Gene-flow between populations of cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae) is highly variable between years

Both large and small scale migrations of Helicoverpa armigera Hübner in Australia were investigated using AMOVA analysis and genetic assignment tests. Five microsatellite loci were screened across 3142 individuals from 16 localities in eight major cotton and grain growing regions within Australia, over a 38-month period (November 1999 to January 2003). From November 1999 to March 2001 relatively low levels of migration were characterized between growing regions. Substantially higher than average gene-flow rates and limited differentiation between cropping regions characterized the period from April 2001 to March 2002. A reduced migration rate in the year from April 2002 to March 2003 resulted in significant genetic structuring between cropping regions. This differentiation was established within two or three generations. Genetic drift alone is unlikely to drive genetic differentiation over such a small number of generations, unless it is accompanied by extreme bottlenecks and/or selection. Helicoverpa armigera in Australia demonstrated isolation by distance, so immigration into cropping regions is more likely to come from nearby regions than from afar. This effect was most pronounced in years with limited migration. However, there is evidence of long distance dispersal events in periods of high migration (April 2001-March 2002). The implications of highly variable migration patterns for resistance management are considered.     

Population dynamics and gene flow of Helicoverpa armigera (Lepidoptera: Noctuidae) on cotton and grain crops in the Murrumbidgee Valley, Australia

The population dynamics of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in the Murrumbidgee Valley, Australia, has been characterized using five highly variable microsatellite loci. In the 2001-2002 growing season, there were very high levels of migration into the Murrumbidgee Valley with no detectable genetic structuring, consistent with previous analyses on a national scale. By contrast, there was significant genetic structuring over the 2002-2003 growing season, with three distinct genetic types detected. The first type corresponded to the first two generations and was derived from local individuals emerging from diapause and their progeny. The second genetic type corresponded to generation 3 and resulted from substantial immigration into the region. There was another genetic shift in generation 4, which accounts for the third genetic type of the season. This genetic shift occurred despite low levels of immigration. During the third generation of the 2002-2003 growing season, different population dynamics was characterized for H. armigera on maize, Zea mays L., and cotton Gossipium hirsutum L. Populations on cotton tended to cycle independently with very little immigration from outside the region or from maize within the region. Maize acted as a major sink for immigrants from cotton and from outside the region. If resistance were to develop on cotton under these circumstances, susceptible individuals from maize or from other regions would not dilute this resistance. In addition, resistance is likely to be transferred to maize and be perpetuated until diapause, from where it may reemerge next season. If low levels of immigration were to occur on transgenic cotton, this may undermine the effectiveness of refugia, especially noncotton refugia.     

Tracking pyrethroid resistance in the polyphagous bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae), in the shifting landscape of a cotton-growing area

In cotton-growing areas of Central Africa, timing of host crops and pest management practices in annual rainfed cropping systems result in a shifting mosaic of habitats that influence the dynamics and resistance of Helicoverpa armigera (Hübner) populations on spatial scales, both within and across seasons. From 2002 to 2006, regional and local resistance was monitored among cotton fields and among the major host plants of the bollworm. From 2002, pyrethroid resistance increased within and across cotton-growing seasons to reach a worrying situation at the end of the 2005 growing season. Cotton crops played a fundamental role in the increase in seasonal resistance, even if the intensive use of insecticides on local tomato crops strongly concentrated resistance alleles in residual populations throughout the off-season. Due to the relative stability of resistance in H. armigera populations despite a long off-season, we believe that after the dispersal of the moths southwards at the end of the growing season, reverse migration mainly accounts for the reconstitution of populations at the onset of the following growing season. In addition, local resistance monitoring in 2005 and 2006 showed that it was possible to control the increase in resistance by temporarily stopping the use of pyrethroids during the period of peak infestation of cotton by H. armigera. On the other hand, the similar resistance frequency of populations sampled from sprayed and unsprayed synchronous hosts confirmed the absence of reproductive isolation between adults. As a result, diversity in cropping systems should be encouraged by planting alternative host plants to provide a mosaic of habitats, which in return would provide insecticide-free refuges. The implications for insecticide resistance management in annual cropping systems are discussed.     

The ecology of Helicoverpa spp. (Lepidoptera: Noctuidae) in the Riverina region of south-eastern Australia and the implications for tactical and strategic management

Decisions on the choice of appropriate tactical and strategic control techniques require an understanding of the seasonal distribution and ecology of the target species. To address this need, data were collected from 1997 to 2000 using crop surveys, field sampling and pheromone trapping to monitor the population trends of Helicoverpa armigera (Hübner) and H. punctigera (Wallengren) in the Riverina region of south-eastern Australia. The data gathered are compared to predictions from the HElicoverpa Armigera and Punctigera Simulation (HEAPS) model, that simulates Helicoverpa population dynamics to assist in identifying the drivers of regional populations and provide a framework to make informed decisions. The results highlight the contrasting seasonal dynamics of H. punctigera and H. armigera within the region. Helicoverpa punctigera populations peak in the spring, driven by large scale spring migration into the region and subsequently decline. Helicoverpa armigera populations, conversely, are characterized by a period of spring recruitment of adults from overwintering pupae within the region, followed by a within-season population increase leading to severe late season pressure. The within-season increase of H. armigera is a result of the succession of crop and non-crop hosts with the main driver being sequentially sown, unsprayed maize. Tactical and strategic management options are discussed in light of these findings.     

Conservation genetics and species status of an endangered Australian dragon, <Emphasis Type="Italic">Tympanocryptis pinguicolla</Emphasis> (Reptilia: Agamidae)

We present a phylogenetic and morphological study of the grassland earless dragon, Tympanocryptis pinguicolla, an endangered habitat specialist that occurs in a few isolated populations in eastern Australia. Tympanocryptis pinguicolla occurred historically in Victoria in south-eastern Australia, but has not been seen since 1990, and current populations are known in New South Wales and Canberra in south-eastern Australia. Recently, new populations identified as T. pinguicolla were discovered on the Darling Downs, Queensland. Translocation of individuals between these populations has been suggested as a conservation management strategy to maintain genetic diversity. To address this issue, we undertook a phylogenetic study of all major populations of T. pinguicolla using a 1838 bp region of mitochondrial DNA, incorporating ND1, ND2, COI and eight tRNA genes. We incorporated specialized degraded-DNA techniques to amplify DNA from historical museum specimens, as no extant tissue was available for Victorian populations. Our results, which include morphological analysis, provide convincing evidence that populations currently identified as T.␣pinguicolla do not comprise a monophyletic species, as the populations from the Darling Downs are more closely related to T. tetraporophora than to T. pinguicolla. In addition, we find that there is a significant level of haplotype divergence between populations of T. pinguicolla, indicating that these lineages separated at least 1.5 mya. Our results suggest translocation may not be an appropriate management strategy and our findings that Darling Downs populations are not T.␣pinguicolla will significantly influence the conservation management of this species in Queensland.     

Resistance monitoring of Helicoverpa armigera (Lepidoptera: Noctuidae) to bt insecticidal protein during 2001-2004 in China

Susceptibility of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) field populations to the CrylAc toxin of Bacillus thuringiensis Berliner (Bt) were monitored from 1997 to 2004 in China. During 2001-2004, 53 strains from the Bt cotton planting region were sampled. The range of concentration producing 50% inhibition of larval development to third instar (IC50) values among different populations in 2001, 2002, 2003, and 2004 was 0.014-0.046, 0.010-0.062, 0.005-0.062, and 0.005-0.035 microg/ml, respectively. Diagnostic concentration studies (IC99) showed that the percentage of individuals reaching third instar ranged from 0 to 9.09%, with only four of the 53 tested populations showing values above 0%. Considering these data, it was determined that the susceptibility to CrylAc of the field populations sampled was not different from the baseline in 1997, and no movement toward resistance among H. armigera populations was apparent.     

Effect of rotational use of insecticides on pyrethroids resistance in Helicoverpa armigera (Lep.: Noctuidae)

Abstract:  To investigate fluctuation in susceptibility to insecticides in the field, natural populations of Helicoverpa armigera were collected from the same field in the region of Multan, Pakistan in 2002 and 2003. The populations were examined against pyrethroids (viz. cypermethrin, esfenvalerate and fenpropathrin) and new insecticides (viz. spinosad, abamectin and indoxacarb). In 2002, the resistance ratio (RR) of cypermethrin and esfenvalerate was significantly higher than fenpropahrin compared with susceptible population. The susceptibility to cypermethrin, esfenvalerate and fenpropathrin increased significantly in 2003; however, the RR for cypermethrin was about half the RR (38) of esfenvalerate (101) and fenpropathrin (89). The toxicity of spinosad, abamectin and indoxacarb was identical in both years. In the field experiments, abamectin was more effective than other compounds tested whereas fenpropathrin, cypermethrin and esfenvalerate had similar toxicity. These results might have important implications in resistance management and suggest that the rotational use of spinosad, abamectin and indoxacarb could help to avoid the development of multiple resistant in H. armigera .     

Temporal Dynamics of Rich Moth Ensembles in the Montane Forest Zone in Southern Ecuador1

We studied temporal dynamics of diverse moth ensembles (Arctiidae and Geometridae) in early and late succession stages of forest recovery in the montane zone of southern Ecuador. Moths were sampled using weak light sources (2 × 15 W tubes per trap) during three sampling periods (March–April 2002, wet season; October–November 2002, and August–October 2003, both “dry” seasons). Arctiid moth abundance hardly varied between sampling periods. Estimates of local diversity were lower in 2002 (wet and dry season) than in the dry season 2003, and ensemble composition was more strongly affected by sampling period rather than habitat differences. Geometridae ensembles revealed stronger temporal patterns. Geometrid abundance increased about twofold from the wet to the dry season, and temporal effects on species composition were far more pronounced that in arctiids. These differences might hint to variation in the dependence of geometrid versus arctiid larvae on ephemeral plant resources. Despite these significant temporal dynamics, in both families only a few of the more common species analyzed individually showed strong temporal changes in abundance. Almost all common species occurred as adults during all sampling periods. Therefore, even though temporal dynamics of moth ensembles are not negligible, both moth families are suitable “indicators” of community diversity and change along the succession gradient. Samples must be large enough, however, and preferably should be collated over various times of the year and in parallel, to allow for valid statements about moth diversity and species compositions in relation to habitat differences. These recommendations undermine the validity of the concept of “rapid biodiversity inventories” for speciose tropical insect communities.     

Frequency of Bt resistance alleles in Helicoverpa armigera in the Xinjiang cotton-planting region of China

Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) is a key insect pest of cotton in Xinjiang cotton-planting region of northwest China. In this region, cotton is grown on average ≈ 1.65 million ha (1.53 ≈ 1.80 million ha) annually in largely monoculture agricultural landscapes, similarly to cropping systems in the United States or Australia. Under such cropping regimes, naturally occurring refuges (with non-Bt crops) may be insufficient to prevent H. armigera resistance development to Bt toxins. Therefore, we assessed frequency of alleles conferring resistance to Cry1Ac toxin of F(1) and F(2) offspring of H. armigera isofemale lines from two distinct localities in the region during 2005-2009. More specifically, a total of 224 isofemale lines was collected from Korla County (≈ 70% Bt cotton adoption) and 402 lines from Shache County (≈ 5% Bt cotton planting). Subsequent offspring was screened on Cry1Ac artificial diet. From 2005 to 2009, resistance gene frequency in Korla fluctuated between 0.0000 and 0.0040, while being 0.0000-0.0008 in individuals collected from Shache, and there were no significant increases in both counties from 2005 to 2009. Relative average development rates (RADRs) of larvae in F(1) tests showed significant increases from Korla, but not in Shache. RADR of F(1) larvae is significantly correlated with RADR of F(2) offspring, indicating genetic variation in response to toxin in field H. armigera population. Although the occurrence of Cry1Ac resistance alleles was low in Xinjiang cotton-planting region of China, particular attention should be given to H. armigera resistance development in Korla County.     

Monitoring and adaptive resistance management in Australia for Bt-cotton: current status and future challenges

In the mid-1990 s the Australian Cotton industry adopted an insect-resistant variety of cotton (Ingard) which expresses the Bt toxin Cry1Ac that is specific to a group of insects including the target Helicoverpa armigera. A conservative resistance management plan (RMP), that restricted the area planted to Ingard, was implemented to preserve the efficacy of Cry1Ac until two-gene transgenic cotton was available. In 2004/05 Bollgard II replaced Ingard as the transgenic cotton available in Australia. It improves on Ingard by incorporating an additional insecticidal protein (Cry2Ab). If an appropriate refuge is grown, there is no restriction on the area planted to Bollgard II. In 2004/05 and 2005/06 the Bollgard II acreage represented approximately 80 of the total area planted to cotton in Australia. The sensitivity of field-collected populations of H. armigera to Bt products was assayed before and subsequent to the widespread deployment of Ingard cotton. In 2002 screens against Cry2Ab were developed in preparation for replacement of Ingard with Bollgard II. There have been no reported field failures of Bollgard II due to resistance. However, while alleles that confer resistance to H. armigera in the field are rare for Cry1Ac, they are surprisingly common for Cry2Ab. We present an overview of the current approach adopted in Australia to monitor and adaptively manage resistance to Bt-cotton in field populations of H. armigera and discuss the implications of our findings to date. We also highlight future challenges for resistance management in Australia, many of which extend to other Bt-crop and pest systems.     

新疆北部棉区作物景观多样性对棉铃虫种群的影响

如何从景观尺度上实现对害虫的科学管理已经成为昆虫生态学的研究热点.利用频振式杀虫灯诱集技术,从2007-2009年在新疆北部棉区16-17个农场近240km2作物范围内,监测和评估棉田周边作物景观对棉铃虫种群的影响.结果表明:农业景观多样化显著地影响棉铃虫种群数量,复杂作物系统中(棉花比例＜50％作物面积)棉铃虫成虫数量明显大于简单作物系统(棉花比例≥50％作物面积;棉铃虫种群数量与景观多样性指数(Simpson's Reciprocal Index)呈正相关;同时棉铃虫成虫与加工番茄、玉米和小麦的比例成正相关,但与棉花比例呈负相关.研究结果为转基因棉花抗性管理提供科学依据,同时农田景观多样性指标可作为修正棉区棉铃虫预测模型的重要指标.     

Forecasting Helicoverpa populations in Australia： A comparison of regression based models and a bioclimatic based modelling approach

Abstract Long-term forecasts of pest pressure are central to the effective management of many agricultural insect pests. In the eastern cropping regions of Australia, serious infestations of Helicoverpa punctigera (Wallengren) and H. armigera (Hübner)(Lepidoptera: Noctuidae) are experienced annually. Regression analyses of a long series of light-trap catches of adult moths were used to describe the seasonal dynamics of both species. The size of the spring generation in eastern cropping zones could be related to rainfall in putative source areas in inland Australia. Subsequent generations could be related to the abundance of various crops in agricultural areas, rainfall and the magnitude of the spring population peak. As rainfall figured prominently as a predictor variable, and can itself be predicted using the Southern Oscillation Index (SOI), trap catches were also related to this variable. The geographic distribution of each species was modelled in relation to climate and CLIMEX was used to predict temporal variation in abundance at given putative source sites in inland Australia using historical meteorological data. These predictions were then correlated with subsequent pest abundance data in a major cropping region. The regression-based and bioclimatic-based approaches to predicting pest abundance are compared and their utility in predicting and interpreting pest dynamics are discussed.     

人为干扰下荒漠啮齿动物群落格局——变动趋势与敏感性反应

2002～2004年,在阿拉善荒漠区的典型地区,选择了4种不同干扰条件的样地,分别为开垦区、轮牧区、过牧区和禁牧区,在两种尺度上研究啮齿动物群落的变动趋势及其种群的敏感性反应,在每种干扰条件的地段设计了标志流放区,面积为0.95hm2,采用标志重捕法,每月连捕4d,同时在4种不同干扰条件的地区选择了4条线路取样,每条线路面积约10 km2,采用铗日法调查,分别在4、7、10月份取样.用不同干扰条件下每个群落组成种的捕获量构成变量矩阵,应用PCA（主成分分析）方法分析群落中种群对不同干扰条件的敏感性反应.结果表明,3个年度中在两个观察尺度上,啮齿动物群落的格局在4种不同的干扰条件下表现出不同特征,各个群落的组成种类和主要种类的数量均有较大差异,特别是在开垦区和过牧区两种干扰条件下啮齿动物群落的组成种类及主要种类的数量均有较大的改变.同时PCA分析结果表明,在3个年度的两种观察尺度上,啮齿动物群落中的主要种群在4种不同干扰条件下的敏感性反应具有明显的差别.在开垦区黑线仓鼠的敏感性反应最强,在禁牧区的反应也较明显;在轮牧区各鼠种的敏感性反应差别不明显,而在过牧区三趾跳鼠和小毛足鼠的反应最强.     

Monitoring of diamondback moth (Lepidoptera: Plutellidae) resistance to spinosad, indoxacarb, and emamectin benzoate

Six to nine populations of the diamondback moth, Plutella xylostella (L.), were collected annually from fields of crucifer vegetables in the United States and Mexico from 2001 to 2004 for baseline susceptibility tests and resistance monitoring to spinosad, indoxacarb, and emamectin benzoate. A discriminating concentration for resistance monitoring to indoxacarb and emamectin benzoate was determined based on baseline data in 2001 and was used in the diagnostic assay for each population in 2002-2004 together with a discriminating concentration for spinosad determined previously. Most populations were susceptible to all three insecticides, but a population from Hawaii in 2003 showed high levels of resistance to indoxacarb. Instances of resistance to spinosad occurred in Hawaii (2000), Georgia (2001), and California (2002) as a consequence of a few years of extensive applications in each region. The collaborative monitoring program between university and industry scientists we discuss in this article has provided useful information to both parties as well as growers who use the products. These studies provide a baseline for developing a more effective resistance management program for diamondback moth.     

The Role of Integrative Taxonomy in the Conservation Management of Cryptic Species: The Taxonomic Status of Endangered Earless Dragons (Agamidae: Tympanocryptis) in the Grasslands of Queensland,Australia

Molecular phylogenetics is increasingly highlighting the prevalence of cryptic species, where morphologically similar organisms have long independent evolutionary histories. When such cryptic species are known to be declining in numbers and are at risk of extinction due to a range of threatening processes, the disjunction between molecular systematics research and conservation policy becomes a significant problem. We investigate the taxonomic status of Tympanocryptis populations in Queensland, which have previously been assigned to T. tetraporophora, using three species delimitation approaches. The taxonomic uncertainties in this species-group are of particular importance in the Darling Downs Earless Dragon (T. cf. tetraporophora), which is ranked as an endangered ‘species’ of high priority for conservation by the Queensland Department of Environment and Heritage Protection. We undertook a morphological study, integrated with a comprehensive genetic study and species delimitation analyses, to investigate the species status of populations in the region. Phylogenetic analyses of two gene regions (mtDNA: ND2; nuclear: RAG1) revealed high levels of genetic divergence between populations, indicating isolation over long evolutionary time frames, and strongly supporting two independent evolutionary lineages in southeastern Queensland, from the Darling Downs, and a third in the Gulf Region of northern Queensland. Of the three species delimitation protocols used, we found integrative taxonomy the most applicable to this cryptic species complex. Our study demonstrates the utility of integrative taxonomy as a species delimitation approach in cryptic complexes of species with conservation significance, where limited numbers of specimens are available.     

Genetic Structure and Demographic History Reveal Migration of the Diamondback Moth Plutella xylostella (Lepidoptera: Plutellidae) from the Southern to Northern Regions of China

The diamondback moth Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae) is one of the most destructive insect pests of cruciferous plants worldwide. Biological, ecological and genetic studies have indicated that this moth is migratory in many regions around the world. Although outbreaks of this pest occur annually in China and cause heavy damage, little is known concerning its migration. To better understand its migration pattern, we investigated the population genetic structure and demographic history of the diamondback moth by analyzing 27 geographical populations across China using four mitochondrial genes and nine microsatellite loci. The results showed that high haplotype diversity and low nucleotide diversity occurred in the diamondback moth populations, a finding that is typical for migratory species. No genetic differentiation among all populations and no correlation between genetic and geographical distance were found. However, pairwise analysis of the mitochondrial genes has indicated that populations from the southern region were more differentiated than those from the northern region. Gene flow analysis revealed that the effective number of migrants per generation into populations of the northern region is very high, whereas that into populations of the southern region is quite low. Neutrality testing, mismatch distribution and Bayesian Skyline Plot analyses based on mitochondrial genes all revealed that deviation from Hardy-Weinberg equilibrium and sudden expansion of the effective population size were present in populations from the northern region but not in those from the southern region. In conclusion, all our analyses strongly demonstrated that the diamondback moth migrates within China from the southern to northern regions with rare effective migration in the reverse direction. Our research provides a successful example of using population genetic approaches to resolve the seasonal migration of insects.     

Long range forecasts of the numbers of Helicoverpa punctigera and H. armigera (Lepidoptera: Noctuidae) in Australia using the southern oscillation index and the sea surface temperature

The use of long-term forecasts of pest pressure is central to better pest management. We relate the Southern Oscillation Index (SOI) and the Sea Surface Temperature (SST) to long-term light-trap catches of the two key moth pests of Australian agriculture, Helicoverpa punctigera (Wallengren) and H. armigera (Hübner), at Narrabri, New South Wales over 11 years, and for H. punctigera only at Turretfield, South Australia over 22 years. At Narrabri, the size of the first spring generation of both species was significantly correlated with the SOI in certain months, sometimes up to 15 months before the date of trapping. Differences in the SOI and SST between significant months were used to build composite variables in multiple regressions which gave fitted values of the trap catches to less than 25% of the observed values. The regressions suggested that useful forecasts of both species could be made 6-15 months ahead. The influence of the two weather variables on trap catches of H. punctigera at Turretfield were not as strong as at Narrabri, probably because the SOI was not as strongly related to rainfall in southern Australia as it is in eastern Australia. The best fits were again given by multiple regressions with SOI plus SST variables, to within 40% of the observed values. The reliability of both variables as predictors of moth numbers may be limited by the lack of stability in the SOI-rainfall correlation over the historical record. As no other data set is available to test the regressions, they can only be tested by future use. The use of long-term forecasts in pest management is discussed, and preliminary analyses of other long sets of insect numbers suggest that the Southern Oscillation Index may be a useful predictor of insect numbers in other parts of the world.     

Characteristics of resistance to Bacillus thuringiensis toxin Cry2Ab in a strain of Helicoverpa punctigera (Lepidoptera: Noctuidae) isolated from a field population

In 1996, the Australian cotton industry adopted Ingard that expresses the Bacillus thuringiensis (Bt) toxin gene cry1Ac and was planted at a cap of 30%. In 2004-2005, Bollgard II, which expresses cry1Ac and cry2Ab, replaced Ingard in Australia, and subsequently has made up >80% of the area planted to cotton, Gossypium hirsutum L. The Australian target species Helicoverpa armigera (Hübner) and Helicoverpa punctigera (Wallengren) are innately moderately tolerant to Bt toxins, but the absence of a history of insecticide resistance indicates that the latter species is less likely to develop resistance to Bt cotton. From 2002-2003 to 2006-2007, F2 screens were deployed to detect resistance to CrylAc or Cry2Ab in natural populations of H. punctigera. Alleles that conferred an advantage against CrylAc were not detected, but those that conferred resistance to Cry2Ab were present at a frequency of 0.0018 (n = 2,192 alleles). Importantly, the first isolation of Cry2Ab resistance in H. punctigera occurred before significant opportunities to develop resistance in response to Bollgard II. We established a colony (designated Hp4-13) consisting of homozygous resistant individuals and examined their characteristics through comparison with individuals from a Bt-susceptible laboratory colony. Through specific crosses and bioassays, we established that the resistance present in Hp4-13 is due to a single autosomal gene. The resistance is fully recessive. Homozygotes are able to survive a dose of Cry2Ab toxin that is 15 times the reported concentration in field grown Bollgard II in Australia (500 microg/ml) and are fully susceptible to Cry1Ac and to the Bt product DiPel. These characteristics are the same as those described for the first Cry2Ab resistant strain of H. armigera isolated from a field population in Australia.     

Competition between the larvae of the introduced cane toad Bufo marinus (Anura: Bufonidae) and native anurans from the Darling Downs area of southern Queensland

Bufo marinus (L) has been present in the northern edge of the Darling River catchment for more than 25 years and the species currently occupies an area north of Chinchilla on the northern Darling Downs. This paper reports on preliminary findings of competition trials between larvae of B. marinus and native anurans in the Darling Downs area. Trials conducted in artificial ponds (1.4 × 1.2 × 0.2 m) indicated that Bufo reduced the growth of three native species (Limnodynastes tasmaniensis (Gunther), Limnodynastes terraereginae (Fry) and Notaden bennetti (Gunther)), and in some trials reduced the survival of two species (L. tasmaniensis and L. terraereginae). A fourth species (Limnodynastes ornatus (Grey)) showed higher growth rates with Bufo resulting from a non-significant reduction in survival in those treatments. One of two trials conducted in enclosures (1.0 × 0.5 × 0.4 m) placed in a permanent water body indicated that B. marinus had a negative effect on growth of L. tasmaniensis. A survey of 30 breeding sites in the area found that Bufo used only a small number of water bodies in one breeding season and showed little overlap of pool use with most native species. Therefore, although B. marinus may negatively affect growth and survival of native anurans under some circumstances, the potential impact of B. marinus may be minimal if there are always many breeding sites where native anurans can breed in the absence of B. marinus. A more extensive assessment of temporal and spatial overlap of water body use by B. marinus and native anurans is needed to understand the exact impact of B. marinus in this region.     

Return migration of Helicoverpa armigera (Lepidoptera: Noctuidae) during autumn in northern China

The autumn migration of Helicoverpa armigera (Hübner) was observed with radar and two types of light-trap at Langfang, Hebei province, China in 2001 and 2002. The sudden increase in the proportion of H. armigera moths in the searchlight trap indicated migration into the area and catches increased 10-fold during the second half of the night due to the landing of migrants before dawn. The moths' migratory flights took place at up to 2000 m above the ground, and moths flew differentially at times, and heights, when favourable (i.e. northerly) winds occurred. This facilitated the maximum displacement of moths towards the south during these 'return' migrations. The moths flew over the radar site at consistently high densities through the night, and the resulting flight durations of c. 10 h, at displacement speeds of 30-33 km h-1, would allow moths emerging in the far northeast of China (i.e. Liaoning and Jilin provinces and the Inner Mongolia autonomous region) to migrate into northern China (Hebei, Shandong and Henan provinces). The association of the seasonal migratory movements of H. armigera with crops in northern China is briefly discussed.