Effet de l'application d'un mélange lambda-cyhalothrin (pesticide chimique) et de spores de Metarhizium anisopliae (flavoviride) var. acridum Driver and Milner (biopesticide) appliqué sur les larves de sauteriaux au Mali

A mixture of lambda-cyhalothrin (lambda-cyhalothrin: chemical insecticide) and Metarhizium anisopliae ( flavoviride ) var. acridum Driver and Milner, an entomopathogenic fungus (bioinsecticide) was used for grasshopper control in Mali. An oil-based formulation of Metarhizium anisopliae ( flavoviride ) var. acridum Driver and Milner has been developed by LUBILOSA a collaborative project for locust and grasshoppers control. It takes 6 to 10 days for the biopesticide to kill the hosts, which is not a problem for larvae in fallows because they will die before reaching the farmers' fields. However, if crops are infested by adults, the farmers can not wait for 6 to 10 days. An experiment was conducted in Mali using a mixture of a biopesticide and chemical pesticide. The mixture of lambda-cyhalothrin (chemical insecticide) and Metarhizium anisopliae ( flavoviride ) var. acridum (biopesticide: oil-based entomopathogenic fungus spore suspension) was applied to nymphs of Sahelian grasshoppers, using ultra low volume (ULV) sprayers. Both the mixture and lambda-cyhalothrin alone gave quick mortality, with slightly higher mortality for the mixture. Mortality due to the Metarhizium treatments began 2 days after application and subsequently reached similar levels of mortality to the lambda-cyhalothrin mixture treatments. The efficacy of the mixture was greater than Metarhizium alone. The efficacy of lambda-cyhalothrin reached 80% on the day following application, but declined after 10 days, due probably to immigration of untreated grasshoppers.     

Field observations of the effects of fenitrothion and Metarhizium anisopliae var. acridum on non-target ground dwelling arthropods in the Sahel

The effect of the chemical insecticide, fenitrothion, and a mycoinsecticide based on Metarhizium anisopliae var. acridum on the activity of non-target epigeal arthropod scavengers was investigated in areas of open savannah in southeast Niger Republic, West Africa. Both insecticides were applied as full cover sprays to unreplicated 800 ha plots to assess their season-long control of Sahelian grasshoppers. Compared with control plots, fenitrothion caused an immediate but temporary reduction in grasshopper numbers, whereas M. anisopliae var. acridum provided delayed but prolonged control. Scavenging rates of pyrethroid-killed grasshoppers placed along transects in unsprayed plots and those treated with fenitrothion and M. anisopliae var. acridum at various intervals after spraying were assessed. In the fenitrothion plot, an immediate reduction in scavenging activity occurred that was still apparent after 40 days at the plot center, although recovery at the plot edges was more rapid. By contrast scavenging rates remained high over equivalent areas in the M. anisopliae var. acridum and two untreated plots. Concurrent to the scavenging study, counts of grasshopper cadavers resulting from the spray treatments were conducted. These counts revealed that the density of grasshopper cadavers remained low throughout the M. anisopliae var. acridum plot and explained <1% of the reduction in live grasshoppers resulting from treatment, compared with >20% in the fenitrothion plot. This shortfall in grasshopper cadavers resulting from the spray treatment in the M. anisopliae var. acridum plot was unexpected because in a monitoring study, fungus-killed (unlike pyrethroid-killed) grasshoppers were unattractive to scavengers and readily persisted in this plot, and thus should have become apparent. Given we did not observe significant grasshopper dispersal, the scarcity of cadavers generated in the M. anisopliae var. acridum plot, together with unquantified visual observations, suggests that predation of infected but living grasshoppers was high. Our data provide circumstantial evidence that the different effects of chemical and biological grasshopper control on grasshopper natural enemies may influence the efficacy of large-scale treatments.     

黑河上游天然草地蝗虫空间异质性与分布格局

蝗虫空间分布格局是物种长期适应自然的结果,是蝗虫与环境、蝗虫之间关系的反映,有助于理解蝗虫发生学的环境背景。采用地统计学方法,在黑河上游山区天然草地研究了微生境影响下的蝗虫空间格局与异质性。结果表明:该区域5种优势种蝗虫的半变异函数模型均为非线性模型,表现为聚集分布;不同种类蝗虫样点之间空间依赖的范围为2.29—24.59 m;在蝗虫种群总异质性中随机部分引起的空间异质性占15.77%—88.64%。受食性和栖息地选择的影响,蝗虫种群形成了片状和斑块状的分布格局;尺度依赖性使蝗虫分布格局趋于多元化和繁杂化的特点,不同蝗虫种群之间相互交错嵌插,同种蝗虫高低值呈非均匀扩散,整体上形成了均衡性与互补性的斑块镶嵌结构,这种分布格局反映了蝗虫对生境和气候变化的多元适应性结构。     

Epizootics of the entomopathogenic fungus,Entomophaga grylli (Entomophthorales: Entomophthoraceae), in a grasshopper population in Northwest China

Plagues caused by locusts and grasshoppers have led to severe crop damage and great economic loss in many countries. Nevertheless, populations of these pests are often suppressed by naturally occurring predators and disease. Among such natural control factors, the entomopathogenic fungus, Entomophaga grylli, can markedly disrupt the dynamics of grasshopper populations. However, there are few reports of epizootics of this entomopathogenic fungus occurring in consecutive years. Here we report on a consecutive 2-year field survey of E. grylli epizootics in Xinjiang, Northwest China. E. grylli were observed to infect at least four species of grasshopper, Calliptamus italicus, Gomphocerus sibiricus, Chorthippus sp., and Stauroderus scalaris. This is the first record of infection of the last two species by this pathogen. The highest infection rates at the two study sites (Chonghuer and Jiadengyu, Altay Prefecture) were ≥50%, observed in mid-July 2011, and the lowest rate was >16% in early summer. The density of infected grasshoppers was positively correlated with the density of total grasshoppers collected (r?=?0.981). Therefore, E. grylli is an important natural factor regulating the dynamics of grasshopper populations in regions that are not subjected to artificial treatments.     

Persistence of <Emphasis Type="Italic">Paranosema</Emphasis> (<Emphasis Type="Italic">Nosema</Emphasis>) <Emphasis Type="Italic">locustae</Emphasis> (Microsporidia: Nosematidae) among grasshopper (Orthoptera: Acrididae) populations in the Inner Mongolia Rangeland,China

Paranosema (Nosema) locustae Canning has persisted in grasshopper populations in the Inner Mongolia Rangeland since spore treatment was applied in 1993. In the treatment year, a 58.32–71.43% reduction of grasshoppers was recorded and 59.26–80.36% of surviving grasshoppers of various species were infected. In the years following application, prevalence of P. locustae varied from 13.65% to 60.71%, demonstrating that P. locustae remains in grasshopper populations for many years. Infection prevalence was more than 60.00% for Dasyhippus barbipes (F.-W.), Bryodema luctuosum luctuosoma (Stoll) and Angaracris barabensis (Pall.) in 1993 but was very variable, ranging from 20.00% to 60.71% over the subsequent nine years. Disease prevalence was 43.72–60.71% in 1993 and 1994 for Oedaleus asiaticus B.-Bienko and Myrmeleotettix palpalis (Zub.) but gradually declined to approximately 20%, where it remained. Persistence of P. locustae in grasshopper populations may be important in keeping densities below economic thresholds for a number of years after application. Handling Editor: Helen Roy.     

The persistence of Paranosema locustae after application in Qinghai Plateau,China

The percentage of grasshoppers infected by Paranosema locustae showed peaks in the first, third and eighth year since the pathogen was applied in 1998 in the Qinghai-Tibet rangelands, demonstrating that it remained present in grasshopper populations for more than 9 years after application.     

Comparison of an Organophosphate Insecticide with a Mycoinsecticide for the Control of Oedaleus senegalensis (Orthoptera: Acrididae) and Other Sahelian Grasshoppers at an Operational Scale

Operational scale field trials were conducted in 1996 and 1997, in the east of the Niger Republic, on 50 and 800 hectare plots, to compare the efficacy of an oil based formulation of the entomopathogenic fungus, Metarhizium anisopliae (flavoviride) var. acridum (Deuteromycotina: Hyphomycetes) with fenitrothion for the control of Sahelian grasshoppers. The Senegalese Grasshopper Oedaleus senegalensis Krauss was the most abundant species in the trials. M. anisopliae was applied at 5 x 1012 spores ha-1 at volume application rates of 2 and 0.5 l ha-1 in successive years. Fenitrothion was applied at 220 g/ha-1 at 1.25 and 0.22 l ha-1 volume application rates. Ultra low volume equipment mounted on a vehicle (1996) or a fixed wing aircraft (1997) was used for application. The M. anisopliae treatment reduced the grasshopper population significantly after 7 days and by 93% within 16 days. Fenitrothion caused a population reduction of more than 90% shortly after application, but due to immigration, the grasshopper population recovered to the initial level within 16 days. Grasshoppers treated with the fungus and given the opportunity to thermoregulate in the sun died more slowly than grasshoppers incubated in the shade. The survival of spores in the spray residue of the M. anisopliae plots assessed by exposing grasshoppers to the sprayed vegetation at intervals and monitoring disease levels during subsequent laboratory incubation, showed the spray residue to remain highly infective, for three weeks after spraying. At the end of the 1997 season, egg pod density and viability in the plot treated with the fungus was reduced compared with both untreated and the fenitrothion plots. Compared with the existing practice of large-scale treatment of grasshopper infestations with fenitrothion, use of M. anisopliae would not only be safer to mammals and less damaging to non-target organisms, but also be more effective in the long-term control of grasshoppers.     

Insect herbivory and vertebrate grazing impact food limitation and grasshopper populations during a severe outbreak

1. Competition between herbivores often plays an important role in population ecology and appears strongest when densities are high or plant production is low. Phytophagous insects are often highly abundant, but relatively few experiments have examined competition between vertebrates and phytophagous insects. 2. In grassland systems worldwide, grasshoppers are often the dominant phytophagous insect, and livestock grazing is a dominant land use. For this study, a novel experiment was conducted examining competition between vertebrates and invertebrates, where both grasshopper densities and sheep grazing were manipulated inside 10‐m² caged mesocosms during a grasshopper outbreak. We examined how grasshopper densities and the timing of vertebrate herbivory affected grasshopper densities, if the effects of vertebrates on survival and reproduction changed with grasshopper density, and how a naturally occurring grasshopper outbreak affected grasshopper populations in the following year. 3. Densities of grasshoppers at the site peaked at 130 m^–2. Food‐limited competition was stronger in treatments with higher grasshopper densities and repeated or late livestock herbivory, leading to reduced survival, femur length, and functional ovarioles, a measure of future reproduction. Strong food‐limited density‐dependent reproduction and survival led to reduced hatching densities in 2001. 4. As competition was typically stronger with high grasshopper densities than with livestock grazing, competition from vertebrates could be relatively less important for phytophagous insect population dynamics during outbreaks. The experiment provides insights into how competition between insect and vertebrate herbivores influences insect population dynamics, and indicates that severe outbreaks can rapidly subside with strong competition from vertebrate and insect herbivores.     

Does microclimate affect grasshopper populations after cutting of hay in improved grassland?

The microclimate of an improved hay meadow was studied using Tinytag dataloggers to record sward temperature after cutting. Temperatures in the sward were then compared to grasshopper abundances to see if mowing created an excessively hot microclimate unfavourable for sustained grasshopper activity in mid summer. The abundance of Chorthippus albomarginatus and Chorthippus parallelus was significantly reduced on the hay plots compared to the unmanaged control swards, which may have been due to high sward temperatures created by the absence of tall, shady vegetation in which grasshoppers may take refuge to avoid overheating. This study suggests that a combination of mortality caused by the physical process of mowing, and high sward temperatures created by removal of the standing crop by cutting may cause the low abundance of grasshoppers in improved grassland in eastern England. This research is particularly important when considering the orthopteran assemblages of Environmental Stewardship Scheme field margins where mowing for hay in July and August may seriously reduce grasshopper populations. If mowing of grassland has to occur during the grasshopper season, we suggest a later cut in September or a system of rotational mowing, leaving areas of uncut grassland as shelter.     

Review of the Methods Frequently Used to Estimate the Abundance of Orthoptera in Grassland Ecosystems

Ecologists have quantified Orthoptera (grasshoppers and crickets) density in a wide variety of conservation studies. Objective determination of Orthoptera population size is possible using mark-release recapture techniques but these are time-consuming and of little use for all but the smallest scale studies. Therefore, a wide range of sampling techniques have been devised to quantify population density and the most commonly used methods include sweep netting and quadrat counts. It is the aim of this paper to critically review studies that have used these techniques and to provide useful suggestions for non-specialists on which method may be most applicable to their study site. This paper reviews a selection of the extensive literature reporting studies estimating the abundance of grasshoppers (Acrididae) in a wide range of grassland ecosystems. Where possible, studies on bush-crickets (Tettigoniidae) and crickets (Gryllidae) are included reflecting their overall contribution to assemblage diversity in grassland ecosystems and to highlight the need for further investigations of sampling efficiency on these two under-researched families.The most rapid and inexpensive sampling methods, such as quadrat and transect counts, involve ‘flushing’ grasshoppers from the sward. These techniques are fairly accurate in short, open swards (<50 cm sward height) where grasshopper densities are low (<2 adults per m²). At higher population densities (>2 adults per m²), methods which require the capture of grasshoppers such as box quadrats and sweep netting may be more appropriate. Sampling grasshopper populations in taller vegetation (>50 cm sward height) is more problematic as the efficiency of many techniques may be reduced by vegetation structure. Methods such as timed counts can be used at low densities (<2 adults per m²) and night trapping might be most applicable where high numbers of grasshoppers are present (>2 adults per m²).There is an urgent need for development of a standardised sampling technique that can produce comparable data from studies with a wide variety of observers in grasslands with differing vegetation structures and grasshopper densities.     

Between-season Survival of the Grasshopper Pathogen Metarhizium flavoviride in the Sahel

A study is presented showing that the entomopathogenic fungus, Metarhizium flavoviride, can persist in fragments of infected grasshopper cadaver and survive the Sahelian dry season. A significant positive relationship was identified between the probability of mortality at the beginning of one season and the density of infected cadavers present in the habitat at the end of the previous season. Furthermore, survival analysis revealed a steady decline in the mean survival time of grasshoppers exposed to the infected habitats as the density of infected cadavers used to seed the habitat increased. The consequences of these findings are discussed in the context of the use of M. flavoviride for locust and grasshopper control.     

Status of the alien pathogen Paranosema locustae (Microsporidia) in grasshoppers (Orthoptera: Acridoidea) of the Argentine Pampas

After experimental introductions from North America in 1978–1982, the biocontrol agent Paranosema locustae became established in grasshopper communities of the western Pampas region of Argentina. The use and establishment of P. locustae in Argentina constitute both a case of neoclassical or new association biological control (use of an alien species against native pests) and a case of pathogen pollution (anthropogenic introduction–establishment of an infectious disease in populations of native species). Since P. locustae is a multihost pathogen among grasshoppers, its presence in the western Pampas represents an additional factor disrupting grasshopper communities according to the differential susceptibility of each species and possibly threatening some species. Microscopic examination of 504 grasshopper samples (the mean number of individuals per sample = 185) belonging to 43 species from 93 localities throughout the Pampas revealed an establishment area of approximate 90,000 km² from about 35° North to 38° South and from 61° East to 65° West. Field infections by P. locustae have now been detected in 21 grasshopper species in the western Pampas. Susceptible species with geographic distributions mostly restricted to the establishment area and with numerically small populations, like the melanopline Scotussa daguerrei, are predicted to be the ones facing higher risks of negative impacts.     

New case of long-term persistence of Paranosema locustae (Microsporidia) in melanopline grasshoppers (Orthoptera: Acrididae: Melanoplinae) of Argentina

We report an additional case of long-term persistence of Paranosema locustae in grasshoppers of Argentina. The pathogen was introduced from North America on rangeland at Loncopué, Neuquén province. Microsporidia were not detected in pre-introduction samples whereas infected grasshoppers were found 11 years after introduction. Affected grasshoppers were the melanoplines Dichroplus elongatus, Dichroplus maculipennis, and Scotussa lemniscata, some of them with high spore loads. The case highlights the ability of P. locustae to recycle in local grasshopper communities by parasitizing susceptible species other than the natural hosts.     

Populations of the northern grasshopper, Melanoplus borealis (Orthoptera: Acrididae), in Alaska are rarely food limited

In some systems, grasshoppers appear to be food limited in most years, whereas in other systems top down forces, for example, predators, are more often implicated in population regulation. Sustainable strategies to manage grasshopper populations through habitat management require knowledge of the forces that regulate grasshopper populations. This experiment was undertaken to determine whether populations of Melanoplus borealis (Fieber), a common pest species in Alaska, are food-limited in Alaska. Cages were set up in a fallow field near Delta Junction, AK, in 3 yr (2007-2009). In 2007 and 2008, fertilizer was added to half the plots to increase primary production, and, in all years, cages within each plot were stocked with 0, 5, 9, or 13 fourth-instar M. borealis (equivalent to 0, 20, 36, or 52 grasshoppers/m(2)). Grasshoppers in each cage were counted weekly. Near the end of the growing season, surviving female grasshoppers (≈40% of the original number) were collected. Femur length was taken as a measure of adult size, and functional ovarioles were counted as a measure of current fecundity. If the grasshoppers were food limited, we expected to see significant effects of either density or fertilizer on grasshopper survival, size, or fecundity. The fertilizer treatment greatly increased primary production in both years. Neither fertilizer treatment nor grasshopper density had consistent effects on survival, size, or potential fecundity, leading us to conclude that food is seldom limiting to populations in the interior of Alaska at densities <50 m(-2).     

Linking trophic interactions to plasticity in thermal sensitivity of geographically separated populations of a herbivore

The ability of species to tolerate a warming climate has important implications for ecological functioning. Theory and empirical synthesis suggest species adapted to more thermally variable climates are more capable of acclimating to rising temperatures, and are therefore characterized by greater phenotypic plasticity, than species adapted to less thermally variable environments. But this pattern has not been extensively evaluated for populations within a species that may inhabit different parts of a thermal gradient. In addition, it remains unclear whether different populations with different thermal sensitivities will maintain the same functional ecological roles as thermal regimes shift. To address this question, we conducted a reciprocal transplant experiment using Melanoplus femurrubrum grasshopper populations from Connecticut and Vermont, USA. During summer, the Vermont site was 3 °C cooler on average with 1.5-fold greater temperature variation than the Connecticut site. We measured thermal sensitivity (metabolic rate Q₁₀) of individuals from each population reared in home field and transplanted sites and the nature and strength of trophic interactions with grasses and goldenrod (Solidago). Both grasshopper populations exhibited plasticity, but Q₁₀ of both populations at Vermont was 1.5-fold broader than populations at the Connecticut site. All grasshoppers had similar survivorship but not similar effects on plants, exhibiting stronger effects on grasses in their home fields relative to their transplanted sites. Only Vermont grasshoppers transplanted to Connecticut significantly impacted Solidago. The study shows populations may physiologically acclimate quickly under new thermal conditions, suggesting stronger tolerance to change than often presumed. But, thermal acclimatization may not translate into the maintenance of a species’ functional role. The work underscores the need to link analyses of physiological performance with ecological function to obtain a complete picture of climate change effects on communities.     

Development of a model for evaluating the effects of environmental temperature and thermal behaviour on biological control of locusts and grasshoppers using pathogens

1 Recent years have seen an upsurge in locust and grasshopper populations in many parts of the world. Environmentally sustainable approaches to locust and grasshopper control may be possible through the use of biopesticides based on entomopathogenic fungi. Unfortunately, the performance of these biopesticides is highly variable with environmental temperature and host thermoregulatory behaviour critically determining the pattern and extent of mortality after applications. Here, we present a temperature‐dependent model that enables us to predict the field performance of Metarhizium anisopliae var. acridum, the key fungal pathogen used in locust biopesticides. 2 The model was constructed using mortality rate data generated across a range of temperatures in the laboratory and is driven by environmental temperature data linked through host body temperature models. 3 Model predictions were validated against empirical field data obtained for five species, Locustana pardalina, Oedaleus senegalensis, Zonocerus variegatus, Nomadacris septemfasciata and Chortoicetes terminifera. Mortality predictions were accurate to a 2‐day error in every 10 days. This level of resolution is satisfactory to guide operational use of the biopesticide. 4 The model was subsequently used for a prospective evaluation of the performance of M. anisopliae var. acridum against two additional pest species, Dociostaurus maroccanus and Calliptamus italicus in Spain. Results suggest that this pathogen would work reasonably well against these species as long as early instars are targeted. 5 The model could provide a useful tool to assist in interpreting effectiveness of control operations, develop improved application strategies to optimize the performance of the biopesticide and identify appropriate target species and environments.     

Isolation and growth of the grasshopper pathogen, Entomophthora grylli

Entomophthora grylli was isolated and grown in pure culture in protoplast form. Cultures were obtained by germinating conidia collected from naturally infected adult Carolina grasshoppers, Dissosteira carolina, in Grace's tissue culture medium supplemented with 5% fetal bovine serum and an aqueous extract of grasshopper tissue. Grasshopper extract was not necessary for subsequent growth and subculture of the protoplasts. Healthy adult grasshoppers could be reinfected with the fungus by injection of a protoplast suspension.     

Dynamics of two Montana grasshopper populations: relationships among weather,food abundance and intraspecific competition

The population dynamics of two grasshoppers (Melanoplus femurrubrum and M. sanguinipes) were studied using experimental microcosms over 8 years at a Palouse prairie site in Montana. Grasshopper density, survival and reproduction in the experimental populations responded in a density-dependent fashion to natural and experimental changes in food availability for all grasshopper developmental stages, both within and between all years. We observed that field populations of the grasshoppers at the site exhibited density, survival and reproductive responses similar to the experimental populations over the period of the study. Because we could not identify any differences between the field and microcosm environments or the grasshopper individuals in them, we contend that field populations were ultimately limited by food within and between years. Density-dependent food limitation occurred for all age categories over the entire summer, because food abundance declined relative to grasshopper food requirements over the summer. Food limitation occurred between years, because in years with the lowest food abundance, the populations produced more hatchlings for the next year than could be supported by the highest observed food abundance. Finally, the observed annual changes in food abundance were correlated with the annual variation in weather (rainfall and temperature), which indicated that the long established relationship between grasshopper densities and weather conditions does not imply population limitation by density-independent processes.     

Effect of prolonged storage of spores on field applications of Nosema locustae (Microsporida: Nosematidae) against grasshoppers

Spores of Nosema locustae that were freshly prepared, stored in water at ?10°C for 8 months to 3 years, or stored in cadavers for 1 year at ?10°C were applied on bran at the rate of 10⁹ spores/1.5 lb bran per acre. Applications of fresh spores resulted in higher density reductions and higher incidence of infection among survivors than applications of spores stored in water or cadavers in both a complex of grasshoppers predominated by a single species and in a mixed species complex. Density reductions due to treatment with fresh spores were similar in the two populations, but the mixed species complex had a lower incidence of infection than the complex in which one species predominated. Applications of fresh spores reduced grasshopper densities in both complexes to levels below the economic thresholds.     

Changes in western wheatgrass foliage quality following defoliation: consequences for a graminivorous grasshopper

We determined the effects of defoliation by a graminivorous grasshopper on the foliage quality of the C3 plant, western wheatgrass (Pascopyrum smithii [Rydb] A. Love). Additionally, we determined the effects of this defoliation upon the subsequent feeding of the graminivorous grasshopper Phoetaliotes nebrascensis Thomas (Orthoptera: Acrididae). In field and greenhouse studies, graminivorous grasshopper herbivory altered the quality of remaining western wheatgrass foliage. In the greenhouse, severe (50% foliage removal) grasshopper grazing (638 grasshoppers/m² for 72h) resulted in decreased foliar nitrogen (–12%), carbohydrate (–11%) and water (–2.5%) concentrations, and increased phenolic concentrations (+43%). These changes were associated with decreased adult female grasshopper mass gain, consumption rate, approximate digestibility, and food conversion efficiencies. In the field, moderate (14% foliage removal) grasshopper grazing (20 grasshoppers/m² for 20 days) led to a 10% reduction in foliar nitrogen concentrations. Foliage quality changes in the field were not associated with any reductions in grasshopper mass gain, consumption rates, food digestibility, or conversion efficiencies. The results presented here are consistent with the hypothesis that defoliation leads to a reallocation of carbon and nitrogen compounds within the plant such that foliage quality for P. nebrascensis is reduced.