 1996, by examining each plant. All plants were examined during a 2-d observation period for each sample date. The overall plant was examined by gently lifting each of the terminal branches and recording the number of nymph and adult lace bugs on 3 leaves with the heaviest infestation. Visual evaluations for leaf bronzing, defoliation, overall loss of plant vigor, and the late summer and fall reduction in flowering were all good visual indicators of cultivars with high lace bug populations.
Data were analyzed by analysis of variance procedures (ANOVA and GLM) in PC-SAS (SAS Institute 1990) to determine the differences in susceptibility among the cultivars at each observation period. Adult and nymph infestations were analyzed separately to show colonization levels. All count data were transformed as square root of n + 0.001 before analysis to stabilize variances. Untransformed means are reported. A Resistance Performance Index = the number of times a cultivar ranked in the top statistical grouping, was calculated for each cultivar as a measure of overall resistance (Engelke et al. 1994).
Results and Discussion
A naturally occurring infestation of lantana lace bugs invaded the replicated lantana planting in mid Jul 1996, and was first detected on plants of the cultivar ‘Pink Frolic’. By mid Aug, populations were also causing damage to foliage of ‘Golden King’, ‘Irene’, ‘Lemon Drop’, ‘LSG Red-Orange’, ‘Silver Mound’, and ‘Spreading Sunset’. By early Sep, damage was widespread across the planting and relatively consistent across the replicates of the more susceptible cultivars.
The mean total of lace bugs per plant (Table 1) represents the average number of lace bugs (nymph + adult) per 3-leaf sample over the 5 observation periods. Data for 12 Sep showed nymphal development on 21 of the 28 cultivars. Highest populations were present on Pink Frolic (40.0 nymphs/3-leaf sample/plant) and LSG Red-Orange (37.7) whereas no populations of either nymphs or adults were observed on ‘Weeping White’, ‘White Lightning’, ‘Weeping Lavender’, ‘Patriot Rainbow’, ‘Denholm Dwarf White’, Patriot Dove Wing, or ‘Patriot Desert Sunset’. A significantly lower population of only 0.2 nymphs/3-leaf sample/plant was present on ‘Imperial Purple’. By 26 Sep, overall populations had decreased but were still highest on the cultivars that had supported the high populations throughout the season. The highest nymphal populations of 81.7 and 55.3 nymphs/3-leaf sample/plant were present on Patriot Desert Sunset and ‘Patriot Sunburst’, respectively. Patriot Dove Wing and Patriot Desert Sunset no longer appeared to be resistant as they had during the evaluation 2 wk earlier. By 11 Nov, the populations of lace bugs had declined on most of the susceptible cultivars. A high and damaging level, however, had been present on most of these cultivars throughout the 8-wk evaluation period and many of the cultivars were severely damaged with bronzed leaves and a considerable loss of leaves, flowers, and plant thriftiness. Once a plant was damaged to the extent that bronzed leaves were evident, it remained disfigured throughout the remainder of the growing season.
Lace bugs were never detected on Weeping White, White Lightning, and Weeping Lavender during the test period. Imperial Purple, Patriot Rainbow, and Denholm Dwarf White had mean populations of 0.1 total lace bugs per sample and never exceeded ≤0.7 insects per sample. The Resistance Performance Index shows that in addition to the aforementioned cultivars, ‘Radiation’, ‘Dallas Red’, ‘Gold Mound’, ‘New Gold’, and ‘Lemon Swirl’ also ranked either 9 or 10 (out of 10) times in the top statistical groupings. However, ‘Patriot Honeylove’, ‘Confetti’, ‘Samantha’ and ‘American Red Bush’ were also in the top statistical group for mean total lace bugs per 3-leaf plant sample, but these cultivars sustained significant lace bug populations during Sep and early-Oct and only occurred in the top statistical ranking either 6 or 7 times.
When cultivars are grouped by species and analyzed, the species, L. montevidensis (4 cultivars with a mean of 0.02 lace bugs/3-leaf sample) is highly resistant, whereas several of the L. camara and L. hybrida cultivars were resistant but most of them were susceptible to the lantana lace bug (Table 2). Cultivars of L. montevidensis produce either white or purple flowers.
Cultivars were analyzed separately for flower color. A cultivar with two predominant flower colors was analyzed as bicolor for the 2 colors. Cultivars with purple or white flower color had far fewer lantana lace bugs (means of 0.03 and 1.73, respectively) developing on them than did cultivars with other flower colors (Table 3). For the 2 white-flowered L. camara, Denholm Dwarf White is resistant while Patriot Dove Wing is a highly susceptible cultivar. A cultivar with low infestations of lace bugs and in the top statistical ranking or resistant was identified for each flower colors except for 2 bicolors, white/yellow and red/yellow (Table 3). Overall, it appears that cultivars with either yellow or yellow bicolor flowers are among the most susceptible to the lantana lace bug. Flower color has been implicated as an indicator of resistance in other ornamental plants. In studies with Canna spp., cultivars with red-, orange-, and scarlet-flowers were more susceptible to canna leafroller, Calpodes ethlius Stoll than those with yellow- or rose-flowers (Reinert et al. 1983). Also, in studies with oleander, Nerium oleander L., susceptibility to oleander caterpillar, Syntomeida epilais jucundissima Dyar, was much higher on cultivars with certain flower colors than on those with other flower colors (J. A. Reinert et al. unpublished data). Resistance may not be determined by flower color, but there appears to be a relationship to color, although not independent. Additional work is needed to fully understand what the relationship is between flower color and resistance to lantana lace bug and other insects.
This information on the range of susceptibility among cultivars within each of the flower color groupings should be of considerable value to commercial growers, retail nurserymen, landscapers, and consumers. The species, L. montevidensis, provides resistant purple- (Weeping Lavender and Imperial Purple) or white-flowered (Weeping White and White Lightning) cultivars. Additionally, Denholm Dwarf White is a resistant white-flowered L. camara cultivar with a more upright, mounding growth habit. When lantana lace bug was being evaluated as a biocontrol agent in Australia, Haseler (1966) observed that it defoliated white-flowered lantana (no species or cultivars given) and caused the plants to die. Our data show both resistance and susceptibility among the white-flowered cultivars. For the other flower color or bicolor groupings, there is a range of susceptibility among cultivars as well, typically with at least 1 cultivar ranking in the top statistical grouping and expressing resistance. For example, in the pink/yellow-flowered group, Patriot Rainbow is resistant, whereas all the other cultivars are susceptible with Irene and Pink Frolic being extremely susceptible. Harley & Kassulke (1971) and Radunz (1971) reported that lantana lace bug showed a preference for red-flowered lantana species, pink-flowered were least preferred, and white and orange showing intermediate damage, but they did not identify cultivars or species. Their statement, and the results presented here, emphasize the need to understand the potential genetic resistance of each cultivar regardless of the flower color. This range of susceptibility among the cultivars within each color grouping should allow the consumer to install landscape plantings of lantana that have an array of flower color but still provide a high level of natural (genetic) protection against this destructive pest.
Resistance among lantana cultivars to the lantana lace bug (6 replicated field plots) summer, 1996, Dallas, TX.
Impact of species of lantana on the infestation level of lantana lace bug.
Impact of the flower color of lantana cultivars on the population levels of lantana lace bug.