Arthur G. Appel

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

ABSTRACT The fumigant toxicity of 12 essential oil components [carvacrol, 1,8-cineole, trans-cinnamaldehyde, citronellic acid, eugenol, geraniol, S-(-)-limonene, (-)-linalool, (-)-menthone, (+)-&agr;-pinene, (-)-&bgr;-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. 1,8-Cineole was the most toxic essential oil component to adult males and females, gravid females, and large nymphs, with LC50 values of 6.8, 8.4, 5.3, and 11.4 mg/liter air at 24 h, respectively. (-)-Menthone and carvacrol were the most toxic essential oil components to medium and small nymphs, with LC50 values of 9.0 and 3.6 mg/liter air at 24 h, respectively. Citronellic acid was the least toxic essential oil component to all stages of the German cockroach. There was not a consistent relationship between body mass and toxicity; the susceptibility of the stages differed for each oil. LC50 values of all stages were correlated negatively with vapor pressure and positively with molecular weight of the essential oil components. The most toxic essential oil components to the majority of cockroach stages were cyclic aliphatic hydrocarbons [1,8-cineole, (-)-menthone, (+)-&agr;-pinene, (-)-&bgr;-pinene, and S-(-)-limonene]. Ring size and the presence of a carbonyl functional group also may have contributed to the toxicity of the compounds. Citronellic acid had no effect on ootheca hatch (100% hatch), whereas (-)-menthone had the greatest effect on ootheca hatch (73% hatch). Percentage of hatched oothecae decreased linearly with increasing concentration for (-)-menthone, S-(-)-limonene, (+)-&agr;-pinene, and (-)-&bgr;-pinene. No essential oil component prevented ootheca hatch, suggesting that multiple treatments would be required in the field to eliminate infestations.

Standard metabolic rate of the fire ant, Solenopsis invicta Buren: effects of temperature, mass, and caste

Standard metabolic rates of S. invicta workers, males, female alates, larvae and pupae were determined using closed-system respirometry. Vdot;(O(2)) (ml h(-1)) of all castes and life stages scaled with temperature and mass. Differences between castes and life stages are discussed in light of their different life histories and the different functions of these stages within the colony. Workers, female alates, male alates, larvae and pupae had mass-specific Vdot;(O(2)) (ml O(2) g wet weight(-1) h(-1), corrected to 25 degrees C) of 0.404+/-0.023, 0.316+/-0.010, 0.674+/-0.024, 0.291+/-0.020, and 0.227+/-0.015 (mean+/-SE), respectively. Measurement of CO(2) and O(2) made possible the examination of temperature and mass effects on respiratory quotient (RQ), as well as accurate transformation of O(2) consumption to metabolic rate (&mgr;W) for comparison with other ant species. Mass-specific metabolic rates of S. invicta females and workers compare favorably with data from 17 other ant species, but metabolic rates of males (177%) and pupae (42%) fall above and below predicted rates, respectively. Several equations relating temperature and mass to Vdot;(O(2)) are presented.

Seasonal Variation of Critical Thermal Limits and Temperature Tolerance in Formosan and Eastern Subterranean Termites (Isoptera: Rhinotermitidae)

Abstract Critical temperatures and the upper lethal limit (ULL) of field collected workers of Formosan subterranean, Coptotermes formosanus Shiraki, and eastern subterranean termites, Reticulitermes flavipes (Kollar), were measured monthly from September 2001 to August 2002. Monthly mean critical thermal maxima (CTMa), ULL, and critical thermal minimum (CTMin) fluctuated significantly throughout the year. Seasonal variations of CTMax and ULL of both species were slightly, but significantly, statistically correlated with seasonal variation of habitat soil temperatures at 15-cm depth. Regression analyses revealed a significant linear relationship between CTMin and habitat temperatures for both termites as well. The two termite species responded positively to temperature changes in a similar manner. The values of all three parameters were significantly greater for C. formosanus (CTMax: 44.8–45.9°C, ULL: 49.1–50.4°C, CTMin: 7.2–9.0°C) than R. flavipes (CTMax: 43.5–44.9°C, ULL: 46.9–48.3°C, CTMin: 1.0–4.9°C). R. flavipes had a wider range between the upper and lower critical temperatures than C. formosanus. The three thermal tolerance parameters were not correlated with worker body mass. The significance of the critical and lethal temperatures and comparisons with previous studies are discussed.

Discontinuous gas exchange in the fire ant, Solenopsos invicta Buren:: Caste differences and temperature effects

The discontinuous gas exchange cycle (DGC), the cyclic release of CO(2) and uptake of O(2), were investigated in workers and female and male alates of the red imported fire ant, Solenopsis invicta Buren, using real-time CO(2) emission measurement by flow-through respirometry. All S. invicta castes displayed discontinuous emission of CO(2) in the temperature range of 15-25 degrees C, but only male alates and workers exhibited a DGC at 30 degrees C. The closed (C) and flutter (F) periods of the DGC were distinguishable in alates of both sexes at the lowest temperature, but not clearly differentiated in females at temperatures above 15 degrees C, in males above 20 degrees C, or workers at any temperature. DGC frequency increased for all castes as temperature increased, ranging from a low of 0.9+/-0.05 mHz (male alates at 15 degrees C) to 18+/-0.79 mHz (workers at 30 degrees C). O period (or burst) volumes of all castes decreased as temperature increased, and increased with body mass - this mass effect was most pronounced at lower temperatures. Q(10) values for DGC frequency (4.27, 5.81, and 5.62 for workers, female and male alates, respectively) were high compared with Q(10)s for standard Vdot;(CO(2)). Differences in the salient characteristics of the DGC between castes are presented and discussed, and S. invicta DGC patterns are compared to known values for some other ant species.

Host stress response is important for the pathogenesis of the deadly amphibian disease, Chytridiomycosis, in Litoria caerulea.

Chytridiomycosis, a disease caused by Batrachochytrium dendrobatidis, has contributed to worldwide amphibian population declines; however, the pathogenesis of this disease is still somewhat unclear. Previous studies suggest that infection disrupts cutaneous sodium transport, which leads to hyponatremia and cardiac failure. However, infection is also correlated with unexplained effects on appetite, skin shedding, and white blood cell profiles. Glucocorticoid hormones may be the biochemical connection between these disparate effects, because they regulate ion homeostasis and can also influence appetite, skin shedding, and white blood cells. During a laboratory outbreak of B. dendrobatidis in Australian Green Tree Frogs, Litoria caerulea, we compared frogs showing clinical signs of chytridiomycosis to infected frogs showing no signs of disease and determined that diseased frogs had elevated baseline corticosterone, decreased plasma sodium and potassium, and altered WBC profiles. Diseased frogs also showed evidence of poorer body condition and elevated metabolic rates compared with frogs showing no signs of disease. Prior to displaying signs of disease, we also observed changes in appetite, body mass, and the presence of shed skin associated with infected but not yet diseased frogs. Collectively, these results suggest that elevated baseline corticosterone is associated with chytridiomycosis and correlates with some of the deleterious effects observed during disease development.

Carbon dioxide release in Coptotermes formosanus Shiraki and Reticulitermes flavipes (Kollar): effects of caste, mass, and movement

Movement and carbon dioxide (CO(2)) release of individual Formosan, Coptotermes formosanus Shiraki and Eastern, Reticulitermes flavipes (Kollar) subterranean termites were recorded simultaneously in real time. Worker, soldier, and pre-alate (nymph) caste termites were recorded over 1-h periods at ambient temperature and normoxia in dry, CO(2)-free air. No evidence of discontinuous gas exchange cycles (DGCs) was observed in 344 recordings. Intensity of movement was constant in video tape recordings of termites under respirometry conditions. Duration of movement did not have a significant effect on residuals of &Vdot;(CO(2)) regressed on mass. Thus, movement did not effect &Vdot;(CO(2)) for these two species. Overall CO(2) release values were calculated for all recordings resulting in mean &Vdot;(CO(2)) (ml CO(2) g(-1) h(-1)), and compared among caste, colony, and species with a nested ANOVA. There was significant interaction (P=0.0161) only for species. Mean CO(2) release was significantly greater for R. flavipes (0.507 ml CO(2) g(-1) h(-1)) than C. formosanus (0.310 ml CO(2) g(-1) h(-1)). Mass scaling of termite &Vdot;(CO(2)) was investigated by regressing log(10)&Vdot;(CO(2)) on log(10)mass. The overall model combining species gave a mass scaling coefficient of 0.861(+/-0.0791), which approximates a previously published value for the arthropods as a whole (0.825).

Laboratory and Field Performance of an Imidacloprid Gel Bait Against German Cockroaches (Dictyoptera: Blattellidae)

Abstract An experimental 2.15% imidacloprid gel bait containing ≈44% water was evaluated in laboratory and field studies against the German cockroach, Blattella germanica (L.). In continuous exposure tests, toxicity and presumably bait consumption varied with cockroach stage, deprivation of competitive food, and temperature. The LT50 values for cockroaches provided with competitive food ranged from ≈0.9 h for adult females to 190 h for small nymphs. The LT50s for cockroaches not provided competitive food ranged from ≈1.7 h for adult females to ≈31 h for adult males. The LT50s decreased exponentially with temperature between 10 and 30°C. Even though the bait was significantly more repellent (≈38%) than an untreated control (≈14%) when tested in Ebeling choice boxes, performance index values were positive and increased to nearly 100 (indicating high mortality and low repellency) after 14 d. When applied at 15–45 g per kitchen, the bait significantly reduced German cockroach trap catch in infested homes during a 4-wk period. There was a ≈50% reduction after 1 wk and ≈80% reduction 4 wk after treatment.

Effects of Bacillus thuringiensis Cry1C toxin on the metabolic rate of Cry1C resistant and susceptible Spodoptera exigua (Lepidoptera: Noctuidae)

Abstract.  The effects of Bacillus thuringiensis (Bt) Cry1C toxin on the metabolic rate of Cry1C resistant and susceptible Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) are investigated using closed‐system respirometry. Mechanisms of resistance to the Bt toxin may be associated with an energetic cost that can be measured as an increase in metabolic rate compared with Bt‐susceptible insects. This hypothesis is tested using third‐ and fifth‐instar larvae and 1–7‐day‐old pupae. Metabolic rate is measured as the amount of O2 consumed and CO2 produced. V̇O2 and V̇CO2 (mL g−1 h−1) of third‐instar Cry1C resistant larvae reared continuously on a diet containing 320 µg Cry1C toxin per g diet (CryonT) are significantly greater than third‐instar Cry1C resistant larvae reared on toxin for 5 days and reared thereafter on untreated diet (Cry5dT), Cry1C resistant larvae reared on untreated diet (CryReg) and the susceptible parental strain (SeA) reared on untreated diet. There are no differences in V̇O2 and V̇CO2 (mL g−1 h−1) among treatment groups for fifth‐instar larvae. CryonT larvae and pupae weigh significantly less than larvae and pupae receiving other treatments. Smaller body mass may be an important biological cost to individuals exposed continuously to Bt toxin. One‐day‐old pupae of all treatment groups exhibit a high V̇O2 (mean approximately 0.174 mL g−1 h−1) with CryonT having a significantly greater value than all other treatments; there are no differences among the other treatments. Pupal metabolic rates of all treatment groups decline to a minimum between days 2 and 4 then increase linearly between days 4 and 7 until adult emergence. These results demonstrate no difference in metabolic rates, and possibly fitness costs, between resistant (CryReg and Cry5dT) and susceptible (SeA) S. exigua except when larvae were reared continuously on toxin (CryonT).

Cyclic carbon dioxide release in the dampwood termite, Zootermopsis nevadensis (Hagen).

Real-time traces of CO(2) release of pseudergates of the dampwood termite, Zootermopsis nevadensis (Hagen) were obtained using flow-through respirometry. Traces were made at each of six temperatures, between 10 and 35 degrees C. Termites released CO(2) in a cyclic pattern at each of the six temperatures. CO(2) release rate (as V(CO(2)) in ml h(-1)) increased significantly with temperature and body mass. Rate of change in V(CO(2)) with temperature (or Q(10)) was 2.11. Degree of cycling in CO(2) traces was estimable using the coefficient of variability. Coefficient of variability for both acyclic and cyclic traces declined exponentially with increasing temperature.

Olfactory responses of the antennal trichoid sensilla to chemical repellents in the mosquito, Culex quinquefasciatus.

Insect repellents are widely used to protect against insect bites and thus prevent allergic reaction and the spread of disease. To gain insight into the mosquitos response to chemicals repellents, we investigated the interaction between the olfactory system of the mosquito Culex quinquefasciatus Say and chemical repellents using single sensillum recording. The interactions of 50 repellent chemicals with olfactory receptor neurons were measured in six different types of mosquito sensilla: long sharp trichoid (LST), short sharp trichoid (SST), short blunt trichoid I (SBT-I), short blunt trichoid II (SBT-II), short blunt trichoid-curved (SBT-C), and grooved peg (GP). A single olfactory neuron reacted to the chemical repellents in each of the sensilla except for SBT-I and SBT-II, where two neurons were involved. Other than LST and GP, which showed no or very weak responses to the repellents tested, all the sensilla showed significant excitatory responses to certain types of repellents. Terpene-derived chemicals such as eucalyptol, α-pinene, and camphor, stimulated olfactory receptor neurons in a dose-dependent manner and mosquitoes responded more strongly to terpene-derived chemical repellents than to non-terpene-derived chemicals such as dimethyl phthalate. Mosquitoes also exhibited a similar response to stereoisomers of chemicals such as (-)-β-pinene versus (+)-β-pinene, and (-)-menthone versus (+)-menthone. This study not only demonstrates the effects of chemical repellents on the mosquito olfactory system but also provides important information that will assist those screening new mosquito repellents and designing new mosquito control agents.