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PubMed2003

The multicolored Asian lady beetle, Harmonia axyridis: a review of its biology, uses in biological control, and non-target impacts.

Throughout the last century, the multicolored Asian lady beetle, Harmonia axyridis (Pallas) has been studied quite extensively, with topics ranging from genetics and evolution to population dynamics and applied biological control being covered. Much of the early work on H. axyridis was conducted in the native Asian range. From the 1980's to the present, numerous European and North American studies have added to the body of literature on H. axyridis. H. axyridis has recently gained attention in North America both as a biological control agent and as a pest. This literature review was compiled for two reasons. First, to assist other researchers as a reference, summarizing most of the voluminous body of literature on H. axyridis pertaining to its biology, life history, uses in biological control, and potential non-target impacts. Secondly, to be a case study on the impacts of an exotic generalist predator.

Animals↗
PubMed2000

Biological control of an insect pest by gut-colonizing Enterobacter cloacae transformed with ice nucleation gene.

The ice nucleation (IN) gene inaA of epiphytic Erwinia (Pantoea) ananas IN10 was transformed into Enterobacter cloacae WBMH-3-CMr originated from the faeces of silkworms. The transformant designated as Ent. cloacae WBMH-3-CMr(pICE6S13) exhibited IN activity, unlike the parent strain. The transgenic strain was ingested by mulberry pyralid larvae, fed on detached mulberry leaves, and the supercooling capacity and cold hardiness of these larvae were examined. The mean supercooling point (SCP) of the larvae ingesting the transgenic strain was - 3.3 degrees C, 8 degrees C higher than that of larvae treated with distilled water (control) and 1.5 C higher than an ice nucleation active (INA) strain of Erw. ananas. The SCPs of the larvae were stably maintained over the 9 d after ingestion. The maintenance of these high SCPs was due to transgenic Ent. cloacae having a more stable and efficient gut colonization than Erw. ananas, which is identified by the distribution of a narrower range of SCPs (-2 to -5 degrees C) in larvae treated with the transgenic stain. Furthermore, most of the larvae ingesting the transgenic strain froze and died when they were exposed to cold conditions of -5 degrees C for 18 h, 3 or 7 d after ingestion. In contrast, most of the larvae ingesting no bacterium did not die under similar conditions. On the other hand, the growth ability of Ent. cloacae WBMH-3-CMr on mulberry leaves tended to be lower than that of epiphytic Erw. ananas, as assayed by pot tests. These findings would expand the possibility of biological control using INA bacteria since Ent. cloacae would harbour a broader host (insect) range for gut colonization and a smaller affinity to plants to benefit from prevention of plant frost injury.

Animals↗
PubMed2005

Soil suppressiveness to Rhizoctonia solani and microbial diversity.

Rhizoctonia solani anastomosis group 2-2IIIB causes damping-off, black root rot and crown rot in sugar beet (Beta vulgaris). Based on experiences of growers and field experiments, soils can become suppressive to R. solani. The fungus may be present in the soil, but the plant does not show symptoms. Understanding the mechanisms causing soil suppressiveness to R. solani is essential for the development of environmentally friendly control strategies of rhizoctonia root rot in sugar beet. A bioassay that discriminates soils in their level of disease suppressiveness was developed. Results of bioassays were in accordance with field observations. Preliminary results indicate an active role of microbial communities. Our research is focused on the disentanglement of biological mechanisms causing soil suppressiveness to R. solani in sugar beet. Therefore, we are handling a multidisciplinary approach through experimental fields, bioassays, several in vitro techniques and molecular techniques (PCR-DGGE).

Antibiosis↗
PubMed2004

A PCR-based approach to distinguish important Diadegma species (Hymenoptera: Ichneumonidae) associated with diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae).

The diamondback moth, Plutella xylostella (Linnaeus) has a cosmopolitan distribution and is one of the major pests on cruciferous plants. Biological control, especially with species of the genus Diadegma, has been successfully employed in several parts of the world, mainly in South East Asia. The taxonomy of this genus based on classical morphological characters is still unclear and misidentifications are reported. In the present study seven Diadegma species associated with P. xylostella were separated using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analyses. The second internal transcribed spacer (ITS2) of the ribosomal DNA (rDNA) was successfully amplified in all 167 individuals and digested using 11 different restriction enzymes. One restriction enzyme (CfoI) showed different restriction profiles in all species and also between two population samples of D. mollipla (Holmgren) from eastern and southern Africa. In addition, a new Diadegma species associated with P. xylostella from Ethiopia was discovered.

Animals↗
PubMed1999

Modelling density-dependent resistance in insect-pathogen interactions.

We consider a mathematical model for a host-pathogen interaction where the host population is split into two categories: those susceptible to disease and those resistant to disease. Since the model was motivated by studies on insect populations, we consider a discrete-time model to reflect the discrete generations which are common among insect species. Whether an individual is born susceptible or resistant to disease depends on the local population levels at the start of each generation. In particular, we are interested in the case where the fraction of resistant individuals in the population increases as the total population increases. This may be seen as a positive feedback mechanism since disease is the only population control imposed upon the system. Moreover, it reflects recent experimental observations from noctuid moth-baculovirus interactions that pathogen resistance may increase with larval density. We find that the inclusion of a resistant class can stabilise unstable host-pathogen interactions but there is greatest regulation when the fraction born resistant is density independent. Nonetheless, inclusion of density dependence can still allow intrinsically unstable host-pathogen dynamics to be stabilised provided that this effect is sufficiently small. Moreover, inclusion of density-dependent resistance to disease allows the system to give rise to bistable dynamics in which the final outcome is dictated by the initial conditions for the model system. This has implications for the management of agricultural pests using biocontrol agents-in particular, it is suggested that the propensity for density-dependent resistance be determined prior to such a biocontrol attempt in order to be sure that this will result in the prevention of pest outbreaks, rather than their facilitation. Finally we consider how the cost of resistance to disease affects model outcomes and discover that when there is no cost to resistance, the model predicts stable periodic outbreaks of the insect population. The results are interpreted ecologically and future avenues for research to address the shortfalls in the present model system are discussed.

Animals↗
PubMed2006

Antennal structure of male and female Aphidius rhopalosiphi DeStefani-Peres (Hymenoptera:Braconidae): description and morphological alterations after cold storage or heat exposure.

Several species of the genus Aphidius are used in biological control programs against aphid pests throughout the world and their behavior and physiology are well studied. But despite knowing the importance of sensory organs in their behavior, their antennal structure has never been described. We describe here the types and distribution of antennal sensilla in Aphidius rhopalosiphi, a larval parasitoid of several aphid species and observe how this antennal structure is modified after cold storage or heat exposure. Six types of sensilla were found on both male and female antennae. Male and female antennae differed in the total number of antennomeres (16 in males, 14 in females) and in the number and distribution of three of the six types of sensilla. After cold storage or heat exposure, we observed the appearance of a small number of abnormal sensilla.

Animals↗
PubMed1996

New insights into the mechanisms of fungal pathogenesis in insects.

Entomopathogenic fungi are attracting attention as potential biological control agents of insect pests. The mechanisms of pathogenesis have parallels with those of some plant-pathogenic fungi, particularly in the areas of formation of an infection structure, entry into the host and toxin-mediated host death. Understanding these processes will provide a rational basis for strain selection and improvement.

Animals↗
PubMed2006

A model describing the effect of sex-reversed YY fish in an established wild population: The use of a Trojan Y chromosome to cause extinction of an introduced exotic species.

A novel means of inducing extinction of an exotic fish population is proposed using a genetic approach to shift the ratio of male to females within a population. In the proposed strategy, sex-reversed fish containing two Y chromosomes are introduced into a normal fish population. These YY fish result in the production of a disproportionate number of male fish in subsequent generations. Mathematical modeling of the system following introduction of YY fish at a constant rate reveals that female fish decline in numbers over time, leading to eventual extinction of the population.

Animals↗
PubMed2004

Periodic local disturbance in host-parasitoid metapopulations: host suppression and parasitoid persistence.

Within many agricultural systems, insect pests and their natural enemies are forced to persist as a metapopulation, continuously recolonizing patches following disturbance through harvesting or spraying with insecticides. Despite the need to understand factors influencing biocontrol success, few theoretical studies of host-parasitoid interactions have examined the potential impact of local disturbance within a metapopulation framework. Here, we add periodic local mortality to series of classical host-parasitoid models to examine its effect on host suppression and parasitoid persistence. Using a deterministic lattice model, we show that despite the wide range of complex dynamics generated at the patch level, the region wide pattern of disturbance is the key factor influencing host suppression. The level of host suppression achieved can be understood in terms of both the strength of density dependent parasitism, and the relative amounts of host and parasitoid mixing amongst patches of different ages. Local dispersal among patches is sufficient to ensure coexistence of the host and parasitoid, though persistence is not necessarily associated with the formation of self-organized spatial structures reported in previous studies. Finally, a stochastic version of the model is developed, in order to highlight how the effects of demographic stochasticity may influence biocontrol success in highly disturbed agricultural systems.

Animals↗
PubMed1998

Biophysical properties of the surface of desiccation-tolerant mutants and parental strain of the entomopathogenic nematode Heterorhabditis megidis (strain UK211).

Entomopathogenic nematodes (EPN) are useful biological control agents of insect pests. However, the infective juvenile (IJ) stage which is the only stage to occur outside the host is susceptible to environmental extremes such as desiccation. We have isolated desiccation-tolerant strains of the EPN Heterorhabditis megidis. In this paper we describe the surface properties of these desiccation-tolerant mutants. Heterorhabditid IJs retain the sheath of the previous larval stage. The mutant lines possess alterations in the surface properties of the sheath. Differences were observed in fluorescent lipid analogue insertion into the surface of the sheath. Furthermore, cationized ferritin-binding studies demonstrated that the mutant lines possessed an increase in net negative surface charge. Removal of the surface layer of the sheath resulted in the loss of the mutant phenotype and in a reduction in the desiccation tolerance of the parental strain. Therefore, the negatively charged 'surface coat' appears to play an important role in the desiccation tolerance of Heterorhabditis species.

Animals↗
PubMed2001

Diapause induction and termination in the predatory mite Euseius finlandicus in peach orchards in northern Greece.

The course of diapause induction as well as of diapause termination in females of the predatory mite Euseius (Amblyseius) finlandicus Oudemans (Acari: Phytoseiidae) in Northern Greece was determined by transferring females during winter and early spring from peach trees to a short day (LD 8:16) or a long day (LD 16:8) photoperiod both at 20 degrees C. The first diapause females were found in mid September and by the first week of October all the females were in diapause. The mean number of days required for diapause termination under the short day photoperiod LD 8:16 was gradually reduced from 93.7 days in the beginning of October to less than 20 days in mid February and early March. Under the long day photoperiod of LD 16:8 diapause was terminated in less than 20 days irrespective of the date of collection. These results indicate that by mid February photoperiodic sensitivity of females was lost and diapause was terminated. However, females were found in their overwintering sites until the second half of March, probably because of the prevailing relatively low temperatures and lack of adequate food.

Animals↗
PubMed2005

The Pseudomonas chlororaphis PCL1391 sigma regulator psrA represses the production of the antifungal metabolite phenazine-1-carboxamide.

The rhizobacterium Pseudomonas chlororaphis PCL1391 produces the antifungal metabolite phenazine-1-carboxamide (PCN), which is a crucial trait in its competition with the phytopathogenic fungus Fusarium oxysporum f. sp. radicis-lycopersici in the rhizosphere. The expression of the PCN biosynthetic gene cluster in PCL1391 is population density-dependent and is regulated by the quorum-sensing genes phzI and phzR via synthesis of the autoinducer N-hexanoyl-L-homoserine lactone (C6-HSL). Here, we describe the identification of an additional regulatory gene of PCN biosynthesis in PCL1391. A mutation in the psrA gene (Pseudomonas sigma regulator), the gene product of which is a member of the TetR/AcrR family of transcriptional regulators, resulted in increased production of autoinducer molecules and PCN. Expression studies showed that inactivation of psrA resulted in increased expression of the phzI and phzR genes and the phz biosynthetic operon and that introduction of functional copies of psrA represses the expression of these genes, resulting in reduced production of autoinducer signal and PCN. Surprisingly, inactivation of psrA in the phzI or phzR quorum-sensing mutants, which do not produce detectable amounts of PCN and autoinducers by themselves, restored PCN biosynthesis. This phenomenon was accompanied by the appearance of compounds with autoinducer activities migrating at the positions of C4-HSL and C6-HSL on C18 reverse phase-thin-layer chromatography. These observations indicate that PsrA also represses at least one silent, yet unidentified, quorum-sensing system or autoinducer biosynthetic pathway in PCL1391. The expression of psrA declines at the onset of the stationary phase at the same moment at which quorum-sensing (-regulated) genes are activated. In addition, expression studies in a psrA- and a multicopy psrA background showed that psrA is autoregulated. Multiple copies of psrA repress its own expression. Mutation of gacS, encoding the sensor kinase member of a two-component global regulatory system significantly reduced production of autoinducers and PCN. We show a novel link between global regulation and quorum sensing via the PsrA regulator.

Antifungal Agents↗
PubMed2004

Delaying evolution of insect resistance to transgenic crops by decreasing dominance and heritability.

The refuge strategy is used widely for delaying evolution of insect resistance to transgenic crops that produce Bacillus thuringiensis (Bt) toxins. Farmers grow refuges of host plants that do not produce Bt toxins to promote survival of susceptible pests. Many modelling studies predict that refuges will delay resistance longest if alleles conferring resistance are rare, most resistant adults mate with susceptible adults, and Bt plants have sufficiently high toxin concentration to kill heterozygous progeny from such matings. In contrast, based on their model of the cotton pest Heliothis virescens, Vacher et al. (Journal of Evolutionary Biology, 16, 2003, 378) concluded that low rather than high toxin doses would delay resistance most effectively. We demonstrate here that their conclusion arises from invalid assumptions about larval concentration-mortality responses and dominance of resistance. Incorporation of bioassay data from H. virescens and another key cotton pest (Pectinophora gossypiella) into a population genetic model shows that toxin concentrations high enough to kill all or nearly all heterozygotes should delay resistance longer than lower concentrations.

Animals↗
PubMed1992

Insecticidal properties of genetically engineered baculoviruses expressing an insect juvenile hormone esterase gene.

Exploring the possibility of enhancing the properties of baculoviruses as biological control agents of insect pests, we tested the effect of expressing an insect gene (jhe) encoding juvenile hormone esterase. Juvenile hormone esterase inactivates juvenile hormone, which regulates the outcome of an insect molt. A cDNA encoding the juvenile hormone esterase of Heliothis virescens was inserted into the genome of Autographa californica nuclear polyhedrosis virus such that the gene was expressed under the control of a strong, modified viral promoter. This virus, however, naturally encodes an ecdysteroid UDP-glucosyltransferase which inactivates ecdysone, the hormone which initiates molting. Since ecdysteroid UDP-glucosyltransferase could mask the effects of jhe expression by blocking molting entirely, jhe-expressing viruses in which the ecdysteroid UDP-glucosyltransferase gene was deleted or disrupted were constructed. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of proteins from infected cells revealed several intracellular proteins and two major secreted proteins which reacted with antibodies to authentic juvenile hormone esterase. Western blot analysis coupled with tunicamycin treatment indicated that differential glycosylation was responsible for the multiple products. Hemolymph of recombinant virus-infected fourth-instar Trichoplusia ni larvae contained levels of juvenile hormone esterase activity 40-fold higher than maximal levels found in uninfected larvae. However, little or no difference in developmental characteristics, weight gain, or time of mortality was observed between insects infected with the jhe-expressing viruses and control viruses.

Animals↗