The principal raw material of modern U.S. agriculture is fossil fuel, whereas the labor input is relatively small (about 9 hours per crop acre). As agriculture is dependent upon fossil energy, crop production costs will also soar when fuel costs increase two- to fivefold. A return of 2.8 kcal of corn per 1 kcal of fuel input may then be uneconomical. Green revolution agriculture also uses high energy crop production technology, especially with respect to fertilizers and pesticides. While one may not doubt the sincerity of the U.S. effort to share its agricultural technology so that the rest of the world can live and eat as it does, one must be realistic about the resources available to accomplish this mission. In the United States we are currently using an equivalent of 80 gallons of gasoline to produce an acre of corn. With fuel shortages and high prices to come, we wonder if many developing nations will be able to afford the technology of U.S. agriculture. Problems have already occurred with green revolution crops, particularly problems related to pests (57). More critical problems are expected when there is a world energy crisis. A careful assessment should be made of the benefits, costs, and risks of high energy-demand green revolution agriculture in order to be certain that this program will not aggravate the already serious world food situation (58). To reduce energy inputs, green revolution and U.S. agriculture might employ such alternatives as rotations and green manures to reduce the high energy demand of chemical fertilizers and pesticides. U.S. agriculture might also reduce energy expenditures by substituting some manpower currently displaced by mechanization. While no one knows for certain what changes will have to be made, we can be sure that when conventional energy resources become scarce and expensive, the impact on agriculture as an industry and a way of life will be significant. This analysis is but a preliminary investigation of a significant agricultural problem that deserves careful attention and greater study before the energy situation becomes more critical.

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In a choice test among six life stages of Phenacoccus herreni Cox & Williams, Epidinocarsis diversicornis (Howard) used its antennae to examine adult and 3rd stadium females more than other stages and preferentially attempted to oviposit in these plus 2nd stadium females. Success of ovipositor insertion was unaffected by host stage. The outcome of these behaviors was preferential oviposition by E. diversicornis in the large female host stages. Acerophagus coccois Smith also preferentially examined larger female mealybugs (second and third stadium nymphs and adults) more than other stages and successfully inserted its ovipositor in these stages more often than in second stadium male nymphs and male cocoons, resulting in a similar preference in this species for larger female host stages. When given a choice between adult female hosts of two species, P. herreni and Phenacoccus gossypii Townsend & Cockerell, E. diversicornis exhibited a clear preference for P. herreni; whereas A. coccois preferred P. gossypii. RÉSUMÉ Choix opéré par deux encyrtides parasitoïdes parmi des espèces colombiennes de Phenacoccus, cochenilles du manioc Epidinocarsis diversicornis (Howard), ayant la possibilité de choisir entre six stades différents de Phenacoccus herreni Cox & Williams, examine avec ses antennes plus particulièrement les adultes et les larves femelles du 3ème stade, et essaie de pondre de préférence dans ces stades et les larves femelles de second stade. L'insertion de la tarière s'effectue aussi bien quel que soit le stade de l'hôte. Il résulte de ces différents aspects du comportement que E. diversicornis pond de préférence dans les femelles des stades les plus avancés. Acerophagus coccois Smith préfère aussi examiner les cochenilles femelles les plus grosses (second et 3ème stade larvaires et adulte), et introduit sa tarière avec succès dans ces stades plus souvent que dans les larves mâles de second stade ou les cocons mâles; il en résulte aussi pour cette espèce une préférence pour les femelles des stades les plus gros. Quand on leur a donné le choix entre des femelles des deux espèces de cochenilles (P. herreni et Phenacoccus gossypii Towsend & Cockerell), E. diversicornis manifestait une nette préférence pour P. herreni, tandis que A. coccois préférait P. gossypii.

Previous investigations showed that (1) predatory mites use odours volatilizing from spider-mite infested plants for remote prey selection and (2) the response to the volatiles is correlated to the predator's ability to control populations of the prey species. Based on this correlation, it is hypothesized that preselecting predatory mites with the aid of olfactometer experiments will increase the probability of finding an efficient natural enemy. Y-tube olfactometer experiments with 11 species of phytoseiids showed that only four species were attracted by the odour of cassava leaves infested with cassava green mite Mononychellus tanajoa (Bondar). If the hypothesis mentioned above is valid, the probability of finding an efficient natural enemy within this group of four will be higher than finding one by randomly taking a species from the initial group of 11 species. Since testing of phytoseiids with an olfactometer can be done in a few hours, it is suggested that these tests precede more laborious evaluation methods.

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Between 3 and 15% of all parasitized cassava mealybugs of the species Phenacoccus herreni Cox & Williams successfully defeated the parasitoid Epidinocarsis diversicornis (Howard) through encapsulation.Adult mealybugs were less successful at encapsulating all parasitoids than were nymphs in the second stadium. Encapsulation rates were higher at 25 ~ than 30 ~ in both nymphs and adults. No encapsulation of E. diversicornis was observed in Phenacoccus gossypii Townsend & Cockerell. No significant encapsulation of another encyrtid, Acerophagus coccois Smith, was observed in either species of mealybug.