RESUMEN
ABSTRACT Parasitoids of the genus Trichogramma are promising for the biological control of insect pests in several crops, including cassava, which is severely attacked by Erinnyis ello L., 1758 (Lepidoptera: Sphingidae). Evaluating the biological aspects of these parasitoids to understand their dynamics is an important step towards the implementation of this control strategy in the field. Thus, our objective was to evaluate the biology of Trichogramma manicobai Brun, Moraes & Soares, 1984, and T. marandobai Brun, Moraes & Soares, 1986 in E. ello eggs. The parasitoids were obtained by collecting E. ello eggs from a commercial production of cassava, and the host's eggs were obtained from laboratory and greenhouse rearings. The average duration of a generation (T), net reproduction rate (R0), intrinsic rate of increase (rm), and the finite rate of increase (λ) were estimated, and from these, the fertility life table was calculated. The results indicated that T. marandobai has both higher net reproduction rate and a higher intrinsic rate of increase as well as requires less time to double its population than T. manicobai. Thus, T. marandobai has potential for natural and conservative biological control of E. ello. In addition, its potential in applied biological control should be evaluated through studies on the viability of its mass rearing in alternative hosts and its dispersion behavior in the field.
RESUMEN
El gusano cachón Erinnyis ello (L.) es una plaga polífaga que puede causar graves pérdidas en cultivos de caucho. El uso de granulovirus representa una alternativa interesante para el control biológico de este insecto. Tres aislamientos colombianos del granulovirus de E. ello (EeGV) recuperados en larvas de campo, fueron caracterizados morfológica y molecularmente. Los cuerpos de inclusión de los tres aislamientos presentaron forma ovoide con una única nucleocápside, con tamaño promedio de 302,9 ± 22 x 181,5 ± 16 nm. El análisis de los perfiles de restricción con diferentes endonucleasas no mostró diferencias entre los tres aislamientos, lo cual sugiere que son muestras de la misma cepa viral, denominada VG010, cuyo tamaño del genoma se estimó en 88,7 Kb. El análisis de las relaciones filogenéticas basado en las secuencias de lef-8, lef-9 y gran mostró con alta consistencia la estrecha relación entre VG010 y un aislamiento de EeGV (M34-4) previamente descrito, lo cual sugiere que son variantes genotípicas de la misma especie viral. La eficacia del aislamiento VG010 en condiciones de laboratorio sobre larvas de segundo y cuarto estadio fue de 100 % y 64 % respectivamente, mientras que la concentración letal media (CL50) fue 4,3 x 103 CI/mL. La productividad viral, osciló entre 2,1 x 109 y 3,8 x 109 CI/gramo de larva. Estos resultados representan la base para el desarrollo de un nuevo bioinsecticida para el control de la plaga en campo.
Erinnyis ello (L.) is a polyphagous lepidopteran pest that may cause serious annual losses in the rubber industry. The use of granulovirus represents an interesting alternative as a biological control agent for this insect. Three Colombian isolates of granulovirus for E. ello (EeGV) were obtained from field larvae and characterized at morphological, biological and molecular level. Occlusion bodies (OB) of the three isolates showed an oval morphology with a unique nucleocapsid, with a size of 302.9 ± 22 x 181.5 ± 16 nm. Analysis of DNA endonuclease restriction profiles did not showed differences among the three viral isolates, which means that they correspond to samples of the same viral strain, denominated VG010. The VG010 viral genome size was estimated to be approximately 88.7 kb. The analysis of the phylogenetic relationships based on selected gene sequences lef-8, lef-9 and gran showed a close relationship between VG010 and the previously described isolate EeGV (M34-4). These sequence similarities suggest that the three isolates are genotypic variants of the same viral species. The in vitro efficacy of the VG010 isolate against second and fourth instar larvae was 100 and 64%, respectively, while the mean lethal concentration (LC50) was 4,3 x 103 OB/mL. The viral productivity ranged between 2.1 x 109 and 3.8 x 109 OB/g of larvae. These results represent the basis to develop a new biopesticide control agent for the pest in the field.
RESUMEN
O consumo foliar de mandioca (Manihot esculenta Crantz) e a caracterização da injúria potencial por Erinnyis ello L. foram determinados em quatro variedades de mandioca. Lagartas deprimeiro ínstar foram criadas individualmente em folhas de quatro variedades de mandioca. Foi usado o delineamento experimental de blocos ao acaso com nove repetições. Folhas frescas com áreas previamente determinadas foram fornecidas às larvas diariamente. O consumo foliar em cada ínstar e o peso das lagartas e pupas foram registrados. Não houve diferença significativa no consumo foliar nas quatro variedades (P=0,82). O total de área foliar consumida (cm2) para as variedades testadas foi: 1030,5 (Fio de Ouro), 971,5 (Aipim Bravo), 968,6 (Urubu), 956,1 (Jaburu), sendo de 981,7 o consumo médio das quatro variedades. Aproximadamente 94% do consumo ocorreu durante os dois últimosínstares. Variedades não afetaram o desenvolvimento larval (P=0,96). Os pesos médios de lagartas (g) em cada variedade foram: 4,9 (Jaburu), 4,8 (Fio de Ouro), 4,7 (Urubu), 4,6 (Aipim Bravo) e 4,8 (média das quatro variedades). Dois modelos, um relacionando a área foliar consumida e desenvolvimento larval ( y = abxcx2) e outro do crescimento larval (y=5/1+ea+bx), foram estabelecidos. Os dados obtidos indicam que as variedades testadas neste estudo foram nutricionalmente semelhantes para odesenvolvimento de E. ello. Como o consumo foliar de E. ello foi semelhante para todas as variedades, a mesma taxa de consumo pode ser usada para o cálculo dos níveis de dano econômico para manejar E. ello nessas variedades.
A laboratory experiment to determine the consumption rates of cassava (Manihot esculenta Crantz) and characterize the injury potential by Erinnyis ello L. was conducted. First instar larvae were individually reared on excised cassava leaves of four varieties. A randomized block designwith nine replications was used. Fresh leaves were provided to the larvae daily. Leaf area was determined for each leaf before the leaves were provided to the larvae. Foliage consumption per instar, developmentaltime and weight of larvae and pupae were recorded. There were no significant differences in the larvalconsumption on the four varieties (P=0.82). Total leaf area consumption (square cm) for the varieties were: 1030.5 (Fio de Ouro), 971.5 (Aipim Bravo), 968.6 (Urubu), 956.1 (Jaburu) and across varieties was 981.6. About 94% of the feeding occurred during the last two larval instars. Varieties also had no effect on larval development (P=0.96). Mean larval weight (g) were: 4.9 (Jaburu), 4.8 (Fio de Ouro), 4.7 (Urubu), 4.6 (Aipim Bravo), and across varieties was 4.8. Two models, one relating larval leaffeeding and larval development ( y = abxcx2) and another for larval growing (y=5/1+ea+bx), were established. These data indicate that the varieties tested in this study were equally suitable for E. ello development. In addition, because the consumption rates of E. ello are the same across varieties, a single value can be used in determining economic injury levels to manage E. ello on these varieties.