Topical Toxicity of Essential Oils to the German Cockroach (Dictyoptera: Blattellidae)

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. Ϸ80% RH and Ϸ28ЊC. The carrot slice provided both food and moisture. Data Analysis. One-way analysis of variance (ANOVA) and TukeyÕs multiple comparison tests Materials and Methods were used to determine the signiÞcance of differences Chemicals. Essential oil components (Table 1) in body mass among stages (Proc GLM, SAS 9.1, SAS were obtained from Sigma-Aldrich (St. Louis, MO; Institute 2003). Probit analysis for independent data http://www.sigmaaldrich.com). Some of the essential was used to estimate toxicity in the topical application oil components were chosen because they are present tests (LD50) (Proc Probit, SAS 9.1, SAS Institute in the essential oil extracts of numerous plant species, 2003). Nonoverlap of the 95% conÞdence intervals whereas others were chosen because they occur at (CIs) was used to estimate signiÞcant differences high concentrations in the essential oils of selected among LD50 values. A t-test was used to test for sig- plants. Both aromatic and aliphatic hydrocarbons niÞcant differences in the mean number of hatched were tested; the functional groups represented in- nymphs for control and treated females (Proc Ttest, cluded acids, alcohols, aldehydes, ketones, and ethers. SAS 9.1, SAS Institute 2003). One-way ANOVA and Physical and chemical properties of essential oil com- TukeyÕs multiple comparison tests were used to study ponents were either obtained from Sigma-Aldrich or differences in the number of nymphs responding to estimated using Advanced Chemistry Development doses of individual essential oils (Proc GLM, SAS 9.1, software version 12.0 (ACD Labs 2008). SAS Institute 2003). Regression analysis was used to Table 1. Essential oil components J 450

Physical and chemical properties a b Oil component Structure Derivation Density Assay Boiling Vapor pressure Solubility Log Pa (g/ml)c (%)c point (ЊC)c (mmHg at 25ЊC)a (g/liter water)a

Carvacrol Thyme plant 3.16 0.98 98 236 0.030 0.96

1,8-Cineole Eucalyptus trees 2.8 0.92 99 176 1.648 0.91 OF OURNAL

trans-Cinnamaldehyde Bark of cinnamon trees 1.9 1.05 99 250 0.027 2.98 E CONOMIC

Stems and leaves of Citronellic acid 3.16 0.92 98 121 0.005 200.41 citronella grass E NTOMOLOGY

Dried ßower buds of Eugenol 2.4 1.07 99 254 0.010 1.79 clove trees

Geraniol Petals of various roses 2.94 0.88 98 229 0.013 0.9 Geraniums Lemongrass

S-(Ϫ)-Limonene Rind of citrus fruits 4.55 0.84 Ն95 175 1.541 0.0034

(Ϫ)-Linalool Sweet basil 2.79 0.86 Ն95 198 0.091 1.03 Plants in Lauraceae family o.13 o 2 no. 103, Vol.

(Ϫ)-Menthone Peppermint plant 2.75 0.89 90 207 0.256 0.85 Downloaded from https://academic.oup.com/jee/article/103/2/448/2199422 by guest on 28 September 2021 September 28 on guest by https://academic.oup.com/jee/article/103/2/448/2199422 from Downloaded April 2010 PHILLIPS ET AL.: TOPICAL TOXICITY OF ESSENTIAL OILS 451

a Table 2. Mean masses of German cockroach stages measured in grams

Stage n Mean Ϯ SDa

Solubility Adult females 30 0.0861 Ϯ 0.0140a (g/liter water) Gravid females 30 0.0853 Ϯ 0.0110a Large nymphs 30 0.0452 Ϯ 0.0080b Adult males 30 0.0443 Ϯ 0.0042b

a Medium nymphs 30 0.0105 Ϯ 0.0037c

C) Ϯ

Њ Small nymphs 30 0.0015 0.0009d

a Means within a column followed by the same letter are not signiÞcantly different (P Ͻ 0.05). Vapor pressure Downloaded from https://academic.oup.com/jee/article/103/2/448/2199422 by guest on 28 September 2021 (mmHg at 25

Timmer et al. (1971), Antonelli et al. (1997), examine the linear relationship between doses applied

c to gravid females and the mean number of hatched or et al. (2004), respectively. C) Њ nymphs, percentage of dropped oothecae, and percentage of hatched oothecae (SigmaPlot 11.0, SPSS Boiling

point ( Inc. 2008). Correlation analysis was used to relate essential oil toxicity with physical and chemical properties (SigmaPlot 11.0, SPSS Inc. 2008). Physical and chemical properties c (%) Assay Results

c Body Mass. Differences in body mass among stages were signiÞcant (P Ͻ 0.0001), with the exception be- Density (g/ml) tween adult males and large nymphs and adult and gravid females (Table 2). Topical Applications. No control mortality was ob- a served for any stage during the 24-h test period. Car-

vacrol had LD50 values ranging from 0.06 to 0.19 mg Log P per cockroach for small nymphs and adult females, respectively (see Tables 4 and 8). Homogeneity of response (slope of the log-dose probit relationship) was similar among adult stages (6.42, 6.94, and 6.69 for adult males, adult females, and gravid females, respec- b tively; Tables 3Ð5), but as a group, approximately twice that of immature stages (Tables 6Ð8).

The LD50 values of 1,8-cineole ranged from 0.13 mg Derivation per cockroach for small nymphs to 0.51 mg per cockroach for gravid females (Tables 5 and 8). Homoge-

Pine treesPine treesThyme plants 4.32 0.86 4.24 3.25 98neity 0.87 of 0.97 response 99 155 99 was 165 greatest 3.489 233 for 2.399 adult 0.0089 males 0.038 (7.87) 0.0106 0.87 and least for small nymphs (2.49) (Tables 3 and 8).

Trans-Cinnamaldehyde had LD50 values ranging from 0.04 to 0.19 mg per cockroach for small nymphs and adult females, respectively (Tables 4 and 8). Homogeneity of

a response was greatest for adult males (12.62) and least for small nymphs (4.93) (Tables 3 and 8).

The LD50 values of citronellic acid ranged from 0.13 to 0.64 mg per cockroach for small and large nymphs, respectively (Tables 6 and 8). Homogeneity of response was similar among all stages (3.62, 2.14, 3.83, 3.03, 4.05, and 2.27 for adult males, adult females, gravid females, large nymphs, medium nymphs, and small nymphs, respectively) (Tables 3Ð8).

The LD50 values for eugenol ranged from 0.07 mg per cockroach for small nymphs to 0.29 mg per cockroach for adult females (Tables 4 and 8). Homogeneity of response was similar for adult females, medium

-Pinene -Pinene nymphs, and small nymphs (4.19, 4.20, and 4.42 for

␣ ␤ Oil component Structure Compounds were described by Mockute and Bernotiene (1999); Yang et al. (2004); Senanayake et al. (1978); Nakahara et al. (2003); Park and Shin (2005); ACD/Labs (2008). Sigma-Aldrich (St. Louis, MO). )- )- Table 1. Continued adult females, medium nymphs, and small nymphs, a b c Ϫ ϩ and Dudai et al. (2001); Usai et al. (1992); Caredda et al. (2002) and Yousif et al. (1999); Baldinger (1942); Palmer (1942); Palmer (1942); and Sotomay ( Thymol ( respectively) (Tables 4, 7, and 8). 452 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 103, no. 2

Table 3. Toxicity of essential oils applied topically to adult male German cockroaches

Ϯ ␹2 Essential oil n Slope SE LD50, mg/cockroach (95% CI) P Carvacrol 108 6.42 Ϯ 1.36 0.101 (0.084Ð0.122) 22.32 0.0001 1,8-Cineole 108 7.87 Ϯ 1.59 0.156 (0.131Ð0.181) 24.57 0.0001 trans-Cinnamaldehyde 234 12.62 Ϯ 2.70 0.078 (0.071Ð0.086) 21.88 0.0001 Citronellic acid 126 3.62 Ϯ 1.08 0.252 (0.149Ð0.391) 11.17 0.0008 Eugenol 108 6.42 Ϯ 1.36 0.109 (0.091Ð0.132) 22.31 0.0001 Geraniol 126 4.79 Ϯ 0.95 0.262 (0.219Ð0.305) 25.73 0.0001 S-(Ϫ)-Limonene 126 5.45 Ϯ 1.94 0.285 (0.183Ð0.406) 7.91 0.0049 (Ϫ)-Linalool 126 6.86 Ϯ 1.41 0.316 (0.279Ð0.358) 23.75 0.0001 (Ϫ)-Menthone 126 3.71 Ϯ 1.60 0.126 (0.025Ð0.160) 5.35 0.0207 (ϩ)-␣-Pinene 126 4.49 Ϯ 2.16 0.644 (0.463Ð11293.438) 4.32 0.0377 (Ϫ)-␤-Pinene 126 3.57 Ϯ 1.45 0.481 (0.351Ð8.434) 5.98 0.0144

Thymol 198 23.10 Ϯ 7.03 0.070 (0.063Ð0.073) 10.81 0.0010 Downloaded from https://academic.oup.com/jee/article/103/2/448/2199422 by guest on 28 September 2021

The LD50 values of geraniol ranged from 0.05 to 0.83 cockroach. LD50 values for adult males were 0.48 and mg per cockroach for small nymphs and adult females, 0.64 mg per cockroach, respectively (Table 3). Ho- respectively (Tables 4 and 8). Homogeneity of re- mogeneity of response for adult males for (Ϫ)-␤- sponse was greatest for gravid females (5.13) and least pinene and (ϩ)-␣-pinene was 3.57 and 4.49, respec- for large nymphs (1.79) (Tables 5 and 6). tively (Table 3). Ϫ The LD50 values for S-( )-limonene ranged from 0.06 The LD50 values of thymol ranged from 0.05 mg per mg per cockroach for small nymphs to 0.60 mg per cock- cockroach for small nymphs to 0.22 mg per cockroach roach for large nymphs (Tables 6 and 8), but S-(Ϫ)- for large nymphs (Tables 6 and 8). Homogeneity of limonene was not signiÞcantly toxic to adult females or response was greatest for adult males (23.10) and least gravid females (PϾ0.05) (Tables 4 and 5). Homogeneity for medium nymphs (1.85) (Tables 3 and 7). of response was greatest for adult males (5.45) and least Ootheca Hatch. Combining all doses for each es- for adult females (0.85) (Tables 3 and 4). sential oil component, there were signiÞcant differ- Ϫ The LD50 values for ( )-linalool ranged 0.10 mg per ences in the numbers of nymphs hatching from ooth- cockroach for small nymphs to 0.32 mg per cockroach ecae attached to gravid females treated with essential for adult males (Tables 3 and 8); however, (Ϫ)-lina- oil. The percentage of oothecae that dropped before lool was not toxic to adult females, gravid females, and hatch for the control treatment, the percentage of large nymphs at doses up to 0.45 mg per cockroach. oothecae that hatched for the control treatment, and Homogeneity of response for adult males, medium the mean number of nymphs that emerged from ooth- nymphs, and small nymphs was 6.86, 3.61, and 3.64, ecae attached to control females was 93.79 Ϯ 0.02, respectively (Tables 3, 7, and 8). 93.79 Ϯ 0.02, and 31.65 Ϯ 0.83, respectively. The per- Ϫ The LD50 values of ( )-menthone ranged from 0.06 centage of oothecae that dropped before hatch for to 0.77 mg per cockroach for small nymphs and adult essential oil components ranged from 32.71 Ϯ 0.05 for females, respectively (Tables 4 and 8). Homogeneity thymol to 100 for S-(Ϫ)-limonene (Fig. 1b). The per- of response was similar among all stages (3.71, 4.19, centage of oothecae that hatched for the essential oil 3.04, 4.51, 4.48, and 2.28 for adult males, adult females, components ranged from 72.22 Ϯ 0.04 for (Ϫ)-men- gravid females, large nymphs, medium nymphs, and thone to 95.33 Ϯ 0.02 for S-(Ϫ)-limonene (Fig. 2b). small nymphs, respectively) (Tables 3Ð8). The mean number of nymphs that emerged from ooth- Both (Ϫ)-␤-pinene and (ϩ)-␣-pinene were slightly ecae attached to females treated with essential oil toxic to adult males, but neither were toxic, to adult components ranged from 20.89 Ϯ 1.38 to 35.21 Ϯ 1.08 females, gravid females, large nymphs, medium for (Ϫ)-menthone and S-(Ϫ)-limonene, respectively nymphs, or small nymphs at doses up to 0.44 mg per (Fig. 3b). Oothecae that were attached to females

Table 4. Toxicity of essential oils applied topically to adult female German cockroaches

Ϯ ␹2 Essential oil n Slope SE LD50, mg/cockroach (95% CI) P Carvacrol 108 6.94 Ϯ 1.30 0.186 (0.156Ð0.214) 28.60 0.0001 1,8-Cineole 108 3.30 Ϯ 1.11 0.273 (0.164Ð0.531) 8.86 0.0029 trans-Cinnamaldehyde 126 7.68 Ϯ 1.53 0.188 (0.158Ð0.216) 25.23 0.0001 Citronellic acid 126 2.14 Ϯ 0.64 0.491 (0.337Ð1.298) 11.28 0.0008 Eugenol 108 4.19 Ϯ 0.77 0.294 (0.244Ð0.349) 29.53 0.0001 Geraniol 126 1.86 Ϯ 0.66 0.832 (0.477Ð11.840) 8.00 0.0047 S-(Ϫ)-Limonene 126 Ͼ0.50a 0.4579 (Ϫ)-Linalool 126 Ͼ0.50a 0.0747 (Ϫ)-Menthone 90 4.19 Ϯ 1.83 0.773 (0.628Ð6.047) 5.23 0.0222 (ϩ)-␣-Pinene 126 Ͼ0.50a 0.7931 (Ϫ)-␤-Pinene 126 0 Ͼ0.50a Thymol 108 2.88 Ϯ 0.68 0.195 (0.122Ð0.280) 17.84 0.0001

a Probit model did not work because Ͻ20% mortality occurred. April 2010 PHILLIPS ET AL.: TOPICAL TOXICITY OF ESSENTIAL OILS 453

Table 5. Toxicity of essential oils applied topically to gravid female German cockroaches

Ϯ ␹2 Essential oil n Slope SE LD50, mg/cockroach (95% CI) P Carvacrol 126 6.69 Ϯ 1.23 0.146 (0.121Ð0.171) 29.56 0.0001 1,8-Cineole 126 3.61 Ϯ 1.10 0.507 (0.400Ð1.023) 10.75 0.0010 trans-Cinnamaldehyde 126 8.02 Ϯ 1.79 0.133 (0.112Ð0.157) 20.12 0.0001 Citronellic acid 126 3.83 Ϯ 1.25 0.518 (0.411Ð1.140) 9.34 0.0022 Eugenol 126 8.73 Ϯ 2.05 0.287 (0.232Ð0.333) 18.17 0.0001 Geraniol 126 5.13 Ϯ 1.61 0.452 (0.382Ð0.722) 10.19 0.0014 S-(Ϫ)-Limonene 126 Ͼ0.50a 0.3215 (Ϫ)-Linalool 126 Ͼ0.50a 0.9999 (Ϫ)-Menthone 126 3.04 Ϯ 1.33 0.395 (0.226Ð23.295) 5.21 0.0224 (ϩ)-␣-Pinene 126 0 Ͼ0.50a (Ϫ)-␤-Pinene 126 Ͼ0.50a 0.3215

Thymol 126 4.77 Ϯ 1.08 0.122 (0.082Ð0.164) 19.36 0.0001 Downloaded from https://academic.oup.com/jee/article/103/2/448/2199422 by guest on 28 September 2021

a Probit model did not work because Ͻ20% mortality occurred. treated with S-(Ϫ)-limonene had a signiÞcantly nymphs decreased linearly with increasing dose and greater mean number of nymphs (35.21 Ϯ 1.08) hatch this relationship was highly signiÞcant [mean number than oothecae attached to females treated with other of nymphs ϭ 35.13 (Ϯ0.81) Ϫ 21.46 (Ϯ2.73) dose, r2 ϭ essential oil components; therefore, S-(Ϫ)-limonene 0.93 (F ϭ 61.95; df ϭ 1, 5; P ϭϽ0.001)] (Table 9). treatment had the least effect on ootheca hatch (Fig. The mean number of nymphs that emerged from 3a and b). Oothecae that were attached to females oothecae attached to citronellic acid-treated females treated with (Ϫ)-menthone had a signiÞcantly lower ranged from 33.33 Ϯ 1.08 to 18.89 Ϯ 3.75 for 0 and 0.47 mean number of nymphs (20.89 Ϯ 1.38) hatch than mg per cockroach, respectively (Fig. 3a). SigniÞcantly oothecae attached to females treated with the other fewer nymphs hatched for 0.47 mg per cockroach essential oil components; therefore, the (Ϫ)-men- (18.89 nymphs) than 0 mg per cockroach (33.33 thone treatment had the greatest effect on ootheca nymphs) and for 0.47 mg per cockroach (18.89 hatch (Fig. 3a and b). The essential oil components nymphs) than 0.09 mg per cockroach (31.50 nymphs) having the greatest to least effect on ootheca hatch (Fig. 3a). The number of nymphs decreased linearly were (Ϫ)-menthone Ͼ geraniol Ͼ thymol Ͼ 1,8-cin- with increasing dose [mean number of nymphs ϭ eole Ͼ citronellic acid Ͼ (Ϫ)-linalool Ͼ eugenol Ͼ 31.20 (Ϯ2.04) Ϫ 23.58 (Ϯ7.72) dose, r2 ϭ 0.65 (F ϭ (Ϫ)-␤-pinene Ͼ carvacrol Ͼ trans-cinnamaldehyde ϭ 9.34; df ϭ 1, 5; P ϭ 0.028)] (Table 9). (ϩ)-␣-pinene Ͼ S-(Ϫ)-limonene (Fig. 3a and b). The mean number of nymphs that emerged from The mean number of nymphs that emerged from oothecae attached to geraniol-treated females ranged oothecae attached to carvacrol-treated females from 29.28 Ϯ 2.62 to 18.94 Ϯ 3.44 for 0 and 0.44 mg per ranged from 32.06 Ϯ 2.51 to 13.94 Ϯ 3.77 for 0 and 0.50 cockroach, respectively (Fig. 3a). SigniÞcantly fewer mg per cockroach, respectively (Fig. 3a). The number nymphs hatched for 0.36 mg per cockroach (15.61 of hatched nymphs was not signiÞcantly different be- nymphs) than 0 mg per cockroach (29.28 nymphs) tween 0 and 0.40 mg per cockroach; however, signif- (Fig. 3a). The number of nymphs decreased linearly icantly fewer nymphs hatched for 0.50 mg per cock- with increasing dose [mean number of nymphs ϭ roach (13.94 nymphs) than for all other doses (Fig. 28.04 (Ϯ1.94) Ϫ 23.38 (Ϯ7.67) dose, r2 ϭ 0.65 (F ϭ 3a). 9.30; df ϭ 1, 5; P ϭ 0.028)] (Table 9). The mean number of nymphs that emerged from The mean number of nymphs that emerged from trans-cinnamaldehyde-treated females ranged from oothecae attached to (Ϫ)-menthone-treated females 35.06 Ϯ 1.47 to 24.11 Ϯ 3.16 for 0 and 0.53 mg per ranged from 32.11 Ϯ 2.24 to 14.61 Ϯ 3.36 for 0 and 0.50 cockroach, respectively (Fig. 3a). The number of mg per cockroach, respectively (Fig. 3b). SigniÞcantly

Table 6. Toxicity of essential oils applied topically to large nymph German cockroaches

Ϯ ␹2 Essential oil n Slope SE LD50, mg/cockroach (95% CI) P Carvacrol 108 3.84 Ϯ 0.59 0.129 (0.102Ð0.157) 42.57 0.0001 1,8-Cineole 108 6.11 Ϯ 1.26 0.333 (0.292Ð0.386) 23.55 0.0001 trans-Cinnamaldehyde 198 10.43 Ϯ 2.66 0.117 (0.110Ð0.131) 15.37 0.0001 Citronellic acid 108 3.03 Ϯ 1.07 0.643 (0.458Ð2.968) 8.10 0.0044 Eugenol 108 3.68 Ϯ 0.64 0.246 (0.199Ð0.296) 33.39 0.0001 Geraniol 126 1.79 Ϯ 0.57 0.736 (0.441Ð4.700) 9.92 0.0016 S-(Ϫ)-Limonene 126 4.40 Ϯ 1.91 0.598 (0.447Ð13.565) 5.28 0.0216 (Ϫ)-Linalool 126 Ͼ0.50a 0.4820 (Ϫ)-Menthone 126 4.51 Ϯ 1.04 0.370 (0.315Ð0.456) 18.75 0.0001 (ϩ)-␣-Pinene 126 0 Ͼ0.50a (Ϫ)-␤-Pinene 126 0 Ͼ0.50a Thymol 108 2.65 Ϯ 0.48 0.220 (0.169Ð0.280) 29.67 0.0001

a Probit model did not work because Ͻ20% mortality occurred. 454 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 103, no. 2

Table 7. Toxicity of essential oils applied topically to medium nymph German cockroaches

Ϯ ␹2 Essential oil n Slope SE LD50, mg/cockroach (95% CI) P Carvacrol 108 3.35 Ϯ 1.33 0.061 (0.005Ð0.107) 6.37 0.0116 1,8-Cineole 108 3.93 Ϯ 1.03 0.208 (0.133Ð0.285) 14.58 0.0001 trans-Cinnamaldehyde 198 10.92 Ϯ 2.37 0.082 (0.074Ð0.087) 21.24 0.0001 citronellic acid 108 4.05 Ϯ 0.76 0.248 (0.203Ð0.295) 28.72 0.0001 Eugenol 108 4.20 Ϯ 0.71 0.109 (0.086Ð0.134) 34.86 0.0001 Geraniol 126 2.99 Ϯ 0.49 0.145 (0.110Ð0.181) 36.63 0.0001 S-(Ϫ)-Limonene 126 4.49 Ϯ 0.77 0.207 (0.170Ð0.243) 34.03 0.0001 (Ϫ)-Linalool 126 3.61 Ϯ 0.72 0.195 (0.142Ð0.255) 24.83 0.0001 (Ϫ)-Menthone 126 4.48 Ϯ 1.03 0.175 (0.120Ð0.234) 19.07 0.0001 (ϩ)-␣-Pinene 126 0 Ͼ0.50a (Ϫ)-␤-Pinene 126 0 Ͼ0.50a

Thymol 90 1.85 Ϯ 0.48 0.060 (0.023Ð0.092) 14.95 0.0001 Downloaded from https://academic.oup.com/jee/article/103/2/448/2199422 by guest on 28 September 2021

a Probit model did not work because Ͻ20% mortality occurred. fewer nymphs hatched for 0.40 mg per cockroach The toxicity of each essential oil component dif- (18.33 nymphs) than 0 mg per cockroach (32.11 fered among the stages. We used one-way ANOVA nymphs), and for 0.50 mg per cockroach (14.61 and TukeyÕs multiple comparison tests to verify that nymphs) than 0 mg per cockroach (32.11 nymphs) there were signiÞcant differences in body mass among (Fig. 3b). The number of nymphs decreased linearly stages (P Ͻ 0.0001). The most frequently occurring with increasing dose [mean number of nymphs ϭ susceptibility ranking for the stages was small 28.04 (Ϯ2.35) Ϫ 25.07 (Ϯ8.38) dose, r2 ϭ 0.642 (F ϭ nymphs Ͼ medium nymphs Ͼ adult males Ͼ large 8.948; df ϭ 1, 5; P ϭ 0.030)] (Table 9). There were no nymphs Ͼ gravid females Ͼ adult females. Suscepti- signiÞcant effects (P Ͼ 0.05) of 1,8-cineole, eugenol, bility differences were positively correlated to the S-(Ϫ)-limonene, (Ϫ)-linalool, (ϩ)-␣-pinene, (Ϫ)-␤- mass of each insect stage, but not proportionally. Our pinene, and thymol on ootheca hatch (Fig. 3a and b). general results are consistent with the studies of Gish and Chura (1970), who found that animals with a larger body mass were less susceptible to insecticides Discussion (Table 2). Toxicity. Trans-cinnamaldehyde, thymol, eugenol, Adult females and large nymphs have greater pro- and carvacrol were the most toxic essential oil com- portions of body lipid than gravid females and adult ponents to adult and large and medium nymphs of the males, respectively (Abd-Elghafar et al. 1990). The German cockroach. Trans-cinnamaldehyde, thymol, lipid-soluble oils may become trapped in body lipid, geraniol, and carvacrol were the most toxic essential inhibiting the oils from reaching the target site (Yu oil components to small nymphs. The topical toxicity 2008). In addition, stage-dependent susceptibility also of the four most toxic essential oil components was less may be the result of different metabolic rates. Valles than those of the conventional insecticides, such as at al. (1996) found that nymphs were more tolerant to ϭ ␮ permethrin (LD50 0.072 g per cockroach), delta- propoxur because they were able to metabolize it ϭ ␮ methrin (LD50 0.006 g per cockroach) (Pridgeon faster that adults; nymphs have higher levels of cyto- ϭ ␮ et al. 2002), and bendiocarb (LD50 0.36 g per chrome P450 (detoxifying enzymes) than adults cockroach) (Scott et al. 1990). These results are con- (Valles et al. 1994, 1996). Therefore, because the sistent with those reported by Jang et al. (2005), who stages metabolize xenobiotics differently and not pro- demonstrated that components of marjoram oil were portionally with body mass, we report toxicity in units less toxic than permethrin and deltamethrin to adult of mg per cockroach similar to Pridgeon et al. (2002). female German cockroaches. Because adult females require the greatest dose of

Table 8. Toxicity of essential oils applied topically to small nymph German cockroaches

Ϯ ␹2 Essential oil n Slope SE LD50, mg/cockroach (95% CI) P Carvacrol 90 3.50 Ϯ 1.32 0.056 (0.007Ð0.091) 7.00 0.0081 1,8-Cineole 90 2.49 Ϯ 0.48 0.133 (0.096Ð0.175) 26.68 0.0001 trans-Cinnamaldehyde 198 4.93 Ϯ 0.98 0.036 (0.031Ð0.042) 25.36 0.0001 Citronellic acid 108 2.27 Ϯ 0.51 0.131 (0.075Ð0.188) 19.61 0.0001 Eugenol 90 4.42 Ϯ 1.04 0.066 (0.047Ð0.083) 18.19 0.0001 Geraniol 126 3.00 Ϯ 0.70 0.049 (0.028Ð0.067) 18.64 0.0001 S-(Ϫ)-Limonene 126 1.68 Ϯ 0.41 0.057 (0.022Ð0.088) 17.28 0.0001 (Ϫ)-Linalool 126 3.64 Ϯ 0.59 0.096 (0.074Ð0.119) 38.60 0.0001 (Ϫ)-Menthone 126 2.28 Ϯ 0.48 0.060 (0.031Ð0.086) 22.76 0.0001 (ϩ)-␣-Pinene 126 0 Ͼ0.50a (Ϫ)-␤-Pinene 126 0 Ͼ0.50a Thymol 90 4.94 Ϯ 1.73 0.047 (0.023Ð0.059) 8.08 0.0045

a Probit model did not work because Ͻ20% mortality occurred. April 2010 PHILLIPS ET AL.: TOPICAL TOXICITY OF ESSENTIAL OILS 455 Downloaded from https://academic.oup.com/jee/article/103/2/448/2199422 by guest on 28 September 2021

Fig. 1. Effect of dose on the percentage of dropped Fig. 2. Effect of dose on the percentage of hatched oothecae. oothecae. essential oil for mortality to occur, they should be the fect penetration through the cuticle, degradation of determining factor when selecting Þeld application the essential oil component, movement of the com- rates. pound to the target site (Rice and Coats 1994), and the The Pearson product-moment correlation was used ability of the insect to excrete the compound. The to determine the correlation between toxicity and most toxic essential oil components to the majority of physical properties of the essential oils. LD50 values of cockroach stages were aromatic rather than aliphatic all stages were correlated negatively with the density compounds. These compounds included carvacrol, (grams per milliliter) of the essential oil components trans-cinnamaldehyde, eugenol, and thymol. The most (r ϭϪ0.421, P ϭ 0.0011). The density of the essential toxic essential oil components to small nymphs were oil components may effect the penetration of the com- carvacrol, trans-cinnamaldehyde, geraniol (aliphatic), pounds through the cuticle. Essential oil components and thymol. Benzene is a relatively nonpolar com- with high densities were generally more toxic than pound due to the delocalization of electrons in the those with low densities. LD50 values of all stages were ring (Morrison and Boyd 1992). Metabolism of aro- negatively correlated with the boiling point of the matic compounds is relatively difÞcult because detox- essential oil components (r ϭϪ0.389, P ϭ 0.0028). The iÞcation involves a series of processes that make the boiling point of a compound reßects the strength of compound more hydrophilic and polar so that it can intermolecular forces, such as dipole-dipole forces be easily excreted (Yu 2008). Therefore, essential oil and hydrogen bonds. It represents the temperature at components containing a benzene ring are not easily which the molecules of the compound hold enough metabolized and detoxiÞed in the insect body. Be- energy to overcome the intermolecular forces holding cause the aromatic compounds are not easily metab- the molecules together (Chang 2003). A compound olized, they are more toxic than aliphatic compounds. with a low boiling point evaporates more rapidly than Our results are consistent with those of Rice and Coats a compound with a high boiling point, which would (1994) who found that aromatic alcohols were more make it less available for penetration through the in- toxic than aliphatic alcohols to the house ßy, Musca sect cuticle. domestica (L.). Structural characteristics such as chemical class, We found that monocyclic aliphatic compounds saturation, and lipophilicity also may contribute to the tended to be more toxic than bicyclic aliphatic com- toxicity of compounds. These characteristics can af- pounds to all stages of the German cockroach. Rice 456 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 103, no. 2

strained state caused by lack of ßexibility (Morrison and Boyd 1992). The chemical bonds may be inclined to break more easily in response to detoxifying enzyme activity, which could lead to faster degradation in the insect body. 1,8,-Cineole is a bicyclic compound consisting of two six-membered carbon rings, which would make it more ßexible than (ϩ)-␣-pinene and (Ϫ)-␤-pinene but less ßexible than a six-membered monocyclic carbon ring; however, the toxicity of 1,8- cineole was not consistently lower than that of the monocyclic compounds for all stages. Compound saturation affected toxicity to German cockroaches. The saturated essential oil components Downloaded from https://academic.oup.com/jee/article/103/2/448/2199422 by guest on 28 September 2021 used in this study contained only single bonds, with the exception of double bonds present in the benzene ring. The unsaturated components used contained at least one double bond other than the double bonds present in the benzene ring. Saturated components, such as thymol and carvacrol, were highly, or moder- ately, toxic to all stages of the German cockroach. The majority of the components with low toxicity were unsaturated compounds, such as (ϩ)-␣-pinene and (Ϫ)-␤-pinene. Multiple unsaturated compounds did not decrease toxicity. The degree of compound saturation may affect degradation in the insect body. It is possible that the unsaturated compounds are unable to group as closely together as the saturated compounds (Tortora et al. 2007), due to steric hindrance (Morrison and Boyd 1992). Steric hindrance may increase the solubility, allowing it to be excreted at a faster rate. In phase 1 of the metabolism of xenobiotics, a polar reactive group is attached to the compound to Fig. 3. Effect of dose on the mean number of hatched make it a more suitable substrate for enzyme attach- nymphs per ootheca. ment (Hodgson 1987). Unsaturated compounds may provide more sites for a polar group and enzyme to and Coats (1994) also found that monocyclic com- attach. The enzymes will attack substrates, such as pounds, such as menthol and carvone, were more toxic sugars and amino acids, creating water soluble com- than bicyclic compounds, such as verbenol and thu- pound that can be more easily excreted (Hodgson jone. The monocyclic compounds used in our study 1987). consisted of six-membered carbon rings. Six-mem- The results from a study by Rice and Coats (1994) bered carbon rings are predicted to have bond angles on the insecticidal properties of several monoterpe- of Ϸ109Њ, which adds to their ßexibility (Morrison and noids to the house ßy, red ßour beetle, and southern Boyd 1992). Two of the bicyclic compounds used in corn rootworm demonstrated a positive correlation our study, (ϩ)-␣-pinene and (Ϫ)-␤-pinene, consisted between toxicity and lipophilicity (log of the octanol/ of one six-membered carbon ring and one four-mem- water partition coefÞcient, log P); however, the re- bered carbon ring. Because the four-membered car- sults from our study did not show such a correlation. bon rings have bond angles of Ϸ90Њ, they are in a Our results were consistent with those of Jang et al.

Table 9. Relationship between doses applied to gravid females and the mean no. of hatched nymphs

Treatment Slope Ϯ SE Intercept Ϯ SE r2 df FP Carvacrol 6 4.11 0.098 1,8-Cineole 6 0.00 0.974 trans-Cinnamaldehyde Ϫ21.46 Ϯ 2.73 35.13 Ϯ 0.81 0.93 6 61.95 0.001 Citronellic acid Ϫ23.58 Ϯ 7.72 31.20 Ϯ 2.04 0.65 6 9.34 0.028 Eugenol Ϫ13.45 Ϯ 3.41 30.49 Ϯ 1.03 0.76 6 15.52 0.011 Geraniol Ϫ23.38 Ϯ 7.67 28.04 Ϯ 1.94 0.65 6 9.30 0.028 S-(Ϫ)-Limonene 6 0.45 0.533 (Ϫ)-Linalool 6 5.78 0.061 (Ϫ)-Menthone Ϫ25.07 Ϯ 8.38 28.04 Ϯ 2.35 0.64 6 8.95 0.030 (ϩ)-␣-Pinene 6 0.58 0.482 (Ϫ)-␤-Pinene 6 1.63 0.258 Thymol Ϫ9.81 Ϯ 3.68 27.08 Ϯ 1.03 0.59 6 7.11 0.045 April 2010 PHILLIPS ET AL.: TOPICAL TOXICITY OF ESSENTIAL OILS 457

Table 10. Relationship between doses applied to gravid females and percentage of dropped oothecae

Treatment Slope Ϯ SE Intercept Ϯ SE r2 df FP Carvacrol Ϫ135.54 Ϯ 27.96 97.66 Ϯ 7.86 0.83 6 23.50 0.005 1,8-Cineole 6 0.02 0.890 trans-Cinnamaldehyde Ϫ188.44 Ϯ 57.24 90.97 Ϯ 17.01 0.68 6 10.84 0.022 Citronellic acid Ϫ138.24 Ϯ 35.81 97.88 Ϯ 9.48 0.75 6 14.91 0.012 Eugenol Ϫ200.61 Ϯ 39.61 90.72 Ϯ 12.00 0.84 6 25.65 0.004 Geraniol Ϫ167.74 Ϯ 24.93 95.85 Ϯ 6.30 0.90 6 45.28 0.001 S-(Ϫ)-Limonene 6 1.87 0.229 (Ϫ)-Linalool Ϫ73.97 Ϯ 24.74 93.27 Ϯ 6.26 0.64 6 8.94 0.030 (Ϫ)-Menthone 6 1.08 0.346 (ϩ)-␣-Pinene 6 0.35 0.579 (Ϫ)-␤-Pinene 6 3.26 0.131

Thymol Ϫ190.17 Ϯ 31.52 83.05 Ϯ 8.85 0.88 6 36.41 0.002 Downloaded from https://academic.oup.com/jee/article/103/2/448/2199422 by guest on 28 September 2021

(2005) who determined the toxicity of marjoram oil Þeld to prevent reinfestation. There also were signif- components to the adult female German cockroach. A icant differences in the mean number of nymphs high log P value may be related to enhanced cuticular among the doses for carvacrol, trans-cinnamaldehyde, penetration (Matsumura 1985); however, the essential citronellic acid, geraniol, and (Ϫ)-menthone; signiÞ- oil components with the highest log P value in our cantly fewer nymphs hatched from the higher doses, study were (ϩ)-␣-pinene and (Ϫ)-␤-pinene, which and fewer nymphs hatched from dead females. These were the least toxic to all stages of the German cock- results are consistent with those of Abd-Elghafar and roach. Depending upon epicuticular lipid composi- Appel (1992), who found that the numbers of nymphs tion, it is possible that a compound can be too li- hatching from oothecae declined as insecticide dose pophilic to completely penetrate the cuticle (Yu increased. We also found that signiÞcantly fewer ooth- 2008). A cuticle with high lipid content may act as a ecae dropped from treated than control females (Ta- lipid reserve, trapping lipophilic compounds and in- ble 10). These results demonstrate that trans-cinnamal- hibiting them from reaching the target site (Yu 2008). dehyde, citronellic acid, geraniol, and (Ϫ)-menthone The injection of essential oil components under the reduced ootheca hatch (Table 11), in part, because insect cuticle would determine whether the low tox- the large doses killed the females before they had time icity of these compounds could be attributed to the to deposit their oothecae, a naturally occurring pro- sequestering of the oils in the cuticle; however, we cess for the German cockroach before ootheca hatch injected 0.44 mg/␮l(ϩ)-␣-pinene and (Ϫ)-␤-pinene (Ross and Mullins 1995). Oothecae receive nutrients under the cuticle and observed negligible mortality and water while attached to their living motherÕs body (unpublished data). (ϩ)-␣-Pinene and (Ϫ)-␤-pinene (Roth 1970). Contamination with essential oil com- may become trapped in other body lipids, such as fat ponents or the lack of nutrients and water from dead body and lipids present in the hemolymph and muscle, females may also have contributed to nymph mortal- inhibiting the oils from reaching the target site. ity. It is also possible that the body of the dead females Ootheca Hatch. Our results showed that an ootheca absorbed water from the developing embryos by a attached to a dead female can hatch, which is consis- passive wicking action. tent with the results of Abd-Elghafar and Appel Essential oil components, such as trans-cinnamal- (1992). Four of the essential oil components had a dehyde, thymol, carvacrol, and eugenol, that are toxic signiÞcant effect on ootheca hatch (trans-cinnamal- to adult females, can potentially be used as direct dehyde, (Ϫ)-menthone, geraniol, and citronellic contact sprays against German cockroaches in areas acid). No essential oil components prevented ootheca where traditional insecticide use is restricted. How- hatch; therefore, from a practical standpoint, addi- ever, there are several limitations that must be over- tional treatments of these oils would be required in the come before essential oil components can successfully

Table 11. Relationship between doses applied to gravid females and percentage of hatched oothecae

Treatment Slope Ϯ SE Intercept Ϯ SE r2 df FP Carvacrol Ϫ74.06 Ϯ 23.74 100.90 Ϯ 6.67 0.66 6 9.73 0.026 1,8-Cineole 6 0.03 0.865 trans-Cinnamaldehyde Ϫ30.44 Ϯ 8.42 98.40 Ϯ 2.50 0.72 6 13.07 0.015 Citronellic acid Ϫ61.06 Ϯ 12.86 100.05 Ϯ 3.40 0.82 6 22.56 0.005 Eugenol 6 1.70 0.250 Geraniol 6 3.27 0.130 S-(Ϫ)-Limonene 6 0.17 0.700 (Ϫ)-Linalool 6 2.53 0.173 (Ϫ)-Menthone Ϫ65.22 Ϯ 24.64 90.63 Ϯ 6.92 0.58 6 7.01 0.046 (ϩ)-␣-Pinene 6 1.71 0.248 (Ϫ)-␤-Pinene 6 0.06 0.822 Thymol 6 0.17 0.700 458 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 103, no. 2 be used in the Þeld. Previous studies have shown them Antonelli, A., C. Fabbri, M. E. Giorgioni, and I. Bazzocchi. to be repellent (Appel et al. 2001) and have little 1997. Characterization of 24 old garden roses from their residual activity (Isman 2006). Appel et al. (2001) volatile compositions. J. Agric. Food. Chem. 45: 4435Ð reported that the repellency of mint oil to the German 4439. cockroach ranged from 92.3 to 100% for days 14 and 1, Baldinger, L. H. 1942. The analysis of peppermint oil. Ind. respectively. Because of their repellency, a pest con- Eng. Chem. 14: 15Ð20. Barcay, S. J. 2004. Cockroaches, pp. 121Ð215. In S. A. Hedges trol operator would have to apply the essential oils [ed.], Handbook of Pest Control. GIE Media, Inc., Rich- carefully in the Þeld. Avoiding contact of the spray on Þeld, OH. or near insecticidal baits, bait stations, and traps would Caredda, A., B. Marongiu, S. Porcedda, and C. Soro. 2002. be necessary to preserve their attractiveness to Ger- Supercritical carbon dioxide extraction and characteriza- man cockroaches (Appel 2004). If used cautiously, tion of Laurus nobilis essential oil. J. Agric. Food. Chem. essential oils could be used as ßushing agents and 50: 1492Ð1496. inspection tools for locating infested areas and reduc- Chang, R. 2003. General chemistry: the essential concepts, Downloaded from https://academic.oup.com/jee/article/103/2/448/2199422 by guest on 28 September 2021 ing the availability of suitable harborages. A microen- 3rd ed. McGraw-Hill, New York. capsulated formulation might be useful to increase the Dudai, N., Z. G. Weinburg, O. Larkov, U. Ravid, G. Ashbell, residual, decrease the repellency, and eliminate the and E. Putievsky. 2001. Changes in essential oil during enzyme-assisted ensiling of lemongrass (Cymbopogon ci- odor of the essential oils. Microcapsule formulations tratus Stapf.) and lemon eucalyptus (Eucalyptus citri- contain active ingredient in microscopic polymeric odora Hook). J. Agric. Food. Chem. 49: 2262Ð2266. capsules that rupture overtime or when stimulated by [EPA] Environmental Protection Agency. 2000. Pesticide pressure, such as an insect walking over the capsule registration (PR) notice 2000-6. Environmental Protec- (Barcay 2004). The essential oil components do have tion Agency, Washington, DC. (http://www.epa.gov/ an effect on ootheca hatch, but they do not eliminate PR_Notices/pr2000-6.pdf). hatch. Follow-up treatment would be necessary to Gish, C. D., and N. J. Chura. 1970. Toxicity of DDT to prevent reinfestation by the hatched nymphs. The use Japanese quail as inßuenced by body weight, breeding of essential oil components along with other inte- condition, and sex. Toxicol. Appl. Pharmacol. 17: 740Ð751. grated pest management techniques can be an effec- Grace, K. J., and D. L. Wood. 1987. Delusory cleptoparasi- tosis: delusion of arthropod infestation in the home. Pan- tive method for controlling the German cockroach in Pac. Entomol. 63: 1Ð4. food preparation areas, storage buildings, apartments, Hodgson, E. 1987. Metabolism of toxicants, pp. 51Ð83. In E. and homes. Hodgson and P. E. Levi [eds.], A textbook of modern toxicology. Elsevier, New York. Isman, M. B. 2000. Plant essential oils for pest and disease Acknowledgments management. Crop Prot. 19: 603Ð608. Isman, M. B. 2006. Botanical insecticides, deterrents, and We thank Xing Ping Hu and Nannan Liu (Department of repellents in modern agriculture and an increasingly reg- Entomology and Plant Pathology, Auburn University) for ulated world. Annu. Rev. Entomol. 51: 45Ð66. helpful comments that improved this manuscript. We also Jang, Y. S., Y. C. Yang, D. S. Choi, and Y. J. Ahn. 2005. Vapor thank Marla J. Eva for laboratory assistance. This research phase toxicity to marjoram oil compounds and their was partially supported by an AAES Hatch grant and by related monoterpenoids to Blattella germanica (Or- Whitmire Micro-Gen Research Laboratories, Inc. (BASF thoptera: Blattellidae). J. Agric. Food. Chem. 53: 7892Ð Pest Control Solutions, St. Louis, MO). 7898. Kang, B. 1976. Study on cockroach antigen as a probable causative agent in bronchial asthma. J. Allergy Clin. 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