HOUSEHOLD AND STRUCTURAL INSECTS Topical Toxicity of Essential Oils to the German Cockroach (Dictyoptera: Blattellidae) 1,2 1 3 ALICIA K. PHILLIPS, ARTHUR G. APPEL, AND STEVEN R. SIMS J. Econ. Entomol. 103(2): 448Ð459 (2010); DOI: 10.1603/EC09192 ABSTRACT The toxicity of 12 essential oil components [carvacrol, 1,8-cineole, trans-cinnamalde- Downloaded from https://academic.oup.com/jee/article/103/2/448/2199422 by guest on 28 September 2021 hyde, citronellic acid, eugenol, geraniol, S-(Ϫ)-limonene, (Ϫ)-linalool, (Ϫ)-menthone, (ϩ)-␣- pinene, (Ϫ)-␤-pinene, and thymol] to adult male; adult female; gravid female; and large, medium, and small nymphs of the German cockroach, Blattella germanica (L.) (Dictyoptera: Blattellidae), was determined. Thymol was the most toxic essential oil component to adult males, gravid females, and medium nymphs, with LD50 values of 0.07, 0.12, and 0.06 mg per cockroach, respectively. trans- Cinnamaldehyde was the most toxic essential oil component to adult females, large nymphs, and small ϩ ␣ nymphs, with LD50 values of 0.19, 0.12, and 0.04 mg per cockroach, respectively. ( )- -Pinene was the least toxic essential oil component to all stages of the German cockroach. The most frequently occurring susceptibility ranking for the stages was small nymphs Ͼ medium nymphs Ͼ adult males Ͼ large nymphs Ͼ gravid females Ͼ adult females. Adult females were the least susceptible to the essential oils, so they will be the determining factor when considering a rate for Þeld application. Toxicity was positively correlated with essential oil component density and boiling point; however, there was no signiÞcant correlation between toxicity and lipophilicity. The effect of essential oil components on ootheca hatch was also investigated. S-(Ϫ)-limonene had the least effect on ootheca hatch, with 35.21 (mean) nymphs hatching per ootheca. (Ϫ)-menthone had the greatest effect on ootheca hatch with 20.89 nymphs hatching per ootheca. The numbers of nymphs hatching from each ootheca generally declined as dose increased. No essential oil component completely prevented ootheca hatch suggesting that multiple treatments might be required in the Þeld to prevent reinfestation. KEY WORDS Blattella germanica, essential oils, toxicity, ootheca The German cockroach, Blattella germanica (L.) The publicÕs increasing concern about potentially (Dictyoptera: Blattellidae), is an important economic negative effects of traditional insecticides and the re- pest because its feces and exuviae can cause allergic stricted use of traditional insecticides in commercial reactions in sensitive people (Schal and Hamilton food preparation areas, storage buildings, apartments, 1990). It can also induce asthmatic reactions in asthma and homes (Barcay 2004) has stimulated the investi- sufferers (Kang 1976). German cockroaches can vec- gation of botanical alternatives. Essential oils are safer tor numerous microorganisms that are pathogenic to alternatives to traditional insecticides that could be humans and wildlife, including viruses, bacteria, pro- used in areas where traditional insecticides are pro- tozoa, and helminthes (Roth and Willis 1957, 1960). hibited. They are secondary plant substances (Isman The German cockroach also can cause psychological 2006) composed of many compounds, including problems. Some people experience delusory clepto- monoterpenoids, that are responsible for a plantÕs ar- parasitosis, imagining a home cockroach infestation omatic characteristics. They have been used in the that does not exist (Grace and Wood 1987). The Ger- past and are still used as fragrances for perfumes and man cockroach has a short generation time and high ßavorings for food items (Isman 2006). fecundity that makes it difÞcult to control. Its short Essential oils are an excellent alternative to tradi- generation time increases the chance of developing tional insecticides because of their low toxicity to resistance to insecticides used to manage populations humans and wildlife and short residual period (Isman (Barcay 2004). Populations of German cockroaches 2006). Compared with other botanical insecticides, have become resistant to the organochlorine, organo- such as neem and pyrethrum, the active ingredients of phosphate, carbamate, and pyrethroid classes of in- many essential oils are reasonably priced because they secticide (Scott et al. 1990). are commonly used as ßavors and fragrances (Isman 2006), but they usually require application at higher 1 Department of Entomology and Plant Pathology, Auburn Uni- rates than pyrethrum and neem-based insecticides. versity, 301 Funchess Hall, Auburn, AL 36849-5413. Minimum risk pesticides, which contain one or more 2 Corresponding author, e-mail: [email protected]. 3 BASF Pest Control Solutions, 3568 Tree Court Industrial Blvd., St. essential oils, are currently exempt from United States Louis, MO 63122-6682. Environmental Protection Agency registration re- 0022-0493/10/0448Ð0459$04.00/0 ᭧ 2010 Entomological Society of America April 2010 PHILLIPS ET AL.: TOPICAL TOXICITY OF ESSENTIAL OILS 449 quirements (EPA 2000). Insecticides that are exempt Insects. An insecticide susceptible strain of the Ger- from EPA registration requirements can reach the man cockroach was used in all experiments. This strain market faster than conventional insecticides (Isman (American Cyanamid, Clifton, NJ) has been in con- 2000). tinuous laboratory culture for Ͼ35 yr. The stages used Constituents of marjoram oil were tested against were adult males, adult females, gravid females, large female German cockroaches to determine if they nymphs (ÞfthÐseventh instars, Ն8.5 mm in length), could be used as insecticides (Jang et al. 2005). Results medium nymphs (thirdÐfourth instars, 5Ð8 mm in from the contact toxicity bioassay demonstrated that length), and small nymphs (ÞrstÐsecond instars, Յ4.5 1,8-cineole, linalool, ␣-terpineol, and thymol, the ma- mm in length). Laboratory cultures were maintained jor constituents of marjoram oil, were more toxic than at 28 Ϯ 2ЊC, 40Ð55% RH, and a photoperiod of 12:12 a conventional insecticide, propoxur, but less toxic (L:D) h. Colonies were provided water and dog chow than deltamethrin, dichlorvos, and permethrin (Jang (Purina, St. Louis, MO) as needed. Cockroaches were Ͻ Downloaded from https://academic.oup.com/jee/article/103/2/448/2199422 by guest on 28 September 2021 et al. 2005). brießy ( 5 min) anesthetized with CO2 to facilitate The toxicity and repellency of corn mint, Mentha handling during topical applications. Each stage of arvensis L., oil to American cockroaches, Periplaneta the German cockroach was weighed to determine americana (L.), and German cockroaches was deter- whether the difference in toxicity of each essential oil mined by Appel et al. (2001). Corn mint oil, containing component among the stages was due to signiÞcant menthol and menthone as main components, was re- differences in the mass of each stage. pellent and toxic to both species. The LD50 values for Topical Applications. Serial dilutions of essential oil corn mint oil were 10 ␮l of 2.57% for American cock- components were made in Fisher CertiÞed ACS ace- roaches and 2 ␮l of 3.83% for German cockroaches tone (99.7% purity; Fisher, Fair Lawn, NJ) to obtain (Appel et al. 2001). the desired concentrations of 0.05Ð0.5 mg per cock- Essential oils and their constituents have also been roach. A hand microapplicator (Burkard Manufactur- tested, for contact toxicity, against a variety of other ing Co., Hertfordshire, United Kingdom) was used to insects including the turnip aphid, Lipaphis pseudo- topically apply 1-␮l doses of essential oil solutions in brassicae (Davis) (Sampson et al. 2005); red imported acetone between the metathoracic legs of each cock- Þre ant, Solenopsis invicta (Buren) (Appel et al. 2004); roach. Control cockroaches were treated with 1 ␮lof confused ßour beetle, Tribolium confusum (Jacquelin acetone. Three replicates containing six cockroaches du Val) (Stamopoulos et al. 2007); granary weevil, each (total n ϭ 18) were used for each concentration. Sitophilus granarius (L.) (Kordali et al. 2006); lesser After treatment, the cockroaches were placed in grain borer, Rhyzopertha dominica (F.); rice weevil, 162.65-ml (5.5-oz) plastic cups (Georgia-PaciÞc, At- Sitophilus oryzae (L.); red ßour beetle, Tribolium cas- lanta, GA) and covered with a lid. Mortality was as- taneum (Herbst) (Rozman et al. 2007); and the human sessed at 24 h. head louse, Pediculus humanus capitis De Geer (Yang Effects of Essential Oils on Ootheca Hatch. After et al. 2004). Results demonstrated that all of the above- mortality was recorded for the topical application mentioned species were susceptible to several of the tests, the live and dead gravid females and the dropped essential oils and their constituents. oothecae were held individually in 50- by 9-mm trans- Because essential oils have a relatively short period parent plastic petri dishes (Becton Dickinson Lab- of residual activity (Isman 2006) the potential efÞcacy ware, Franklin Lakes, NJ) and observed every5dfor of these materials as active ingredients in contact spray 30 d. Mortality, ootheca drop, ootheca hatch, and the formulations for control of the German cockroach was number of nymphs present in each petri dish were investigated. The purpose of this study was to deter- recorded. Cockroaches were supplied with carrot mine and compare the toxicity of several pure essen- slices ad libitum and maintained in an incubator at tial oils to several life stages of the German cockroach.