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At least 163 records · Page 9Linked to original sources
PubMed1995

Chaos: a potential problem in the biological control of insect pests.

Erratic variations are normally observed in the populations of insect pests that destroy crop plants. To establish a scientific basis for developing effective control procedures, we have developed a model system for the European Corn Borer (ECB) (Ostrinia nubilalis) for which extensive field data, as well as laboratory results, have been accumulated during the past four decades. The model includes both a natural ECB pathogen and a genetically engineered toxin-producing agent as possible means of biological control. Our aim was to determine the conditions that could cause the population to vary erratically, as observed in the field. The erratic behavior in our simulations was analyzed to determine whether it is chaotic; chaos is a distinct type of erratic behavior which shows extreme sensitivity to initial conditions, i.e., the starting size of the population. Our simulations show that an increase in the death rate of the infected ECB, or a decrease in the birth rate of uninfected ECBs from infected ones, variables that are known to be affected by weather conditions, can induce a chaotic regime in which ECB population peaks reach values far higher than before chaos set in. Population peaks are even greater in the presence of both biological control agents. The results show that a biological control regime cannot be effective under conditions that induce chaotic population dynamics. Microcosm studies could be used to determine whether this situation would occur in the field.

Animals↗
PubMed1985

Laboratory evaluation of controlled-release insect repellent formulations.

Seven microcapsule formulations and two polymer formulations of deet were tested on white rabbits for their repellency against the mosquito, Aedes aegypti. Two microcapsule formulations and one polymer formulation provided more than 80% protection for 12 hours. Results demonstrated that the protection period of deet can be extended through controlled-release techniques.

Administration, Cutaneous↗
PubMed1992

A bifunctional heterodimeric insect neuropeptide analog.

The synthesis and biological activity of a bifunctional, heterodimeric insect neuropeptide analog are described. The heterodimer is composed of the C-terminal pentapeptide active core regions of the leucokinin/achetakinin and pyrokinin neuropeptide families linked via their N-terminal amino groups with a succinyl diacid moiety. Members of the leucokinin/achetakinin family can induce fluid secretion in malpighian tubules of the house cricket, Acheta domesticus, whereas the pyrokinins demonstrate activity in a cricket oviduct myotropic bioassay. No cross-activity is observed for the two neuropeptide families in these bioassays. However, the heterodimer elicits responses in both Acheta bioassays. Such a bifunctional analog may in future serve as a template for the design of stable, bifunctional pest insect control agents of greater efficiency.

Amino Acid Sequence↗
PubMed1975

Male-linked translocations and the control of insect pest populations.

Published data on an experimental release of Culex pipiens carrying a male-linked translocation are re-examined and it is shown that the steady decline in translocation frequency after termination of releases agrees with theoretical expectations, because of the selective disadvantage of translocation heterozygote males. Systems based on negative heterosis or meiotic drive are considered whereby it might be possible to prolong the population control which would be achieved by a short term release.

Animals↗
PubMed1993

Insect neuropeptides: discovery and application in insect management.

New approaches to the development of insect control agents have been revealed through the molecular description of neuropeptides, their biogenesis, action, and degradation. Prerequisite to the exploitation of a neuropeptide as a lead to control agent development is a thorough understanding of the biochemistry of the neuropeptide and appreciation of its physiological impact. Reliable bioassays must be coupled with advanced biochemical and molecular genetic technologies to overcome limitations imposed by the typically low endogenous levels of individual neuropeptides. Purification, amino acid sequencing, and gene cloning provide the molecular tools necessary for studies on neuropeptide synthesis, processing, secretion, receptor binding, and inactivation. Each of these areas consists of a number of amino acid sequence-, and enzyme-dependent steps which may be considered as targets for the development of highly specific control agents. These agents will include antagonist and superagonists, peptidomimetics, recombinant peptides delivered through the baculovirus technology, receptor blockers, and enzyme inhibitors.

Amino Acid Sequence↗
PubMed1995

Evolution and structural conservation of the control region of insect mitochondrial DNA.

The control regions of mitochondrial DNA of two insects, Schistocerca gregaria and Chorthippus parallelus, have been isolated and sequenced. Their sizes are 752 bp and 1,512 bp, respectively, with the presence of a tandem repeat in C. parallelus. (The sequences of the two repeats are highly conserved, having a homology of 97.5%.) Comparison of their nucleotide sequences revealed the presence of several conserved sequence blocks dispersed through the whole control region, showing a different evolutionary pattern of this region in these insects as compared to that in Drosophila. A highly conserved secondary structure, located in the 3' region near the small rRNA gene, has been identified. Sequences immediately flanking this hairpin structure rather than the sequences of this structure themselves are conserved between S. gregaria/C. parallelus and Drosophila, having a sequence consensus of "TATA" at 5' and "GAA(A)T" at 3'. The motif "G(A)nT" is also present in the 3' flanking sequences of mammalian, amphibian, and fish mitochondrial L-strand replication origins and a potential plant mitochondrial second-strand-replication origin, indicating its universal conservation and functional importance related to replication origins. The stem-and-loop structure in S. gregaria/C. parallelus appears to be closely related to that found in Drosophila despite occupying a different position, and may be potentially associated with a second-strand-replication origin. This in turn suggests that such a secondary structure might be widely conserved across invertebrates while their location in the control region may be variable. We have looked for such a conserved structure in the control regions of two other insects, G. firmus and A. mellifera, whose DNA sequences have been published, and their possible presence is discussed. Mitochondrial control regions characterized to date in five different insect taxa (Drosophila, G. firmus, A. mellifera, S. gregaria, and C. parallelus) may be classed into two distinct groups having different evolutionary patterns. It is observed that tandem repetition of regions containing a probable replication origin occurred in some species from disjunct lineages in both groups, which would be the result of convergent evolution. We also discuss the possibility of a mechanism of "parahomologous recombination by unequal crossing-over" in mitochondria, which can explain the generation of such tandemly repeated sequences (especially the first critical repetition) in the control region of mtDNA, and also their convergent evolution in disjunct biological lineages during evolution.

Animals↗
PubMed1981

Effects of red-headed in sawfly, Neodiprion lecontei, nuclear polyhedrosis virus on rainbow trout, Salmo gairdneri, and Daphnia pulex.

The effects of a nuclear polyhedrosis virus (NPV) of the red-headed pine sawfly, Neodiprion lecontei, on rainbow trout, Salmo gairdneri, were investigated. The fish were exposed to this virus by intubation and topical application and no ill-effects were observed. Similarly, no ill-effects were detected in Daphnia pulex when the same NPV was added to their culture medium. The materials were lyophilized, NPV-infected sawfly larvae (normally used for insect control), lyophilized, uninfected larvae and purified, polyhedral inclusion bodies. On the basis of these laboratory tests, this virus, when disseminated as a biocontrol agent, should present no hazard to rainbow trout or to the aquatic invertebrate Daphnia pulex, two species frequently used in toxicity tests of chemical pesticides.

Animals↗
PubMed1994

VSG gene expression site control in insect form Trypanosoma brucei.

When the African trypanosome Trypanosoma brucei is taken up from mammals by a tse-tse fly, it replaces its variant surface glycoprotein (VSG) coat by a procyclin coat. Transcription of VSG genes stops in the fly, but transcription of sequences derived from the promoter area of the VSG expression site(s) remains high. Whether this is due to continuing high activity of one promoter or to low activity of many promoters was unclear. We have used the small differences between the sequences of different expression sites to show that multiple expression site promoters are active in insect form trypanosomes. This is confirmed by the low expression of single copy marker genes introduced into the transcribed area. However, if the expression site promoter is removed from the genomic location of the expression site and inserted in the non-transcribed spacer of the ribosomal DNA (rDNA), it is derepressed. Derepression of transcription can also be accomplished by replacing the promoter of an expression site by an rDNA promoter. We conclude that the down-regulation of VSG gene expression site promoters in insect form trypanosomes is affected by both the DNA sequence of the promoter and the genomic context in which it resides.

Animals↗