Unequal coupling between locomotor pacemakers of the German cockroach,Blattella germanica (L.)

Male adult German cockroaches, Blattella germanica (L.), expressed robust locomotor circadian rhythmicity under 28 degrees C and constant darkness (DD) conditions. By surgically severing the connections between the optic lobes and midbrain and their subsequent regeneration, we demonstrated that the locomotor circadian pacemaker was located in the optic lobes and that it controlled the locomotor circadian rhythm through neural pathways. From the results that unilaterally optic tract severed males still showed locomotor circadian rhythmicity (93.1%, n=29) without significantly changing the circadian period (tau) or level of motor activity, we concluded that the right and left optic lobes each contain a circadian pacemaker competent to drive the locomotor circadian rhythm. These two pacemakers were strongly coupled since only one rhythm was expressed when the pacemakers were independently exposed to opposite lighting conditions (DD or LL) at the same time. However, an unequal contribution of each pacemaker in determining the overt circadian period was found under constant dim light (10 lux) conditions, revealing a major-minor coupling relationship between these two pacemakers, so that the unilaterally blinded male expressed either a LL-rhythm with a circadian period of 24.27+/-0.21 h (41.7%, n=24) or a DD-rhythm with a circadian period of 23.43+/-0.19 h (58.3%, n=24). However, higher intensity of photic information (200-300 lux) could overpower this relationship and cause the minor pacemaker to lead the rhythm.     

Cuticular extracts inducing aggregation in the German cockroach,Blattella germanica (L.)

German cockroaches Blattella germanica (L.) are gregarious insects. An aggregation pheromone contributes to the maintenance of aggregates. Choice experiments checked the efficiency of different solvents, i.e. dichloromethane, methanol and pentane, in extracting attractive substances and compared the attractiveness of extracts of different parts of the body. Dichloromethane and pentane were the most efficient solvents tested for extracting the attractive substances. Methanol whole body extracts appeared inefficient to induce aggregation. The proportion of larvae attracted to conditioned papers decreased in relation to the size of cuticular surface washed, from whole body to half-body and again to a section of the body cut in three. Attractive substances appear to be present on all parts of the body. Chemical analysis by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) showed that the active extracts contained only cuticular hydrocarbons. In addition to behavioural tests, differences between the composition of methanol extracts and that of the extracts for the other two solvents were revealed by GC. These results indicated that the cuticular hydrocarbons operate as an aggregation pheromone in Blattella germanica.     

Aspergillosis in German cockroach Blattella germanica (L.) (Blattoidea: Blattellidae)

Natural infection of Aspergillus flavus was observed in adults of Blattella germanica. Though the adult insects exhibited no external symptoms, they became hypoactive and later died. The dead and experimentally infected insects repeatedly yielded Aspergillus flavus in culture on Czapek's medium. Direct microscopic observation of the tissues of infected insects revealed fungal material. The blood films stained with Giemsa stain showed granulocytes (GRs) engulfing fungal hyphae. A remarkable increase in GR and plasmatocyte (PL) counts occurred in differential haemocyte counts (DHCs) of the infected insects. Two main types of immunological responses of the insect noticed were phagocytosis and encapsulation. DHC showed maximum involvement of GRs and PLs in immune mechanism. This revised version was published online in June 2006 with corrections to the Cover Date.     

Inconsistency in the expression of locomotor and ERG circadian rhythms in the German cockroach, Blattella germanica (L.).

ERG recordings from German cockroaches showed that the amplitude of light-evoked responses have a circadian rhythmicity in adult males that coincided with the locomotor circadian rhythm. The peak of the response occurred during the subjective night, and the circadian period was less than 24 h under DD condition. In contrast, although the locomotor circadian rhythm was masked by the development of ovaries and pregnancy in females, their visual responses displayed circadian rhythmicity. This inconsistency in expression of locomotor and visual sensitivity circadian rhythms in females implied separate pacemakers for these two overt rhythms. After severing the optic nerves, changes in ERG amplitude of the operated cockroaches still displayed a circadian rhythm under DD condition, demonstrating that the visual sensitive pacemaker was located in the eye and independent from the locomotor pacemaker.     

Biosynthesis of methyl branched hydrocarbons of the German cockroach Blattella germanica (L.) (orthoptera,blattellidae)

The precursors and directionality of synthesis of the methyl branched cuticular hydrocarbons and the female contact sex pheromone, 3,11-dimethyl-2-nonacosanone, of the German cockroach, Blattella germanica, were investigated by radiotracer and carbon-13 NMR techniques. The amino acids [G-³H]valine, [4,5-³H]isoleucine and [3,4-¹⁴C₂]methionine labeled the hydrocarbon fraction in a manner indicating that the carbon skeletons of all three amino acids serve as the methyl branch group donor. The incorporation of [1,4-¹⁴C₂]- and [2,3-¹⁴C₂]succinates into the hydrocarbon and acylglycerol/polar lipid fractions indicated that succinate also served as a precursor to methylmalonyl-CoA. Carbon-13 NMR analyses showed that [1-¹³C]propionate labeled the carbon adjacent to the tertiary carbon, and, for the 3,x-dimethylalkanes, that carbon-4 and not carbon-2 was enriched. [1-¹³C]Acetate labeled carbon-2 of these hydrocarbons. This indicates that the methyl branching groups of the 3,x-dimethylalkanes were inserted early in the chain elongation process. [3,4,5-¹³C₃]Valine labeled the methyl, tertiary and carbon adjacent to the tertiary carbon of the methyl branched alkanes. Thus, the methyl branched hydrocarbon was formed by the insertion of methylmalonyl units derived from propionate, isoleucine, valine, methionine and succinate early in chain elongation.     

Induction of P450 monooxygenases in the German cockroach,Blattella germanica L

The cytochrome P450 monooxygenases are an important metabolic system whose level of activity can be influenced by several dietary constituents. We examined the effects of six known P450 inducers on the levels of total cytochromes P450, cytochrome b(5), and six monooxygenase activities in adult German cockroaches. In addition, the levels of CYP6L1 and CYP9E2 mRNA were also investigated. Phenobarbital treatment resulted in increases in total cytochromes P450 and metabolism of three resorufin analogues, but not CYP6L1 nor CYP9E2 mRNA. There was no significant effect of the other five inducers on any of the monooxygenase parameters we measured. In comparison with other insects, the German cockroach seems unusually refractory to most inducing agents.     

Synergism of chlorpyrifos against the German cockroach, Blattella germanica

Of fifteen compounds tested as synergists for chlorpyrifos against susceptible and resistant strains of Blattella germanica, the German cockroach, eleven were active against the resistant strain but only seven were synergistic against the susceptible strain. Overall, the most effective synergist was S,S,S-tributyl phosphorotrithioate (DEF) followed by phenyl saligenin cyclic phosphonate (PSCP) and two substituted N,N-dimethylcarbamates: SK-102 and SK-37. The most effective synergist for overcoming chlorpyrifos resistance was SK-37 which reduced the resistance ratio by 3.2-fold. Four other synergists which reduced chlorpyrifos resistance, in order of their effectiveness, were: SK-102 > PSCP > DEF > tridiphane. The potential usefulness of these synergists for German cockroach control is discussed.     

Insecticidal activity of Artemisia sieberi,Eucalyptus camaldulensis,Thymus persicus and Eruca sativa oils against German cockroach,Blattella germanica (L.)

The German cockroach, Blattella germanica (L.) (Blattodea: Blattellidae), has been recognized as a serious health problem because of its potential to harbor and transmit human disease-causing pathogens. The development of new and environmentally friendly control agents is essential as alternative tool to conventional chemical insecticides. The aim of the current study was to determine the fumigant and contact toxicity of essential oils (EOs), Artemisia sieberi Besser, Eucalyptus camaldulensis Dehn. and Thymus persicus (Ronniger ex Rech. f.) and cold press oil of Eruca sativa (Miller) (ESO) against first instar nymphs and adults. According to results, the LC₅₀ values of EOs were between 15.01 and 28.80 μl/l air for fumigant toxicity, 2202.8 and 5600.2 mg/l for dipping toxicity and 9484.2 and 34,421.1 mg/l for applied surface toxicity. Fumigant activity of the oils were significantly more toxic than other methods. In general, the toxicity of A. sieberi was higher than other EOs. Also, the first instar nymphs were more susceptible than adults. Additionally, the results showed that the EOs were significantly more toxic than ESO in both fumigant and dipping methods. In addition to contact effects, the fumigant activity of ESO was proved, although the toxicity was lower than the EOs. Hence, it is important to consider the production cost benefit of ESO in comparison with the EOs. So, the ESO could be considered as a good candidate in control of the cockroach but in enclosed spaces such as inaccessible cockroach hiding places, the EO of A. sieberi can be useful.     

Endocrine regulation of female contact sex pheromone production in the German cockroach, Blattella germanica

ABSTRACT The amount of the major component of the cuticular sex pheromone, 3, 11-dimethyl-2-nonacosanone, on individual female German cockroaches, Blattella germanica (L.), as a function of age was determined by gas-liquid-chromatographic analysis. Accumulation of phermone increased with age in both virgin and mated females. During the first gono-trophic cycle, the pheromone accumulated most rapidly when oocyte growth rates were maximal (days 5–10), and least rapidly while the female carried an ootheca (days 11–32). Pheromone accumulation was similar in virgin and mated females when the same physiological stages (determined by oocyte maturation) were considered. Inhibition of Juvenile Hormone release, through allatectomy, chemicals (precocene or fluoromevalonate), or through mechanical egg case implants, suppressed or delayed pheromone production and oocyte growth. The Juvenile Hormone analogue ZR512 induced allatectomized or head-ligated females and females with chemically or mechanically inhibited corpora allata to produce pheromone and enlarge their basal oocytes. Finally, ZR512 applied to intact females stimulated pheromone production in a dose-dependent manner.     

Role of feeding in the reproductive 'group effect' in females of the German cockroach Blattella germanica (L.)

We have found that whether a female German cockroach, Blattella germanica (L.), is kept alone or in the presence of another female has a major impact on how fast it reproduces and how much it eats. By the sixth day of adulthood, females paired since adult eclosion had substantially larger o?cytes than did females isolated during the same time, and females paired with intact females, or with ones rendered incapable of feeding, consumed more rat chow in the first six days of adulthood than did isolated females. The stimulatory effect of pairing on reproduction was, however, partially independent of feeding because the o?cytes of solitary and paired females differed in size on day 6 even when they were given, and had consumed, the same amount of food. This result was confirmed with analysis of covariance using the total food intake of a female as the covariate in the analysis. A female's social condition probably influenced the development of its o?cytes by affecting the quantity of juvenile hormone synthesized by its corpora allata. The corpora allata of paired females produced more hormone than did those of isolated ones, even when all females had consumed an equivalent amount of food. Moreover, females treated with a juvenile hormone analog, fenoxycarb, reproduced more quickly than identically reared and fed control females, showing that juvenile hormone could influence reproduction independently of feeding. We conclude that both group rearing and food intake accelerate o?cyte development by diminishing the brain's inhibition on the synthesis of juvenile hormone.     

Resistance of the German cockroach (Blattella germanica) to bendiocarb

Two field strains of the German cockroach Blattella germanica (L.) were collected in England from survivors of treatments with bendiocarb wettable powder, and bred in the laboratory. These and a laboratory susceptible strain were compared by a tarsal contact method to test for resistance to bendiocarb, fenitrothion and dieldrin. The field strains after exposure to the insecticide for 24 h were resistant to bendiocarb in terms of mortality by factors of 5.6 and 6.2 at the LC₅₀ level, but at the LC₉₅ level the resistance factors were only 1.7 and 2.0; however knockdown resistance was detected, with resistance factors at the KD₅₀ level of 10.6 and 8.1. At shorter exposure times of 5 min and 60 min, 2–20% of cockroaches from the field strains survived 55 or 110 mg bendiocarb/m²; there were no survivors from the susceptible strain. Some cockroaches from the field strains were able to recover from knockdown after and during exposure to 110 mg bendiocarb/m². Both field strains showed some resistance to dieldrin; however, there was no resistance to fenitrothion. When all three strains were exposed to 55 mg fenitrothion/m² for 5 min, all the insects were knocked down within 3 h, and all had died within 96 h. There was no recovery from knockdown to fenitrothion or dieldrin.     

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.     

Nutritional regulation in nymphs of the German cockroach,Blattella germanica

Synthetic foods varying in protein-carbohydrate ratio and total nutrient concentration were used in food selection experiments to investigate the ingestive and post-ingestive regulation of macronutrients by male and female nymphs of the German cockroach, Blattella germanica (L.) (Dictyoptera: Blattellidae). For both nutrient imbalance and food dilution, food ingestion varied between treatments with the effect that nutrient ingestion was regulated. However, this mechanism was insufficient to compensate for some food dilution treatments. In those cases, the regulation of protein intake was prioritised over that of carbohydrate intake, and two additional regulatory responses were seen. Firstly, cellulose digestion supplemented shortfalls in dietary soluble carbohydrates, and secondly the feeding period within the stadium was prolonged. These ingestive, post-ingestive and developmental responses were orchestrated in such a way that, in all treatments, nutrient gain approached similar levels, despite the variation in food properties.     

Ultrastructure and maturation of a sex pheromone gland in the female German cockroach, Blattella germanica

A volatile sex pheromone is produced in an adult female-specific gland located on the anterior of the last abdominal tergite of the female German cockroach, Blattella germanica (L.). In this area, the cuticle forms deep depressions in which a large number of cuticular orifices are located. The cuticular orifices are connected to secretory cells via cuticular ducts surrounded by duct cells. The pheromone gland exhibits a clear developmental maturation in relation to sexual maturation of the female. The secretory cells of a newly formed gland in the imaginal female are small and contain few secretory vesicles. The amount of extractable pheromone in the gland is low on day-0 but it increases with age and peaks on day-6. The secretory cells in a mature day-6 gland are characterized by a large number of electron-lucid secretory vesicles. abundant RER and SER, a large nucleus and a long, convoluted end apparatus which is lined with numerous microvilli. The contents of the secretory vesicles are exocytosed into extracellular reservoirs at the base of microvilli and then transported to the cuticular surface through the long ducts. The supportive function of the duct cell in the glandular organization and developmental regulation of the gland are discussed.     

Inter- and intra-instar food consumption in the German cockroach, Blattella germanica

Food consumption was measured in an insecticide-susceptible (Orlando) and-resistant (Village Green) strain of German cockroach, Blattella germanica (Dictyoptera: Blattellidae), throughout each stadium. All instars exhibited a similar pattern of consumption over the course of the instar; consumption was low to moderate at the beginning of each instar, climbed steadily to a maximum near the middle, declined progressively from the mid-instar maximum, and ceased or was minimal several days before the next molt. Consumption ceased or was minimal during the final two to four days of each instar. Cumulative consumption for the six instars was significantly greater in the Village Green strain as compared with the Orlando strain. Village Green nymphs consumed 79.6±0.7 mg of rat chow while Orlando nymphs consumed 63.7±3.4 mg. Total consumption by instar increased significantly with each successive instar in the Village Green strain. In addition, Village Green sixth instar females consumed significantly more food than sixth instar males. A similar trend was observed for the Orlando strain; consumption tended to increase in each successive instar. Relative consumption rate (food consumed/cockroach/instar divided by the mean weight of the instar) was highest in the first two instars and decreased in subsequent instars.     

Phospholipid composition and pheromonal activity of nuptial secretion of the male German cockroach, Blattella germanica

As a part of the sequential courtship behavior of the German cockroach, Blattella germanica, females feed on the nuptial secretion from the male tergal glands. The pheromonal secretion, consisting mainly of oligosaccharides and phospholipids, strongly elicits a feeding response in virgin females. The phospholipids were composed of phosphatidylethanolamine and phosphatidylcholine. Their fatty acid compositions were determined by chromatographic and enzymatic methods. Although an authentic blend of phospholipids (1,2-dioleoylphosphatidylethanolamine and 1,2-dioleoylphosphatidylcholine) showed a marginal phagostimulant activity, addition of the blend to an authentic blend of oligosaccharides (maltose and maltotriose) strongly enhanced the activity to nearly the level of the crude extract. These results indicate that the nuptial feeding behavior is elicited by a synergistic action between phospholipids and oligosaccharides.     

Feeding and activation of corpora allata in the cockroach Blattella germanica (L.) (Dictyoptera,Blattellidae)

Adult females of the cockroach Blattella germanica have clearly-defined feeding cycles related to oogenesis. In the first cycle, food ingestion precedes volumetric increase in the corpora allata, which in turn precedes juvenile hormone production, whereas starved females do not develop the corpora allata and produce very low amounts of juvenile hormone. When the second gonadotropic cycle is provoked by removing the ootheca, the first event observed is an increase in food consumption, followed by an increase in corpora allata volume and activity. However, this increase in corpora allata volume (and activity) does not occur if females are starved, thus indicating that the ootheca in the genital chamber inhibits primarily feeding, and indirectly corpora allata development and activity. Corpora allata volume in isolated heads from starved and decapitated females was able to increase to levels similar to fed controls, but this increase was abolished by allatostatin treatment. We suggest that a factor produced in the thoracico-abdominal compartment, which reaches the head mainly through a nervous pathway, is released during starvation and inhibits corpora allata development. This factor may stimulate allatostatin production or release, or may well be allatostatin itself.