Biology and Management of the Easter Lubber Grasshopper (Orthoptera: Acrididae)

Timothy Schowalter  |  4/6/2018 2:28:16 PM

T. D. Schowalter

Entomology Department, Louisiana State University Agricultural Center, Baton Rouge, LA 70803 (tschowalter@agcenter.lsu.edu)

Subject Editor: Eric Rebek

Received 29 November 2017; Editorial decision 9 February 2018

Abstract

The eastern lubber grasshopper, Romalea microptera (Beauvois) (Orthoptera: Acrididae), is locally common in swamps, open woodlands, weedy fields, and ditches in the southeastern United States. This species displays bold color patterns that vary from primarily lighter yellows and oranges in eastern portions of its range (although the black form occurs throughout the range) to shiny black with red markings in western portions, exemplifying aposematic (warning) coloration. This grasshopper has a wide host range, with more than 100 known host plants, from which it can sequester or synthesize a variety of toxic chemicals. Lubber defenses are highly effective against vertebrate predators, but not against a variety of parasitoids and entomopathogens. Lubbers rarely cause serious damage, and their saliva is known to stimulate compensatory plant growth. Nevertheless, they can cause economic damage to citrus orchards, vegetable crops, and landscaping vegetation that border natural habitats. Damage typically is localized and can be managed effectively using an integrated pest management (IPM) approach. Insecticides are relatively ineffective and generally not recommended. Selecting less preferred host plants for landscaping where lubbers have been nuisances is a recommended strategy. When control is warranted, hand-picking and killing lubbers is effective at low densities. Several insecticides, including the microbial product, spinosad, are effective against nymphs. A granular bait containing 5% carbaryl is effective against lubbers of all stages, especially in areas dominated by less preferred hosts. Treatment can be focused in strips along the margins of orchards, crops, or landscaping to prevent lubbers from moving in. All insecticides should be used only according to label directions.

Key words: chemical defense, aposematic coloration, parasitism, insecticide, bait


The eastern lubber grasshopper, Romalea microptera (Beauvois) (Orthoptera: Acrididae), is a locally common species in the south- eastern United States. It can be found from North Carolina south through Georgia and Florida and west to central Texas(Capinera and Scherer 2016). These lubbers are commonly found in swamps, open woodlands, weedy fields,and drainage ditches. This species is familiar to many students as the representative insect dissected in introductory Biology and Entomology labs (Carolina Biological Supply 2017). However, they also gain widespread attention as pests in citrus orchards, gardens, and landscape vegetation (Capinera 2014, Capinera and Scherer 2016).

Adult eastern lubbers are the largest grasshoppers in the United States, reaching lengths of up to 9 cm(3.5″).They are flightless and jump clumsily, but climb well and are capable of defending themselves via a combination of loud hissing and secretion of toxic foam (Blum 1992, Capinera and Scherer 2016). Their bold coloration is a warning to potential predators. Although harmless to humans, lubber grasshoppers attract much attention, especially when they defoliate residential plantings or young citrus orchards (Capinera 2014).

Eastern lubbers are broadly polyphagous and can cause substantial losses in landscaping plants, vegetable gardens, crops, and young citrus orchards (Capinera 2014). Although well defended against vertebrate predators (Blum 1992), lubbers are vulnerable to a variety of parasites (Lamb et al. 1999, Capinera and Scherer 2016). Control is rarely war- ranted, but if control is necessary, several options are available.

Description

Adult lubbers are colorful, but their aposematic color pattern varies considerably across their range (Fig. 1). In the eastern portions of its range, adult lubbers are mostly yellow or tawny, with black on the distal portion of the antennae, on the pronotum, and on the abdominal segments (Fig. 1A) (Capinera and Scherer 2016), whereas in the western portions of its range, adults are shiny black with red or yellow markings (Fig. 1C). Morphs with blended characteristics (Fig. 1B) occur in intervening areas. Both sets of wings are short, extending less than three-fourths the length of the abdomen and incapable of providing flight. The forewings are pink or rose-colored centrally, and the hind wings are entirely rose-colored (Fig. 2). Adult males measure 4.3–5.5 cm in length (1.7–2.2″), and females usually 5.0–7.0 cm (2–2.8″), but up to 9.0 cm (3.5″). Though flightless and a poor jumper, this grasshopper is an adept climber and is frequently observed on low branches of trees (Capinera and Scherer 2016).

fig 1jpg

Fig. 1. Adult eastern lubbr grasshopper. (A) Light (eastern) form, (B) intermediate form, (C) black (western) form. A and B photos by John Capinera, University of Florida; C photo by T.D.S.


fig2jpgFig. 2. Adult eastern lubber grasshopper showing rose-colored hind wing.


fig 3jpgFig. 3. Defensive froth of an adult lubber grasshopper. This secretion includes repellent chemicals sequestered from host plants. Reproduced from Blum (1992).

Jannot et al. (2009a,b) reported that a geographic line of increasing developmental time and female growth rates from west to east in south Florida could not be explained by ontogenetic factors but appeared to be related to population density. Experimental manipulation of density confirmed that higher densities led to larger adult masses, longer developmental times, and lower survivorship.

Both sexes stridulate by rubbing the forewing against the hind wing. When alarmed, lubbers spread their wings, hiss by expelling air from the spiracles, secrete foul-smelling froth from their spiracles (Fig. 3), and regurgitate recently consumed plant material as a dark brown liquid, commonly called ‘tobacco spit’, which can stain skin and clothing (Blum 1992, Capinera and Scherer 2016). Lubbers can spray toxic chemicals for a distance of 15 cm (5.9″) (Capinera and Scherer 2016).

Eggs are yellowish or brown and elongate elliptical, measuring about 1 cm (0.4″) long and 0.25 cm (0.1″) wide (Capinera and Scherer 2016). Eggs are laid in neatly arranged pods, with parallel rows of eggs held together by a secretion. Each pod contains 30–50 eggs.

fig4jpgFig. 4. Eastern lubber grasshopper nymphs. Photo by T.D.S.

fig5jpgFig. 5. Large aggregation of eastern lubber grasshopper nymphs on swamp lily. Photo by T.D.S.


Nymphs typically are shiny black, with a distinctive dorsal yellow, orange, or red stripe (Fig. 4). Nymphs progress through five, occasionally six, instars. Hunter-Jones (1967) noted that nymphs with yellow or red stripes could hatch from the same egg pod, butby the last instar, all had yellow stripes. Instars can be distinguished by a combination of body size, number of antennal segments, and form of the developing wings. Nymphs are gregarious through most of the nymphal period, but the tendency to aggregate may dimin-ish over time. Nymphs are particularly prone to aggregate at night and may climb vegetation to rest during the evening (Capinera and Scherer 2016). Aggregations can include >100 individuals (Fig. 5). Aggregations often move into lower-lying, moist areas where nymphs feed on aquatic or semi-aquatic vegetation (Fig. 5), as well as into neighboring crops, orchards, and landscape vegetation (Watson 1941, Capinera and Scherer 2016).

The bold appearance of these grasshoppers exemplifies aposematic coloration, warning potential predators of their toxic defenses. The chem- ical defense consists of both sequestered and synthesized compounds, primarily phenolics such as catechol and hydroquinone (Jones et al.1987, 1989; Blum et al. 1990). However, individual lubbers vary greatly in chemical defense. Lubbers lose chemical defenses during molts, and chemical concentration increases with age and is higher in females than males (Whitman et al. 1992). Lubber behavior may enhance this defense. Hatle et al. (2001) found that the combination of sluggish movement and repugnant odor deterred attack by northern leopard frogs, Lithobates pipiens (Schreber) (Anura: Ranidae), better than either trait alone.

Ecology

Habitat, Phenology, and Life Cycle

Eastern lubber grasshoppers are found in a variety of terrestrial and semi-aquatic habitats in the southeastern United States. Adults apparently prefer mixed hardwood-pine habitats and open fields with intermediate moisture levels (Watson 1941, Kuitert and Connin 1953), but nymphs often are found in wetter areas, such as swamps and marshes with semi-aquatic vegetation (Fig. 3) (Squitier and Capinera 2002). Lubbers often congregate in weedy drainage ditches, bringing them to the attention of neighboring farmers or homeowners.

This species has a single generation each year under natural conditions. Overwintering occurs in the egg stage, with hatching beginning in early February. Adults appear in early June, with oviposition starting in July (Hunter-Jones 1967).

Females deposit an egg pod in the soil at a depth of 3–5 cm (1.2–2.0″) and seal the hole with a frothy plug. Oviposition timing is related to photoperiod and resource availability. Lubbers in northern portions of their range oviposit earlier in response to photoperiod, but egg production may be reduced by food limitation (Luker et al. 2002, Homeny and Juliano 2007). Oviposition depth depends on female size and soil moisture and density (Herrmann et al. 2010). The plug allows the hatching nymphs to easily reach the soil surface. Females preferentially oviposit at sites containing previously laid egg pods, suggesting that egg pods release attractive or arresting phero- mones (Stauffer et al. 1998). This behavior leads to aggregation of pods (Capinera and Scherer 2016). Females can produce pods about every 2 weeks, each pod containing 25–50 eggs, and eachfemale can produce 1–3 pods (Hunter-Jones 1967, Stauffer and Whitman 2007). Grasshopper longevity and reproductive output show geo- graphic and genetic variation (Gunawardene et al. 2004, Taylor and Whitman 2010), but maternal condition apparently is not a factor in reproductive output (Taylor and Whitman 2010).

Eggs require a cool period (e.g., 20°C for 3 months) but do not have an obligate dormancy period (Capinera and Scherer 2016). Eggs hatch when exposed to warmer temperatures. Typically, egg hatch occurs in the morning (Capinera and Scherer 2016).

Factors Affecting Population Dynamics

Food Availability

Eastern lubbers have a wide host range. Feeding has been observed on at least 100 species from 38 plant families, though their mouthparts are best adapted for feeding on forbs (broad-leaf plants), not grasses (Squitier and Capinera 2002). Watson (1941) reported that nymphs preferentially fed on narcissus, Narcissus spp., swamp lilies, Crinum americanum L. (both Asparagales: Amaryllidaceae), and pokeberry, Phytolacca americana L. (Caryophyllales: Phytolaccaceae), as well as several semi-aquatic plants. Watson (1941) also noted that nymphs were attracted to fields of narcissus and developed most rapidly when fed narcissus, compared to other host plants.

Squitier and Capinera (2002) confirmed that lubbers readily feed on a variety of semi-aquatic plant species, including cattail, Typha latifolia L. (Poales: Typhaceae), common arrowhead, Sagittaria latifolia Willd. (Alismatales: Alismataceae), poorland flatsedge, Cyperus compressus L. (Poales: Cyperaceae), sprangletop, Leptochloa dubia (Kunth) Nees (Poales: Poaceae), and hairy smartweed, Persicaria hirsuta (Walt.) Small (Caryophyllales: Polygonaceae). Capinera (2014) compared lubber feeding on 104 plant species, standardized to consumption of Romaine lettuce, Lactuca sativa L. var. longi- folia (Asterales: Asteraceae), a highly palatable species. Test plants included ornamental, garden, weed, shrub, tree, vine, and aquatic or semi-aquatic species. Lubbers did not show a statistically significant difference in preference (relative to Romaine lettuce) for 20% of the plant species tested. A few (3%) plant species were preferred more than lettuce. Most (77%) of the plant species tested were significantly less preferred, but would be readily eaten when more preferred hosts are not available. Generally, lubber grasshoppers preferred young foliage over old foliage. Plant species that were readily consumed by grasshoppers represented 14 plant families, including (amaryllis, Amaryllis spp., onion, Allium cepa L., spider lily, Hymenocallis spp., and swamp lily) (Asparagales: Amaryllidaceae), oleander, Nerium oleanderL.(Gentianales:Apocynaceae),lettuce (Asterales: Asteraceae), various beans (Fabales: Fabaceae), and citrus, especially orange, Citrus × sinensis (L.) Osbeck (Sapindales: Rutaceae), demonstrating that eastern lubber grasshoppers are broadly polyphagous.

Diet breadth has a significant effect on lubber defensive chemistry. Jones et al. (1987) reported that lubbers fed a diet of onion alone produced fewer compounds and lower concentrations of their normal defensive compounds than did lubbers fed a diet of 26 host species that included onion. However, lubbers fed an onion diet sequestered threefold more sulfur-containing plant defensive com- pounds that were more effective in repelling predators, compared to lubbers fed natural or artificial diets (Jones et al. 1989). Hatle and Spring (1998) also found that lubbers fed a diet of onion produced more secretion and had higher concentrations of total sulfur in their secretions than lubbers fed other diets. However, the variety of plant toxins sequestered from a broad diet also may augment the efficacy of lubber defenses (Chapman and Joern 1990).

In addition, lubbers readily accept exotic hosts, such as catnip, Nepeta cataria L. (Lamiales: Lamiacea), and sequester or synthesize new defenses from the novel chemicals derived from these hosts (Blum et al. 1990). For example, Snook et al. (1993) and Blum et al. (1990) found that lubbers secrete more catechol and terpenoid lac- tones from their defensive glands when fed diets containing only cat- nip. This catechol apparently was synthesized from caffeoyltartronic acid derived from catnip leaves.

Mortality Factors

fig6jpg

Fig. 6. Carolina anole, Anolis carolinensis Voigt (Iguania: Dactyloidae), vomiting adult eastern lubber grasshopper. Reproduced from Blum (1992).

Lubber grasshoppers are protected from most vertebrate and inver- tebrate predators by the combination of chemical defense and warn- ing coloration (Jones et al. 1987, 1989; Blum 1992; Whitman et al. 1992; Hatle and Spring 1998). The bold coloration of lubbers adver- tises toxic chemicals to would-be predators, but even young nymphs that produce less chemical defense are avoided by lizards(Hatle and Townsend 1996, Hatle et al. 2001). Birds and mammals vomit violently after ingesting a lubber (Fig. 6) (Blum 1992, Yousef and Whitman 1992). Yousef and Whitman (1992) reported that 21 tested bird and lizard species were unable to consume lubbers and some died. Loggerhead shrikes, Lanius ludovicianus L. (Passeriformes: Laniidae), captured lubbers and impaled them on thorns or barbed wire fences. After 1–2 days the toxins degraded, and the shrikes were able to eat the dead lubbers (Yousef and Whitman 1992).

However, lubbers are vulnerable to a variety of parasites. Lamb et al. (1999) reported that lubber parasitism by Anisia serotina (Reinhard) (Diptera: Tachinidae) is 60–90%. At high lubber densities in 1997, the parasitism rate was 82%. Two sarcophagids, Blaesoxipha opifera (Coquillett) and Blaesoxipha hunteri (Hough) (Diptera: Sarcophagidae), also parasitize lubbers. Larvae develop within the nymphs, killing their hosts upon emergence (Capinera and Scherer 2016). Lange et al. (2009) discovered a new microsporidian species, Encephalitozoon romaleae Lange, Johny, Baker, Whitman & Solter (Microsporidia: Unikaryonidae), in lubbers collected from Louisiana, Georgia, and Florida. This microsporidian infects the gastric caecae and midgut tissues of lubber hosts. In the laboratory, all lubbers became infected, but mortality varied among populations, with lubbers from Georgia and Louisiana becoming lethargic and dying quickly, whereas lubbers from Florida showed no symptoms (Lange et al. 2009). Johny and Whitman (2005) described a new microbial parasite, Boliviana floridensis Johny & Whitman, from lubbers collected in south Florida, but no mortality data were provided. However, Stauffer and Whitman (2007) reported that 46% of lubbers at one site and 100% at a second site were infected by this pathogen.

Effects on Vegetation

Because lubber nymphs are gregarious, they can completely defoli- ate host plants on which they congregate (Capinera 2014). Adult lubbers cause less damage than might be expected for their size (Capinera and Scherer 2016). Defoliation is most often observed in areas that support weeds or semi-aquatic plants, such as irrigation and drainage ditches and edges of ponds. Consumption of at least some weed hosts could be beneficial, if their removal leaves more palatable vegetation for livestock feeding. However, lubbers may dis- perse from these sources to crops and residential areas, where they cause more conspicuous, if less extensive, damage.

Loss of tissues may not be entirely damaging to host plants, however. Plants often tolerate or compensate for loss of tissues to grasshoppers or other herbivores, in response to pruning of less productive plant parts (Mattson and Addy 1975, Trumble et al. 1993, Dyer et al. 1995). Grasshoppers and otherherbivoresalso can increase primary production at low to moderate levels of her- bivory through changes in plant species composition (Belovsky and Slade 2000, 2017; Schowalter 2016). Grasshoppers and other her- bivores typically deposit salivary fluids on plant tissues as they feed. These materials may signal plants to recognize herbivore damage


and respond in various ways, including compensatory responses and induced defenses targeted to particular herbivore species (Schmelz et al. 2006, 2007; Uesugi et al. 2013). In particular, Dyer etal.(1995) reported that salivary extracts from eastern lubbers signifi- cantly stimulated coleoptile growth of sorghum (Sorghum bicolor (L.) Moench (Poales: Poaceae)), suggesting a mechanism whereby herbivores can increase plant productivity at low to moderate levels of herbivory and thereby stabilize primary production and ecosys- tem services in natural ecosystems (Schowalter 2016).

Management

Eastern lubbers are not management concerns in forests or other natural areas, although they may periodically cause localized defoliation (Drooz 1985). Their largesizeanddefensivebehav-ior make them appear to be more serious threats than warranted. Nevertheless, lubber grasshoppers can cause substantial losses in young citrus orchards, vegetable gardens,andlandscapingplants in areas bordering lubber habitats or when lubbers are numerous (Kuitert and Connin 1953, Capinera 2014). However, damage is rarely significant in older orchards or landscape plantings (Capinera 2014). Insecticides are rarely warranted, and other options are pre- ferred where lubbers are a nuisance.

As recommended for most grasshoppers and other nuisances, monitoring of lubber abundance and early treatment of areas where nymphal development occurs are the best ways to prevent damage to economically important plants. Where lubbers are a nuisance, mow- ing bordering vegetation can be an effective preventative treatment because short vegetation is less favorable to grasshoppers, perhaps by altering thermal balance or exposing them to parasites (Capinera and Scherer 2016).

A number of ornamental plant species, especially amaryllis, spider lily, swamp lily, and oleander, that are particularly susceptible to lubber grasshopper have become widely planted in Southern residential landscapes. In areas where lubber grasshoppers historically have been a problem, other less preferred ornamental species are recommended. Maintaining less preferred host plants also may increase the efficacy of insecticide use, when necessary(Barbara and Capinera 2003). Capinera (2014) found that insecticide-laced bait caused significantly higher mortality to lubbers in cages containing non-preferred plant species than in cages with preferred plant species.

When control of lubbers is necessary, especially in residential ornamental plantings, they can be hand-picked and killed by throwing them into a bucket of soapy water or a trash bag (Capinera and Scherer 2016). If there are too many to control by hand-picking, especially in orchards and crops, insecticides can be applied. However, small amounts of insecticide residue on sprayed plants often are not adequate to kill these insects because of their ability to detox-ify plant chemicals and because adult lubbers are too large to be killed easily even with direct contact (Capinera and Scherer 2016). Insecticides containing carbaryl, bifenthrin, cyhalothrin, permethrin, and esfenvalerate as active ingredients will kill lubbers (Capinera and Scherer 2016), especially when applied directly on nymphs. Spinosad is a microbial product that is relatively safe to use where children or pets are concerned, but it is rather slow-acting, so results may not be apparent for a few days. A granular bait formulation containing 5% carbaryl (Mole Cricket Bait, Southern Agricultural Insecticides, Inc., Palmetto, FL) is effective for all stages, especially if applied in areas dominated by less preferred hosts (Barbara and Capinera 2003, Capinera 2014). Given the flightless nature of these insects, insecticide need not be applied broadly. Rather, a 1–20 m (3–60′) margin around the protected area can be treated to prevent entry by lubbers (Capinera and Scherer 2016). Insecticides should only be used according to label directions, especially near residential areas, water, or food crops.

Acknowledgment

G. E. Belovsky and J. A. Lockwood provided constructive comments on the manuscript. Work was supported by USDA Hatch project LAB 94214. This manuscript is published with approval of the Director of the Louisiana Agricultural Experiment Station, as manuscript number 2017-234-31527.

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© The Author(s) 2018. Published by Oxford University Press on behalf of Entomological Society of America. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), 1 which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com

Schowalter, T.D. 2018. Biology and management of the eastern lubber grasshopper (Orthoptera: Acrididae). Journal of Integrated Pest Management 9(1): 10; 1–7. doi.org/10.1093/jipm/pmy004.

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