While examining the various options for biological control, it soon became apparent that oil formulations of the spores of certain fungi belonging to the form phylum Deuteromycota (Anamorphic fungi) offered the most promising option. Such fungi will grow on artificial substrates and so can be mass-produced relatively quickly in large quantities. Their spores are lipophilic and therefore suspend much more readily in oils than in water. As most locust control is carried out using oil formulations at ultra-low volume (ULV) rates of application, developing an oil formulation of fungal spores enabled operators to use the same equipment for applying a chemical pesticide and maximise efficacy. Usually, fungi are most active under moist conditions and in early attempts to use them as control agents, they were therefore applied in water formulations. However, the results in practice were often disappointing and the approach was largely abandoned during most of the 20th century. When interest in microbial control was revived, water formulations of fungi started to be used successfully in greenhouses, but the results in open fields continued to disappoint. In the 1980s, Prior discovered that some anamorphic fungi are more effective when applied in oil. During the first phase of LUBILOSA, the technical feasibility of using such oil formulations against locusts was demonstrated in the laboratory, then field cage and "arena" trials. An extensive survey was launched in West Africa and the Arabian Peninsula to look for isolates virulent to locusts and grasshoppers, because few such isolates were available in public collections. The survey made use of a network of collaborators and came up with some 180 isolates, many of which belonged to "Metarhizium acridum", some to other "Metarhizium" species and to "Beauveria bassiana" with a few records of "Syngliocladium acridiorum" (syn. "Sorosporella"). Laboratory screening of these isolates showed that "M. acridum" was easily the most virulent species under warm conditions (30 °C), and confirmed the selection of isolate IMI 330189 for further development. Subsequent trials in cages and arenas confirmed that oil formulations were infective even under very dry conditions. IMI 330189 and similar isolates were assigned to "Metarhizium flavoviride" in early papers, then "Metarhizium anisopliae" var. "acridum", but are now described as "Metarhizium acridum" (Driver & Milner) J.F. Bisch., Rehner & Humber.