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.     

Development of strategies for the incorporation of biological pesticides into the integrated management of locusts and grasshoppers

• 1 Effective biological pesticides based on oil formulation of deuteromycete fungal spores have been developed for use against locusts and grasshoppers. The isolate IMI 330189 of Metarhizium anisopliae (flavoviride) var. acridum has been registered, extensively field tested and its operating characteristics explored. It should form an powerful component technology in the integrated management of locust and grasshopper pests.
• 2 The particular advantages of Metarhizium anisopliae were found to be efficacy and persistence, low vertebrate toxicity, little environmental impact, conservation of natural enemies and potential for recycling. Additional socio-economic advantages include the possibility of local production, ease of disposal and versatility in use. The principal disadvantages relate to operating characteristics such as slower speed of kill and slightly greater lability in storage than chemical pesticides.
• 3 Strategies are being developed to integrate biological control agents into locust and grasshopper management schemes; for Metarhizium the accent is placed on: (i) treating the pest before it invades crops and (ii) situations with a high premium on environmental issues.
• 4 For some pest situations, fast-acting chemical pesticides will still be necessary for crop protection.
• 5 A cheaper biological agent, such as Nosema locustae, with the capacity to persist in the pest insect population would be useful. Research is recommended on the long-term impact of Nosema in Africa.
• 6 An evaluation of the utility of the manual destruction of egg pods leads to the conclusion that we should consider the possibility of importing egg parasitoids, such as Scelio parvicornis from Australia, into Africa.
• 7 Further development work is needed to clarify the economics and politics of locust and grasshopper control; to improve the regulatory framework for biopesticides; to inform key decision makers of the availability and potential of Metarhizium; and to implement the bio-intensive IPM strategies described.

     

Suggestions for unifying the terminology in biological control

This paper gives suggestions forunifying the terminology in biological controlacross different research disciplines, such asbiological control of arthropods, weeds andplant pathogens. It is suggested that use ofthe term `biological control' is restricted tothe use of living organisms. Four strategiesof biological control are outlined anddefined: (1) Classical biological control, (2) Inoculation biological control, (3) Inundationbiological control, and (4) Conservationbiological control. It is proposed to usethese four terms as defined, and avoid usageof the term `augmentation'. Terms for specificprocesses and modes of action (for example,`parasitoid' and `competitor') can be definedby usage within the different biologicalcontrol disciplines. Microbial control usuallyindicates biological control of invertebratesusing microbes and, as such, is a subdivisionof biological control. Use of additionalauxiliary terms such as biopesticide isdiscussed.     

Susceptibility of the Hymenopteran Parasitoids Apoanagyrus ( = Epidinocarsis ) lopezi (Encyrtidae) and Phanerotoma sp. (Braconidae) to the Entomopathogenic Fungus Metarhizium anisopliae var. acridum (Deuteromycotina: Hyphomycetes)

Laboratory and so-called extended laboratory bioassays were conducted in Benin, West Africa, to investigate the pathogenicity and virulence of the entomopathogenic fungus Metarhizium anisopliae var. acridum , a biocontrol agent against locusts and grasshoppers, to two hymenopteran parasitoids, Apoanagyrus ( = Epidinocarsis ) lopezi and Phanerotoma sp. Treatments were carried out under simulated field conditions at standard field dose rates of 2.5 and 5.0 ×10 12 conidia ha -1 . Test organisms were continuously (3 weeks) exposed to spray residues in artificial or simulated natural environments. The standard strain IMI 330 189 of the mycopesticide Green Muscle caused a significant reduction of 24% in the longevity ( = average survival time, AST) of A. lopezi , relative to the untreated control. Mycosis was confirmed in 16% of all cadavers. AST was shorter under low relative humidity (RH) conditions, and these conditions seemed to enhance susceptibility to fungal infection. However, this effect was only marginally significant. In contrast, average longevity of untreated A. lopezi was slightly yet significantly shorter at low RH (50-60%) than at high RH (80-90%). In the extended laboratory assay, the same isolate had no significant effect on mortality, parasitoid emergence ( = beneficial capacity) and sex ratio. In a further screening test with isolates IIBC I91 609, IIBC I93 833 and IMI 330 189 (reference), no infection of A. lopezi was confirmed. Similarly, Phanerotoma sp. was not susceptible to IMI 330 189. It is concluded that mycopesticides based on the three strains tested pose a low risk to parasitic hymenopterans under field conditions.     

Field Infection of Zonocerus variegatus following application of an oil‐based formulation of Metarhizium flavoviride conidia

Conidia of Metarhizium flavoviride grown in diphasic culture with sporulation on rice, were extracted in kerosene and formulated with peanut oil. The formulation led to high mortality when applied to field populations of Zonocerus variegatus; between 70 and 95% of insects in samples collected from the field 0, 3 or 7 days after spraying died. Sporulation of M. flavoviride was observed in 70–80% of the dead‐treated insects, which compares favourably with results obtained in laboratory bioassays. Many dead Z. variegatus, some with internal sporulation, were found in shaded niches and oviposition sites in the treated plots. No sporulation was observed in samples collected prior to application, and both sporulation and mortality differed significantly between control and treated plots. Some infections were observed in insects collected 16 and 23 days after treatment; these late infections may be a consequence of contact with spores surviving in the environment.     

Operational and Economic Analysis of a West African Pilotscale Production Plant for Aerial Conidia of Metarhizium spp. for Use as a Mycoinsecticide Against Locusts and Grasshoppers

Aerial conidia of Metarhizium anisopliae (flavoviride) var. acridum strain IMI 330189 used for the inundative biological control of grasshoppers and locusts in sub-Saharan Africa are produced in a purpose-built facility at the International Institute for Tropical Agriculture in Benin using a standard, two-stage mass-production system. The yields average 31.1 g of dry conidia powder/kg of rice substrate, the production capacity is 300-350 kg of conidia/year and the production costs are estimated at US$21/100 g (the recommended dose for 1 ha). The production process parameters vary within narrow limits established during optimization, but the yield is characterized by a high level of variation over time. The incubation period and temperature are identified as key factors, although they account for less than 40% of the yield variation. The variation in conidial viability and contamination are correlated with several parameters, but none can adequately explain this variation. The handling time, a principal limiting factor, could be reduced by increasing the substrate quantity/unit of production. An awareness of these factors presents the opportunity to fine tune production, although the options for increasing or improving production efficiency are limited within the constraints of the system.     

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.     

Field Evaluation of Brazilian Isolates of Neozygites floridana (Entomophthorales: Neozygitaceae) for the Microbial Control of Cassava Green Mite in Benin,West Africa

Two Brazilian isolates and one Benin (indigenous) isolate of Neozygites floridana were released against the cassava green mite, Mononychellus tanajoa , in January 1999 in the Adjohoun district, Ouémé administrative region, Republic of Benin. Post-release monitoring conducted 8, 14, 22 and 36 weeks later showed very low mean infection rates on M. tanajoa by isolate (0.03-0.4%). However, 48 weeks after releases, mean infection rates increased noticeably to between 2.3 and 18.7%, and higher infection rates were observed for the Brazilian isolates compared with the indigenous one. The highest infection rate for the indigenous isolate was 4.5% while it reached over 30% for the Brazilian isolates (36.5 and 34.0%). Observations made to study dispersal from inoculated plants showed the absence of infected mites at 4 m from the inoculated plants in all fields 8 weeks after the releases, while they were already present on those at 2 m away. From the next monitoring, 14 weeks after the releases, infection was found at all three sampling positions (inoculated plants and plants at 2 and 4 m away). Only four mites with resting spores were found in over 460 000 mites examined. The highest infection levels were observed in December during 'harmattan' a period characterized by hot days and cool nights with high relative humidity.     

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.     

Pathological and physiological responses of ring-necked pheasant chicks following dietary exposure to the fungus Metarhizium flavoviride, a biocontrol agent for locusts in Africa

Metarhizium flavoviride, a fungal pathogen of grasshoppers and locusts, appears to be an effective, non-chemical insecticide (mycoinsecticide) for control of grasshoppers and locusts. This study, conducted during June and July, 1997, examined the pathogenic potential of this entomopathogenic fungus to non-target avian species that encounter infected insect prey items or contaminated food sources. Ring-necked pheasant (Phasianus colchicus) chicks were exposed to one of three diets, (spore-coated feed, infected insects, or untreated feed), either from 4 to 9 days of age, or, from 35 to 40 days of age. Necropsies were conducted on birds 10 days and 46 days old, respectively. Neither consumption of infected insects, nor of spore-coated feed, resulted in pathological changes, or significant changes in weight, growth rate, behavior, or mortality rate. Histological examination of organs indicated either no changes related to treatment, or normal tissue responses to antigenic challenge.