Plant host associations of Penthaleus species and Halotydeus destructor (Acari: Penthaleidae) and implications for integrated pest management

Integrated pest management programs seek to minimise reliance on pesticides and provide effective long-term control of pests. Cultural control strategies, such as crop rotations, trap and border crops, and weed management, require a thorough understanding of pest host associations. This paper examines the effects of different plant hosts on the persistence and reproduction of blue oat mites, Penthaleus spp., and the redlegged earth mite, Halotydeus destructor (Tucker), which are major agricultural pests in southern Australia. Field and shade-house experiments were conducted testing several crop and plant types. All species survived and reproduced from one mite season to the next when confined to pasture. Canola and a common weed, 'bristly ox-tongue', were suitable hosts for H. destructor and Penthaleus falcatus (Qin and Halliday), whereas Penthaleus sp. x and Penthaleus major (Dugés) failed to persist on these plants. A mixture of wheat and oats sustained P. sp. x and H. destructor, but not P. falcatus or P. major. Lentils were generally a poor host plant for all mite species. These findings show that earth mite species differ in their ability to persist on different plant types, highlighting the importance of distinguishing mite species before implementing control strategies. Results are discussed with respect to cultural control options for the management of these winter pests.     

Competitive interactions among four pest species of earth mites (Acari: Penthaleidae)

Earth mites are major winter pests of a variety of crops and pastures in southern Australia. Competition between four earth mite species was investigated using field and shadehouse experiments. The influence of different plant hosts on the frequency and intensity of competitive interactions also were examined. This information is important, because control attempts that eradicate one species of mite could be directly followed by an increase in abundance of another earth mite species. There were strong effects of intraspecific competition on the reproductive rate of species, while interspecific interactions between Halotydeus destructor (Tucker) and Penthaleus species and between the three Penthaleus species also were detected. Competitive abilities were altered on the different plant types. On pasture, the competitive advantage swayed between Penthaleus major (Dugés), H. destructor, and Penthaleus falcatus (Qin & Halliday). Penthaleus sp. x was the strongest competitor in a mixture of wheat, Triticum aestivum (L.), and oats, Avena sativa (L.), whereas on canola, Brassica napus (L.), and bristly ox-tongue, Picris echioides (L.), P. falcatus, and H. destructor were superior competitors. These results suggest that competition is a strong force influencing the abundance of earth mites in the field and that host plant factors are important in shaping the type of interactions. This highlights the importance of identifying mite species when considering control options and suggests that effective control recommendations need to be developed for each individual species.     

The biology of Penthaleus species in southeastern Australia

Earth mites are major pests of pastures and crops within southern Australia. While the biology and ecology of the redlegged earth mite (Halotydeus destructor) have been studied extensively, the blue oat mite (Penthaleus major) and its recently discovered relative, Penthaleus falcatus, have received little attention. The distribution of H. destructor, P. major and P. falcatus is described in Victoria, Australia, and the inland borders in central New South Wales are re-described. A new undescribed Penthaleus species identified from mallee samples is recognized, and its restricted distribution in Victoria is mapped. Electrophoretic data and the complete absence of males indicate that all Penthaleus species are obligate thelytokous parthenogens. The three Penthaleus species differ in clonal diversity. All species are pests of pastures and/or crops, however the preferred plant hosts of P. major and P. falcatus differ. Tolerance of a commonly used pesticide (omethoate) differs between the species. P. falcatus shows the highest LC₅₀, and may be responsible for pesticide control failures. Rearing methods for P. major and P. falcatus are described. The large differences between these blue oat mite species point to difficulties in interpreting early published data that failed to distinguish them.     

Competitive interactions between two pest species of earth mites, Halotydeus destructor and Penthaleus major (Acarina: Penthaleidae)

Competition was investigated between two pest earth mite species, Penthaleus major Dugés and Halotydeus destructor Tucker, which occur sympatrically and are major pests of southern Australian pastures and crops. Three geographically separate pasture sites within Victoria were sampled monthly. Abundance patterns were similar across sites in that there was a marked increase in number of H. destructor in spring. Field competition plots were set up on pasture. In the first season, H. destructor had a negative effect on P. major but not vice versa. During the summer, diapause and ensuing generation, density-dependent (intraspecific) competition was evident in P. major but not in H. destructor. The interspecific asymmetry was switched in the following season, with P. major dominating most plots and having a negative effect on the reproductive output of H. destructor. These findings indicate that suppression or eradication of one species of earth mite from pastures may result in another species increasing in relative abundance.     

Predictions of summer diapause in the redlegged earth mite, Halotydeus destructor (Acari: Penthaleidae), in Australia

A prediction for the onset of a summer diapause in the eggs of the redlegged earth mite, Halotydeus destructor, was developed for Australia. In this species diapause eggs pass the summer in the cadavers of adult female mites. Adult female mites were collected for several weeks from pastures in spring at 18 sites in south-western Australia and dissected to determine the timing of the production of diapause eggs. Some sites were sampled for several years between 1990 and 1997. A model was developed to predict the time for onset of diapause. The week at which 90% of eggs were in diapause was predicted best by daylength (80.1% of the variability), then by duration of the long-term plant growing season (10.4%, of variability), leaving 9.5% due to other factors. A single chemical spray in spring 2 weeks before the production of 90% diapause eggs resulted in 99% fewer mites present in autumn 7-8 months later at three sites. The timing of the spring spray was the factor leading to successful control. This model was tested at 17 sites across the whole geographical distribution of the redlegged earth mite in Australia between 1998 and 2001. The observed week of 90% diapause was within 1 week of the predicted week on 81% of occasions, and 2 weeks earlier on 15% of occasions. A database was created for the predicted date of onset of 90% diapause for the whole distribution of the redlegged earth mite in southern Australia on a 10 km(2) grid. Australian farmers are using this for timing a spring spray to control mites in the following autumn.     

Dispersal patterns of pest earth mites (Acari: Penthaleidae) in pastures and crops

Control methods in pest earth mites and other mites often depend on low dispersal rates, yet there are no experimental estimates of these rates. To rectify this, adult movement rates were estimated in the earth mite Halotydeus destructor Tucker and the winter grain mite, Penthaleus major (Duges), using mark-release-recapture techniques. Mean square dispersal distances were used to estimate diffusion coefficients. In pasture, coefficients were in the range 0.3-1.3 for these species. This suggests that 90% of the population moves < 5-11 m in a 10-d period, or 7-16 m within their adult lifetime. Releases of mites in adjacent pea/wheat crops indicated directional movement toward the more favored pea host. However, there was no directional movement when adjacent plots of peas and lupins were compared, even though lupins are poor hosts. These results indicate that broad border sprays or border culturing will be needed to prevent mite movement from adjacent paddocks.     

Systematics and biology of Penthaleus tectus sp. n. (Acari: Penthaleidae), a recently discovered pest of grain crops in eastern Australia

Abstract  A new species of pest mite, Penthaleus tectus sp. n. (Acari: Penthaleidae) is described from south-eastern Australia, where it attacks several grain crops including wheat, in which it can cause significant damage. It has previously been confused with the blue oat mite Penthaleus major (Dugès). Penthaleus tectus differs from P. major morphologically and genetically, and in geographical distribution, response to pesticides, and the timing of diapause. Previous records of ' P. major ' from Australia and other countries probably include a mixture of several species. Penthaleus minor (Canestrini) is recorded from South Africa for the first time.     

Timing of diapause induction and its life‐history consequences in Nezara viridula: is it costly to expand the distribution range?

Abstract. 1. From the early 1960s to 2000 Nezara viridula (Heteroptera: Pentatomidae) expanded its range northwards in Japan and reached Osaka following climate warming recorded in the region. 2. The timing of diapause induction and its effect on life‐history traits were studied under quasi‐natural conditions in Osaka. Egg masses were placed outdoors in six series in July–November 1999. Developmental events were monitored until September 2000. 3. Adult diapause was induced in September–October in agreement with the photoperiodic response obtained under laboratory conditions. Induction of diapause in early October ensured the highest winter survival. Nymphs that hatched after late September died by December–April showing that the species cannot survive winter in the nymphal stage. 4. Life‐history traits varied between the early (non‐diapause reproduction) and late (post‐diapause reproduction) series. Thus, non‐diapause females produced significantly fewer egg masses than did females that reproduced only after diapause. The timing of diapause induction strongly affected overwintering success and post‐diapause performance: females that became adults and entered diapause in October lived longer, had a longer period of oviposition, and produced more eggs in larger egg masses than females that attained adulthood and entered diapause in September. 5. Females from the early series reproduced until late November, although progeny from the late September eggs were destined to die during the winter. Pre‐winter reproduction of adults that emerged in mid‐September or later was a result of the imperfect timing of diapause induction. It is an ineffective allocation of resources and may be considered the ecological cost of range expansion. 6. To establish in the region, N. viridula will probably evolve a lengthening of the critical photoperiod of the diapause induction response. This will allow the species to enter diapause earlier and, thus, avoid maladaptive late‐autumn reproduction but, perhaps, increase the cost of diapause because of a possible adverse impact of pre‐winter high temperature conditions on overwintering.     

Biology, ecology and control of the Penthaleus species complex (Acari: Penthaleidae)

Blue oat mites, Penthaleus spp. (Acari: Penthaleidae), are major agricultural pests in southern Australia and other parts of the world, attacking various pasture, vegetable and crop plants. Management of these mites has been complicated by the recent discovery of three cryptic pest species of Penthaleus, whereas prior research had assumed a single species. The taxonomy, population genetics, ecology, biology and control of the Penthaleus spp. complex are reviewed. Adult Penthaleus have a dark blue-black body approximately 1 mm in length, and eight red-orange legs. Within Australia, they are winter pests completing two or three generations a season, depending on conditions. The summer is passed as diapausing eggs, when long-distance dispersal is thought to occur. The Penthaleus spp. reproduce by thelytokous parthenogenesis, with populations comprising clones that differ ecologically. The three pest Penthaleus spp. differ markedly in their distributions, plant hosts, timing of diapause egg production and response to pesticides, highlighting the need to develop control strategies that consider each species separately. Chemicals are the main weapons used in current control programs, however research continues into alternative more sustainable management options. Host plant resistance, crop rotations, conservation of natural enemies, and improved timing of pesticide application would improve the management of these pests. The most cost-effective and environmentally acceptable means of control will result from the integration of these practices combined with the development of a simple field-based kit to distinguish the different mite species.     

Field associations of first generation densities of the pest mites <Emphasis Type="Italic">Halotydeus destructor</Emphasis> and <Emphasis Type="Italic">Penthaleus major</Emphasis> in pasture

Halotydeus destructor and Penthaleus major are species of earth mite commonly found at high densities in agricultural fields in Australia and other parts of the world. These mites pose a risk to a range of winter crops and pastures when seedlings emerge in autumn. In order to predict likely mite pressure, we investigated whether autumn densities in pastures can be determined from agronomic and environmental field variables. For H. destructor, field densities showed little association with a range of vegetation variables but could largely be explained using the variable field type, with high densities present when fields had mixtures of grass, clover and weeds. For P. major, we found a regional effect. In the region where most data were available, P. major field densities were associated with grass abundance, whereas an association with field type was significant but different to that found for H. destructor. For both species, densities were not associated with rainfall, but there was a weak association with soil moisture capacity. We discuss how these results can help in managing these important pest mites.     

Does the Number of Diapausing Eggs Laid on Bark Affect the Population Dynamics of the Spider Mite Panonychus mori?

We studied the relationship between number of diapausing eggs produced by the spider mite Panonychus mori and the subsequent population trend for a period of 3 years. Panonychus mori showed a single population density peak on its host plant moonseed, Cocculus trilobus. The position and height of this peak were correlated with the density of diapausing eggs around the moonseed leaf buds produced the winter before. In 1994 the density of diapausing eggs measured in February was 4.3/bud, which was 6–14 times higher than the density of diapausing eggs for the same period in 1995 (0.3/bud) and 1996 (0.7/bud). The subsequent population density peak in 1994 occurred in mid June and was about 2.5 times higher than the peaks in 1995 and 1996, which both occurred early September. Thus, the present study showed a positive correlation between the density of diapausing eggs on the host plant and the start and the extend of the population increase the next growing season. Predators associated with the spider mite population were phytoseiid mites, especially Amblyseius eharai was well synchronized with the spider mite density in 1994. Field observations revealed that P. mori produced diapausing eggs in response to short photoperiod in early October each year, which corresponded with the timing predicted by the critical photoperiod around 13 h at 18°C, as assessed in laboratory trials. Diapause ended by early April when egg hatchability attained about 50% and eggs took 9 days to hatch at 25°C and a 16L:8D photoperiod. Hatching in early April was twice faster than in late February.     

Egg development and diapause: ecophysiological and genetic basis of phenological polymorphism and adaptation to varied hosts in the green oak tortrix,Tortrix viridana L. (Lepidoptera: Tortricidae)

Experiments concerned 8 tortrix populations associated with varied oak species. They showed that the egg development included a phase of diapause. Completion of embryogenesis at 20 degrees C was used as a criterion for whether diapause was completed. Under semi-natural conditions diapause terminated in late autumn or early winter, then eggs developed continuously, without postdiapause winter quiescence, even in severe cold. The eggs from the populations associated with holm or cork oak completed diapause then hatched later than those from the populations associated with sessile or pubescent oak. Reciprocal crossbreedings confirmed that this phenological polymorphism was genetically determined. Under constant temperatures the physiological state of diapausing eggs, assessed by measuring their cold requirements to complete diapause by exposure to 8 degrees C, varied gradually with increasing age. This diapause development was strongly temperature-dependent. Cold requirements of diapausing eggs were much higher in a late-hatching than in an early-hatching population. This explains the phenological polymorphism of the tortrix: the more eggs need cold, the later they complete diapause in autumn, and the later they hatch in spring. Egg cold requirements varied widely within populations too, which resulted in large variations in the date of diapause end among individuals. The date of egg hatch was influenced by the temperatures occurring during diapause and postdiapause, but apparently not by photoperiod.     

中国植绥螨资源及其生物学研究进展

植绥螨是许多害螨和小型有害昆虫的重要捕食性天敌 ,在农业生产中极具利用价值。我国植绥螨资源相当丰富 ,大量的资源调查工作是在 2 0世纪 70年代末开始的。到目前为止 ,我国已经从不同地区作物上鉴定出植绥螨 2 60余种 ,其中有利用价值的约 2 0种左右。在 2 5～ 3 0℃的适宜温度下 ,植绥螨从卵到羽化为成螨约需 6～ 7d ,而寿命能长达 3 0～ 5 0d。它们对大多数的害螨的功能反应基本成HollingⅡ型。多数成螨为喜湿类型 ,较高的湿度对于孵化和存活尤为重要。在夏季高温和冬季低温来临时进行越夏和越冬 ,以度过不良的环境。植绥螨行两性生殖 ,不交配或交配时间不够 ,不产卵或少产 ,有些种类需要多次交配才能完全产卵。     

Sex-ratio adjustment in response to local mate competition is achieved through an alteration of egg size in a haplodiploid spider mite

Sex-ratio adjustments are commonly observed in haplodiploid species. However, the underlying proximate mechanisms remain elusive. We investigated these mechanisms in Tetranychus urticae, a haplodiploid spider mite known to adjust sex ratio in response to the level of local mate competition (LMC). In this species, egg size determines fertilization probability, with larger eggs being more likely to be fertilized, and thus become female. We explored the hypothesis that sex-ratio adjustment is achieved through adjustment of egg size. By using spider mites from a large population, we found that females produced not only a higher proportion of daughters under high levels of LMC, but also larger eggs. Moreover, in populations experimentally evolving under varying levels of LMC, both the proportion of females and the egg size increased with LMC intensity. These results suggest that sex-ratio adjustment in spider mites is mediated by egg size, although the causal relationship remains to be tested.     

Effects of host-plant species on diapause induction of the Kanzawa spider mite, Tetranychus kanzawai

In many herbivorous arthropods, incidence of diapause, which is considered to reflect the timing of diapause, changes depending on the host plants they utilize. Several theoretical studies suggest that the optimal timing of diapause induction depends on life‐history traits; if the development time of the arthropod is short, fecundity is high, or survival rate remains high throughout the season, the optimal timing of diapause induction would be shifted toward the end of the season. For herbivorous arthropods, these life history traits may change among their host plants. Here we examined whether a population of the Kanzawa spider mite, Tetranychus kanzawai Kishida (Acari: Tetranychidae), shows the predicted pattern of diapause induction on two host plants, the kidney bean [Phaseolus vulgaris (Leguminosae)] and Japanese Orixa [Orixa japonica (Rutaceae)], on which the mites show different performances. Rearing conditions were controlled in two ways. In the first experiment, day length and temperature were kept constant throughout the mite lifetime at either of three conditions from mid October to early November. In the second experiment, the conditions were changed from 20 °C and L11.5:D12.5 at immature stages to 18 °C and L11:D13 at adult stage in order to better approximate field conditions. In the first experiment, diapause incidence on P. vulgaris was lower than on O. japonica. This tendency became stronger in the second experiment, suggesting a difference in the timing of diapause induction among host plants. On the other hand, P. vulgaris was proven to allow high performance, i.e., greater lifetime fecundity and shorter development times, although it had no effect on the survival rate. The relationship between diapause incidence and performance is consistent with the prediction of theoretical studies that a short development time or high fecundity delays the timing of diapause induction.     

Diapause duration, survival in relation to desiccation and egg-pod morphology of the Senegalese grasshopper, Oedaleus senegalensis

Abstract. The Senegalese grasshopper, Oedaleus senegalensis (Krauss) (Orthoptera: Acrididae), is periodically a devastating pest of subsistence crops in the sahelian zone of West Africa.Egg diapause has been suggested as an important component of the mechanism acting to generate outbreaks and therefore diapause duration, egg survival in relation to desiccation and egg-pod morphology were investigated in this study.
Three months after oviposition, 50% of initially diapausing egg pods maintained in the laboratory exhibited 'partial emergence' and produced hoppers.No difference in diapause duration was evident between egg pods maintained at a constant 30 ± 1°C and those maintained under alternating temperature conditions of 23 ± 1°C and 35 ± 1°C.Laboratory maintained eggs showed significant variation in diapause duration with diapause lasting between 2 months and 4 years.Diapause duration was shorter in the field with only c. 1.4% of eggs remaining in diapause after a single dry season (6–7 months).Survival of eggs in relation to desiccation was high in the field and low in the laboratory, and field eggs lost only c. 20% of their body weight over the dry season.Survival of diapausing and non-diapausing egg pods in the laboratory was similar, indicating that diapause in this species is primarily a mechanism for preventing emergence at an inappropriate time of year, rather than conferring any additional resistance to desiccation.Egg pods oviposited under diapause-inducing conditions (LD 14:10 h, 25°C) were significantly shorter than those laid under non-diapausing conditions (LD 10:14 h, 40°C).These results are discussed both in relation to possible O.senegalensis 'bet-hedging' strategies and to the probable mechanism operating behind major outbreaks of this species.     

Invertebrate pests of canola and their management in Australia: a review

Abstract  In Australia, canola is subject to attack by at least 30 species of invertebrate pests, although the composition of this pest complex can vary between regions. Mites (e.g. the redlegged earth mite Halotydeus destructor and the blue oat mites Penthaleus spp.), lucerne flea ( Sminthurus viridis ) and false wireworms (e.g. the grey false wireworm Isopteron punctatissimus and the bronzed field beetle Adelium brevicorne ) are the major pests threatening the seedling establishment, whereas aphids (the cabbage aphid Brevicoryne brassicae , the turnip aphid Lipaphis erysimi and the green peach aphid Myzus persicae ), the native budworm ( Helicoverpa punctigera ), the diamondback moth ( Plutella xylostella ) and the Rutherglen bug ( Nysius vinitor ) can cause irregular and unpredictable damage to the flowering and podding plants. Current tactics of pest management for canola rely largely on the use of synthetic pesticides, but this single-technology approach is likely to incur negative effects on natural enemies and the risk of pest resistance. Thus, the sustainable production of canola requires integrated pest management (IPM) strategies, in which cultural control, crop resistance and biological control are used as important components, with chemical inputs applied only when absolutely needed to restrict pests from reaching economically damaging densities. Such IPM strategies should be built around a fundamental understanding of pest ecology at both regional and local farm levels and the integration of renewable technologies. Therefore, future research efforts need to be focused on the canola-cropping system, with a particular emphasis on the impact of pest species, natural enemies of the pests, varietal resistance to pests and the spatial ecology of pest species.     

Oviposition-site shift in phytophagous mites reflects a trade-off between predator avoidance and rainstorm resistance

Predators can reduce prey population densities by driving them to undertake costly defences. Here, we report on a remarkable example of induced antipredator defence in spider mites that enhances the risk to rainstorms. Spider mites live on the undersides of host plant leaves and usually oviposit on the leaf undersurface. When they are threatened by predatory mites, they oviposit on three-dimensional webs to avoid egg predation, although the cost of ovipositing on webs has not yet been clearly determined. We prepared bean plants harbouring spider mite (Tetranychus kanzawai) eggs on either leaf surfaces or webs and exposed them to rainstorms outdoors. We found that fewer eggs remained on webs than on leaf surfaces. We then examined the synergistic effect of wind and rain by simulating both in the laboratory. We conclude that ovipositing on webs comes at a cost, as eggs are washed off the host plants by wind and rain. This may explain why spider mite populations decrease drastically in the rainy season, although they inhibit leaf undersides where they are not directly exposed to rainfall.     

The natural history ofPetrobia (Tetranychina) harti (Ewing) andPetrobia (Mesotetranychus) tunisiae Manson (Acari: Tetranychidae) in the laboratory

Petrobia harti (Ewing) developed more rapidly, deposited more eggs and lived longer onOxalis corniculata than onO. articulata. No development took place on several other recorded host plants. In the field this mite was most abundant during early summer. Males made up less than 10% of the population, and no diapause eggs were seen in the field.Petrobia tunisiae Manson developed on various winter Gramineae, produced about 17 non-diapause eggs during its first generation and mostly diapause eggs in the second. A few diapause eggs kept in the laboratory and dipped in chloroform hatched even after 3 years. A summer diapause is postulated for this species.     

The effect of modified atmospheres on the survival of the eggs of four storage mite species

The results of a laboratory investigation into the effects of modified atmospheres (MA) on the eggs of mite pests of grain and cheese are presented. Four species of astigmatid mite were tested; Acarus farris (Oudemans). A. siro L., Lepidoglyphus destructor (Schrank) and Tyrophagus longior (Gervais). All are found in many habitats including grain and cheese stores. Three low oxygen (O2) MA mixtures were used, based on carbon dioxide (CO2), nitrogen (N2) or simulated burner gas (0.5 or 2% O2, 10% CO2, balance N2) plus 60% CO2 in air (8% O2). The mites were exposed at 15 degrees C and 80% r.h., a combination of conditions that occurs at the surface of stored grain during the autumn which promotes mite population growth. The exposure periods required to prevent egg hatch for each species in every mixture are given. Tyrophagus longior was the most tolerant species, followed by A. siro and A. farris, with L. destructor the most susceptible. Burner gas was the most effective mixture overall with 0.5% O2 but with an increase in the O2 level to 2% for all the mixtures, CO2 became the more effective control agent. With 60% CO2 in air some loss of efficacy was observed against the three most tolerant species and even more so for L. destructor. Sublethal exposures to MAs for at least 4 days in L. destructor, 6 days in A. farris and A. siro and 8 days for T. longior caused a delay in egg hatch.