Management of a German cockroach population with a juvenoid bait formulation: computer simulation

A computer model was applied to simulate responses of German cockroach populations to feeding on juvenoid baits during an equilibrium, exponential, and the earliest phase of population growth. The simulations show that the renewal potential of the cockroach populations will be exhausted when about 80% or more adults become sterile. The attainment of this activity threshold will be preceded by a lag time with no apparent control effect. The time delay appears substantially shorter for both growing populations (30–60 days) than for the equilibrious one (90–120 days), but, the former ones will continue growing throughout this lag. The simulations predict that even a worse baits' performance can give sufficient control effect in the field if the baits are laid in an early phase of population growth. Thus, optimum tactics should integrate administration of juvenoid baits with an introductory reduction of cockroach population.     

Differential consumption of baits by pest blattid and blattellid cockroaches and resulting direct and secondary effects

Consumption was measured of three commercially available cockroach gel baits (0.01 and 0.05% fipronil and 0.6% indoxacarb) by two pest blattellid (German cockroach, Blattella germanica L., and brownbanded cockroach, Supella longipalpa Fabricius) and three pest blattid [oriental cockroach, Blatta orientalis L., American cockroach, Periplaneta americana L., and smokybrown cockroach, Periplaneta fuliginosa (Serville)] species (Dictyoptera), and direct and secondary effects were quantified. All three baits were greatly preferred for consumption over dog food; however, virtually all consumption (ca. 98%) by pest blattids was gel baits containing sugar feeding stimulants and water. Pest blattid greater preference for gel baits was probably due to their greater need for nutrients in baits due to their greater cuticular water permeability and higher metabolism than the pest blattellids. Brownbanded cockroaches had lowest percentage gel bait selection. Pest blattellids consumed greater amounts of bait per g body weight than pest blattids. Cockroaches consumed more active ingredient than needed to cause mortality; however, based on bait consumption, a 30‐g tube of gel bait potentially killed from 394 to 6 966 adult cockroaches, depending on species. Mortality for all cockroach species was faster for adults (≥3 days) than for nymphs (≥7 days); however, most brownbanded cockroaches exposed to indoxacarb survived despite consuming 1.5‐ to >3‐fold more than other baits, suggesting low enzyme production by brownbanded cockroaches and consequently lower conversion of indoxacarb into its toxic form. Besides direct mortality, German cockroaches died from indirect effects: exposure to debris from other cockroaches that had direct access to the gel baits or bait contact without ingestion. Although maximization of bait consumption is important, factors that enhance secondary mortality and contact toxicity should also be considered.     

Potential of Periplaneta fuliginosa densovirus as a biocontrol agent for smoky-brown cockroach, P. fuliginosa

A densovirus, named Periplaneta fuliginosa densovirus (PfDNV), affects smoky-brown cockroach (P. fuliginosa), which is a major peridomestic cockroach in China, southeastern United States, Japan, and Southeast Asia. We reported here that PfDNV could be mass-produced using virus rescue technology. Pathology and ultrastructural studies revealed the presence of enlarged and dense nuclei in hindgut cells of infected smoky-brown cockroach nymphs and adults. Laboratory bioassays of the PfDNV against P. fuliginosa showed that it has the potential to be used as a biocontrol agent. High mortality was recorded in adult smoky-brown cockroaches treated with PfDNV baits at the dosage of 6 × 10⁴ virions per gram against P. fuliginosa in both no-choice tests and two-choice tests (LT₅₀’s were 13.37 and 13.50 days, respectively). PfDNV was also effective in large population chamber tests. LT₅₀ was 17.57 days and mortality achieved was 95.6% in 28 observation days.     

Cost-effectiveness of integrated pest management compared with insecticidal spraying against the German cockroach in apartment buildings

This study assessed the cost and effectiveness of an integrated pest management (IPM) program using hydramethylnon gel baits compared with conventional spraying for controlling the German cockroach, Blattella germanica (L.) (Blattodea: Blattellidae), in two residential buildings in Yasuj, Iran. The IPM approach was based on educational programs using pamphlets, posters and lectures, sanitation using vacuuming and application of hydramethylnon gel baits. Conventional approach used cypermethrin (10% EC) on baseboard and cracks-and-crevices. Sticky traps were used as tools for monitoring cockroach population densities. The IPM approach reduced (943%) the rate of insecticide application compared to the conventional spray. Cockroach populations in the IPM treatment were significantly reduced from an average of 12.2 ± 3.01 cockroaches per unit before treatment to zero cockroach per unit by week four and thereafter. Cockroach populations in the conventional spray treatment were reduced from an average of 11.5 ± 4.43 cockroaches per unit before treatment to an average of 3.4 ± 0.99 cockroach per unit after 11 weeks of post treatment. The IPM treatment improved 100% of infested units compared to 78% for spray treatment to obtain a clean level of infestation (< 1cockroach per trap per unit). The results suggest that the intervention by IPM using hydramethylnon gel baits significantly reduced cockroach infestation compared to cypermethrin spray throughout the 11 weeks of post-treatment period. However, within the study period, the IPM system involving gel baits, educational program and sanitation was 363.2% more expensive than the conventional method.     

Laboratory and field performance of an indoxacarb bait against German cockroaches (Dictyoptera: Blattellidae)

Experimental indoxacarb powder and gel baits were evaluated in the laboratory, and a gel bait was evaluated in subsequent field studies against the German cockroach, Blattella germanica (L.). In continuous exposure tests, LT50 values were 1.90 and 1.10 d for 0.25 and 1% indoxacarb powder baits, respectively. However, 0.25% indoxacarb gel bait had an LT50 value of 0.68 d, similar to a 0.05% abamectin gel bait formulated with the same bait base. There was no difference in toxicity between fresh and 7-d-old gel bait deposits. A pyrethroid-resistant strain of German cockroaches was significantly resistant to both abamectin and indoxacarb gel baits. Gel bait contained approximately 40% water, desiccated rapidly at 25-28 degrees C and 30-45% RH, but did not rehydrate when held at 56.7% RH for 3 d. Powder indoxacarb baits contained <1% water and did not desiccate or gain water. Indoxacarb gel bait (0.25%) was relatively nonrepellent (approximately 30%) and had positive maximum performance index values (approximately 100) in Ebeling choice box experiments. In field experiments in cockroach-infested kitchens, the 0.25% indoxacarb gel bait significantly reduced visual counts of German cockroaches approximately 74% at 3 d and >95% at 14 d. Indoxacarb baits are toxic, relatively nonrepellent, and can significantly reduce German cockroach populations.     

Attractiveness of insecticide baits for cockroach control (Dictyoptera: Blattellidae): laboratory and field studies.

Several insecticide bait formulations were evaluated for their attractiveness to cockroaches in olfactometer assays in the laboratory and in trapping experiments in the field. Included in the assays were bait stations, gels, pastes, and a powder that contained one of the following active ingredients: abamectin, boric acid, chlorpyrifos, or hydramethylnon. There were significant differences among the baits in their attractiveness to the German cockroach, Blattella germanica (L.). In trapping experiments, Avert powder (abamectin), Maxforce station and gel, and Siege gel (all hydramethylnon) were consistently attractive to B. germanica adults and nymphs. Laboratory olfactometer assays with adult males confirmed these results and showed that nymphs were as responsive as males whereas females were less responsive. Our bioassays also demonstrate that attractiveness of bait can be dramatically affected by the age of the bait. One week of aging significantly reduced the attractiveness of Avert powder in both laboratory and field assays. Aging, however did not diminish the attractiveness of Maxforce gel, indicating that the formulation may be critical for retention of attractiveness of baits. Baits that were most attractive to the German cockroach were also the most attractive to nymphs and adults of the brownbanded cockroach, Supella longipalpa (F.).     

Incorporation of pyriproxyfen in a German cockroach (Dictyoptera: Blattellidae) management program

Pyriproxyfen (Nylar), a juvenile hormone analog (JHA), and acephate were used in a German cockroach, Blattella germanica (L.), management program. Monthly applications of acephate for 6 mo reduced nightly trap catches from 24.68-25.25 to 4.46-5.31 at 2 mo, and trap catches averaged 1.49-8.04 from 2-6 mo. After acephate applications were discontinued, trap catches increased from 6.86 at 7 mo to 28.08 at 12 mo. Pyriproxyfen was applied at months 0, 3, and 6. Monthly pyriproxyfen treatments were applied from 7 to 11 mo because, at month 6, only 21.00-27.30% of adults had wing twisting (one effect of pyriproxyfen exposure). These monthly applications resulted in 74.55-78.53% of adults with twisted wings in the German cockroach population at 12 mo. Trap catches in apartments treated with pyriproxyfen aerosol were significantly lower at 7, 8, 10, and 12 mo after the initial treatment than those that did not receive JHA treatment. At 7-12 mo, the pyriproxyfen residual spray did not significantly reduce German cockroach populations, but trap catches were consistently lower. German cockroach populations were sampled for 1 yr (from 13 to 24 mo) after pyriproxyfen applications were discontinued. Compared with those in apartments treated with acephate, trap catches in apartments treated with pyriproxyfen were significantly reduced from 12 to 18 mo after the initial treatment. At 18-24 mo, trap catches in apartments treated with pyriproxyfen aerosol were consistently lower than those treated with acephate, but these differences were not significant.     

Improvement of German cockroach (Dictyoptera: Blattellidae) population control by fragmented distribution of gel baits

The aim of this study was to test the efficiency of gels in relation to fragmentation of baits and population density against the German cockroach, Blattella germanica (L.). We hypothesized that the efficiency of cockroach control could be improved by fragmentation of gel baits, i.e., by distributing the same amount of bait in several small drops instead of one large one. Our results show that bait fragmentation increased the number of cockroaches gaining access to the gel. However, bait fragmentation increased cockroach mortality only at high population densities. Our results allow us to recommend modulation of bait application in relation to cockroach population density. At low population densities (42 individuals/m2), the recommended dose, one single 30-mg drop/m2, can be applied. At high population densities (> or = 208 individuals/m2), the same recommended dose would be more efficient if applied as several 3-mg drops.     

Effects of hydroprene exposure on the physiology and insecticide susceptibility of German cockroaches (Orthoptera: Blattellidae).

We determined nonlethal physiological effects of hydroprene on the German cockroach, Blattella germanica L., and the effects of hydroprene exposure on German cockroach susceptibility to traditional insecticides. Live and dry weights of German cockroach adults exposed as nymphs to the juvenile hormone analog hydroprene increased significantly (6-35%) in both sexes. The change in weight was affected by hydroprene dose and time after adult emergence. Hydroprene treatment did not affect total body lipids and carbohydrates consistently. However, total body urates of males and females increased significantly. The susceptible and multiresistant German cockroach strains were significantly more susceptible to propoxur at the lower hydroprene application rate (0.697 mg per tub) than the untreated cockroaches. Hydroprene application also significantly lowered the LD50 for chlorpyrifos of the multiresistant strain at the lower hydroprene application rate. However, hydroprene failed to affect chlorpyrifos susceptibility of the susceptible strain.     

Transfer of ingested insecticides among cockroaches: effects of active ingredient, bait formulation, and assay procedures.

Foraging cockroaches ingest insecticide baits, translocate them, and can cause mortality in untreated cockroaches that contact the foragers or ingest their excretions. Translocation of eight ingested baits by adult male Blattella germanica (L.) was examined in relation to the type of the active ingredient, formulation, and foraging area. Ingested boric acid, chlorpyrifos, fipronil, and hydramethylnon that were excreted by adults in small dishes killed 100% of first instars within 10 d and >50% of second instars within 14 d. Residues from these ingested baits were also highly effective on nymphs in larger arenas and killed 16-100% of the adults. However, when the baits and dead cockroaches were removed from the large arenas and replaced with new cockroaches, only residues of the slow-acting hydramethylnon killed most of the nymphs and adults, whereas residues of fast acting insecticides (chlorpyrifos and fipronil) killed fewer nymphs and adults. Excretions from cockroaches that ingested abamectin baits failed to cause significant mortality in cockroaches that contacted the residues. These results suggest that hydramethylnon is highly effective in these assays because cockroaches that feed on the bait have ample time to return to their shelter and defecate insecticide-laden feces. The relatively high concentration of hydramethylnon in the bait (2.15%) and its apparent stability in the digestive tract and feces probably contribute to the efficacy of hydramethylnon. To control for differences among baits in inert ingredients and the amount of active ingredient, we compared 1% chlorpyrifos with 1% hydramethylnon in identical baits. Again, hydramethylnon residues provided greater secondary kill, but the results highlighted the importance of the inert ingredients. We conclude that, in the absence of cannibalism and necrophagy, translocation of baits and secondary kill are most effective with slow acting insecticides in palatable baits that can traverse the digestive tract and be deposited within and around the cockroach aggregation.     

Evaluations on the Lethal, Choice and Secondary Effects of Four Insecticidal Baits against the German Cockroach (Blattaria, Blattellidae)

ABSTRACT The laboratory studies were carried out for evaluating control effects of four commercial insecticidal baits such as two different hydramethylnon [2.0%(AI)] products (DBK^® and Combat‐Gold^®), fipronil [0.05 %(AI)] (Combat‐Power^®) and (0.6% chlorpyrifos [0.6%(AI)] (Raid‐Roachbait^®) against German cockroaches (Blattella germanica). The control rates of four kinds of toxic baits were all 100.0% mortality of German cockroaches in 5 days after treatment. The results of chlorpyrifos and fipronil brought 100.0% mortalities in 2 to 3 days after treatment, respectively. After 3 day treatment, there was no significant difference of control effect among the four toxic baits. As a result of this study, fipnonil and chlorpyrifos showed faster killing action against German cockroaches than the two hydramethylnon formulation products. In the choice test, DBK^® (hydramethylnon) (average 17.0 ind.) significantly attracted more German cockroaches than Combat‐Gold^® (hydramethylnon) (avg. 7.0 ind.), Combat‐Power^® (fipronil) (avg. 5.3 ind.) and Raid‐Roachbait^® (chlorpyrifos) (avg. 3.3 ind.). The difference in attraction effects came 10 minutes after treatment. In order to evaluate the secondary killing effect of toxic baits by coprophagy against adult Blattella germanica, the comparative test was carried out. The adult mortality rates were significantly different among the four toxic baits showing 86.7% mortality for fipronil, 60.0% for hydramethylnon (DBK^®), 30.0% for chlorpyrifos, and below 13.3% for hydramethylnon (Combat‐Gold^®) in 6 days. During the first 12 days, fipronil showed the highest mortality rate (90.0%), followed by hydramethylnon (DBK^®) (60.0%). The secondary killing effect of toxic baits by coprophagy appeared in all of the baits against adult Blattella germanica.     

Water solutions of boric acid and sugar for management of German cockroach populations in livestock production systems

Pest management in confinement swine production relies primarily on calendar-based applications of broad-spectrum insecticides. However, regulatory restrictions imposed by the U.S. Food Quality Protection Act of 1996, the large financial obligation of pesticide registration, and development of insecticide resistance have led to a renewed search for alternative control methods. Boric acid dust has long served as an insecticide in urban pest management and has been shown an effective alternative for use in sensitive environments such as swine production. However, dust formulations are difficult to apply and require specialized equipment. The purpose of this study was to evaluate the efficacy of liquid baits containing boric acid for the control of German cockroaches in a commercial swine nursery. Bait, consisting of 1 or 2% boric acid and 0.5 M sucrose, was deployed in 21 bait delivery tubes per room. Results of a 2-yr study showed significant reductions in cockroach populations. When baits were withdrawn in the summer, the cockroach population increased significantly faster than when the baits were removed during the winter. These data indicate that liquid formulations of boric acid effectively reduce the burden of cockroach infestation in swine production. This approach should have applications in structures in other urban and agricultural environments.     

Laboratory and field performance of consumer bait products for German cockroach (Dictyoptera: Blattellidae) control.

Bait formulations containing boric acid, chlorpyrifos, or hydramethylnon were evaluated in field and laboratory experiments against the German cockroach, Blattella germanica (L.). In continuous exposure tests, chlorpyrifos formulations produced 100% mortality in less than 24 h, boric acid formulations had LT50's of approximately 5.5 d, and hydramethylnon had an LT50 of 0.86 d. LT50's estimated in Ebeling choice boxes were 1.6 to 10.8 times greater than those from continuous exposure tests for chlorpyrifos formulations and 2.5 times greater for the hydramethylnon formulation. The same LT50's were produced by choice box and continuous exposure tests for boric acid formulations. Relative repellency, measured as the mean percentage of live cockroaches in the light side of the choice box, was greatest for chlorpyrifos formulations, followed by boric acid formulations, then hydramethylnon. A performance index (PI) that combined choice box repellency and mortality data indicated that hydramethylnon (Combat) had the greatest potential for field effectiveness. Only hydramethylnon significantly reduced German cockroach populations in the field. Apartments treated with the IT WORKS formulation of boric acid bait had significantly greater cockroach trap catches. The PI is an accurate predictor of the field performance of toxic baits for German cockroach control.     

The potential use of entomopathogenic nematodesagainst Typhaea stercorea

Four entomopathogenic nematode species, Steinernema carpocapsae, S. feltiae, Heterorhabditis bacteriophoraand H. megidis, were tested in a petri dish assay against larvae and adults of the hairy fungus beetle Typhaea stercorea. In general, adults were less susceptible than larvae and the LC₅₀ decreased with the duration of the exposure to nematodes. S. carpocapsae was the most effective species against adult beetles (LC₅₀ after 96 hours exposure =67 nematodes/adult). Against larvae S.carpocapsae and H. megidis were comparablyeffective with an LC₅₀ of 30 and 55nematodes/larvae, respectively. S. carpocapsaewas tested at 70 and 100% RH against adults in baits of either chicken feed or crushed wheat, both supplemented with horticultural capillary matting pieces in order to obtain a wet weight of 50–60%. At70% RH no significant effect of the nematodes was obtained due to desiccation of the bait. In chickenfeed at 100% RH the mortality reached 80% with 500nematodes/adult. In wheat significant mortality was obtained only at 5000 nematodes/adult. Heavy growth of mould probably limited the nematode infection. When the bait was used in tube traps, desiccation and growth of mould was prevented, but nematode efficacy dropped to 4.4% in the traps and 12% in the surrounding litter. This revised version was published online in July 2006 with corrections to the Cover Date.     

Origin and extent of resistance to fipronil in the German cockroach, Blattella germanica (L.) (Dictyoptera: Blattellidae)

Fipronil, a phenylpyrazole insecticide, was made available in 1999 in bait formulations for use against the German cockroach, Blattella germanica (L.). We have investigated resistance to fipronil in the descendants of cockroaches collected just before, or contemporaneously with, the introduction of fipronil baits. Cockroaches were obtained in two types of settings: homes that either had or had not been serviced by a pest management professional while occupied by their current residents. Thorough inspections by us turned up no evidence that fipronil had been used in any of the homes, and in addition, no residents claimed to have used baits containing fipronil. Resistance to fipronil was detected by topically dosing adult males with the LC99 of fipronil, the value of which was determined in a dose-response assay with males of an insecticide-susceptible strain. Fewer than 99 of 100 males of all field-collected strains died within 72 h of being treated. Moreover, substantial numbers of males survived doses three and 10-fold greater than the LC99. Regression analysis showed that 67% of the variation in the percentage of males that died after being treated with fipronil was explained by a linear relationship with the percentage that died after being treated with dieldrin. Therefore, it appears that resistance to fipronil in German cockroaches--whose ancestors had never been exposed to it--is attributable to enduring resistance to the cyclodienes, which were formerly used for cockroach control and have a similar mode of action as fipronil. Lastly, we found that insects resistant to topically administered fipronil were likewise resistant, and to a similar degree, to ingested fipronil.     

Performance of gel and paste bait products for German cockroach (Dictyoptera: Blattellidae) control: laboratory and field studies.

Gel and paste bait formulations containing boric acid or hydramethylnon were evaluated in field and laboratory experiments with the German cockroach, Blattella germanica (L.). Bait formulations contained 14-62% water by weight and lost the most water after 1 d of desiccation. Bait age and water content did not alter the toxicity (LT50) of boric acid-based baits. Toxicity of hydramethylnon (Maxforce) bait, however, increased with bait age. In continuous exposure tests without harborage, boric acid formulations had LT50s of 8.5 and 10.1 d for Blue Diamond and IT WORKS, respectively. Maxforce bait had an LT50 of 4.2 d. LT50s determined with cardboard harborage or in Ebeling choice boxes were 1.5 to 2.2 times lower than those from continuous exposure tests without harborage. Relative repellency, measured as the mean percent of live cockroaches in the light side of the choice box, was greatest for IT WORKS (21.4%) and Maxforce (25.4%) formulations, followed by Blue Diamond (10.9%). A performance index that combined choice box repellency and mortality data indicated that Maxforce had the greatest potential for field effectiveness. Blue Diamond and Maxforce significantly reduced German cockroach populations in the field. Maxforce performed best in field trials when applied at 10 or 20 placements per apartment. Apartments treated with IT WORKS had significantly greater cockroach trap catches. Factors that may affect the predictive power of the performance index are discussed.     

Expression of tropomyosin from Blattella germanica as a recombinant non-fusion protein in Pichia pastoris and comparison of its IgE reactivity with its native counterpart

Tropomyosins derived from invertebrates are well-known pan allergens. However, the allergenicities of recombinant tropomyosins are variable. Here, we undertook to compare the IgE-binding reactivities of native and recombinant German cockroach tropomyosins. Native tropomyosin was purified by ammonium sulfate fractionation, hydroxyapatite column chromatography, and electroelution, and recombinant tropomyosin was expressed in Pichia pastoris. The allergenicities of the native and recombinant tropomyosins were compared by ELISA inhibition analysis. Native German cockroach tropomyosin showed 18% IgE-binding reactivity to German cockroach sensitized sera. Recombinant tropomyosin was produced without fusion protein and its N-terminus was blocked like that of the native counterpart. The IgE-binding reactivity of the recombinant was found to be comparable to that of native tropomyosin over the concentration range 1-1000 ng/ml by ELISA inhibition testing. Recombinant German cockroach tropomyosin expressed in Pichia pastoris showed better allergenicity than that expressed in Escherichia coli. Other factors in addition to the structural differences of native and recombinant proteins may also influence the IgE reactivities of tropomyosins.     

Toxicity, sublethal effects, and performance of sulfluramid against the German cockroach (Dictyoptera: Blattellidae)

Topical and oral toxicity of sulfluramid (N-ethyl perfluorooctane sulfonamide) were determined for the German cockroach, Blattella germanica (L.). The topical LD50 of sulfluramid was 175.6 micrograms/g for adult males, 117.8 micrograms/g for adult females, and 122.3 micrograms/g for gravid adult females. Ingestion increased toxicity approximately 1.4 times for adult male B. germanica. Twenty-four hours after topical treatment with 20 micrograms/insect sulfluramid, the percentage of female cockroaches that dropped their oothecae increased approximately 50% compared with controls treated with acetone. Sulfluramid also decreased oothecal hatch of both dropped and retained oothecae. Approximately 90% of oothecae from untreated females hatches, whereas less than 20% hatched from females treated with 20 micrograms/insect. Mean time for oothecal hatch increased linearly with increasing sulfluramid concentration. In arena studies in Ebeling choice boxes, LT50's ranged between approximately 2.3 and 3.9 d for a 0.331 mg/cm2 deposit and a 1.5% bait, respectively. Higher concentrations of sulfluramid were more repellent in both bait and residual formulations. Performance index values indicated excellent potential field efficacy. Field trials with 1.0 and 1.5% (AI) baits showed up to a 71.3% reduction in cockroach numbers. Baits controlled cockroaches throughout the 12-wk test.     

Toxicity of fipronil to German and American cockroaches

Topical and oral toxicity of fipronil, compared to chlorpyrifos, was determined for the German cockroach, Blattella germanica (L.), and American cockroach, Periplaneta americana (L.). Fipronil and Combat bait matrices were evaluated for their attractancies to both species. In the topical toxicity tests, LD50's of fipronil, at 72 h after topical application, were 0.03 and 0.02 µg/g for adult B. germanica and P. americana, respectively. Fipronil was significantly more toxic than topically applied chlorpyrifos (LD50's were 0.06 and 0.16 µg/g for B. germanica and P. americana, respectively). The oral toxicity of fipronil and chlorpyrifos in Petri dish experiments, against both species, was affected by stage (for B. germanica), diet concentration, and feeding assay. Fipronil caused higher mortality of B. germanica than chlorpyrifos in two feeding assays (continuous and abbreviated). Both compounds were equally toxic to adult males of P. americana at all rates. Fipronil caused higher nymphal mortality than chlorpyrifos 48–72 h after exposure in both feeding assays. In large population chamber tests, fipronil bait was more effective and faster in killing P. americana than Raid and Combat. LT50's were 0.8, 2.4, and 7.6 d for fipronil, Raid (a.i. = chlorpyrifos), and Combat (a.i. = hydramethylnon) baits, respectively. Mortality reached 96.5, 93.4, and 84.6%, respectively, at the end of the 14 d test. In the bait attractancy tests, both strains of B. germanica were attracted similarly to fipronil and Combat bait matrices. P. americana were attracted more to fipronil than to Combat bait matrix or to other alternative foods.     

Shifts in Social Structure of Black Howler (Alouatta pigra) Groups Associated with Natural and Experimental Variation in Population Density

We examined variation in the group structure of black howlers (Alouatta pigra) using the adult composition of 48 social groups. We compared the structure of groups at 5 sites with different population densities and variation in group structure over time with rising population density. In addition, we examined changes in the group structure of monkeys that were translocated from an area of high population density to an area with a much lower population density. We found at low population densities, groups comprised either heterosexual pairs or a single male with two females. At high population densities groups tended to be multimale and often contained >2 adult females. We suggest the relative costs and benefits of dispersal by maturing adults varies with population density, and in Alouatta pigra results in a shift from single to multimale groups of larger size with increasing population density.