Chromosome organisation in the Australian plague locust Chortoicetes terminifera

In Chortoicetes terminifera 45 independently-occurring B-chromosomes were tested and 23 distinct banding variants were detected with either G- or C-banding; six types were found more than once. In particular the Type I banding morph was detected 12 times indicating that individuals carrying this type may be under a different regime of selection compared with individuals bearing other types of banding morph; or the Type I may be subjected to a higher rate of meiotic drive in either or both sexes than other types. Also the Type I appeared to be obviously related to four other banding morphs whereas most types were not obviously related to any other banding morphs, but a few were similar in banding pattern to one or two other types. Three types of B-chromosomes were found in three or more different populations. A relatively high frequency of the Type I banding morph was found in one population, which was probably mainly composed of non-migratory individuals, and also in a laboratory-raised population. The most likely mechanisms for small changes in the banding sequence of the B-chromosomes are three-break insertions which are often indistinguishable from inversions. Rearrangements which add or delete bands, or sequences of bands, to or from B-chromosomes are probably the result of exchanges which are now known to take place in rare individuals with two B-chromosomes. The most distal region of all the banding morphs of the B-chromosome in C. terminifera, plus a short interstitial region in some types, is not late-replicating and has the banding characteristics of euchromatin. The rest of the chromatin of the B-chromosomes is heterochromatic and is the latest replicating heterochromatin in the whole genome. It consists of G-bands, which are also deeply stained with C-banding, and alternating G-interbands, which in turn are stained grey with C-banding. Both of these staining combinations are seen in heterochromatin of the normal complement. The heterochromatin of the B-chromosomes is condensed throughout 1st meiotic prophase in the male and in all somatic interphase nuclei where it can be quickly detected using the G-banding technique. The B-chromosome has a relatively constant, acrocentric morphology with a tendency to increase of length of the long arm as band numbers increase. Isochromosomes of the long arm have been seen only in laboratoryraised embryos. From egg pods with significantly fewer than expected B-chromosomes it is strongly suggested that more than one male may fertilize the eggs in a single pod.     

Behavioural phase polyphenism in the Australian plague locust (Chortoicetes terminifera)

Swarming and the expression of phase polyphenism are defining characteristics of locust species. Increases in local population density mediate morphological, physiological and behavioural changes within individuals, which correlate with mass marching of juveniles in migratory bands and flying swarms of adults. The Australian plague locust (Chortoicetes terminifera) regularly forms migratory bands and swarms, but is claimed not to express phase polyphenism and has accordingly been used to argue against a central role for phase change in locust swarming. We demonstrate that juvenile C. terminifera express extreme density-dependent behavioural phase polyphenism. Isolated-reared juveniles are sedentary and repelled by conspecifics, whereas crowd-reared individuals are highly active and are attracted to conspecifics. In contrast to other major locust species, however, behavioural phase change does not accumulate across generations, but shifts completely within an individual''s lifetime in response to a change in population density.     

Isolation and characterization of nine polymorphic microsatellite loci from the desert locust,Schistocerca gregaria

Because of the scarcity of polymorphic genetic markers, only a few genetic studies on the population structure of the desert locust, Schistocerca gregaria, have been carried out. We isolated and characterized nine polymorphic dinucleotide microsatellite loci. These markers were evaluated using individuals from Niger and Senegal. Seven of these microsatellite markers are also applicable to the nongregarious subspecies Schistocerca gregaria flaviventris. Cross‐species applicability was limited to one of the loci in the sister species S. americana and in the locust Locusta migratoria.     

Outbreaks, gene flow and effective population size in the migratory locust, Locusta migratoria: a regional-scale comparative survey

The potential effect of population outbreaks on within and between genetic variation of populations in pest species has rarely been assessed. In this study, we compare patterns of genetic variation in different sets of historically frequently outbreaking and rarely outbreaking populations of an agricultural pest of major importance, the migratory locust, Locusta migratoria . We analyse genetic variation within and between 24 populations at 14 microsatellites in Western Europe, where only ancient and low-intensity outbreaks have been reported (non-outbreaking populations), and in Madagascar and Northern China, where frequent and intense outbreak events have been recorded over the last century (outbreaking populations). Our comparative survey shows that (i) the long-term effective population size is similar in outbreaking and non-outbreaking populations, as evidenced by similar estimates of genetic diversity, and (ii) gene flow is substantially larger among outbreaking populations than among non-outbreaking populations, as evidenced by a fourfold to 30-fold difference in F _ST values. We discuss the implications for population dynamics and the consequences for management strategies of the observed patterns of genetic variation in L. migratoria populations with contrasting historical outbreak frequency and extent.     

Analysis of the development of major plagues of the Australian plague locust Chortoicetes terminifera (Walker) using a simulation model

The development and decline of all the past major plagues of Chortoicetes terminifera in Australia has been analysed using all available locust data and a simulation model to estimate the course of events for periods when few locusts were reported. The model is based on the developmental biology of the locust and includes methods of estimating the duration of egg, nymphal and adult development and uses a pasture growth index and potential night displacement index to assess likely survival and migration. The analysis shows that five of the six plagues originated in the arid interior, where good spring and summer rain allowed two or three consecutive generations of successful breeding, before emigration to the agricultural country occurred in the late summer or early autumn. This is contrary to the idea held previously that most plagues developed from local breeding in established outbreak areas in the agricultural belt. The applications of these results, to improve population monitoring and control strategy by suggesting the best timing for surveys and when control would have most effect, are discussed.     

Isolation and characterization of polymorphic microsatellite loci in the Australian smelt,Retropinna semoni

Five polymorphic microsatellite loci were isolated from the Australian smelt, Retropinna semoni, in order to study levels of connectivity among populations at various spatial scales. Screening of one natural population (n = 30) from central Victoria, southeastern Australia, yielded nine to 14 alleles per locus with observed levels of heterozygosity ranging from 0.40 to 0.80. All loci were in Hardy–Weinberg equilibrium after Bonferroni correction for multiple tests. These loci should provide a useful tool in further understanding the population genetics of this species.     

Eleven novel microsatellite markers for the Asian oyster Crassostrea ariakensis

Clones from four partial genomic libraries of the Asian oyster Crassostrea ariakensis were screened to reveal 64 microsatellite-containing sequences. Polymerase chain reaction primers were designed for 34 of these loci. Reactions were optimized for 11 primer pairs and markers were evaluated in eight family crosses and one wild population from northern China. Zero to three null alleles per locus were identified in family crosses, and two of the 11 loci showed allele frequency deviations from Hardy-Weinberg equilibrium in the wild population. These markers have proven useful for genetic studies of C. ariakensis.     

Eight polymorphic microsatellite markers for Rhinanthus minor

Little research has been carried out on the genetics of Rhinanthus minor to date. To enable study of this species, eight polymorphic microsatellite loci were developed, using a genomic library enriched for microsatellites. All loci are polymorphic in the two UK populations tested, Bardister and Oxwich Bay. These microsatellite markers will be useful for studying genetic structure and subspecies differences of R. minor.     

Aerial treatment of the Australian plague locust, Chortoicetes terminifera (Orthoptera: Acrididae) with Metarhizium anisopliae (Deuteromycotina: Hyphomycetes)

Between October 1999 and April 2000, nearly 4000 ha of nymphal bands and adult swarms of Chortoicetes terminifera (Walker) were aerially treated using a ULV oil formulation of strain FI-985 of Metarhizium anisopliae var. acridum. During the mild weather (maxima 22-30 degrees C) of spring (October), there was little change in nymphal bands during the first week but at all doses between 25-100 g (1-4 x 10(12) conidia) ha(-1), the bands rapidly declined 9-12 days after treatment reaching > 90% mortality by 14 days. Metarhizium persisted for some time as there was 50% mortality of locusts fed vegetation collected from the treated blocks seven days after treatment. Persistence was confirmed by the high mortality of bands that invaded from untreated areas and of nymphs that hatched on the plot five to seven days after treatment, though mortality was then delayed until early in the third week. During summer (January), temperatures were high (maxima 36-42 degrees C), and at all doses between 25 and 125 g (1-5 x 10(12) conidia) ha(-1), there was a rapid decline seven to ten days after treatment. By 12-14 days, there was a > 90% decline in numbers in most blocks which was confirmed by helicopter surveys two weeks after treatment that found very few adults within or near treated areas. Mortality was delayed in the high dose where there were blockages of spray equipment during treatment. The clear demonstration that Metarhizium can suppress small local populations of C. terminifera led to the limited operational use of Metarhizium on an organic farm and in a National Park where nearly 2500 ha of bands and swarms were treated. Continued research is needed to develop a commercially viable product so that Metarhizium can form a significant part of a programme of integrated pest management of locusts in Australia.     

Twelve new polymorphic microsatellite loci and PCR multiplexing in the whitefly, Bemisia tabaci

Twelve new dinucleotide microsatellite loci of the whitefly, Bemisia tabaci, were obtained from enriched genomic libraries. Three polymerase chain reaction multiplex sets comprising three, five and four loci were optimized and characterized across 133 B. tabaci females from Israeli rearings and natural populations collected in four Mediterranean countries (Tunisia, France, Spain and Morocco). There were three to 24 alleles per locus and the observed heterozygosity was from 0.084 to 0.420. Deviation from Hardy-Weinberg equilibrium was detected at four loci associated with significant heterozygote deficiencies due to null alleles and presence of subpopulations that were mostly in the Tunisian sample. The 12 loci carried independent information.     

The effects of temperature and photoperiod on the morphology of the egg-pod of the Australian plague locust (Chortoicetes terminifera Walker,Orthoptera: Acrididae)

Chortoicetes terminifera can detect absolute differences of both temperature and photo-period, as well as the directional change of these parameters. Insects subjected to long-day conditions, or to an increase in photo-period during development lay long straight pods, whereas those subjected to short days or to a decrease in photoperiod during development lay short pods, which are usually curved and/or laid obliquely. Temperature does not affect oviposition behaviour at long photoperiod, but at medium and short photoperiod, high temperature or an increase in temperature promotes the production of long pods, whereas low temperature or a decrease in temperature stimulates the production of short pods. When temperature and photoperiod change in opposite directions, the effects of photoperiod override those of temperature. The significance of these findings is discussed in relation to egg development and survival.     

Isolation and characterization of microsatellite markers in the Atlantic slipper shell Crepidula fornicata for use in paternity analysis

Crepidula fornicata is an ideal species in which to study the evolution and timing of sex change. In order to test current theory on the timing of sex change, male reproductive success must be quantified. Because C. fornicata is polygamous, this can only be achieved through the development of molecular markers and paternity analysis. Here, I report the development of five polymorphic microsatellite loci that are inherited in a Mendelian fashion. The levels of polymorphism and the inheritance patterns of these loci make them suitable for paternity analysis despite the presence of null alleles.     

The role of pressure in controlling the entry of water into the developing eggs of the Australian plague locust Chortoicetes terminifera (Walker)

The normal internal hydrostatic pressure and the additional pressure necessary to rupture the egg shell was measured in the eggs of Chortoicetes terminifera, Newly laid white eggs burst at c 0.15 kg cm^-2, but after external tanning the chorion withstands c 0.5 kg cm^-2 when removed from its tanned foam ‘corset’ and 1.0 kg cm^-2 if left embedded in the egg pod material. Older eggs with formed cuticles often withstand 2.0 kg cm^-2 but yield at rather lower pressures if they develop ‘pin-holes’. As the OP of the egg contents always exceeds 7.7 kg cm^-2 the rigidity of the wall is clearly insufficient to permit the generation of high hydrostatic pressures capable of preventing water entry during the non-absorbing phases of development. Real hydrostatic pressures are lower than 0.06 kg cm^-2 in the young intact egg and reach only c 0.5 and 0.3 kg cm^-2, respectively, during the absorptive and post-absorptive phases of development. Several events contribute to the sigmoid form of the water uptake curve. Water is at first excluded by a permeability barrier associated with the chorion. Absorption is delayed until the yolk is completely enclosed by the serosal cell layer. After undergoing cleavage, the yolk is then rapidly mobilized to furnish precursors for cuticle synthesis; in consequence, the internal OP rises from δ 0.76d?K to 0.93d?K despite the massive inflow of water which is governed by the osmotic gradient. At blastokinesis the serosa becomes detached from the cuticle; cuticle deposition and yolk mobilization are halted, the OP falling rapidly to cδT 0.53d?K. The bulk entry of water then ceases. Any excessive hydrostatic pressures which develop later are relieved by the formation of self-sealing ‘pin-holes’.     

Eight polymorphic microsatellite loci for the aquatic fungus Tetracladium marchalianum

We have identified eight polymorphic microsatellite loci from the aquatic haploid fungus Tetracladium marchalianum. Microsatellite polymorphism was evaluated using 90 fungal isolates, each of single spore origin, from submerged leaves in Illinois and Wisconsin rivers in the USA. The number of alleles observed for a single locus ranged from three to 13, with up to 10 observed from a population. These genetic markers will be useful to evaluate population structure, genotypic diversity, and the reproductive mode of T. marchalianum.     

Ten polymorphic microsatellite loci for the trematode Gymnophallus sp.

Ten polymorphic loci were isolated and characterized from the intertidal New Zealand trematode Gymnophallus sp., a common parasite of the abundant local bivalve Austrovenus stutchburyi. Observed heterozygosities ranged from 0.17 to 0.96, and three to 23 alleles were detected in 24 trematode metacercariae. These loci are currently being used to investigate the molecular ecology of this species within the bivalve host.     

Eleven polymorphic microsatellite markers for Oedaleus decorus (Orthoptera, Acrididae), an endangered grasshopper in Central Europe

We isolated and characterized 11 microsatellite loci in the grasshopper Oedaleus decorus (Orthoptera: Acrididae), an endangered species in Central Europe. Polymorphism was studied from two populations, one out of two populations known from Switzerland (n = 20 individuals) and one site from south of France (n = 20). The number of alleles and the expected heterozygosity ranged from five to 12 and from 0.559 to 0.898, respectively, in the Swiss population, and from 14 to 23 and from 0.895 to 0.974, respectively, in the French population. These microsatellite markers are suitable for further conservation genetic studies of O. decorus.