Formulatio& Novodor and Raven, for Control of Cottonwood Leaf Beetle (Coleoptera: Chrysomelidae)

Laboratory and field experiments were conducted to determine the efficacy of two t~uring&x.sis Berliner formulations, Novodor and Raven, for controlling cottonwood leaf beetle, Cluysomekz scripta F. (Coleoptera: Chrysomelidae) . In laboratory bioassays, larvae or adults were added to petri dishes containing Pop&s X euramericunu Guinier ‘Eugenei’ foliage that had been treated with distilled water (control) or one of the commercial Bt formulations at either high or low label rates. Survival was recorded on a 24-h basis, and leaf area consumed was measured at the conclusion of all trials. Significant differences from the control in mortality and leaf area consumption resulted in the Novodor and Raven treatments for all life stages tested; however, adults were better able to withstand the effects of B. thuringiensis toxins than were the immatures. Earlyand late instar C. scripta populations were monitored in the field (1998 and 1999) after treatment with either water or various concentrations of one of the commercial Bt formulations. Significant mortality resulted with all concentrations and for all life stages tested compared with the control (tap water). The commercial formulations also were tested under plantation conditions as part of a long-term defoliation study. Both Novodor and Raven reduced cottonwood leaf beetle defoliation damage after a single application, giving high efficacy for control of cottonwood leaf beetle under the conditions and concentrations evaluated. K E Y W O R D S Chqsom& scripta, cottonwood leaf beetle, Bwdus thuringiensis, defoliation, mortality, short-rotation woody crops AS WENEAR the 21st century, additional fuel and energy resources are needed to accommodate the world’s growing population and industry. Short-rotation woody crop systems may provide a partial answer to these demands. Intensively managed monocultures of trees can produce large aounts of woody biomass for products or biofuels in a short time. Pop&s spp. show excellent potential for use in these systems because of their high biomass yield, regeneration ability, and well-developed agronomic techniques (Dickman and Stuart 1983, Zsuffa et al. 1996, Bauer 1997). Cottonwood leaf beetle, Chrymmelu scripta F. (Coleoptera: Chrysomelidae) is a major defoliator of young plantation Pop&s (Abrahamson et al. 1977, Head et al. 1977, Burkot and Benjamin 1979). Both larvae and adults prefer feeding on young, succulent leaf tissue (Bingaman and Hart 1992). A large proportion of young short-rotation woody crop Populus plantations is composed of trees with a higher percentage of preferred leaf tissue, and these trees are most susceptible to cottonwood leafbeetle damage during the This article presents the results of research only. Mention of a commercial or proprietary product does not constitute endorsement or recommendation by the USDA or Iowa State University for its use. ’ USDA Forest Service, Pact& Ranger District, Rapid City, SD 57702 ‘Abbott Laboratories, North Chicago, IL 60064-6316. first 3 yr of growth (Bingaman and Hart 1992, Augustin et al. 1997). Defoliation can result in reduced vigor and growth rate, increased susceptibility to insect and pathogen damage, or death of the individual terminal shoot or entire tree (Bassman et al. 1982). Carbofuran (Abrahamson et al. 1977)) chlorpyrifos (Page and Lyon 1976)) and carbaryl (James et al. 1999) have been used effectively for controlling cottonwood leaf beetle. However, chemical control is costly, can damage the environment, and is often looked upon negatively by the consumer or general public. Biorational control methods are both more preferred and accepted. Cottonwood leaf beetle has shown susceptibility to various Bacillus thurin~ensis Berliner (Bt ) Gendotoxins (Bauer and Pankratz 1992, Frederici and Bauer 1998, James et al. KEN), but few commercial formulations have been tested according to label application rates and directions. From an economical standpoint, it is necessary to know whether the products available to the consumer will work under field condiKons. Although a toxic Bt gene is currently -being evaluated in genetically engineered Pop&s (Bauer 1997)) these transgenic trees may not be available for some time, and certainly should not be relied upon for all plantings. Plantation managers and growers need more immediate control measures for C. scripta. Therefore, 714 J O U R N A L O F kONOMIC &TOMOLOCY Vol. 93, no. 3 our objectives were to test the efficacy of two commercially available Bt formulations, Novodor and Raven, for control of cottonwood leaf beetle. These formulations were evaluated according to label rates and directions. Materials and Metho& Iusects. All laboratory experiments (with the exception of the egg mass studies) used beetles from a laboratory colony started from adults received from Leah S. Bauer (USDA Forest Service, East Lansing, MI). Beetles were reared in ventilated plastic crisper containers (27 by 19 by 9 cm) with a photoperiod of 16:8 (L:D) h at a 24:18”C temperature regime. Colonies were fed greenhouse-grown Pqv1~1u.s X eurammicana Guinier ‘Eugenizi’ foliage. Foliage was replaced daily. Field experiments and egg mass studies used native Iowa cottonwood leaf beetle populations. Eugenei leaves with egg masses attached to them were picked in the field and brought immediately to the laboratory for treatment. &rciUu.s thuringimsis Formulations. Novodor (15,000 Leptinotarsai units [ LTU] /g formulation, 3% [AI] B. thuringien& ‘subsp. ten&r-ion& Cry3Aa toxin [Abbott Laboratori&$, North Chicago, IL] ) was one commercial formulatZon used. This product contained both spores and toxib, and was registered for use on Colorado potato beietle, Leptirwtarsa aTmen&eata (Say) (Coleoptera: Chrysomelidae) and elm leafbeetie, Pgrrhulta luteola (Miiller) (Coleopteraz Chrysomelidae). The label cited potatoes, tomatoes, and eggplant as the host range of L. demlineata. The host range listed for P. luteolu included shade trees and omamentals. Raven (1,300,000 LTU/g formulation, 10% [AI] B. thuringiensis subsp. kurstaki, CrylAc toxin [Ecogen, Langhome, PA]) was the second formulation evaluated, and also contained both spores and toxin. This strain contained a coieopteran active toxin (8% [AI] ) that worked synergistically with a lepidopteran active toxin (2% [AI] ) . Th& product was registered for use on L. decemlineata, yhose host range also was listed as potatoes, tomatoes, wd eggplant. Laboratory Trials. For all trials, six cottonwood leaf beetle life stages were tested: egg masses, neonate ( <24 h posthatch), second instar (4 d old), third instar (6 d old), newly emerged adult (<24 h postemergence), and mature adult (10 d postemergence). Mature adults were reared using Eugenei leaves from pupal emergence until experimental trials. Whole Eugenei leaves of the same phenological development stage (e.g., leaf plastbchron index [LPI] = 3, Larson and Isebrands 1971); were used for the larvae and adults because leaves at this stage are the most highly preferred for feeding (Bingaman and Hart 1992). Egg masses or leaves were treated with a hand-held Plant & Garden Sprayer (Sprayco, Detroit, MI) rather than dipped because a protocol simulating field-like application was desired. Novodor treatments included 1.25 and 5.00% solutions ‘(125 and 500 mg Novodor, respectively, in 1 liter of distilled water). Distilled water served as the control. These solutions represented the range of recommended label application rates (1.25% = 2.34 liter/ha [l qtlacre], 5.00% = 9.36 liter/ha [4 qt/acre]) for light or single-aged cottonwood leaf beetle infestations. Raven treatments included 0.625% (62.5 mg Raven in 1 liter of distilled water) and 3.75% (375 mg Raven in 1 liter of distilled water) solutions, and a distilled water control. These solutions also represented the range of recommended label application rates (0.625% = 1.17 liter/ha [0.5 qt/acre], 3.75% = 7.02 liter/ ha [ 3 qtlacre] ) . One spray was applied per leaf side and the solution was allowed to air-dry for I5 min. Leaves, along with egg masses, larvae (five neonate or second instars, or three third instars), or three adults were placed in petri dishes with moistened Whatman #l filter paper (Whatman, Hillsboro, OR). Filter paper was moistened daily with distilled water to prevent leaf and insect desiccation. Neonate, second, and third instars did not receive new leaves throughout the experiment. New, untreated leaves were added to petri dishes containing both freshly emerged and mature adults every 48 h if there were any surviving insects. New leaf tissue was added because the control insects had nearly run out of leaf material at this time. Fifteen replications were included for all treatments and the control, and were arranged in a randomized complete block design inside a growth chamber under a photoperiod of l&8 (LD) h and 24:18’C temperature regime. Mortality was recorded at 24,48,72,96, and 168 h after application, or until 100% mortality occurred in the Bt treatments. Third-instar pupation and adult emergence were recorded and compared with that of the control. Total leaf area consumed (cm’) was recorded at the conclusion of all larval and adult trials using a Delta T area meter (Decagon Devices, Pullman, WA). 1998 Field Trials. Field experiments were conducted near the Iowa State University Institute for Physical Research and Technology (IPRT) , Ames, IA, on a mixture of I-yr-old hybrid poplar (Pupulus spp.) clones. Novodor treatments included 5.00% (500 mg Novodor in 1 liter of tap water) and 2.50% (250 mg Novodor in 1 liter of tap water) solutions and tap water alone (control). These Novodor solutions represented the range of recommended label application rates (2.50% = 4.68 liter/ha [2 qtlacre], 5.00% = 9.36 liter/ha [4 St/acre]) for heavy or mixed (both larvae and adults present) populations of cottonwood leaf beetles. Novodor was applied with a backpack sprayer (Solo, Newport News, VA) at 40 psi over the entire tree to the point of wetting. Ten replications (one C scripta larval cohort each) were included for each treatment. Five of the 10 replications used first instar populations and the other five replications used second or third instar populations, or a combination of second and third instar populations. In addition to the field efficacy trials, Novodor was evaluated under field conditions as part of an ongoing study designed to compare the effects of cottonwood leaf beetle defoliation on the long-term (6-8 yr) growth of four hybrid poplar clones. Using a split plot June 2006 COYLE ET AL.: CONTROL OF C. scripta wm~ I?. thutingiensis 7 1 5 Table 1. Larvalhateh(meanfSE) an d mortality of cottonwood leafbeetle larvae 24 and 48 h after treatment (mean *SE) in l&oratory #ludlea where egg masses were treated F0tmulati0!l Cone, % Larval hatch, % Mortality at 24 h a&r treatment, % Mortality at 48 h