Evidence for pyroelectric and piezoelectric sensory mechanisms in the insect integument.

Quantitative pyroelectric (PE) and piezoelectric (PZE) measurements were carried out on the insect integument of live Blaberus giganteus (cockroach) and on dry integument preparations of the same species. Voltage responses to optical pulses of 10--500 ms, absorbed in the live integument, were PE: interference filter measurements showed the responses to be proportional to the absorbed thermal radiation flux and independent of the wavelength. The voltage/time-course of the responses was in agreement with theoretically calculated PE signals. Voltage responses to mechanical pulses were PZE. The responses of the inner and outer integument surfaces always had opposite electric signs. The polar character of the integument was confirmed by means of a separate dielectric heating method. To explain these results, we hypothesize that the PE properties are for the most part localized in the two outermost layers (outer and inner epicuticle) of the integument, which consists mainly of polar lipids and proteins. Parallel alignment of these polar molecules perpendicular to the integument surface is very likely. PE and PZE responses, therefore, will not only occur in live insects but will also be measurable in dead, dry integument preparations as long as the polar tissue texture remains intact. Due to its polar texture, the insect integument will react to rapid changes in temperature, illumination, or uniaxial pressure in the same way as nonbiological PE materials, where the voltage responses depend on dX/dt (X, pressure or temperature). It seems clear, therefore, that the well-known physiological reactions of various arthropods to such physical outside influences may be related to the PE property of their integument.     

Citrus limonoid by-products as insect control agents

Limonoids are a group of chemically related bitter tetranortriterpene derivatives found predominantly in Rutaceae and Meliaceae plants (Ourison et al., 1964). Interest in the Rutaceae limonoids has centered around limonoid removal from consumable citrus products. For example, bitterness in citrus juices (as well as in other citrus products) due to limonoids has become an increasingly serious economic problem (Wilson & Crutchfield, 1968; Sinclair, 1972). Interest in the Meliaceae limonoids, on the other hand, has centered on their efficacy as pest control and/or antitumor agents (Kubo & Klocke, 1981, 1982; Nakanishi, 1977, 1980). For example, azadirachtin, isolated from several Meliaceae trees, has proven to be a potent natural product against a myriad of insect and nematode pests (Warthen, 1979). In fact, we have isolated azadirachtin from the fresh fruit of Azadirachta indica as a potent insect ecdysis inhibitor against four agricultural pest insects with artificial diet feeding assay (Kubo & Klocke, in litt).     

Molecular control of phenoloxidase-induced melanin synthesis in an insect

The melanization reaction induced by activated phenoloxidase in arthropods must be tightly controlled because of excessive formation of quinones and excessive systemic melanization damage to the hosts. However, the molecular mechanism by which phenoloxidase-induced melanin synthesis is regulated in vivo is largely unknown. It is known that the Sp?tzle-processing enzyme is a key enzyme in the production of cleaved Sp?tzle from pro-Sp?tzle in the Drosophila Toll pathway. Here, we provide biochemical evidence that the Tenebrio molitor Sp?tzle-processing enzyme converts both the 79-kDa Tenebrio prophenoloxidase and Tenebrio clip-domain SPH1 zymogen to an active melanization complex. This complex, consisting of the 76-kDa Tenebrio phenoloxidase and an active form of Tenebrio clip-domain SPH1, efficiently produces melanin on the surface of bacteria, and this activity has a strong bactericidal effect. Interestingly, we found the phenoloxidase-induced melanization reaction to be tightly regulated by Tenebrio prophenoloxidase, which functions as a competitive inhibitor of melanization complex formation. These results demonstrate that the Tenebrio Toll pathway and the melanization reaction share a common serine protease for the regulation of these two major innate immune responses.     

The genetic consequences of a demographic bottleneck in an introduced biological control insect

Population bottlenecks may result in the loss of genetic diversity, with potentially negative consequences for species of interest in conservation biology, including rare species, invasive species and biological control agents. We examined mtDNA sequence data and four variable microsatellite loci (SSRs) in the melaleuca psyllid Boreioglycaspis melaleucae, which was introduced from Australia to Florida as a biological control agent of the invasive plant Melaleuca quinquenervia. We sampled psyllids in the native and introduced ranges as well as individuals stored from the original founding population. There was a clear loss of mtDNA haplotype diversity, as well as a loss of rare microsatellite alleles, in the introduced range. However, there was little genetic differentiation between the home and introduced ranges, and no evidence for a genetic bottleneck based on an analysis of heterozygosity with the microsatellite markers. Overall, the data showed that the demographic bottleneck had a limited effect on the genetics of populations in the new range.     

The Darwinian Revolution,as seen in 1979 and as seen Twenty-Five Years Later in 2004

My book, The Darwinian Revolution gives an overview of the revolution as understood at the time of its writing (1979). It shows that many factors were involved, from straight science through philosophical methodology, and on to religious influences and challenges. Also of importance were social factors, not the least of which was the professionalization of science in Britain in the 19th century. Since the appearance of that book, new, significant factors have become apparent, and here I discuss some of the most important – especially the way in which evolution as an idea came into being as an epiphenomenon of the ideology of cultural progress; the (often tense) interaction between ideas of biological progress and the urge to professionalization, and of how this led to a delay in the full appreciation of what Charles Darwin had done in the Origin; and the ongoing divide between biological functionalists and biological formalists, a Kuhnian-type paradigm difference that persists across the Darwinian revolution.     

The bacterium, Lysinibacillus sphaericus, as an insect pathogen

Since the first bacteria with insecticidal activity against mosquito larvae were reported in the 1960s, many have been described, with the most potent being isolates of Bacillus thuringiensis or Lysinibacillus sphaericus (formerly and best known as Bacillus sphaericus). Given environmental concerns over the use of broad spectrum synthetic chemical insecticides and the evolution of resistance to these, industry placed emphasis on the development of bacteria as alternative control agents. To date, numerous commercial formulations of B. thuringiensis subsp. israelensis (Bti) are available in many countries for control of nuisance and vector mosquitoes. Within the past few years, commercial formulations of L. sphaericus (Ls) have become available. Because Bti has been in use for more than 30 years, its properties are well know, more so than those of Ls. Thus, the purpose of this review is to summarise the most critical aspects of Ls and the various proteins that account for its insecticidal properties, especially the mosquitocidal activity of the most common isolates studied. Data are reviewed for the binary toxin, which accounts for the activity of sporulated cells, as well as for other toxins produced during vegetative growth, including sphaericolysin (active against cockroaches and caterpillars) and the different mosquitocidal Mtx and Cry toxins. Future studies of these could well lead to novel potent and environmentally compatible insecticidal products for controlling a range of insect pests and vectors of disease.     

Photoperiodic diapause under the control of circadian clock genes in an insect

Background  

Most organisms have evolved a circadian clock in order to anticipate daily environmental changes and many of these organisms are also capable of sophisticated measurement of daylength (photoperiodism) that is used to regulate seasonal events such as diapause, migration and polymorphism. It has been generally accepted that the same elements are involved in both circadian (daily) and seasonal (annual) rhythms because both rely upon daily light-dark cycles. However, as reasonable as this sounds, there remains no conclusive evidence of such a molecular machinery in insects. We have approached this issue by using RNA interference (RNAi) in Riptortus pedestris.     

Tn5 as an insect gene vector

The purpose of this study was to explore alternatives to insect-derived transposable elements as insect gene vectors with the intention of improving existing insect transgenesis methods. The mobility properties of the bacterial transposon, Tn5, were tested in mosquitoes using a transient transposable element mobility assay and by attempting to create transgenic insects. Tn5 synaptic complexes were assembled in vitro in the absence of Mg(2+) and co-injected with a target plasmid into developing yellow fever mosquito, Aedes aegypti, embryos. Target plasmids recovered from embryos a day later were screened for the presence of Tn5. Recombinants (transposition events) were found at a frequency of 1.2 x 10(-3). Some transposition events did not appear to be associated with canonical 9 bp direct duplications at the site of insertion and also were associated with either deletions or rearrangements. A Tn5 element containing the brain-specific transgene, 3 x P3DsRed, was assembled into synaptic complexes in vitro and injected into pre-blastoderm embryos of Ae. aegypti. Of the approximately 900 embryos surviving injection and developing into adults, two produced transgenic progeny. Both transgenic events involved the co-integrations of approximately five elements resulting in nested and tandem arrayed Tn5::3 x P3DsRed elements. This study extends the known host range of Tn5 to insects and makes available to insect biologists and others another eukaryotic genome-manipulation tool. The hyperactivity of synaptic complexes may be responsible for the unusual clustering of elements and managing this aspect of the element's behavior will be important in future applications of this technology to insects.     

Opioid involvement in the control of feeding in an insect, the American cockroach

Administration of the kappa opiate agonist, U-50,488H (0.10-10 mg/kg), produced over three hours a significant dose-dependent increase in the ingestive responses of free feeding American cockroaches, Periplaneta americana. These effects could be decreased by the opiate antagonist, naloxone (1.0 mg/kg), with naloxone by itself blocking the augmented feeding responses of food-deprived cockroaches. The mu opiate agonist, morphine (1.0-20 mg/kg) caused a significant dose-dependent and naloxone-reversible increase in the locomotory activity of cockroaches. These results suggest that opioid systems may be involved in the control of the feeding in cockroaches in a manner analogous to that proposed for vertebrates.     

Ethnic populations of India as seen from an evolutionary perspective

It is now widely accepted that (i) modern humans,Homo sapiens sapiens, evolved in Africa, (ii) migrated out of Africa and replaced archaic humans in other parts of the world, and (iii) one of the first waves of out-of-Africa migration came into India. India, therefore, served as a major corridor for dispersal of modern humans. By studying variation at DNA level in contemporary human populations of India, we have provided evidence that mitochondrial DNA haplotypes based on RFLPs are strikingly similar across ethnic groups of India, consistent with the hypothesis that a small number of females entered India during the initial process of the peopling of India. We have also provided evidence that there may have been dispersal of humans from India to southeast Asia. In conjunction with haplotype data, nucleotide sequence data of a hypervariable segment (HVS-1) of the mitochondrial genome indicate that the ancestors of the present austro-asiatic tribal populations may have been the most ancient inhabitants of India. Based on Y-chromosomal RFLP and STRP data, we have also been able to trace footprints of human movements from west and central Asia into India.     

The structure of an insect chymotrypsin

The South American imported fire ant (Solenopsis invicta), without natural enemies in the United States, widely infests the southern United States, causing more than a half billion dollars in health and agriculture-related damage annually in Texas alone. Fire ants are resistant to most insecticides, so control will require a more fundamental understanding of their biochemistry and metabolism leading to the design of selective, ecologically safe insecticides. The 4th instar larvae play a crucial role in the nutrition of the colony by secreting proteinases (especially chymotrypsin) which digest food products for the entire colony. The first structure of an ant proteolytic enzyme, fire ant chymotrypsin, was determined to atomic resolution (1.7 A). A structural comparison of the ant and mammalian structures confirms the "universality" of the serine proteinase motif and reveals a difference at residues 147-148, which are proteolytically removed in the bovine enzyme but are firmly intact in the ant chymotrypsin, suggesting a different activation mechanism for the latter. Likewise, the absence of the covalently attached propeptide domain (1-15) further suggests an uncharacteristic activation mechanism. The presence of Gly189 in the S1 site is an atypical feature of this chymotrypsin and is comparable only to human leukocyte elastase, hornet chymotrypsin and fiddler crab collagenase. Binding studies confirm the chymotrypsin nature of this novel enzyme.     

The formulation of the control of an expression pattern in a gene network by propositional calculus

In this study we model a gene network as a continuous-time switching network. In this model, each gene has a binary state which indicates if the gene expresses or not. We propose a method to control a sequence of expression patterns in the gene network model by adding another continuous-time switching network. By using propositional calculus, we will show that the control problem can be formulated as a mixed-integer linear programming problem with linear constraints.