A microdialysis study of allatostatin degradation in Blattella germanica (L.) (Dictyoptera, Blattellidae)

Allatostatins with a typical C‐terminal sequence YXFGL‐NH₂ are insect neuropeptides with inhibitory properties upon Juvenile Hormone production in the corpora allata, vitellogenin release by the fat body, and gut and dorsal vessel motility. All these biological effects are rapidly reversible, suggesting the occurrence of effective mechanisms for inactivation of the peptides. We have studied the degradation of DRLYSFGL‐NH₂ (BLAST‐2), one of the allatostatins of Blattella germanica, in the internal milieu of adult females of this cockroach. The experimental approach combined the use of the radioiodinated derivative [¹²⁵I‐Tyr⁴]BLAST‐2, microdialysis techniques and HPLC analysis with a radioisotope detector. Under these experimental conditions, the half‐life of BLAST‐2 in the internal milieu of the adult female of B. germanica was between 3 and 6 min. Such a short half‐life explains the high doses of allatostatins required to obtain the expected biological effects when tested in vivo, and suggests that circulating allatostatins are subject to rapid rates of synthesis and degradation in order to be operative physiologically.     

An adaptive benefit of facultative coprophagy in the German cockroach Blattella germanica

1. A possible adaptive benefit of coprophagy was investigated in nymphs of the German cockroach Blattella germanica (L.). 2. Newly ecdysed first instars, given no source of food other than conspecific faeces, survived significantly longer than first instars deprived of faeces. The faeces of adult males and females may be of different quality, however, because nymphs given female faeces were more likely to moult into the second stadium than nymphs given male faeces. 3. In contrast to first instars, second instars provided adult faeces survived only slightly longer than starved counterparts. Faecal feeding is therefore stage‐specific, as is the benefit derived from it. 4. The relationship between the nutrient composition of faeces and the survival of nymphs was also examined. First instars fed the faeces of adults that had been maintained on a high (50%) protein diet, died more slowly than first instars fed the faeces of adults that had been maintained on medium (22.5%) and low (5%) protein diets. Chemical analysis of faeces showed that the concentration of protein in adult faeces increased with the level of protein in the diet. Moreover, food choice assays showed that first instars, unlike adults, ingested more of the high‐protein diets. 5. These data support the idea that coprophagy is a stage‐specific adaptive behaviour that permits first instars to moult into the second stadium with minimal foraging.     

Biological response of German cockroaches fed diets containing allopurinol

The acceptability of dietary allopurinol to German cockroaches, Blattella germanica (L.), was assessed. In diet choice tests between rat chow with or without 0.1% w/w allopurinol there were no significant differences in nymphal development, feeding duration, visits or consumption. The LT50 of cockroaches fed a choice of diets was 3 weeks greater (7.88) than those fed non-choice a 0.1% allopurinol diet. Female cockroaches provided a choice of diets aborted a significantly greater percentage of their oothecae (98.6%) than those fed the untreated diet (1.7%). Choice arena tests of 2% allopurinol in rat chow significantly reduced cockroach populations compared with untreated controls. After 6 weeks, populations were reduced by approximately 50%, and 97% after 14 weeks. These results indicate that allopurinol is acceptable to B. germanica as a dietary supplement which could be used in baits for cockroach control.     

光周期与温度对林地德国小蠊生长发育与繁殖的影响

为弄清湖南株洲(北纬27°50′,东经112°54′)栖息于林地的德国小蠊(Blattella germanica)季节生活史策略,研究了光周期和温度对其若虫发育、龄数变异及成虫繁殖的影响。结果表明,德国小蠊的若虫发育明显受光周期的影响。长日条件(LD 16∶8h)下若虫发育最快,中间日长(LD 14∶10h)次之,短日条件(LD 12∶12h)下若虫发育最慢。将孵化后30日的若虫自长日条件向短日条件转移,则若虫发育受到明显抑制,反方向的转移,则若虫发育迅速。说明德国小蠊若虫存在滞育现象,短日条件诱导并维持滞育,长日条件解除滞育。若虫期经历的龄数受光周期和温度的影响,25℃的温度条件下,LD 16∶8h、LD 14∶10h及LD 12∶12h若虫期的龄数分别为7、8和9龄;长日条件下,30℃和25℃的若虫龄数为7龄,而20℃为9龄。根据实验室观察和林地调查结果,德国小蠊在湖南株洲1年发生1代,以滞育若虫越冬。30℃、25℃、20℃的温度条件下,卵鞘成活率分别为14.3%、90.1%和51.9%,高温和低温均不适合德国小蠊的繁殖。因此,可以认为控制若虫发育和龄数的光周期、温度反应的生态意义在于调控繁殖虫态和繁殖的适宜季节保持同步。     

Effects of myoinhibitory peptides on food intake in the German cockroach

Abstract.  Insect myoinhibitory peptides were discovered through their inhibitory activity on visceral muscle contraction. The present study tests the antimyotropic gut properties of three galanin-related myoinhibitory peptides (Mas-MIP II: GWQDLNSAW-NH2; Grb-AST-B1: GWQDLNGGW-NH₂; and Grb-AST-B3: AWRDLSGGW-NH2) in adult females of the cockroach Blattella germanica (L.) (Dictyoptera, Blattellidae). The three peptides elicit a strong inhibitory effect on both foregut and hindgut contractions, with ID₅₀ values in all the cases within the nanomolar range. In addition, the modulatory effects of these three peptides on food intake are studied on previously starved female cockroaches. The results show that Grb-AST-B3 is the most active peptide, inhibiting food intake by 60–80% at doses between 15 and 50 µg, followed by Grb-AST-B1 (45% inhibition of food intake at the 50 µg dose), whereas Mas-MIP II is inactive even at the 50 µg dose. The differences between the three peptides may be due to a differential effect of their structure on activity or to a differential degradation. These results show that myomodulatory gut activity in vitro and antifeeding effects do not always correlate.     

Expression and activity of 3-hydroxy-3-methylglutaryl-CoA synthase and reductase in the fat body of ovariectomized and allatectomized Blattella germanica

Abstract. . 3-Hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase and HMG-CoA reductase show coordinated regulation in the fat body of Blattella germanica females. Since the profile of activity is parallel to the cycle of vitellogenin production, we postulated a link between the mevalonate pathway and vitellogenesis. Here we have studied both enzymes in females of B.germanica modified by ovariectomy (which leads to a saturable accumulation of vitellogenin) and allatectomy (which supresses vitellogenesis). Protein levels and enzymatic activity for both enzymes in ovariectomized specimens rose early in the first days of imaginal life and remained high until the end of the period studied, whereas controls showed cyclic profiles. In allatectomized specimens the same parameters were measured on day 4 of adult life and values were much lower with respect to controls. The parallelism between the patterns of HMG-CoA synthase and reductase, and that of vitellogenin, suggests a functional relationship between the mevalonate pathway and the glycosylation of vitellogenin through dolichol intermediates.     

Mating effects on the feeding and locomotion of the German cockroach, Blattella germanica

Abstract. Feeding cycles and daily locomotory patterns of the German cockroach, Blattella germanica L. (Dictyoptera: Blattellidae), were correlated with the ovarian development cycle. To meet the nutrient requirement for ovarian development, females increased feeding before forming oothecae. Locomotory activity also increased when females became sexually receptive. All these activities reached a peak just before the formation of oothecae. Ovarian development ceased and locomotion and food consumption decreased during pregnancy. Both mated and virgin females showed similar reproductive cycles, but those of mated females were more precisely timed (intervals between successive oothecae, and pregnancy duration, were 5 ± 0.6 and 17 ± 0.6 days, respectively). However, the intervals between successive oothecae of virgin females were longer and less synchronized. During this longer interval, feeding took place immediately following the discharge of the ootheca, but locomotory activity increased 5 days later when females became sexually receptive. Mated females increased locomotory activities 1 or 2 days before the end of pregnancy, presumably searching for deposition sites for oothecae. Female adults were found to exhibit a daily nocturnal locomotory pattern. However, under the physiological demands of reproduction, the pattern could be changed, for example by increasing activity during photophase when females were sexually receptive. The physiological effects of reproduction override the control of the daily locomotory pattern by its diel clock.     

德国小蠊抗药性机理

德国小蠊(Blattella germanica)是一种重要的室内卫生害虫,化学防治是目前主要的防治手段,但抗药性已逐渐成为制约德国小蠊防治的关键因素。德国小蠊抗药性的产生存在多种机理,本文从行为抗性、表皮穿透性降低、代谢抗性、靶标抗性及微生物降解等方面对德国小蠊抗药性产生机理进行了综述,重点阐述了近年来德国小蠊抗药性机理最新的研究进展。     

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.     

Reproductive biology of the German cockroach,Blattella germanica: Juvenile hormone as a pleiotropic master regulator

Juvenile hormone (JH) exerts major pleiotropic effects on cockroach development and reproduction. The production of JH by the corpora allata (CA) in the adult female German cockroach, Blattella germanica, is dependent upon and modulated by both internal and environmental stimuli. Mating, intake of high-quality food, social interactions, and the presence of vitellogenic ovaries facilitate JH synthesis. Conversely, starvation, deficient diets, enforced virginity, isolation, and a pre- or post-vitellogenic ovary cause the CA to produce less JH. Sensory stimulation of the genital vestibulum by the ootheca also inhibits the CA via signals that ascend the ventral nerve cord. All these stimulatory and inhibitory signals are integrated by the brain, and a preponderance of favorable signals results in a graded lifting of brain inhibition, permitting the synthesis and release of JH. The effects of inhibitory signals on JH biosynthesis can be lifted experimentally by severing nervous connections between the brain and the CA. Such an operation accelerates activation of the CA. Besides controlling gonadal maturation in females, JH concurrently regulates the production of sexual signals, including both attractant- and courtship-eliciting pheromones, and the behavioral expression of calling (pheromone release) and sexual receptivity. Although JH is required for the expression of copulatory readiness in female B. germanica, it appears that signals associated with copulation (spermatophore, sperm, accessory secretions) can inhibit this behavioral state even when titers of JH are permissive for receptivity. These observations suggest that JH might regulate sexual receptivity in females indirectly through other directives. In males, JH accelerates not only the onset of sexual readiness but also synthesis of accessory reproductive products. Lastly, we present a novel cockroach control strategy that is based on the intimate association between food intake and rising JH titers in B. germanica females. JH analogs cause abortion of fertile oothecae in gravid females. In turn, rising JH titers and vitellogenic oocytes induce feeding in females. With strategic placement of insecticidal baits and JH analogs, gravid females, which normally feed little and are difficult to control, can thus be effectively targeted for elimination. Arch. Insect Biochem. Physiol. 35:405–426, 1997. © 1997 Wiley-Liss, Inc.