Potential of Entomopathogenic Fungi as Biological Control Agents of Whitefly (Bemisia tabaci biotype B) (Genn.) (Hemiptera: Aleyrodidae)

The efficiency of isolates from entomopathogenic fungus Beauveria bassiana, Lecanicillium muscarium and Metarhizium rileyi in the control of eggs and third-instar nymphs of whitefly, Bemisia tabaci biotype B, was evaluated by pathogenicity and virulence tests, under laboratory conditions. For the pathogenicity tests, five leaflets of bean (Phaseolus vulgaris) plants containing 20 nymphs or 20 eggs of B. tabaci biotype B were used. The leaflets were immersed in suspension containing a concentration of 108 conidia/ml of each fungus isolate. Nymph mortality and egg viability were evaluated after seven days. The isolates that caused nymph mortality and egg viability above 80% were submitted to virulence tests, in order to estimate the lethal concentration (LC50) of each isolate. All isolates were pathogenic to eggs and third-instar nymphs of B. tabaci Biotype B. JAB07 of B. bassiana and LCMAP3790 of L. muscarium isolates presented the best results, with nymphs mortality of 96.68 ± 2.25% and 97.74 ± 1.56%, respectively. Additionally, JAB07 was the most virulent isolate, both for eggs and third-instar nymphs, with LC50 estimated of 0.012 and 0.006 × 103 conidia/ml, respectively. We suggest, future field trials are required in order to analyze the real efficiency of this isolate in the control of eggs and nymphs of B. tabaci biotype B in field conditions.

SELECTIVITY OF INSECTICIDES TO Encarsia hispida (Hymenoptera: Aphelinidae)

ABSTRACT The use of non-selective insecticides in agricultural production can reduce or eliminate biological agents that regulate insects that are undesirable to humans in production processes. Here, the toxicity of synthetic products on the parasitoid Encarsia hispida was evaluated, the host of which is the whitefly, Bemisia tabaci biotype B, found on cotton plants. The study was carried out using bioassays, in a completely randomized design in a factorial scheme. Pupae and adults of E. hispida were used in the bioassays, which had been sprayed with various chemicals (thiamethoxam, deltamethrin, imidacloprid, and pyriproxyfen) at different concentrations (1.0 g L-1, 1.0 mL L-1, 4.0 mL L-1, and 2.5 mL L-1). The control treatment was distilled water. Chemicals were topically placed in the dorsal region of the tegument of 1 and 3-day old pupae. Then, between 1 and 15-days of emergence of adult parasitoids, residual contact bioassay were used to determine the toxicity of the insecticides. The insecticides thiamethoxam and imidacloprid were harmless to the pupal stage of E. hispida, but were harmful to the adult stage. The insecticides deltamethrin and pyriproxyfen were harmful to both pupal and adult stages of E. hispida.

Weeds associated with cotton crop and hosting whitefly

ABSTRACT: The whitefly can be hosted by weeds and cause damage to cotton crops. The objective of this work was to identify which species of weeds among the floristic compositions occurring in the cotton crop are hosts of whiteflies (Bemisia tabaci biotype B). Bi-weekly evaluations were performed in a cotton area (FM 975 WS) in Sinop, Mato Grosso, Brazil, during the reproductive phase of the crop. An inventory square (0.25 m side) was randomly cast 15 times between the cotton rows. The weeds were cut close to the ground, conditioned and taken to the laboratory to identify the family and species, and to quantify the eggs and nymphs of whiteflies. Eleven families were detected, with the most frequent being Amaranthaceae (16.67%), Convolvulaceae (12.5%), Rubiaceae (12.5%) and Poaceae (12.5%). The most frequent species were Amaranthus spp. (13.79%) and Alternanthera tenella, Ipomea spp., Richardia brasiliensis and Eleusine indica, with 10.34% each. From the 15 collected species, the presence of whitefly eggs or nymphs was only not observed in Portulaca oleracea and E. indica. The highest incidence of B. tabaci occurred in Euphorbia heterophylla. The occurrence of these species should be monitored, so that the whitefly population does not interfere in the cotton fiber quality.

Fungicide application can improve production of tomato coinfected with Begomovirus and Crinivirus

The objective of this work was to evaluate the effect of fungicide application on the concentration of Tomato severe rugose virus (ToSRV, Begomovirus) in the 'Mariana' hybrid tomato coinfected with ToSRV and Tomato chlorosis virus (ToCV, Crinivirus) and the progression of viral concentration by qPCR, as well as to quantify fruit yield and quality. Experiment I consisted in the application of fungicides after sowing (pretreatment): pyraclostrobin+metiram (P+M) (at 3 g L-1) + boscalid (B) (at 0.3 g L-1), followed by biweekly sprayings with P+M (4 g L-1); in experiment II, there was no application at sowing (control treatment), only 4 g L-1 P+M biweekly. ToSRV and ToCV transmissions were performed using sweetpotato whiteflies (Bemisia tabaci, biotype B), at 15, 30, 45, 60, and 70 days after transplanting (DAT). There was an increase in yield, better fruit quality, and a reduction in the ToSRV concentration in the plants, when the viruses were transmitted late and pretreatment was performed. Tray pretreatment in sowing with P+M (3 g L-1) and B (0.3 g L-1), followed by biweekly sprayings with P+M (4 g L-1), increases fruit yield and quality in the 'Mariana' hybrid tomato coinfected at 45, 60, and 75 DAT by ToSRV and ToCV, and there is a reduction in the concentration of ToSRV.