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The susceptibility of third instar larvae of Anticarsia gemmatalis (Lepidoptera: Noctuidae) and Diatraea saccharalis (Lepidoptera: Pyralidae) to ten distinct plaque purified genotypic variants of a selected isolate of the Anticarsia gemmatalis multiple‐embedded nuclear polyhedrosis virus (AgMNPV), was compared. Despite the fact that this isolate, AgMNPV‐Ds20, represents a wild strain of the AgMNPV selected for higher virulence to D. saccharalis, an alternate host, most of the variants are much more virulent to the original host Anticarsia than to Diatraea. Bioassays have shown an over one hundred‐fold variation in LD50 values ranging from 1700 polyhedron inclusion bodies (PIBs) to more than 200 000 PIBs/larva. The PIB production in infected larvae increased with the pathogenicity of the variant to the host, showing an average ten‐fold reduction in Diatraea when compared to Anticarsia for the same variant. The virus particle yield ranged from 6×107 to more than 109 PIBs/g of infected larvae in Diatraea and from 8×108 to more than 1010 PIBs/g of infected Anticarsia larvae. The data show a clear difference of the pathogenicity of the genotypic variants of AgMNPV in vivo both between the original and alternate host and between the individual variants for the same host. These differences found in vivo indicate that monitoring of shifts in variant frequency of wild and laboratory‐propagated viral isolates in these highly heterogeneous populations would help ensure the efficacy of biological control programs.

Development of infection of 4 strains of nuclear polyhedrosis virus (NPV) in third instar Diatraea saccharalis larvae at 10 different temperatures was compared. Two wild strains, the Anticarsia gemmatalis MNPV (AgMNPV) and the Trichoplusia ni MNPV (TnMNPV), and two selected strains, AgMNPV‐D10 and TnMNPV‐D11 were inoculated in 11‐day‐old D. saccharalis larvae and kept in temperatures of 17, 22, 24, 26, 28, 30, 32, 35, 37 and 39°C. The results showed that larval mortality increased with temperature, and the increase of temperature caused also the reduction of lethal time 50% (LT50) values. The maximal polyhedral production was obtained at 28°C for the 4 viral strains and a drastic reduction in the number of polyhedra was observed even for a difference of 2°C above or below this ideal temperature. The selected strains showed a 10‐fold increase in polyhedra yield when compared to the wild type strains.

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RESUMOOs extratos acetato de etila, etanólico e aquoso de raízes de Lonchocarpus floribundus foram utilizados, a fim de avaliar a atividade biológica sobre carrapato bovino. Carrapatos adultos foram coletados em bovinos infestados artificialmente, separados em grupos de dez indivíduos, pesados e imersos, separadamente, nos extratos de raízes de L. floribundus, nas concentrações de 5, 25, 50, 75 e 100 mg mL Biological activity of ethylic acetate, ethanolic and aqueous extracts of timbo (Lonchocarpus floribundus) on cattle tickABSTRACT Ethylic acetate, ethanolic and aqueous roots extracts of Lonchocarpus floribundus were used to evaluate their biological activity on cattle tick Rhipicephalus (Boophilus) microplus. Adult ticks were collected in artificially infested cattle, separated into groups of ten individuals, weighed and immersed separately in the extracts of L. floribundus roots at concentrations of 5, 25, 50, 75 and 100 mg mL -1 . For biological evaluation 14-21-day-old larvae were used, which were immersed in the extracts at concentrations of 1, 5, 10, 15 and 20 mg mL -1 . After treatment, each group was placed in a Petri dish and maintained at 27 ± 1 ºC and 80 ± 5% relative humidity. The extracts evaluated were not effective to induce mortality of over 50%-engorged female. The ethylic acetate and ethanolic extracts induced 100% mortality of larvae. The ethanolic extract was more toxic (median lethal concentration, LC 50 , of 2.1 mg mL -1 ) than the ethylic acetate extract (LC 50 = 4.1 mg mL -1). For the ethanolic extract it was estimated a median inhibitory concentration (IC 50 ) of 3.0 mg mL -1 and it was more toxic than the other extracts on this parameter. Among the three extracts evaluated, the ethylic acetate and ethanolic extracts showed the highest potential for the control of reproduction of R. (B.) microplus, reaching 100% at concentration of 5 mg mL -1 . The L. floribundus root extracts showed biological activity on cattle tick.

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