Compensatory response of cotton plants to simulated carpophagic pest injury / Resposta compensatória de plantas de algodoeiro a injúria simulada de pragas carpofágicas

Due upland cotton crop has a relatively long cycle on Brazilian Savannah areas, varying from 180 to 220 days, abscission and replacement of floral structures is frequent although variable along the phenological phases. The reproductive phase occurs from 45 days after plant emergence until close to the harvest. The objective of this study was to measure the ability of cotton plants to compensate losses caused by carpophagic insects by producing new floral structures. Four cotton cultivars (FM913GLT, FM980GLT, FM966LL and FM975WS) were sowed in an irrigated area, whose soil is characterized as dystrophic latosol. The treatments were arranged in a factorial scheme, with the cultivar being the main factor and the intensity of the injury caused manually by the removal of floral structures as the secondary factor. Simulated damages consisted of five levels of removal of floral buds, flowers and bolls at 75 days after emergence (DAE). We recorded the number of floral structures present in the plants at 140 DAE and at the harvest. The damage boundary (Db) varied among the cultivars, demonstrating a differentiated response of tolerance to injury. FM980GLT and FM975WS were able to compensate and overcompensate the losses; the same does not happen to FM913GLT and FM966LL. We observed tolerance and linearity phases in all the cultivars but FM966LL. FM980GLT showed highest response capability after be injured. The cotton plants compensated for the loss of structures up to a certain limit of injury, which varies with the cultivar. Overcompensation and compensation occurred through the replacement of new structures while the compensatory response into increase in the weight of bolls did not happen

Selection of entomopathogenic fungi to control stink bugs and cotton boll weevil

Entomopathogenic fungi stand out in the biological control of several agriculturally important insects. Six isolates of Metarhizium anisopliae, Cordyceps javanica, Beauveria sp. and B. bassiana were screened to control Anthonomus grandis, Euschistus heros, Oebalus poecilus, O. ypsilongriseus and Thyanta perditor, important insect pests of soybean, cotton and rice. The bioassays were conducted in a completely randomized design, with four replications (10 insects/replication). Significant differences for virulence were observed between the tested fungal species and isolates. For A. grandis, the most virulent isolate was M. anisopliae BRM 2335, followed by Beauveria BRM 14527 and BRM 67744 [82.5 to 97.5 % of mortality; average lethal time (LT50) of 5.9 to 7.8 days]. M. anisopliae BRM 2335 was also highly virulent to the four stink bug species (75 to 97.5 % of mortality; LT50 of 5.2 to 9.7 days). For the stink bugs, Beauveriasp. BRM 67744 was infectious to O. poecilus (75 % of mortality), but failed to control E. heros (16.9 % of mortality). C. javanicaBRM 27666 and BRM 14526 showed average virulence to the stink bugs and A. grandis (17.5 to 57.3 % of mortality; LT50 of 6.0 to 9.7 days). M. anisopliae was consistently more virulent to the stink bugs than the other fungi. Therefore, M. anisopliaeBRM 2335 was selected for further studies under screenhouse and field conditions to control A. grandis and other stink bug species, especially E. heros

Impacto de plantas de cobertura e da distribuição de chuvas sobre Scaptocoris castanea (Hemiptera: Cydnidae)

The objective of this work was to evaluate the population dynamics of the burrower bug (Scaptocoris castanea) in an area with cotton (Gossypium hirsutum) cultivated after cover crops. The insects were counted in soil samples collected at 0–40 cm depth. Insect incidence was documented in 18 cover crops, alone or intercropped, in each plant stage. Rainfall distribution was compared with fluctuations in the burrower bug population. Crotalaria species have a suppressive effect on the insect population, whereas some grass species favor its increase. Rainfall distribution directly influences the insect population.O objetivo deste trabalho foi avaliar a dinâmica populacional do percevejo-castanho (Scaptocoris castanea) em área com algodão (Gossypium hirsutum) cultivado após plantas de cobertura. Os insetos foram contados em amostras de solo coletadas a 0–40 cm de profundidade. A incidência de insetos foi documentada em 18 espécies de cobertura, isoladas ou consorciadas, em cada estágio da planta. A distribuição das chuvas foi comparada com a flutuação populacional do inseto. Espécies de crotalária apresentam efeito supressivo sobre a população do percevejo-castanho, enquanto algumas espécies de gramíneas favorecem o seu aumento. A distribuição das chuvas influencia diretamente a população de insetos