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The fungus Metarhizium anisopliae var. acridum, strain CG 423, was tested under field conditions against the gregarious grasshopper Rhammatocerus schistocercoides (Rehn) (Orthoptera: Acrididae). Conidia formulated in a racemic mixture of soybean oil and kerosene were sprayed under field conditions using an ultralow-volume hand-held atomizer Ulva Plus adjusted to deliver 2.9 L/ha. Bands composed of 2nd instar nymphs were treated with either 5.0x10(12) or 1.0x10(13) viable conidia/ha. The number of insects in each band was estimated at day one following spraying and by the end of the field trial (15 to 16 days post-treatment). Reductions in population size reached, in average, 65.8% and 80.4% for bands treated with the higher and lower dosage, respectively. For both dosages, total mortality rates of insects collected at two days post-application, and kept in cages for 14 days under lab conditions, showed no significant differences as compared to that obtained with insects collected immediately after spraying. Healthy insects were fed to native grasses sprayed on the field with 1.0x10(13) viable conidia/ha. Mortality levels of the nymphs fed on grasses collected two and four days post-application were not affected when compared to nymphs fed on grasses collected immediately following application. O fungo Metarhizium anisopliae var. acridum, isolado CG 423, foi avaliado em condições de campo como agente de controle biológico do gafanhoto gregário Rhammatocerus schistocercoides (Rehn) (Orthoptera: Acrididae). Conídios formulados em uma mistura racêmica de óleo de soja e querosene foram pulverizados no campo com a utilização de um atomizador rotativo manual Ulva Plus, calibrado para aplicação de 2,9 L/ha. Bandos com ninfas de 2º estádio foram tratados com o equivalente a 5,0x10(12) ou 1,0x10(13) conídios viáveis/ha. O número de insetos em cada bando foi estimado no 1º dia após a aplicação e ao final do experimento (15 a 16 dias após tratamento). Reduções populacionais médias de 65,8% e 80,4% foram observadas nos bandos tratados com a maior e menor dosagem, respectivamente. Para as dosagens avaliadas, a mortalidade total de insetos coletados aos dois dias após a aplicação e mantidos em gaiolas durante 14 dias, no laboratório, não apresentou diferença significativa daquela obtida para insetos coletados imediatamente após a pulverização. Insetos sadios foram alimentados com gramíneas nativas pulverizadas no campo com 1,0x10(13) conídios viáveis/ha. As taxas de mortalidade observadas nas ninfas alimentadas com capim coletado aos dois e quatro dias após a pulverização não foram afetadas quando comparadas com ninfas alimentadas com capim coletado imediatamente após a pulverização.

Successful control of greenhouse whitefly may be achieved by complementary activity of the parasitoid Encarsia formosa and the fungus Aschersonia aleyrodis. One way to obtain an additive mortality effect of both entomopathogen and parasitoid would be achieved by the selection of healthy hosts by the parasitoid and rejection of fungus-infected hosts. Third and fourth instar larvae of Trialeurodes vaporariorum which had been treated with a spore suspension of A. aleyrodis 0, 4, 7, 10 or 14 days beforehand, were presented to female parasitoids. The parasitoids adopted the oviposition posture on untreated hosts as well as on treated hosts, irrespective of the different stages of infection in the hosts. However, significantly more hosts were parasitized by E. formosa in the control treatment than in the fungal treatment. The parasitoids offered treated hosts, showed rejection behaviour after probing on hosts showing detectable signs of infection (containing hyphal bodies or mycelium in the haemolymph). For instance, when hosts were offered seven days after spore treatment, the parasitoids showed an oviposition posture on a total of 83 (95.4%) out of 87 infected larvae, but laid only 4 eggs (4.6%). In contrast, on 48 (94.1%) out of 51 noninfected (or showing no detectable signs of infection) hosts an oviposition posture was adopted and 40 eggs (78.4%) were found after dissection. When infected hosts were encountered the oviposition posture lasted less than 1′40″ while rejection of non-infected hosts occurred after more than 1′40″. Other experiments were carried out offering treated hosts for 24 h to the parasitoids. The hosts were dissected afterwards. Again, significantly more eggs were laid in the non-infected hosts. When hosts were parasitized shortly after fungal spore treatment they were colonized by the fungus and the parasitoids did not develop. Transmission of the entomopathogen after probing infected hosts was observed to a limited extent. In conclusion, A. aleyrodis and E. formosa can be used together in a glasshouse situation. The parasitoid will be most effective when introduced more than seven days after application of A. aleyrodis, because from that time onwards it is able to detect and reject fungus-infected hosts.