Factors in the success and failure of microbial agents for control of migratory pests

Microbial control agents generally kill insects more slowly than chemical pesticides, and fast-moving migratory pests may not at first sight appeal' to offer the most promising targets for microbial control. Operators responsible for control may need to have recourse to chemical control agents. Nevertheless, there are many occasions when pests breed and feed outside the crop and a microbial control agent can be used. Similarly, immature stages may cause little damage and early treatment in the crop can avoid damage. Microbial control agents are particularly likely to be favoured if the pest breeds in a conservation area, and if a publicly-accountable agency is responsible for control. Other key points of importance are the IPM context, in particular detection, planning and forecasting of outbreaks and the role of natural enemies. With these points in mind, we identify several locust and grasshopper systems where microbial control is becoming established; additionally, Sunn pest of wheat and Armyworm are identified as promising situations for microbials

Survival and mortality of grasshopper egg pods in semi-arid cereal cropping areas of northern Benin

Surveys of egg pods of agriculturally important grasshoppers were carried out in northern Benin between 1992 and 1995. Searches were made of oviposition sites under shrubs of the perennial legume Piliostigma thonningi along field margins. In 1993 and 1995, surveys were extended to include sorghum, Sorghum bicolor, and the perennial thatch grass Vetiveria nigritana. The four principal grasshopper species found at these oviposition sites were Hieroglyphus daganensis Krauss, Cataloipus fuscocoeruleipes Sjöstedt, Kraussaria angulifera (Krauss) and Tylotropidius gracilipes Brancsik comprising 86% of 4545 identified egg pods while 651 egg pods could not be identified to species level. Predation by meloid beetles (Epicauta, Mylabris and Psalydolytta spp.) varied between 0 and 50% for the four dominant grasshopper species. From 1993 and 1994 data, nymphal eclosion from egg pods damaged by meloids was significantly lower than emergence from undamaged egg pods. The hymenopterous parasitoids Scelio africanus Risbec and S. mauriticanus Risbec were reared from the four dominant grasshopper species and parasitism levels of 0.0-3.3% were recorded from these hosts. There were significant differences in nymphal emergences between parasitized and unparasitized egg pods of H. daganensi

Between season survival of the grasshopper pathogen Melarhizium flavoviride in the Sahel

A study is presented showing that the entomopathogenic fungus , Metarhizium avoviride, 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 cadaver s 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 cadaver s used to seed the habitat increased. The consequences of these endings are discussed in the context of the use of M. flavoviride for locust and grasshopper control

Development of Metarhizium spp. for the control of locusts and grasshoppers

Four research programmes are investigating the entomopathogenic fungal genera Metarhizium and Beauveria for locust and grasshopper control in Africa. In the LUBILOSA programme, surveys for pathogen isolates revealed a morphologically distinctive Metarhizium flavoviride Gams and Rozsypal attacking acridoids in West Africa, Madagascar, and elsewhere. Metarhizium anisopliae (Metschnikoff) Sorokin isolates with virulence to acridoids were also obtained, including several from non-orthopteran hosts. Natural epizootics of both genera are rare in acridoid populations, but do occur. A standardized screening method discriminated virulent from non-virulent isolates. The great majority of the most virulent isolates were from the acridoid group of M. flavoviride. A Niger isolate chosen for development from this group had low virulence to honey bees and parasitic Hymenoptera and was not infective to insects in several other orders. Field tests were carried out on formulations of oil mixtures, using ULV application rates of 1–2 L/ha and 2–5 × 1012 conidia per hectare. In preliminary tests, target insects were sprayed successfully in small field arenas and in large cages. Trials in 1993 on variegated grasshopper gave an approx. 90% reduction in field populations after 15 days. Trials on various acridids, predominantly Hieroglyphus daganensis Krauss, in dense grass in northern Benin showed slower mortality, although up to 70% population reduction was achieved. Trials using a vehicle-mounted ULV sprayer (the Ulva-Mast) in open grassland in Niger gave >90% mortality in samples of mixed acridids. In Mali, a Malian isolate of M. flavoviride was shown to be slightly more virulent than the standard Niger isolate; both isolates gave significant population reductions against nymphs of Oedaleus senegalensis Krauss and Kraussella amabile(Krauss) in 1-ha plots. Successful small-scale field trials have also been carried out using the standard M. flavoviride isolate in South Africa against brown locust and in Australia using an Australian isolate against wingless grasshopper. In Mauritania, a trial using the Niger isolate against desert locust nymph bands gave up to 90% mortality in caged samples by day 9 after spraying. The uncaged treated bands were completely destroyed by predators while untreated bands fledged. Oil-based ULV formulations of M. flavoviride are capable of causing high mortality in the field populations of all acridoids against which they have been field tested and show great promise for development as components of IPM strategies for these pests

Pathogen incidence and their potential as microbial control agents in IPM of maize stem borers in West Africa

A review of the existing basis for maize stem borer IPM is given and the role of pathogens in the system is evaluated. Survey work outlining the major groups of insect pathogens is described; fungi (Beauveria bassiana and Metarhizium anisopliae), bacteria (Bacillus thuringiensis and Serratia marcesens), and viruses (granuloviruses and cytoplasmic polyhedroviruses) were identified. The presence of other unidentified protozoans, nematodes, fungi and viruses was noted. The virulence of some of the more promising known insect pathogens was explored in preliminary bioassays. Considering the cryptic habits of the insects, and the low input agriculture practiced by the majority of maize farmers in sub-Saharan Africa, Beauveria bassiana isolates possessing the capacity to grow systemically in the maize plant are considered one of the more interesting candidates for development as microbial control agents despite limited control in preliminary trials. Further work should also investigate the potential of pathogens of moderate virulence, such as the protozoans and CPVs

Effect of temperature, humidity and inoculation method on susceptibility of Schistocerca gregaria to Metarhizium flavoride

The effects of temperature on conidial germination and susceptibility of adults of the desert locust, Schistocer cagregaria, to four isolates of Meta rhizium flovoviride were determined. In addition, the eff ects of inoculation method (topical or spray), spore carrie r (oil or wat er) and ambient relative humidity (R H ) on susceptibility of the locust to the most thermotolerant isolate (M f324) were investigated. There were differences among the isolates in the effects of temperature on germination of conidia after a 24 -h incubation period. Over 90% of conidia of all isolates germinated after 24 h at 30oC. In contrast, at 40oC, none of the isolates germinated for up to 72 h. However, there were differences in germination between the isolates at 35oC. Locust mortality and disease progression were significantly affected by temperature. At both 25 and 30oC, all isolates induced 98-100% mortality within 8 days; however, there were differences between isolates at 35oC. None of the isolates caused significant mortality at 40oC. Humidity and inoculation method had no influence on levels of mortality in fungus treated locusts. In contrast, carrier type signicantly affected cumulative mortality. Topical oil treatment resulted in higher overall mycosis than the three other treatments. Control mortality on the other hand was strongly affected by inoculation method and to a lesser ex tent by humidity and carrier. In these conditions, application of oil by spray was generally toxic at all humidities whereas topical application of water was most toxic at near saturation. The results of these laboratory studies demonstrate the importance of strain selection, formulation and application method in the development of a microbial control agent against the desert locust .Low R H should not impede use of this fungus under dry conditions

Use of Metarhizium flavoviride for control of Zonocerus variegatus: a model, relating mortality in caged field samples with disease development in the field

A field trial was conducted using an oil formulation of the entomopathogenic fungus, Metarhizium flavoviride Gams & Rozyspal (Deuteromycotina: Hyphomycetes), to control the variegated grasshopper, Zonocerus variegatus L. (Orthoptera: Pyrgomorphidae). The influence of dispersal and secondary pick‐up from the spray residue on mortality was assessed by sampling insects from the treated plots at intervals and monitoring disease levels during subsequent incubation in the laboratory. The cumulative mortality curves showed the pathogen to be highly effective, even in samples taken 8 days after spraying. A model was developed to link the influence of mortality, incubation, secondary pick‐up of spores and insect dispersal, on the shape of these cumulative mortality curves. The model proved useful for data received from an experiment using small plot sizes, where insect dispersal is a big problem. The spray residue had an important influence on overall insect mortality. The model also indicated a difference in speed of kill between field and laboratory samples, suggesting an incubation delay in the fiel

Effects of moisture content and temperature on storage of Metarhizium flavoride conidia

The effects of moisture content and temperature on the medium-term (3-4 months) storage of conidia of Metarhizium flavoviride were investigated. Conidia harvested after 24 days of culturing on rice showed greater tolerance to long storage than conidia from 12-day cultures. The moistut-e content of the conidia was of greatest importance; at harvest from the culture. conidial moisture contents could be > 40%, while the optimal moisture content for storage was found to be 4-5%. Dried conidia stored in oil benefited from the addition of dried silica gel, as did conidia stored as powder. A range of mineral oils proved satisfactory for storage, and when dried silica gel was added to suspensions, germination levels were 79.8% after 105 days at 28-32°C. Dried conidia stored in oil maintained germination levels of up to 96 and 85% after 80 days at IO-14°C and 28-.UoC respectively. Dried conidia stored as powder retained germination levels of 95% at JO-I4°C. but only up to 27% at 28-32°C. In another experiment, dried conidia maintained greater than 90% germination over 128 days, with or without silica gel at JO-14°C or 15- 18°C

Pengendalian Hindola striata Maa. secara Kimiawi

Dua belas macam insektisida diuji untuk mengetahui efektifitas dan persistensinya terhadap imago Hindola striata. Serangga dikurung bersama bibit cengkeh yang diberi perlakuan insektisida pada interval yang berbeda setelah aplikasi. Insektisida yang paling efektif dan persisten ialah sihalotrin (Matador), diikuti oleh insektisida persisten lainnya, yaitu monokrotofos (Azodrin), aldicarb (Temik), carbofuran (Furadan) dan asefat (Orthene)