Pest Of Grain Crops Research Articles

Disruption of a microvitellogenin gene impairs eggshell formation in Mythimna separata

Microvitellogenin (mVg) belongs to the lepidopteran-specific lipoprotein_11 super family and is thought to be involved in insect reproduction. However, the function of mVg in reproduction has not been established. In this study, we identified and characterized MsmVg in Mythimna separata, a destructive insect pest of grain crops. MsmVg is comprised of a 1,310 bp open reading frame (ORF) encoding 437 amino acids. Structural analysis showed that MsmVg contains three conserved domains in the lipoprotein_11 super family, including the all-α-N-terminal domain (NTD), a Pseudomonas putida homologous domain (PPD), and an all-β-C-terminal domain (CTD). MsmVg was highly expressed in mature female adults and enriched in the ovaries of 3-day-old female adults. Disruption of MsmVg by RNA interference did not change the expression of MsmVg, vitellogenin (MsVg) or the vitellogenin receptor (MsVgR) in fat bodies, but it inhibited their transcription in ovaries. Phenotype analysis showed that knockdown of MsmVg did not affect yolk deposition in ovaries, but impaired eggshell formation and led to a reduction in the reproductive capacity. Furthermore, knockdown of MsmVg significantly inhibited the expression of genes associated with eggshell formation (MsChP1-3 and MsFcP3C). Taken together, these data suggest that MsmVg plays an important role in female reproduction by affecting eggshell formation in M. separata, which provides a potential target for managing this insect pest.

High-quality DNA isolation protocol for detection of Khapra beetle (Dermestidae: Trogoderma granarium Everts, 1898) in standard wheat germ trap.

Khapra beetle (Dermestidae: Trogoderma granarium Everts, 1898) is an internationally significant pest of grain crops and stored grain products. Wheat germ traps, routinely used in surveillance sampling of Khapra beetle provide feed-substrates used by the pest throughout its life cycle. However, Khapra beetle larvae, eggs and other traces of the pest, such as larval frass and exuviae, in wheat germ traps are difficult to sort and taxonomically identify. Additionally, high levels of polysaccharides in wheat germ can inhibit PCR based molecular detection of this pest captured in the traps. We have developed a sensitive and low-cost protocol for extracting trace levels of Khapra beetle DNA from an entire wheat germ trap. Overnight digestion of entire trap contents in 6 mL of ATL buffer, followed by a 40min lysis step was optimal for DNA extraction. Paired with reported qPCR assays, this protocol allows the detection of a few hairs of T. granarium in a typical 2-gram wheat germ trap. This DNA extraction protocol makes it possible to perform a more rapid identification of the pest following wheat germ sample collection. The protocol has potential to improve international efforts for Khapra beetle surveillance.

Diagnosis of intrapopulation adaptation genesis of bird cherry aphid <i>Rhopalosiphum padi</i> (L.) under nutrition conditions on various spring common wheat varieties

The widespread cultivation of highly productive varieties of agricultural crops often leads to the emergence and spread of new intraspecific forms of insects capable of mass reproduction. The control of these processes is of environmental importance and is possible based on monitoring the variability of the phenol appearance of pest populations. There has been carried out a vegetative and field estimation of phenogenetic variability of such pest of grain crops as the bird cherry-grass aphid Rhopalosiphum padi (L.) under nutrition on 15 spring common wheat varieties. There has been conducted an ecological phenotyping of the adaptability of the intrapopulation composition of aphids under vegetative conditions according to abundance and dispersal ability in the offspring of summer morphs (emigrants and wingless viviparas) in three different clones. There has been identified a differentiated interaction of clones and morphs of aphids with varieties of fodder plants for both indicators. There has been shown that the reproduction rates of emigrants and wingless viviparous aphids within clones (14, S and 85) differed (t14 = 3.9, p =.000; Fs = 8.8, p = 0.000; F85 = 7.9, p = 0.000). Clone S was more successful than others in reproducing emigrants and wingless vivipares (F14 = 17.8, p = 0.000; F85 = 3.4; p = 0.03; F'14 = 2.98, p = 0.05; F'85 = 5.3, p = 0.003, respectively). Favorability of individual varieties for clones did not match. When the aphid population was destabilized, compensatory mechanisms included a discrepancy in the reactivity of individual morphs to unfavorable conditions. There has been shown a correlation (r = 0.53; p = 0.04) between the degree of favorableness of varieties for feeding aphids in vegetation (antibiosis) and field conditions (antibiosis and antixenosis), which has confirmed the similarity of the genetic nature of these types of resistance.

Transcriptomic analysis of Mythimna separata ovaries and identification of genes involved in reproduction

The migratory insect Mythimna separata is a major pest of grain crops in Asia. Unfortunately, the molecular mechanisms that control and regulate reproduction in this species remain unclear. In this study, transcriptome sequencing was utilized to identify genes associated with ovary development and oogenesis. Clean sequences totaling 117.71 Gb were assembled into 178,534 unigenes with a mean length of 647.37 bp and N50 length of 837 bp. Transcriptome analysis showed that 7921 unigenes were significantly expressed in ovaries with 4403 and 3518 unigenes up- and down-regulated, respectively. Enrichment analysis with the Kyoto Encyclopedia of Genes and Genomes database suggested that 729 differentially expressed genes were significantly enriched in the top 20 pathways (q-values <0.05). Twenty genes were associated with ovary development and oogenesis and included lipases, Nanos, small heat shock proteins (sHsps) and histones; these were further verified by qRT-PCR and may play essential roles in M. separata reproduction. Collectively, our findings reveal underlying mechanisms of M.separata reproduction and may lead to RNAi-based management strategies targeting reproductive physiology.

Economic benefits of conservation biocontrol: A spatially explicit bioeconomic model for insect pest management in agricultural landscapes

Spatially explicit population dynamic models have been successfully used to explore management scenarios in terms of pest suppression across a wide range of systems. However, the economic implications of pest management, particularly in the case of biological control and non-crop management strategies, have not been well considered. A bioeconomic spatially explicit simulation model was developed, that integrates models of pest population dynamics, pest movement and economics of management. The utility of the model is demonstrated here usingNysius vinitor, a pest of grain crops in Australia. The model estimates the short- and long-term economic benefits of three pest management strategies: (1) in-field pesticide spray; (2) pest suppression through weed management in non-crop habitat; and (3) bolstering biocontrol through revegetation with, or maintenance of, native vegetation. Across all management types, high yield and low relative management cost resulted in a greater chance of a gross profit. The impacts of the pests themselves were shown to be non-linear, with an intermediate level of pest pressure maximizing the economic gain from management. Pest dispersal capacity influenced the profitability of management of non-crop vegetation, with lower pest dispersal resulting in a greater likelihood of benefit, as benefits from non-crop management are localized (e.g., increased beneficial insect populations). In an intensively cropped landscape, pesticide management was most profitable over the short-term. Once a 10-year horizon was reached, then the profitability of revegetation was greater and continued to increase. While weeding requirements are low, it is likely to always be profitable in the long-term to maintain or restore native vegetation in good condition to control this pest in an intensively cropped landscape. Using pesticide alongside revegetation gave some short-term gain, but the negative impact of pesticide on beneficials outweighed the benefit and in the long-term it is less profitable. These results do not hold in a low production landscape, due to increased pest pressure and costs of managing non-crop habitat. In summary, when quantified over a 10–20 year time horizon, revegetation or conserving native remnants in good (i.e., non-weedy) condition could be economically more beneficial to control an insect pest than ongoing pesticide use, in intensively cropped landscapes.

The clock gene, period, influences migratory flight and reproduction of the oriental armyworm, Mythimna separata(Walker).

The oriental armyworm, Mythimna separata, is a major long-distance migratory insect pest of grain crops in China and other Asian countries. Migratory flights and reproductive behavior usually occur at night, regulated by a circadian rhythm. However, knowledge about the linkages between adult flight, reproduction, and clock genes is still incomplete. To fill this important gap in our knowledge, a clock gene (designated Msper) was identified and phylogenetic analysis indicated that the encoded protein (MsPER) was highly similar to PER proteins from other insect species. Quantitative RT-PCR assays demonstrated that significantly different spatiotemporal and circadian rhythmic accumulations of mRNA encoding MsPER occurred during development under steady 14h:10h light:dark conditions. The highest mRNA accumulation occurred in adult antennae and the lowest in larvae. Msper was expressed rhythmically in adult antennae, relatively less in photophase and more entering scotophase. Injecting small interference RNA (siRNA) into adult heads effectively knocked down Msper mRNA levels within 72h. Most siRNA-injected adults reduced their evening flight activity significantly and did not exhibit a normal evening peak of flight activity. They also failed to mate and lay eggs within 72h. Adult mating behavior was restored to control levels by 72h post injection. We infer that Msper is a prominent clock gene that acts in regulating adult migratory flight and mating behaviors of M.separata. Because of its influence on migration and mating, Msper may be a valuable gene to target for effective management of this migratory insect.

Physiological and Environmental Influences on Wingbeat Frequency of Oriental Armyworm, Mythimna separata (Lepidoptera: Noctuidae).

The oriental armyworm, Mythimna separata (Walker, 1865) (Lepidoptera: Noctuidae), is a serious global migratory insect pest of grain crops. Although its migratory biology has been studied for a long history, the factors affecting wingbeat frequency (WBF), which is closely related to the flight activity of the insect, remain unclear. In this study, the WBFs of both cultured and migrating moths were tested under different conditions in the laboratory using a stroboscope. The results indicated that age and mating status significantly influenced WBF. One day old adults had the lowest WBF, and unmated females had a significantly higher WBF than that of mated females. In general, the WBF of males was significantly higher than that of female individuals. The WBF decreased gradually with increasing environmental humidity, and WBF had a significant negative binomial regression relationship with temperature change. The WBF of moths that fed on hydromel was much higher than those of the controls that fed on water or without diet. However, wind speed and air pressure had no significant effects on the moth WBF in the test environments. These findings provide a deeper understanding of factors that affect flight ability in M. separata, which will be helpful for developing a regional migratory monitoring and warning system of the pest, such as identifying target insect species based on the WBF from radar observation.

Control efficacy and joint toxicity of metaflumizone mixed with chlorantraniliprole or indoxacarb against the fall armyworm, Spodoptera frugiperda.

The fall armyworm (FAW), Spodoptera frugiperda is the main destructive pest of grain crops, and has led to substantial economic losses worldwide. Chemical pesticides are the most effective way to manage FAW. Here, a laboratory test using an artificial diet-incorporated assay was conducted to determine the toxicity of five insecticides and the joint effect of the binary combination insecticides to FAW larvae. A field plot test using foliar spray was carried out to assess the control efficacy of metaflumizone mixed with chlorantraniliprole or indoxacarb against FAW. The bioassay results showed that metaflumizone had a stronger insecticidal effect than indoxacarb toward FAW larvae. Furthermore, the mixture of metaflumizone and chlorantraniliprole in a volume ratio of 3:7 had the strongest synergistic effect against FAW, with a co-toxicity coefficient (CTC) of 317.18. The best synergistic effect for mixtures of metaflumizone and indoxacarb was observed at a 1:9 volume ratio, with a CTC of 185.98. However, there was an antagonistic effect of metaflumizone mixed with emamectin benzoate and with lufenuron, because the co-toxic factor was less than -20 at volume ratios of 8:2 and 9:1, respectively. According to the results of the field trial, metaflumizone mixed with chlorantraniliprole or indoxacarb at a 50% reduction of the application rate can effectively control FAW with efficacy ranging from 77.73% to 94.65% 1-7 days postapplication. Overall, our findings suggest that metaflumizone and its binary combination insecticides can be utilized in FAW integrated pest management programs. © 2022 Society of Chemical Industry.

Potential of Silicon to Improve Biological Control of Fall Armyworm, Spodoptera frugiperda on Maize

Silicon (Si) accumulation in plants confers a mechanical barrier to insect herbivory and may alter plant chemistry to increase the attraction of natural enemies to host insect herbivores on Si−treated plants. The fall armyworm (FAW), Spodoptera frugiperda, is a major insect pest of grain crops, including maize (Zea mays L.). This study examined whether Si supplementation alters maize volatile compounds that mediate host location in Euthyrhynchus floridanus, a generalist predator of FAW. A four-arm olfactometer was used to test the olfactory preference of nymphs and adults of E. floridanus to the odor of maize leaf materials from plants that were; Si−treated and infested, Si−treated without infestation, Si−deprived and infested, and Si−deprived without infestation. The probabilities of individual insects choosing between the four treatments were estimated using a multinomial generalized linear mixed model. There were no statistical differences in the olfactory preference of E. floridanus between Si−treated and Si−deprived maize leaf materials. However, the median estimate showed that nymphs were almost twice likely to be attracted to Si−supplemented leaf material, indicating a potential positive effect of Si. However, a more robust follow-up study is needed to further assess the impact of Si on E. floridanus.

Development of a Species Diagnostic Molecular Tool for an Invasive Pest, Mythimna loreyi, Using LAMP.

Simple SummaryMythimna loreyi is a serious pest of grain crops and reduces yields in maize plantations. M. loreyi is a native species in East Asia for a long time. However, this species has recently emerged as a migration (or invasive from other Asian countries) pest of some cereal crops in Korea. Little is known about its basic biology, ecology, and it is difficult to identify the morphologically similar species, Mythimna separate, which occur at the cornfield in the larvae stage. Species diagnosis methods for invasive pests have been developed and utilized for this reason. Currently, the molecular biology method for diagnosing M. loreyi species is only using the mtCO1 universal primer (LCO1490, HCO2198) and process PCR and sequencing to compare the degree of homology. However, this method requires a lot of time and effort. In this study, we developed the LAMP (loop-mediated isothermal amplification) assay for rapid, simple, and effective species diagnosis. By analyzing the mitochondrial (mt) genome, the species-specific sequence was found at the coding region of the NADH dehydrogenase subunit 5 gene. A broad range of DNA concentration was workable in LAMP assay, in which the minimum detectable DNA concentration was 100 pg. DNA releasing method was applied, which took five minutes of incubation at 95 °C without the DNA extraction process, and only some pieces of tissue from larvae and adult samples were needed. The incidence of invasive pests is gradually diversifying. Therefore, this simple and accurate LAMP assay is possibly used in the intensive field monitoring for invasive pests and integrated management of Mythimna loreyi.The Mythimna loreyi (Duponchel) is one of the well-known invasive noctuid pests in Africa, Australia, and many Asian countries. However, it is difficult to identify the invasive and morphologically similar species, Mythimna separate, which occur at the cornfield in the larvae stage. Currently, the molecular biology method for diagnosing M. loreyi species is only using the mtCO1 universal primer (LCO1490, HCO2198), which requires a lot of time and effort, such as DNA extraction, PCR, electrophoresis, and sequencing. In this study, the LAMP assay was developed for rapid, simple, effective species identification. By analyzing the mitochondrial genome, the species-specific sequence was found at the coding region of the NADH dehydrogenase subunit 5 gene. Based on this unique sequence, four LAMP primers and two loop primers were designed. The F3 and B3 primers were able to diagnose species-specific, in general, and multiplex PCR and specifically reacted within the inner primers in LAMP assay. The optimal incubation condition of the LAMP assay was 61 °C for 60 min with four LAMP primers, though additional loop primers, BF and LF, did not significantly shorten the amplification time. The broad range of DNA concentration was workable in LAMP assay, in which the minimum detectable DNA concentration was 100 pg. DNA releasing method was applied, which took five minutes of incubation at 95 °C without the DNA extraction process. Only some pieces of tissue of larvae and adult samples were needed to extract DNA. The incidence of invasive pests is gradually diversifying. Therefore, this simple and accurate LAMP assay is possibly applied in the intensive field monitoring for invasive pests and integrated management of Mythimna loreyi.

Parasitism of the conical snail, Cochlicella acuta, by the fly, Sarcophaga villeneuveana, in south-western Europe

The conical snail, Cochlicella acuta, is an introduced pest of grain crops in Australia. Biological control of C. acuta has been attempted using the parasitoid fly, Sarcophaga villeneuveana, sourced from southern France, but has failed. Molecular genetics of the snails and climatic matching have suggested greater success might be realised using flies from southern Iberia (Spain and Portugal) or Morocco. We measured levels of parasitism of C. acuta by S. villeneuveana at several sites within southern Iberia, and near the previous fly release site in Australia. Emergence of flies was slightly higher in Iberia, compared with Australia, but 31% of the S. villeneuveana that reached pupal stage within C. acuta in Iberia were hyperparasitised (up to 63% at individual sites). No hyperparasites emerged from Australian collections of C. acuta. These data encourage further searches in southern Iberia for more effective populations of S. villeneuveana for use as biological control agents.

Susceptibility of fall armyworm, Spodoptera frugiperda (J.E. Smith), to eight insecticides in China, with special reference to lambda-cyhalothrin

Fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is the main destructive insect pest of grain crops that occurs in all maize growing regions of the Americas. It has rapidly invaded the Southern China since January 2019. However, the current status of insecticide resistance in S. frugiperda has not been reported in China. In this study, we determined the susceptibility of eight populations of FAW to eight insecticides by an artificial diet incorporation method. The results showed that among eight insecticides, emamectin benzoate, spinetoram, chlorantraniliprole, chlorfenapyr, and lufenuron showed higher toxicity to this pest, while lambda-cyhalothrin and azadirachtin exhibited lower toxicity. Susceptibility of S. frugiperda to indoxacarb was significantly different (10.0-fold for LC50) across the various geographic populations. To investigate the biochemical mechanism of FAW to lambda-cyhalothrin, we performed the synergism tests and the results showed that piperonyl butoxide (PBO) and triphenyl phosphate (TPP) produced a high synergism of lambda-cyhalothrin effects in the two field populations. Sequencing of the gene encoding the acetylcholinesterase (AChE) gene in the two field populations identified two amino acid mutations, all of which have been shown previously to confer resistance to organophosphates (OPs) in several arthropod species. The results of this study provided valuable information for choosing alternative insecticides and for insecticide resistance management of S. frugiperda.

Genetic variability in the parasitic fly, Sarcophaga villeneuveana, in south-western Europe and Morocco

The snail, Cochlicella acuta (Muller), is an introduced pest of grain crops in southern Australia, and native to Europe and north-west Africa. Parasitoid flies (Sarcophaga villeneuveana (Enderlein)) have previously been sourced from France to attempt biological control of the pest in Australia, but have failed. Cochlicella acuta has three mitochondrial lineages (CO1 & 16S based) within its native distribution. The snails now found in Australia belong to just one of these lineages. Their origins most likely lie in the southern Iberian Peninsula or Morocco, not in France. We collected S. villeneuveana attacking C. acuta in France, Spain, Portugal, Morocco and Australia. Genetic structure (CO1) was not found within the fly that aligned with the lineages recorded for the snail host in the same regions. However, geographical patterns were detected amongst haplotypes of S. villeneuveana which encourage further, better targeted searches in Morocco and the southern Iberian Peninsula for a more effective biological control agent(s).

Sourcing effective biological control agents of conical snails, Cochlicella acuta, in Europe and north Africa for release in southern Australia

The conical snail, Cochlicella acuta, is a major introduced pest of grain crops in southern Australia. In particular, C. acuta aestivates on the heads and upper stalks of crop plants thus fouling grain harvests in late spring - early summer. Previous attempts to control this snail pest included the release, during the early 2000s, of parasitic flies (Sarcophaga villeneuveana) sourced from southern France, within the perceived native distribution of C. acuta. The flies established in southern Australia, but only in very low numbers, such that there was no significant reduction in the snail’s pest status. Sequencing of the snail’s COI and 16S mitochondrial genes has now identified three main maternal lineages within C. acuta, across its distribution in south-western Europe and Morocco. The 1st lineage was only found in north-eastern Spain (near the Pyrenees), throughout southern France and in northern Italy. Both the 2nd and 3rd lineages were found in the U.K., western France, northern and southern Spain, Portugal and Morocco. The 3rd lineage was also collected throughout eastern Spain and just into southern France (near the Pyrenees). All the C. acuta found in Australia belong to the 3rd lineage. Highest levels of genetic diversity in C. acuta were found in the 3rd lineage, in particular in Morocco. A plausible explanation for the poor performance of the biological control agent previously released to control C. acuta in Australia is a mismatch between snail host and selected parasitoid. A different biotype or sub-species of S. villeneuveana, or even a different parasitoid species altogether, that attacks the 3rd lineage of C. acuta in south-western Europe or Morocco, could prove to be a more effective biological control agent than the S. villeneuveana previously released from southern France. Climates in southern Spain, southern Portugal and northern Morocco also best match those areas in southern Australia where C. acuta is a pest, suggesting further searches for effective natural enemies should be focussed there.

Effects of temperatures on the development and reproduction of the armyworm, Mythimna roseilinea: Analysis using an age-stage, two-sex life table

The armyworm Mythimna roseilinea (Walker) is a major pest of grain crops in South China. So far little is known about its basic biology and ecology, making prediction of population dynamics difficult. This study examined the relationships of individual development and population growth with temperature based on an age-stage, two-sex life table of M. roseilinea reared on maize in the laboratory at 18, 21, 24, 27 and 30°C. The highest values of net reproductive rate (R0) and fecundity were observed at 21 and 24°C, respectively. Both the intrinsic rate of increase (r) and finite rate of increase (λ) increased significantly and mean generation time (T) decreased significantly with increasing temperature. M. roseilinea was able to develop, survive and lay eggs at all temperature regimes tested. Development rates of the egg, larval, pupal, as well as the whole pre-oviposition stages had a positive linear relationship with temperature. The calculated development threshold temperatures of egg, larval, pupal, pre-oviposition and total pre-oviposition stages were 13.29, 8.39, 14.35, 7.42, and 12.24°C, respectively, and their effective accumulated temperatures were 63.59, 445.00, 211.11, 89.02, and 698.95 degree-days, respectively. These results provide insight into temperature-based phenology and population ecology of this insect pest and will allow population prediction and management available in the field.

A moderate elevation in [CO2] results in potential hypervirulence on SABBIErica

The Russian Wheat Aphid (Diuraphis noxia Kurdjumov, 1913) (RWA) is a serious pest of grain crops and is of considerable concern in South Africa, particularly in terms of barley grown specifically for the brewing industry. This paper highlights the effect of a small (50ppm) increase in [CO2] on the growth rate of the four South African RWA biotypes on the SABBIErica barley cultivar. Controlled environment experiments revealed that the colony growth rate for RWASA4 was significantly lower than SA1 under ambient conditions as well as significantly lower than SA1, SA2 or SA3 under elevated CO2 conditions. The unexpected difference suggested an atypical, non-preferential feeding habit on SABBIErica, for RWASA4. The small RWASA4 colonies inflicted similar morphological damage to the significantly larger RWASA1 – RWASA3 biotype populations — indicative of potential hypervirulence under elevated CO2. The continuous feeding of RWASA biotypes causes damage to the transport system as well as substantial, catastrophic damage to mesophyll chloroplasts as well as mitochondria within the host plant's leaves. The TEM study revealed evidence of sequential/systematic degeneration of chloroplasts and mitochondria with continued aphid feeding, which we suggest is an indication of potential emergent hypervirulence under elevated CO2 conditions.

Population Projection and Development of the Mythimna loreyi (Lepidoptera: Noctuidae) as Affected by Temperature: Application of an Age-Stage, Two-Sex Life Table.

The Mythimna (=Leucania) loreyi (Duponchel) has recently emerged as a major pest of grain crops in China. Little is known about its basic biology and ecology, making it difficult to predict its population dynamics. An age-stage, two-sex life table was constructed for this insect when reared on maize in the laboratory at five constant temperatures (18, 21, 24, 27, and 30 °C). Both the intrinsic rate of increase (r) and finite rate increase (λ) increased as temperature significantly increased and mean generation time (T) decreased significantly with increasing temperature. The highest values for net reproductive rate (R0) and fecundity were observed at 24 °C. However, M. loreyi was able to develop, survive, and lay eggs at all temperatures tested (18-30 °C). Development rates at different temperatures for the egg, larval, pupal, as well as for a total preoviposition period, fit a linear equation. The lower threshold temperatures of egg, larval, pupal, preoviposition, and total preoviposition period were 8.83, 10.95, 11.67, 9.30, and 9.65 °C, respectively. And their effective accumulated temperatures were 87.64, 298.51, 208.33, 66.47, and 729.93 degree-days, respectively. This study provides insight into the temperature-based phenology and population ecology in M. loreyi. The results will benefit population dynamics monitoring, prediction, and management of this insect pest in the field.

The population dynamics of the mediterranean snail, Cernuella virgata (da Costa, 1778) (Hygromiidae), in continuous-cropping rotations in South Australia

The population dynamics of the mediterranean snail, Cernuella virgata (Hygromiidae), which is a pest of grain crops and pastures in southern Australia, was studied in three adjacent fields used for continuous cropping on Yorke Peninsula, South Australia, for 20 years. The cropping sequence was commonly a rotation of faba beans, wheat and barley. Population densities were measured every month for the first 4 years and thereafter only in autumn and spring each year. Autumn and spring were the respective breeding season for adults and the resultant juvenile population that infested grain harvests. Populations varied greatly in abundance between years and fields. Spring abundance was correlated, albeit weakly, with prevailing spring and previous autumn rainfall. The latter can thus be used as an early warning of harvests suffering from snail contamination. Snails grew largest in faba bean crops and were more abundant in the wheat crops that followed faba beans than they were in the subsequent barley crop. No evidence was found of increased snail abundance near field edges, which would suggest biased seasonal movements of snails between adjacent fields, as has been reported for other studies of C. virgata in different agricultural systems (interfaces between crops and pastures, pastures and woody/weedy roadside vegetation). It seems probable, in this case, that the similarities in vegetative form of adjacent crops provided limited stimulation for differential dispersal between fields. The frequencies of banded (darkly coloured) shells also did not vary with distance from field edges, suggesting that the fence posts and tall weeds that occurred at the interfaces between fields were insufficient to provide (cooler, above-ground) shelter in summer and enhance local survival of banded C. virgata relative to locations further into fields.

Soil moisture and soil type influence the breeding behavior of the pest snail Cernuella virgata (da Costa)

The common white snail ( Cernuella virgata) (da Costa) is an exotic pest of grain crops in southern Australia. In order to better control these snails and develop optimal management strategies, it is important to understand how their breeding behavior is influenced by soil moisture and soil type. Pairs of adult snails were placed into vials containing either a calcareous or a non-calcareous soil at five moisture levels along their soil moisture retention curves: no-water; permanent wilting-point; mid-point; field-capacity; and saturation. Survival analysis was used to estimate the tendency of C. virgata to lay an egg cluster. ANOVA showed that there was no two-way interaction between soil moisture and soil type, however, one-way ANOVA showed that the tendency of C. virgata to deposit the first egg cluster was greater in the non-calcareous soil and increased as soil moisture increased. There was a higher total number of egg clusters laid in the non-calcareous soil. The total number of egg clusters laid in the two soil types increased as soil moisture content increased. No eggs were laid in the no-water treatment. C. virgata breed more frequently in moist soils, and egg laying is greater in wet seasons. Therefore the risk of grain contamination in spring is predicted to be greater following a relatively wet autumn and spring.

A contribution to the cytogenetics of the armoured ground cricket, Acanthoplus speiseri (Orthoptera: Tettigoniidae), a pest of grain crops in Zambia

The nature, number, structure and behaviour of chromosomes during the meiotic and mitotic sequences in the armoured ground cricket, Acanthoplus speiseri Brancsik, were investigated from testicular and ovariole material. The karyotype of A. speiseri is 2n ♂ = 25 (24 autosomes + XO) and 2n ♀ = 26 (24 autosomes + XX). The species exhibits the primitive XO ♂ /XX ♀ type of sex determination mechanism. All chromosomes in the cell complement (including the X sex chromosome), in both sexes, are acrocentric in shape. The X sex chromosome is the largest element in the karyotype while the autosomes comprise three large, four medium and five small pairs. The behaviour of the chromosomes during the meiotic and mitotic processes is normal and typically orthopteran. The study discusses the important role that karyology and cytogenetics can play for species diagnostics in the subfamily Hetrodinae.