Parasitóides no controle de lepidópteros desfolhadores em Eucalipto

Abstract

Species of lepidopterans have been causing significant economic damage in eucalyptus plantations. Trichogramma bruni, Trichogramma pretiosum, Tetrastichus howardi, Trichospilus diatraeae, Palmistichus elaeisis are lepidopteran parasitoids that have the potential to be used in the biological control of these pests. The research was divided into three chapters, with the objectives of comparing the development of T. bruni and T. pretiosum in eggs of Chrysodeixis includens and Iridopsis panopla; estimating the horizontal dispersal capacity of T. bruni in eucalyptus stands and its parasitism capacity on eggs of I. panopla in the field; as well as determining the ideal density to be released per hectare of T. howardi, T. diatraeae, P. elaeisis, and assessing their effectiveness in the population control of Thyrinteina arnobia in eucalyptus stands. The experiments on the development of T. bruni and T. pretiosum were conducted at the Laboratory of Biological Control of Insects (LECOBIOL), and the others were carried out in commercial eucalyptus plantations of silviculturists associated with the South-Mato-Grossense Association of Producers and Consumers of Planted Forests (REFLORE-MS), in the state of Mato Grosso do Sul. In chapter 1, the design consisted of a 2x2 factorial scheme, with two species of parasitoids (T. bruni and T. pretiosum) and two host species (C. includens and I. panopla). The following variables were evaluated: Parasitism (%), duration of egg-to-adult cycle, sex ratio, number of individuals per egg, parasitism viability, and adult longevity. The data on biological characteristics were subjected to analysis of variance (ANOVA, F test) at a 5% probability level, and mean comparisons were performed using Tukey's test at a 5% probability level. For chapter 2, the experimental design was a randomized complete block design, with one control area (without parasitoid release) and five treatments (radii of 5, 10- , 15-, 20- and 25-meters circumference with the release of 5,000 parasitoids at the center of each circle). Cardboards containing non-viable eggs of Ephestia kuehniella and yellow sticky traps were interspersed within the circumference of each radius. After 48 hours in the field, all material was collected and taken to the laboratory to assess the average dispersion of T. bruni per radius. To assess the parasitism of T. bruni on eggs of I. panopla, 30,000 newly emerged adults were released in the field, at eight points per hectare, in a commercial plantation of 3.5-year-old Eucalyptus urograndis. One hectare area without release was used to evaluate natural parasitism. After nine days, eggs of I. panopla were collected from the trunks of 10 eucalyptus trees randomly, in areas with and without release, and taken to the laboratory to observe parasitized eggs and possible emergence of larvae or parasitoids. The percentage of parasitism and emergence were evaluated. Chapter 3 comprises experiments conducted in commercial eucalyptus plantations, with five treatments (Control: area without release (T1) and 4 densities of parasitoids - for T. howardi and T. diatraeae were 30 (T2), 60 (T3), 120 (T4), and 430 females (T5) of the species per pupa, and for P. elaeisis it was 20 (T2), 40 (T3), 80 (T4), and 160 females (T5) of the species per pupa), with four replicates. Each block contained eight units of parasitism with 2 pupae of D. saccharalis in each. The females of the parasitoids, aged 24 to 48 hours, were released at the central point of the plots. Parasitism was allowed for 48 hours, and then the pupae were removed, identified, and taken to the laboratory to determine the occurrence or absence of parasitism. To evaluate the effectiveness of releasing these eulophid wasps in an area infested with T. arnobia, distinct areas were selected for each species, and two treatments were performed (Treatment 1: approximately 1,200 adult females at 4 points/hectare, with an average of 300 adult females per release point, and Treatment 2: Control area without release) in a randomized complete block design, with four replicates for each. The parasitoids were released before the emergence in D. saccharalis pupae, which were placed inside SOS kraft paper bags at a height of 1.5 m from the ground. Evaluations were conducted at 15, 30, and 45 days after release, observing the number of larvae per 100 leaves, number of pupae, number of parasitized pupae, number of adult pests, and defoliation index. As a result, it was found that 4 both T. bruni and T. pretiosum can parasitize and develop in eggs of I. panopla and C. includens. In I. panopla, the parasitism rate was high for both species, with an average percentage of 85.33% for T. bruni and 82.66% for T. pretiosum. T. bruni showed better development in C. includens compared to T. pretiosum, with higher parasitism percentage (53.66% and 40.33%, respectively), longer life cycle duration (11.0±0.0 days and 10.00±0.00 days, respectively), number of parasitized eggs (10.73±0.62 eggs and 8.06±0.62 eggs, respectively), and male longevity (7.20±0.50 days and 6.5±0.50 days, respectively). The average dispersal distance of T. bruni in the treatments was 4.93 m, with an average distribution area in the eucalyptus crop of 110.27 m², and adults were found in all evaluated treatments and dispersal radii, with higher frequency in the 25 m diameter radii. The parasitism of T. bruni on I. panopla eggs was 21.64%, with emergence in 100% of the eggs. For the eulophid wasps, the parasitism found in sentinel pupae of D. saccharalis for the released species densities was similar between treatments T2 and T5 (T. diatraeae: 19.69% and 24.17%, respectively; T. howardi: 42.7±1.04% overall mean, and P. elaeisis: 27.7±16.6% overall mean). The parasitism in T. arnobia pupae at 15 days was 24. 30% for T. diatraeae, 12.30% for T. howardi, and 12.53% for P. elaeisis, differing from the control areas. At 30 days, no infestation of T. arnobia was observed in the areas with releases of T. howardi and T. diatraeae, and there was a reduction in the population of this pest in the area with P. elaeisis release. At 45 days, the population of T. arnobia was practically zero in all three experiments. These results indicate that both T. bruni and T. pretiosum are capable of parasitizing and developing in eggs of I. panopla and C. includens, with some differences in performance between the species. This information is relevant for the development of biological control programs for I. panopla in commercial eucalyptus plantations, both in agricultural and forestry environments. This is the first record of T. bruni development in the host I. panopla under laboratory conditions. It was possible to confirm that T. bruni can disperse up to approximately 25 meters and locate, parasitize, and develop in eggs of I. panopla in eucalyptus plantations. The density of 1,200 individuals per hectare of T. diatraeae, T. howardi, and P. elaeisis is recommended for release in eucalyptus plantations with 5% to 10% defoliation, 1 to 5 larvae per 100 leaves, which is sufficient to reduce the population of T. arnobia. The results of this research provide support for the use of T. bruni, T. pretiosum, T. diatraeae, T. howardi, and P. elaeisis in biological control programs in eucalyptus forests.