Neural influence on corpus allatum activity and egg maturation in starved virgin Periplaneta americana

ABSTRACT. Of sixty-seven adult female Periplaneta americana (L.) isolated when less than 8h old and kept without food at 25–30°C in LD 12:12, only six produced oothecae during 25–35 days. Growth of the basal oocytes was retarded, and maximal oocyte volume, only one-third of that in fed virgins, was achieved after about 12 days. By day 14, 60% of the basal oocytes were being resorbed in the starved females, and corpora lutea were usually all that remained beyond day 20. Oocyte growth was potentiated in starved, virgin females by severing either of the two nervi corporis allati 1 (NCA 1), and oothecae were then produced in 45–80% of cases. Sham-operated controls oviposited in fewer than 27% of the trials. Because oocyte maturation was prevented by extirpating both corpora allata (CA), but not when the glands were replaced, and because the juvenile hormone analogue, ZR 515, was highly effective in causing the starved cockroaches to produce oothecae, the starvation-induced reproductive failure probably reflects diminished hormone production by the CA. The most likely consequence of severing NCA 1 is de-repression of juvenile hormone production. The directness of the neural influence was shown by removing the one denervated CA, in which case stimulation of oogenesis was minimal even though the contralateral innervated gland was present. The incidence of ootheca production was not enhanced by transecting the NCA 2, which suggests that the CA of starved cockroaches are not inhibited via this pathway.     

Normally occurring inhibitory cells for natural killer cell activity. I. Organ distribution

Analysis of natural killer (NK) activity in different organs from mice or rats fractionated using discontinuous density gradients have revealed typical distinct density profiles according to the organ from which the NK cells were derived. High NK level organs thus tended to have significant lytic activity extending into 1.090 density fractions whereas the low NK population had its peak activity more strictly confined to the 1.067 fraction. The reason for this skewedness we find to be dependent upon the presence of an inhibitor cell for NK cells to be found in the higher-density fractions. The significance of this inhibitor cell was more apparent when NK activity was low, thus skewing peak levels to lower fractions. The activity of this inhibitory cell was not found to vary with age, thus failing to explain the age-dependent rise and fall of NK activity in rodents. Presence of such an inhibitory cell also explains why sizeable NK activity can be disclosed in a fraction of cells obtained from a population which before fractionation failed to disclose NK function.     

Exploring large vegetation databases to detect temporal trends in species occurrences

Question: Can vegetation relevé databases be used to analyse species losses and gains in specific vegetation types in Germany over time? Does the type of response (increase or decline in relative frequency) conform to observed large‐scale environmental trends in the last decades? Location: Germany. Exploring the German Vegetation Reference Database Halle (GVRD) that was established for forest and grassland vegetation within the framework of German Biodiversity Exploratories. Methods: Use of generalized linear models (GLMs) for testing changes in temporal frequency of plant taxa in a semi‐dry grassland data set (Mesobromion) and a beech forest data set (Fagion). Data were either aggregated by year, decade or by a balanced re‐sampling approach. Interpretation of the observed changes was based on species traits. Results: In both data sets significant temporal changes were observed, although the frequency of the majority of species remained unchanged. In both data sets, species with a temporal increase in frequency had higher Ellenberg N and F indicator values, compared to species that decreased, thus indicating effects of widespread atmospheric nitrogen deposition. In the forest data set, the observed increase in recruitment of deciduous trees pointed to a change in management, while trends in the grassland data set suggested use abandonment, as seen in an increased frequency of woody species. Conclusion: We demonstrate that vegetation databases represent very valuable resources for analysis of temporal changes in species frequencies. GLMs proved their value in detecting these trends, as also shown by the interpretability of model results with species traits. In contrast, the method of aggregation or re‐sampling had little influence on the general outcome of analyses.     

The effect of adipokinetic hormones on the activity of digestive enzymes

The role of the adipokinetic hormone (AKH) in the control of protease, amylase and lipase activities is examined using the cockroach Periplaneta americana and the fruit fly Drosophila melanogaster as model species. The effects of Peram‐CAH‐I and ‐II on the activity of cockroach digestive enzymes in the gastric caeca and midgut are measured both in vivo and in vitro. The results show the activity of proteases, amylases and lipases in both parts of the gut: amylase activity is higher in the gastric caeca than in the midgut; lipase activity presents the opposite trend; and protease activity is similar in both organs. The applied hormones stimulate the activity of all digestive enzymes, although this stimulation is not uniform; AKHs affect enzymes selectively, and in some cases unequally, in the gastric caeca and midgut. No substantial differences between Peram‐CAH‐I and ‐II stimulation are recorded. The in vitro results demonstrate that AKH stimulates digestive enzyme activity directly. In agreement with the cockroach results, enzymatic activity in D. melanogaster larvae producing nonfunctional AKH is lower than that in the larvae with ectopically expressed Akh gene, where enzyme activity reaches or even exceeds that of the controls. Overall, the results demonstrate the active role of AKHs in the stimulation of digestive enzyme activity in insects.     

Variation in sexual size dimorphism among populations: testing the differential‐plasticity hypothesis

Sexual size dimorphism (SSD) is a common phenomenon in animals and varies widely among species and among populations within species. Much of this variation is likely due to variance in selection on females vs. males. However, environmental variables could have different effects on females vs. males, causing variation in dimorphism. In this study, we test the differential‐plasticity hypothesis, stating that sex‐differential plasticity to environmental variables generates among‐population variation in the degree of sexual dimorphism. We examined the effect of temperature (22, 25, 28, and 31 °C) on sexual dimorphism in four populations of the cockroach Eupolyphaga sinensis Walker (Blattaria: Polyphagidae), collected at various latitudes. We found that females were larger than males at all temperatures and the degree of this dimorphism was largest at the highest temperature (31 °C) and smallest at the lowest temperature (22 °C). There is variation in the degree of SSD among populations (sex*population interaction), but differences between the sexes in their plastic responses (sex*temperature interaction) were not observed for body size. Our results indicated that sex‐differential plasticity to temperature was not the cause of differences among populations in the degree of sexual dimorphism in body size.     

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.     

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.