Natural levels of fungal infections in grasshoppers in Northern Benin

The infection of grasshoppers by naturally occurring, entomopathogenic fungi was monitored at two sites in Malanville, northern Benin, Africa. Grasshoppers were collected and recorded from the sites between June and December 1992 and all of them, barring the first instars, were incubated in ventilated cages. At the first site, 1343 individuals of 35 grasshopper species were incubated, and at the second site, 857 individuals of 36 grasshopper species were incubated. Three hyphomycete fungi (Deuteromycotina: Hyphomycetes), Metarhizium flavoviride Gams and Rozsypal, Beauveria bassiana (Bals.) Vuillemin and Sorosporella sp. were found infecting grasshoppers. The average incidence of M. flavoviride infection was 2.9% and 1.8% at the two sites for all host species. M. flavoviride sporulated on most grasshopper cadavers within 10 days of collection. B. bassiana and Sorosporella sp. were only collected from one and five grasshopper individuals respectively. A significant difference was noted in the time to death of small grasshopper species infected with M. flavoviride compared to larger species. At one site, M. flavoviride infection was positively correlated with rainfall during the 10‐day period in which samples were taken.     

Natural Incidence of Metarhizium flavoviride Infection in Two Grasshopper Communities in Northern Benin

The infection of grasshoppers by naturally occurring entomopathogenic fungi was monitored at two sites in Malanville, northern Benin, Africa. Grasshoppers were collected during the monsoon seasons of 1993, 1994 and 1995. At the first site, 982 individuals of 38 grasshopper species were incubated. At the second site, 899 individuals of 33 grasshopper species were incubated. Two hyphomycete fungi (Deuteromycotina: Hyphomycetes), Metarhizium flavoviride Gams and Rozsypal and Sorosporella sp., were found infecting grasshoppers. The mean incidence of M. flavoviride infection was 0.3-1.7% at the first site and 1.2-3.2% at the second site for all grasshopper species. Sorosporella sp. was only collected from two grasshopper individuals in 1993. The majority of infected species had adult quiescence or continuously reproducing life cycles, and were either arboricolous or terricolous. Comparisons are made with a previous study of the two sites performed during 1992.     

绿僵菌药后草原蝗虫种群空间分布型研究

综合多个聚集度指标对绿僵菌药后田间蝗虫和僵虫的空间分布型进行了研究。结果表明：施药后不同时间随蝗虫种群密度的减小,处理区残虫的分布型呈现聚集随机交错变动,僵虫的空间分布型为聚集分布。采用Taylor幂法则和改进的Iwao模型分析表明,整个调查时段处理区残虫、僵虫的空间分布均为聚集分布。推测认为,药后蝗虫点片状死亡,部分地片相对密度较高,残虫分布型趋向聚集; 自然消除作用使僵虫密度很低,低密度下取样产生大量空样本,僵虫的分布型产生聚集假象。     

Effects of the Sunscreen Oxybenzone on Field Efficacy and Persistence of Metarhizium flavoviride Conidia Against Kraussella amabile (Orthoptera: Acrididae) in Mali,West Africa

A field trial was performed at Mourdiah, northwest Mali, to evaluate whether the performance of Metarhizium flavoviride conidia would improve if 2% oxybenzone, an oil-soluble ultraviolet light protectant, was used. Conidia were applied in an ultra-low volume formulation against nymphs of the grasshopper Kraussella amabile . Mortality was assessed by collecting grasshoppers directly from field plots (sweep net samples) or by exposing untreated nymphs to sprayed vegetation for 48 h (field cage samples). For sweep net samples, the mortalities in M. flavoviride treatments varied between 94.5 and 99.9% up to 7 days after treatment, while control mortalities were significantly lower (20.7-55.0%). There were no significant differences between M. flavoviride treatments with or without oxybenzone. The average survival times were found to be significantly lower for fungal treatments (4.9 days) compared with the control treatment (11.8 days). W ith field cage samples, the mortality in M. flavoviride treatments declined from > 95.0% for nymphs exposed just after application to < 30.0% for nymphs exposed to treated vegetation on the 10th day after application. The control mortalities varied between 5.1 and 37.2%, and were significantly lower than fungal treatments for samples placed just after application and 10 days after application. The overall average survival times were 10.9 and 10.7 days for M. flavoviride with and without oxybenzone respectively, and 13.9 days with the control treatment. An exponential regression was fitted using cage mortality data which indicated that the half-life for conidial infectivity was 4.3 days on treated vegetation.     

Field Trial with the Entomopathogenic Fungus Metarhizium anisopliae var. acridum against Bands of the Grasshopper Rhammatocerus schistocercoides in Brazil

The efficacy of a mycoinsecticide formulated in vegetable oil was tested in Brazil against the grasshopper Rhammatocerus schistocercoides . A set of experiments was conducted in the Chapada dos Parecis region (Mato Grosso state), a permanent zone of outbreaks for this pest. Experiments were performed in zones of natural vegetation, against grasshopper bands in the third nymphal instar. Three nymphal bands were treated with a mycoinsecticide formulation based on conidia of the entomopathogenic fungus Metarhizium anisopliae var. acridum ( =M. flavoviride ), strain CG 423. Three non-treated bands were used as control. The application was made with the aid of a hand-held ULV sprayer adjusted to deliver 2 l of the formulation ha -1 , each containing 1 ×10 13 conidia. Treatments were limited to the surface of the grasshopper bands and their immediate borders (5-10 m). The efficacy of the mycoinsecticide was evaluated through band survival after treatment (grasshopper numbers, surface, density, behaviour and daily movement of the band), allowing the insects to move freely in their natural environment. Insects were regularly surveyed and maintained in the laboratory, allowing estimates of the infection rate. Field and laboratory studies showed a clear effect of the product 10 days after treatment. At 14 days post-spraying, mortality caused by the mycoinsecticide in the field was approximately 88%.     

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).     

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.     

Seasonal patterns of persistence and infectivity of Metarhizium anisopliae var. acridum in grasshopper cadavers in the Sahel

Field-based experiments were conducted to evaluate the fate and infectivity of the entomopathogenic fungus Metarhizium anisopliae var. acridum (Deuteromycotina: Hyphomycetes) in grasshopper cadavers in the Sahel. Unlike uninfected cadavers, which were rapidly scavenged, those infected with the fungus persisted in the environment for a number of weeks. The environmental factor most associated with cadaver disappearance was rainfall. The high environmental humidity associated with rainfall was also required for sporulation of the fungus on host cadavers, although the likelihood of sporulation differed between microsites. Characteristics of the infection profile from infective cadavers were investigated by the sequential exposure of uninfected hosts to sporulating cadavers in field cages. This experiment revealed that cadavers remained infective for > 30 days, with the net infectivity changing through time. The most likely explanation for these changes is climatic influences on both the fungus and host. High humidity was not required for infection. A measurement of the transmission coefficient between healthy hosts and sporulating cadavers in the field was obtained at a realistic density of infectious cadavers. This revealed a figure of 0.45 m² day^–1. Overall, these experiments show that following host death, M. anisopliae var. acridum can be persistent in the environment, sporulate on host cadavers and reinfect new hosts at a realistically low field density, although at least in arid or semi-arid areas, rainfall may be critical to the horizontal transmission of this pathogen.     

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.     

Foraging patterns and dietary mixing in the field by the generalist grasshopperBrachystola magna (Orthoptera: Acrididae)

The foraging behavior of a cryptic romaleine grasshopper was observed in its natural habitat in southern Arizona. Individual polyphagy, dietary mixing, and the pattern of feeding on different substrates were monitored. Individuals were found to be extreme generalists with surprising levels of feeding on other insects. Differences in the foraging behavior between grasshopper species are discussed in relation to the habitat, the season, and the different defensive strategies.     

Laboratory and Field Trials of Bait Formulations of the Fungal Pathogen, Metarhizium flavoviride, Against a Tropical Grasshopper and Locust

Extrusion technology was used to produce maize-starch 'contact bait' carriers, and vegetable-oil suspensions of Metarhizium flavoviride were incorporated into the baits after extrusion. Laboratory bioassays using the locust, Schistocerca gregaria, demonstrated mortality and reduction of 8 1 feeding after exposure to the baits, and gave an LC 50 of 1.5 10 spores l slope 0.63 for fifth instar nymphs. In laboratory trials, maize-starch contact baits showed improved efficacy relative to wheat-bran edible bait formulations of M. flavoviride. Field cage experiments, undertaken in Mali, using fourth and fifth instar nymphs of the grasshopper, Hieroglyphus dagenensis, demonstrated significant mortality with both fresh and weathered maize-starch contact bait formulations of M. flavoviride, relative to untreated controls.     

放牧对蝗虫栖境结构的改变及其对蝗虫栖境选择的影响

放牧是草原植被利用的主要形式,牲畜的牧食极易改变蝗虫生存的栖境结构,本研究表明：在重牧区蝗虫发生的密度最高,而轻牧区蝗虫发生的密度最低,这说明,不同的牧压强度所形成的栖境对蝗虫栖境选择的适合度不一致。     

Prey change behaviour with predation threat, but demographic effects vary with prey density: experiments with grasshoppers and birds

Increasingly, ecologists emphasize that prey frequently change behaviour in the presence of predators and these behavioural changes can reduce prey survival and reproduction as much or more than predation itself. However, the effects of behavioural changes on survival and reproduction may vary with prey density due to intraspecific competition. In field experiments, we varied grasshopper density and threat of avian predation and measured grasshopper behaviour, survival and reproduction. Grasshopper behaviour changed with the threat of predation and these behavioural changes were invariant with grasshopper density. Behavioural changes with the threat of predation decreased per capita reproduction over all grasshopper densities; whereas the behavioural changes increased survival at low grasshopper densities and then decreased survival at high densities. At low grasshopper densities, the total reproductive output of the grasshopper population remained unchanged with predation threat, but declined at higher densities. The effects of behavioural changes with predation threat varied with grasshopper density because of a trade-off between survival and reproduction as intraspecific competition increased with density. Therefore, resource availability may need to be considered when assessing how prey behavioural changes with predation threat affect population and food web dynamics.     

An experimental analysis of grasshopper community responses to fire and livestock grazing in a northern mixed-grass prairie

The outcomes of grasshopper responses to both vertebrate grazing and fire vary across grassland ecosystems, and are strongly influenced by local climactic factors. Thus, the possible application of grazing and fire as components of an ecologically based grasshopper management strategy must be investigated in regional studies. In this study, we examined the effects of grazing and fire on grasshopper population density and community composition in a northern Great Plains mixed-grass prairie. We employed a large-scale, replicated, and fully-factorial manipulative experimental design across 4 yr to examine the separate and interactive effects of three grazing systems in burned and unburned habitats. Grasshopper densities were low throughout the 4-yr study and 1 yr of pretreatment sampling. There was a significant fire by grazing interaction effect on cumulative density and community composition, resulting from burned season long grazing pastures having higher densities than unburned pastures. Shannon diversity and grasshopper species richness were significantly higher with twice-over rotational livestock grazing. The ability to draw strong conclusions regarding the nature of species composition shifts and population changes in the presence of fire and grazing is complicated by the large site differences and low grasshopper densities. The results reinforce the importance of long-term research to examine the effects of habitat manipulation on grasshopper population dynamics.     

Cattle grazing in CRP grasslands during the nesting season: effects on avian reproduction

Bird populations in grasslands have experienced declines coinciding with loss and fragmentation of prairies. The United States Department of Agriculture (USDA)-administered Conservation Reserve Program (CRP) is the most extensive grassland restoration program in North America and it has especially benefitted grassland birds. Grazing by domestic cattle has been restricted in CRP during avian nesting seasons despite the potential improvements in structuring habitat for a greater diversity of grassland bird species. Potential negative consequences of grazing in CRP grasslands include trampling of nests by cattle, reductions in nest concealment from predators, and attraction of brood-parasitic brown-headed cowbirds (Molothrus ater). We designed an experiment to test for effects of cattle grazing in CRP fields during the nesting season on nest survival and brood parasitism of 5 bird species that commonly nest in CRP grasslands: mourning dove (Zenaida macroura), grasshopper sparrow (Ammodramus savannarum), dickcissel (Spiza americana), and eastern (Sturnella magna) and western (S. neglecta) meadowlarks. Grazing was implemented during summers 2017 and 2018 on 17 of 36 fields followed by a year of rest on all fields in 2019. Of the 879 nests on grazed fields, only 4 were likely trampled by cattle (vs. 54% of all nests estimated as failing because of depredation). Experimental grazing (grazed vs. ungrazed fields) had variable effects on nest survival and cowbird parasitism among the bird species analyzed. Negative effects of grazing on daily nest survival of dickcissel and meadowlarks were apparent, at least in some years. We found no direct effects of grazing on nest survival of mourning dove or grasshopper sparrow. Probability and intensity (cowbird offspring/nest) of cowbird parasitism in dickcissel nests was higher on grazed versus ungrazed sites but only in conservation practice (CP) CP2 (vs. CP25 fields). Parasitism probability of grasshopper sparrow nests by cowbirds was higher on grazed fields in the 2 years after introduction of cattle in 2017. Greater vegetative concealment around nest sites was associated with reduced cowbird parasitism of meadowlark and grasshopper sparrow nests and higher nest survival for grasshopper sparrows. Reductions in vegetative height caused by longer-term or high-intensity grazing might therefore have negative consequences for some grassland birds by increasing nest site visibility and exposure to cowbird parasitism. Our results indicate that cattle grazing in CRP fields during the nesting season might have some negative effects on reproductive success of some grassland bird species, at least in the short term; however, the potential improvements of structuring habitat to accommodate more grassland bird species and increasing landowner participation in the CRP are considerable.     

Weather variation and trophic interaction strength: sorting the signal from the noise

Weather can have important consequences for the structure and function of ecological communities by substantially altering the nature and strength of species interactions. We examined the role of intra- and inter-annual weather variability on species interactions in a seasonal old-field community consisting of spider predators, grasshopper herbivores, and grass and herb plants. We experimentally varied the number of trophic levels for 2 consecutive years and tested for inter-annual variation in trophic abundances. Grasshopper emergence varied between years to the extent that the second growing season was 20% shorter than the first one. However, the damage grasshoppers inflicted on plants was greater in the second, shorter growing season. This inter-annual variation in plant abundance could be explained using the foraging-predation risk trade-off displayed by grasshoppers combined with their survival trajectory. Decreased grasshopper survival not only reduced the damage inflicted on plants, it weakened the strength of indirect effects of spiders on grass and herb plants. The most influential abiotic factor affecting grasshopper survival was precipitation. We found a negative association between grasshopper survival and the total yearly precipitation. A finer scale analysis, however, showed that different precipitation modalities, namely, number of rainy days and average precipitation per day, had opposing effects on grasshopper survival, which were inconsistent between years. Furthermore, our results suggest that small changes in these factors should result in changes of up to several orders of magnitude in the mortality rate of grasshoppers. We thus conclude that in this system the foraging-predation risk trade-off displayed by grasshoppers combined with their survival trajectory and relevant weather variability should be incorporated in analytical theory, whose goal is to predict community dynamics.     

Control of Zonocerus variegatus by Ultra-low Volume Application of an Oil Formulation of Metarhizium flavoviride Conidia

An oil-based formulation of Metarhizium flavoviride conidia, applied at 2 1012 spores ha-1 in 1 l ha-1 gave good control of Zonocerus variegatus in 1-ha plots in southern Benin. In a three-replicate, randomized, complete block (RCB) trial in Mono province, a significant reduction in insect counts between treated and control plots was observed 10-15 days after application; treatment reduced the population by about 90%. A four-replicate RCB trial in Oue me province also gave high mortality. Although a significant difference between treated and untreated plots was observed 10-18 days after application, insect dispersal out of cassava fields towards oviposition sites interfered with a clear demonstration of control. Significantly more Z. variegatus cadavers with M. flavoviride infection were found in treated plots than control plots.     

Relationship between physical leaf characteristics and growth and survival of polyphagous grasshopper nymphs, <Emphasis Type="Italic">Parapodisma subastris</Emphasis> (Orthoptera: Catantopidae)

Common types of plant defense mechanisms are thought to affect the host ranges of polyphagous herbivorous insects, yet few studies have examined the relationship between host plant suitability for polyphagous insects and defense against them. We investigated the suitability of the 19 plant species growing in the habitat of the polyphagous grasshopper, Parapodisma subastris, to determine the relationship between the physical characteristics of leaves and the growth and survival of grasshopper nymphs. We examined leaf toughness, trichome density, and length. Nymph survival was greater on plants with characteristics ranging from soft leaves and dense trichomes to tough leaves and few trichomes than on plants with soft leaves and few trichomes. The exception was Rorippa indica, a plant with soft leaves and few trichomes that uses biotic defense, on which nymph survival was maximal. Higher-quality plants that share common physical characteristics over families may favor polyphagy by grasshoppers that possess ability to overcome the physical defense easily with their robust mandibles.An erratum to this article can be found at     

内蒙古镶黄旗草地蝗虫潜在发生可能性评价

以内蒙古草地蝗虫产卵期、越冬期和孵化期的关键气象影响因子作为草地蝗虫气象适宜度指数构建的主要因子,对内蒙古镶黄旗2010年草地蝗虫潜在发生的气象适宜性进行评价;根据当年7月上中旬在镶黄旗的实地调查资料,选取海拔、坡向、土壤类型、土壤含砂量、植被类型、植被盖度、土地覆被类型7个相对稳定的生境因子,用模糊评判方法和3S(GIS、RS、GPS)技术对该旗草地蝗虫潜在发生的生境适宜性进行评价;最后通过构建气象-生境适宜性综合评价模型,得到该旗2010年草地蝗虫潜在发生可能性(POG)等级,并用2010年实测数据和2001-2010年历史数据对模型模拟的蝗虫发生位置和蝗灾发生面积进行验证.结果表明:用本文所建气象-生境适宜性综合评价模型对镶黄旗POG等级的评价结果是可靠的.该旗草地蝗虫潜在发生的气象适宜性等级非常一致,绝大多数为适宜等级;蝗虫潜在发生源地的空间异质性主要与生境因子有关,在海拔1300～1400 m的平地/东坡/南坡、植被盖度30％ ～ 50％的温带丛生禾草草原、土壤含砂量60％～80％的典型栗钙土的生境条件下,草地蝗虫潜在发生的可能性最高.     

Reduction of Feeding by the Variegated Grasshopper, Zonocerus variegatus , Following Infection by the Fungal Pathogen, Metarhizium flavoviride

The effect of infection by the fungal entomopathogen , Metarhizium flavoviride, on feeding by the tropical grasshopper pest , Zonocerus variegatus, was investigated in field - cage studies . A significant reduction in feeding , as indicated by faecal production , was recorded 2 - 3 days after inoculation for a range of spore doses (104 , 105 and 5 105 spores per insect) . This was before any mortality was recorded due to infection . All infected individuals died by day 7 . At this time , faecal production of the treated grasshoppers was equivalent to less than 2 days faecal production by grasshoppers untreated with spores . This reduction in feeding (69 , 71 and 74% total reduction by day 7 in the 104 , 105 and 5 105 doses respectively in comparison to controls) is a substantial contribution to the overall effects of the slow acting pathogen . Furthermore , the rapid reduction in feeding indicated that this effect was not simply due to invasion of the host tissues by the pathogen or production of secondary metabolites . The possibility that reduction in feeding is associated with a behavioural response in which there is a trade - off between host defence and feeding during early stages of infection is discussed