ABSTRACT. We provided the first scientific record of Melanagromyza sojae (Zehntner, 1900), through molecular characterization of partial mtDNA COI gene, that confirms the occurrence of this pest in Paraguay. Previously reported in Brazil, an outbreak of larvae of M. sojae known as the soybean stem fly (SSF) that belongs to the family Agromyzidae, was also noted in soybean fields from the Canindeyú, Alto Paraná and Itapúa Departments in Paraguay. This pest is highly polyphagous, attacking various host plant species from the family Fabaceae, such as soybean and other beans. The implications of SSF detection in 2 J.V.C. Guedes et al. Genetics and Molecular Research 16 (3): gmr16039707 Paraguay are discussed in relation to the current soybean cultivation practices from this agriculturally important South American region, including Brazil.

-Weeds compete with crops for essential inputs, but they are also important hosts for pests, both during the crop and between crops. Hairy fleabane (Conyza bonariensis) is an important weed growing in both summer and winter crops. The aim of this study was to evaluate the occurrence and population fluctuations of soybean pests using hairy fleabane as an alternative host. Samples of hairy fleabane plants were collected fortnightly over twelve months at two sites (Boa Vista do Incra and São Vicente do Sul) in Rio Grande do Sul state, Brazil. The results showed that hairy fleabane plants provided shelter to important soybean pests, including the pentatomid stink bugs Edessa meditabunda, Piezodorus guildinii, Dichelop sp. and Euschistus heros, especially after soybean maturation, and also served as an alternative food source. This weedy species was also an important alternative host for caterpillars such as Anticarsia gemmatalis, Chrysodeixis includens, Spodoptera spp. and Helicoverpa gelotopoeon.Keywords: soybean pests, integrated pest management, weeds, Conyza bonariensis. RESUMO -As plantas daninhas competem com as culturas por elementos essenciais, mas também são importantes hospedeiros para pragas, tanto durante quanto entre os cultivos. A buva (Conyza bonariensis) é uma importante planta daninha que cresce tanto em cultivos de verão quanto nos de inverno. O objetivo deste estudo foi avaliar a ocorrência e flutuação populacional de pragas da soja utilizando a buva como hospedeiro alternativo. Amostras de plantas de buva foram coletadas quinzenalmente durante 12 meses em duas localidades (Boa Vista do Incra e São Vicente do Sul), no

The population fluctuations of spider mites on different soybean cultivars were studied in two experiments performed in the municipalities of São Sepé (experiment 1) and Santa Maria (experiment 2) in the state of Rio Grande do Sul, Brazil. The number of cultivars was 20 in São Sepé and 25 in Santa Maria, and at each location leaves were sampled from 15 plants per cultivar every week throughout the entire plant developmental cycle, amounting to 11 and 10 samplings in experiment 1 and 2, respectively. The statistical analysis revealed that mite densities varied significantly with cultivar and time. Besides, the interaction between soybean cultivars and sampling times was significant at both locations. This indicates that the populations did not vary in the same way among cultivars over time, which is attributed to differences among the cultivars with respect to their phenology and response to spider mites. Equations for describing the mite population dynamics were estimated for each cultivar, mostly by fitting cubic equations to the weekly growth rates (per capita changes) in mite densities. We also found that the highest growth rates for mites on soybean cultivars in both locations occurred after the beginning of flowering, when the plants shifted from the vegetative to reproductive stages, about 3 weeks before reaching the peak densities.

The occurrence, distribution, and intensity of damages caused by Melanagromyza sojae on soybean fields in Brazil and Paraguay indicate the need of information regarding the effect of insecticides and mode of applications to its control. The aim of this study was to evaluate insecticide applications at soybean sowing and during the early soybean stages to control M. sojae. Two experiments were carried. In the 1 st experiment, 12 insecticides were applied at sowing as a seed treatment (ST) or in the sowing furrow (SF) and combined with presence or absence of foliar spray (FS) of insecticides at 18 and 28 days after soybean emergence (DAE) in a factorial scheme. In the 2 nd experiment, 17 insecticides were sprayed foliar at 10 and 22 DAE. Control efficiency of M. sojae was assessed on experiment 1 at 22, 28 and 38 DAE and on experiment 2 at 22 and 38 DAE, by counting the number of larvae, pupae, and damaged plants and length of galleries. The results evidenced the need of a specific management for this pest and recommended application of insecticides such as: Chlorantraniliprole (ST), Imidacloprid + Bifenthrin (ST), Fipronil (ST), Imidacloprid (ST) and Thiamethoxam (SF) at sowing, combined with the foliar spray until 10 DAE of Chlorpyrifos, Thiametoxam + Lambda-Cyhalothrin, Thiodicarb, Bifenthrin and Imidacloprid + Beta-cyfluthrin. The foliar spray should be repeated at least once in an interval shorter than 10 days, to protect soybean plants during the most vulnerable development stages to the attack of M. sojae.

Brazilian growers are facing difficulties to manage the weeds Lolium multiflorum, Conyza sp. and Echinochloa sp. using commercially available agrochemicals in most crops. This study aims to evaluate the use of a bioherbicide based on fermented broth containing secondary metabolites of Diaporthe sp. to control L. multiflorum, Conyza sp. and Echinochloa sp. The bioherbicide activity in preemergence and post-emergence of these weed species and phytotoxicity on soybean, wheat and rice plants were evaluated. In the pre-emergence test using all weed species, the bioherbicide showed 100% control efficiency in comparison with the control group. Phytotoxic symptoms were observed on soybean leaves and horseweed was efficiently controlled using the bioherbicide.