The Behavioral Response of Blattella germanica (Blattodea: Ectobiidae) Exposed to DEET Varies Throughout Its Life Cycle.

The German cockroach, Blattella germanica L., is a hemimetabolous insect pest of economical and medical importance. N,N-diethyl-3-methylbenzamide (DEET) is an insect repellent whose effect on this species has received very little attention. The objective of this work was to determine whether the behavioral response of B. germanica to DEET varies along its life cycle. DEET repellence was assessed in small, medium, and large nymphs, and in adults of both sexes, all originated from the same laboratory colony (CIPEIN). The experimental arena consisted in a piece of filter paper treated with repellent on one half (195 µg/cm2) and solvent alone on the other half. A cockroach was placed on the filter paper, and its behavior was filmed. An image analyzer was used to quantify how long the insect spent on each side of the paper. As a control, a cockroach was exposed to a piece of filter paper treated with solvent (acetone) alone. Each assay was repeated independently six times. Distribution coefficient (DC) values were calculated, a parameter that ranges between 0 (attraction) and 1 (repellence). Small nymphs were more sensitive to DEET (mean DC = 0.93). The mean DC values of the other groups varied between 0.62 (medium nymphs) and 0.71 (male adults). The group of medium nymphs was the only one whose behavior was not significantly altered by exposure to DEET. The results show the importance of assessing insect repellents at different stages of the insect's life cycle in order to obtain a complete panorama of its effect.

The Botanical Monoterpenes Linalool and Eugenol Flush-Out Nymphs of Triatoma infestans (Hemiptera: Reduviidae).

Monoterpenes are the main components of essential oils. Some members of this chemical family present insecticidal activity. Triatoma infestans (Klug) is the main vector of Chagas disease in Argentina, Bolivia, Paraguay, and Perú. The objective of this work was to evaluate the effect of six monoterpenes (1,8-cineole, eugenol, linalool, menthol, α-terpineol, and thymol) on the locomotor and flushing out activity of T. infestans. A video tracking technique was used to evaluate the locomotor activity of nymphs exposed to different concentrations of these chemicals applied as films on filter paper. Papers treated with acetone alone were used as negative controls, while solutions of tetramethrin were applied as positive controls. Only linalool and menthol produced hyperactivation. Flushing out was assessed under laboratory conditions using a standardized aerosolization method. All monoterpenes were applied at 1.5 g/m3. 1,8-Cineole, α-terpineol, and thymol flushed out 10% or less nymphs. The average flushing out produced by eugenol was 36.7%. Values of median flushing out time (FT50) could only be calculated for linalool and menthol (16.67 and 42.98 min, respectively). The FT50 value for the positive control tetramethrin (applied at 0.006 g/m3) was 8.29 min. Following these results, the flushing out activity of a mixture of linalool and eugenol was evaluated. The FT50 of this 2:1 linalool:eugenol mixture was 40.73 min. Finally, flushing out assays performed in semifield conditions showed similar results to those obtained at the laboratory.

Toxicity and Metabolism of Zeta-Cypermethrin in Field-Collected and Laboratory Strains of the Neotropical Predator Chrysoperla externa Hagen (Neuroptera: Chrysopidae).

Resistance to pesticides has been studied in several insect pests, but information on the natural enemies of pests-including the Neotropical predator Chrysoperla externa Hagen (Neuroptera: Chrysopidae), a major biological control agent in South America-is lacking. We report here a comparative study between a field-collected strain of C. externa subjected to monthly sprayings of pyrethroids and neonicotinoids and a laboratory strain without exposure to pesticides. The tolerance of both strains against zeta-cypermethrin was similar, and addition of the synergist piperonyl butoxide increased the toxicity by 30% in both strains. Gas-chromatography analyses and mixed-function-oxidase measurements indicated similar values in both strains and also confirmed the key role of oxidative metabolism in this species. Because C. externa has maintained a tolerance to zeta-cypermethrin without previous pesticide exposure, this species could potentially be mass-reared and released in fields in the presence of pesticide pressure.

Susceptibility of adults of the cerambycid beetle Hedypathes betulinus to the entomopathogenic fungi Beauveria bassiana, Metarhizium anisopliae, and Purpureocillium lilacinum.

The cerambycid beetle Hedypathes betulinus (Klug) (Coleoptera: Cerambycidae) causes severe damage to yerba mate plants (Ilex paraguariensis (St. Hilaire) (Aquifoliales: Aquifoliaceae)), which results in large losses of production. In this study, the pathogenicity of entomopathogenic fungi of the species Beauveria bassiana (Balsamo-Crivelli) Vuillemin (Hypocreales: Cordycipitaceae), Metarhizium anisopliae sensu lato (Metschnikoff) Sorokin (Hypocreales: Clavicipitaceae), and Purpureocillium lilacinum (Thom) Luangsa-ard, Hywel-Jones, Houbraken and Samson (Hypocreales: Ophiocordycipitaceae) on yerba mate were evaluated. Fifteen isolates of B. bassiana, two of M. anisopliae, and seven of P. lilacinum on H. betulinus adults were analyzed under laboratory conditions. The raw mortality rate caused by B. bassiana isolates varied from 51.1 to 86.3%, and their LT50 values varied between 8.7 and 13.6 d. The isolates of M. anisopliae caused 69.6‒81.8% mortality, and their LT50 values varied between 7.4 and 7.9 d. In contrast, isolates of P. lilacinum were not pathogenic. M. anisopliae and B. bassiana isolates were pathogenic against H. betulinus adults, suggesting that they may be useful in biological control programs for insect pests of yerba mate.

Toxicity of cypermethrin on the neotropical lacewing Chrysoperla externa (Neuroptera: Chrysopidae).

The generalist predator Chrysoperla externa (Neuroptera: Chrysopidae) is distributed in the Neotropical Region and presents a strong potential as a biological control agent due to its easily rearing, high voracity and tolerance to several pesticides. This species feeds on relevant pests such as aphids, whiteflies, trips and various lepidopterans. In Argentina, an indiscriminate chemical control with broad spectrum pesticides is still the first option for controlling pests causing resistance problems and reduction of beneficial organisms. Therefore, it would be desirable that predators or parasitoids develop tolerance or resistance as phytophagous pests for their maintenance in the agricultural ecosystems. The objective of this work was to evaluate the tolerance of C. externo to the pyrethroid cypermethrin by topical exposure in laboratory conditions. The symptoms evaluated were tremors, movement, knockdown, inability to walk due to being glued. Recovery from poisoning symptoms was also evaluated. Six different concentrations of the pesticide, including the full field one, were tested. The exposure method was by topical applications on third larval instar. A low toxicity on larvae at 24 h post-treatment was observed, even at the highest concentration evaluated. Most of treated individuals looked normal at 24 h post-treatment; those who were knocked down showed a complete recovery between 48 and 72 h post-treatment. C externa demonstrated a high tolerance to pyrethroids. This could be due to the activity involved in pyrethroids biotransformation (for example, esterases and mixed-function oxidases), or to a low sensitivity of the molecular target. Future studies should be addressed at biochemical and molecular levels to complete our knowledge about insecticide effects on this predator.

Volatile compounds secreted by Brindley's glands of adult Triatoma infestans: identification and biological activity of previously unidentified compounds.

Volatile emissions of adult male Triatoma infestans were collected on non-polar SPME fibers and analyzed by gas chromatography linked to a mass spectrometer. A complex mixture of 16 short-chain esters and acids were identified. The composition of short-chain aliphatic acids (ethanoic to nonanoic acids) was similar to previously reported results. The most abundant aliphatic acid was 2-methylpropanoic acid, constituting 18% of the total volatile content. Also abundant were the esters 2- and 3-methylbutyl 2-methylpropanoate, which constituted 30% and 22%, respectively, of the total volatile content. A similar pattern of compounds was observed in the volatiles secreted by dissected male Brindley's glands; however, in this case, 2- and 3-methylbutan-1-ol were detected which were not found in live insect volatile emissions. Large variability in volatile composition was also observed among the glands excised from different insects. Electroantennographic (EAG) evaluation of the components of Brindley's gland showed significant responses for 2- and 3-methylbutyl 2-methylpropanoate compared to controls. The mixture of volatiles secreted by excised Brindley's glands and the isolated 2- and 3-methylbutyl 2-methylpropanoate had repellent effects on both male and female T. infestans, possibly associated with a defensive strategy.

Repellence and toxicity of Schinus molle extracts on Blattella germanica.

The biological activities of ethanol and petroleum ether extracts from leaves and fruits of Schinus molle against adults of Blattella germanica were examined by repellence test and topical application. All extracts produced significant repellent effect and mortality.

Behavioural response of Triatoma infestans (Klug) (Hemiptera: Reduviidae) to quinazolines.

The behavioural responses of the haematophagous bug Triatoma infestans towards some previously identified components of its faeces: 4-methylquinazoline, 2,4- dimethylquinazoline and their mixtures were evaluated using a video tracking system. Fifth instar nymphs and females but not males were significantly attracted to polyethylene glycol formulations of 4-methyl + 2,4-dimethylquinazoline (50 microg each). Fifth instar nymphs were also attracted to 4-methylquinazoline alone (50 microg) but females were only attracted by the mixture of both methyl quinazolines (50 microg each). Syntheses of both methyl quinazolines were carried out starting from 2-aminoacetophenone by modifying the conditions of reported procedures.

Prevalence and levels of permethrin resistance in Pediculus humanus capitis De Geer (Anoplura: Pediculidae) from Buenos Aires, Argentina.

Permethrin has been used extensively for control of Pediculus humanus capitis De Geer (Anoplura: Pediculidae) in Argentina since 1990, resulting in the development of resistance to this and other pyrethroids. This resistance was first detected in some field populations in 1997. A survey for resistance in Buenos Aires in 2001 revealed significant resistance levels in lice on children at 24 of 26 (92.3%) schools. When compared with a previously unexposed reference population, resistance ratios (RRs) obtained by exposing the insects to filter papers impregnated with permethrin ranged from 2 to 60 in 10 (39%) of the schools. RRs in the remaining 14 (61%) populations were too great to not be measured with the filter paper method (RR > 88.7). As an alternative, we used topical applications of 0.1 microl of acetone solution of permethrin on the dorsal abdomen of adults and third instars. This topical method, which has not been previously reported for head lice, was capable of quantifying higher levels of resistance. Highly resistant populations had RRs from 162.5 to 655.2. When applied to populations with low and intermediate levels of resistance, results from the filter paper and topical application methods were highly correlated, and RRs from topical application were higher than those from the filter paper method. Results from the combination of the two methods indicated that head lice among Buenos Aries school children are highly resistant to permethrin, and the resistance is widespread.

Third instar nymphs of Rhodnius prolixus exposed to alpha-cyanopyrethroids: from hyperactivity to death.

The hyperactivity, incoordination, recovery, and mortality produced by four alpha-cyanopyrethroids usually used for Chagas disease vector control (beta-cypermethrin, beta-cyfluthrin, lambda-cyhalothrin, and deltamethrin) were evaluated on third instar nymphs of Rhodnius prolixus. All pyrethroids modified the locomotor activity of the nymphs, which increased linearly as a function of the log of insecticide concentration. lambda-Cyhalothrin showed the lowest values of Effective Concentration 50%, Lethal Concentration 50%, Effective Time 50%, and Lethal Time 50% when insecticides were applied by contact with treated filter papers. Recovery from incoordination was observed after topical application of the insecticides. The recovery was inhibited by the simultaneous application of piperonyl butoxide, suggesting that biotransformation by mixed-function microsomal oxidases is involved in the process of recovery.

Behavioral response of fifth instar nymphs of Triatoma infestans (Hemiptera: Reduviidae) to pyrethroids.

The hyperactivity (an increase in locomotor activity) and repellency produced by eight pyrethroids, applied as films on filter paper, were evaluated on fifth instar nymphs of Triatoma infestans (Hemiptera: Reduviidae) using a video tracking technique. All the pyrethroids studied produced hyperactivity. As a trend, hyperactivity produced by cyanopyrethroids was higher than that produced by non-cyanopyrethroids. Hyperactivity was not observed when nymphs were pretreated with the sulphydryl reagent N-ethylmaleimide before exposure to the pyrethroids. The eight pyrethroids failed to produce repellency. No repellency was also observed for the flowable formulation of deltamethrin at the concentration recommended for T. infestans control.

Behavioral response of Stomoxys calcitrans (Diptera: Muscidae) to conspecific feces and feces extracts.

The attraction response of Stomoxys calcitrans (L.) to its own feces was evaluated in a triple cage olfactometer. Both time- and concentration-response relationships were obtained for female S. calcitrans exposed to cellulose sponges impregnated with fresh fly feces or filter papers treated with chloroform:methanol extracts of fresh fly feces in 6-min tests. Attraction to feces collected on cellulose sponges decreased as the air flow increased. Feces collected on cellulose sponges and held for 28-31 retained attractive activity. More female flies were attracted than males to feces on sponges or to polar solvent extracts of feces-contaminated cages. The activity of feces extract on filter paper decreased rapidly. Chemical identification of the active compounds present could lead to useful baits for traps.

Repellency of deet to nymphs of Triatoma infestans.

The repellency of N,N-diethyl-3-methylbenzamide (deet) to Triatoma infestans (Klug) (Hemiptera: Reduviidae) was evaluated using third-instar nymphs and a video tracking technique. Three experimental designs were used: (a) the test arena floor was divided into two halves, only one of which was treated with deet; (b) the arena floor was divided into an inner circle and an outer ring, only the latter treated with deet; (c) half of the test arena was covered by a filter paper roof treated with deet (out of reach of the nymphs). In all three types of experiment, a repellent effect was demonstrated proportional to the dose of deet. When a host (pigeon) was shielded by deet-treated gauze, the rate of blood-feeding by the nymphs was inhibited. Topical pre-treatment of the nymphs with N-ethylmaleimide, to block chemoreception, inhibited the repellency.

Evaluation of Stomoxys calcitrans (Diptera: Muscidae) behavioral response to human and related odors in a triple cage olfactometer with insect traps.

A triple cage olfactometer provided with insect traps was used for evaluating behavioral responses of Stomoxys calcitrans (L.) females to human skin and breath, CO2, and L-lactic acid analogs. After demonstrating there were no significant differences caused by cage location or time of day, 3 sets of 3 olfactometer tests were performed in a day, every 2 h beginning at 0900 hours. When a human hand was used as attractant, the attraction (expressed as percentage of trapped flies) increased as a function of the time; an inverted U-shaped relationship between attractancy and air speed was observed; and variation in fly density in the range 25-75 per cage did not affect the attraction response. When human breath was used as attractant the attraction increased linearly as a function of time and it was exhalation frequency dependent; when air flow was absent the highest response was observed; and 24- to 38-h-old flies were more attracted than younger and older. When CO2 was tested, activation and orientation and probing behavior were concentration dependent with flows ranging between 0.0001 and 0.038 liter s(-1), but attraction was not. No attraction was observed with 10, 100, or 1,000 microg of compounds related to L-lactic acid and several synthetic human odors and related compounds, although orientation was often observed.

Incoordination, paralysis and recovery after pyrethroid treatment on nymphs III of Triatoma infestans (Hemiptera: Reduviidae).

Symptoms of poisoning for deltamethrin and cis-permethrin on nymphs III of Triatoma infestans were described. The time required for incoordination and paralysis were determined. Deltamethrin was equal or more rapid in the onset of the first effect (accordingly to dose), and cis-permethrin in the onset of the second one. There were no significant differences between incoordination doses 50% (IncD50s) at different times for the two pyrethroids. They showed equivalent incoordination power, but the nymphs treated with deltamethrin recovered slightly more rapid and in greater amount than the nymphs treated with cis-permethrin. The recovery was inhibited by the simultaneous application of piperonyl butoxide. This result suggests that biotransformation by mixed-function microsomal oxidases are involved in the process of recovery.

Evaluation of hyperactivity produced by pyrethroid treatment on third instar nymphs of Triatoma infestans (Hemiptera:Reduviidae).

The hyperactivity produced in third instar nymphs of Triatoma infestans by their exposure to films of deltamethrin or cis-permethrin was evaluated. Both pyrethroids produced a significant increase in locomotor activity at 26 and 36 degrees C but not at 16 degrees C. At 26 degrees C, only deltamethrin produced hyperactivity when topically applied on the dorsal side of the nymph's abdomen. However, both pyrethroids produced hyperactivity when topically applied on the head of the nymphs. Hyperactivity was not observed when nymphs were treated with N-ethylmaleimide (20 micrograms/insect) before exposure to the pyrethroids. The effect of both insecticides on locomotor activity reversed the inhibitory influence on locomotion elicited by contact with the walls of the experimental arena (thigmotaxis).

Comparative toxicity of deltamethrin and cis-permethrin on first instars of Triatoma infestans (Hemiptera: Reduviidae).

We evaluated the toxicity of deltamethrin and cis-permethrin at 3 temperatures on instars of Triatoma infestans (Klug). After treatment, temperature had an important effect on LD50s of both insecticides, which tended to decrease when temperature decreased. However, the effect of temperature on LT50s was small. Cis-permethrin was slightly more lethal than deltamethrin only at 26 degrees C. Lethal action of deltamethrin was faster than cis-permethrin at all temperatures assayed. The toxicity of both pyrethroids was affected by the age and the nutritional state of the nymphs. We evaluated sublethal effects on blood meal ingestion and moulting. Only deltamethrin yielded a substantial decrease in the number of moulted nymphs.

Temperature effect on the insecticidal activity of pyrethroids on Triatoma infestans.

1. The toxic effect of deltamethrin, asymmethrin, alphamethrin, cypermethrin and cypermethrin High cis in nymphs III of Triatoma infestans was lower at 28 than 16 degrees C. 2. Prostration in treated nymphs III occurred more rapidly at 28 than 16 degrees C. 3. Symptoms of poisoning rapidly disappeared when nymphs III intoxicated were moved from 16 to 28 degrees C. 4. Nymphs III exposed to low doses of pyrethroids at 28 degrees C, which did not show symptoms of poisoning, were rapidly affected when they were moved to 16 degrees C.