RESUMO

Coffee berry borer (CBB) Hypothenemus hampei is a major biotic threat to coffee production worldwide. Studies have reported negative effects on CBB by oil-based formulations of neem (Azadirachta indica), but little information is available for other neem-extract formulations. This study evaluated CBB preference and performance in arabica coffee fruits and artificial diet treated with a neem-extract formulation (Openeem Plus®) in the field and laboratory conditions. Field experiments were performed using CBB females artificially infested in cherry or green coffee fruits confined in voile-fabric cages tied to branches of neem-treated and control plants, recording the adult mortality and offspring production. Dual-choice and no-choice bioassays assessed CBB preference and development in fruits and artificial diet treated with the neem extract compared to controls in the laboratory, respectively. As main results obtained in the field and laboratory experiments, the neem extract significantly reduced CBB oviposition in both cherry and green fruits, as well as in artificial diet compared to controls. However, the botanical product did not affect CBB adult survival and preference in the laboratory bioassays. The neem extract is promising for use in pest management strategies in sustainable arabica coffee crops by reducing CBB oviposition and offspring. These effects can contribute to lowering the pest population buildup along the crop cycle and damage potential to coffee production.

Assuntos

RESUMO

Insect pests such as Spodoptera frugiperda cause significant losses to maize (Zea mays mays). Control of S. frugiperda is difficult, but the use of insect resistant cultivars, including tolerant cultivars, is a promising alternative, and landraces are a potential source of insect resistance. This study investigated tolerance to S. frugiperda in five Brazilian landraces, Amarelão, Aztequinha, Branco Antigo, Palha Roxa, and São Pedro, in relation to one conventional (non-Bt) hybrid, BM207, under field conditions. We assessed tolerance as the ratio of insecticide-free to insecticide-protected plants for plant height, stem diameter, and leaf chlorophyll content at two plant stages. Tolerance ratios varied across the maize genotypes, but inconsistently across plant variables, and cluster analysis revealed three groups based on tolerance ratios. A first group contained genotypes similarly tolerant to S. frugiperda, BM207, Palha Roxa, São Pedro, and Aztequinha, while the second and third groups each contained single genotypes, Amarelão, and Branco Antigo, which were considered not tolerant. Overall, the landraces Palha Roxa, São Pedro, and Aztequinha compared favorably to BM207 in terms of tolerance, and therefore may be valuable for management of this pest, and as germplasm sources to improve tolerance in other cultivars.

RESUMO

Diabrotica speciosa is an important pest of several crops in South America, including soybeans. Adults cause severe defoliation in soybean plants, and damage is significant when cotyledons are attacked. This study evaluated feeding non-preference to D. speciosa adults using 10 soybean genotypes, testing (i) 15-day-old whole plants and (ii) leaf disks of 60-day-old plants, through assessments of soybean attractiveness and leaf area consumed (LAC). Foliar contents of flavonoids and nutrients, and leaf trichome density were quantified for potential correlations with soybean resistance to adult of D. speciosa. In the whole young-plant experiment, under free-choice conditions, the lowest LAC was observed in IAC 100 and PI 227687. In no-choice, PI 227687 and IGRA RA 626 RR showed lower LAC than the other genotypes. In the leaf disk test, in free-choice, the genotypes IAC 100, PI 274454, PI 227687, DM 339, and BR 16 were the least preferred by adult of D. speciosa. In no-choice, PI 274454 was one of the least preferred, similarly to IGRA RA 626 RR, Dowling, and PI 227687. In the whole plant experiment, a high rutin content and low amounts of zinc, calcium, sulfur and manganese were associated with less consumption of D. speciosa on leaves of resistant genotypes. In contrast, in the leaf disk test there was a significant influence of trichomes in soybean resistance to the pest. In conclusion, the PI lines herein assessed are also promising sources for developing cultivars resistant to D. speciosa.

Assuntos

RESUMO

Supplementation with Silicon (Si) is well-known for increasing resistance of grasses to insect herbivores. Although the exact underlying mechanism remains unknown, Si accumulation interacts with the jasmonic acid-signalling pathway, which modulates herbivore-induced plant defences. We examined whether Si supplementation alters direct and induced indirect defences in maize plants in ways that deter the initial infestation by the fall armyworm Spodoptera frugiperda (JE Smith). We assessed the herbivore's oviposition preference, neonate and third-instar larval performance as well as the recruitment of a predator of young larvae, the flower bug Orius insidiosus (Say), by herbivore-induced plant volatiles (HIPVs). In choice tests, S. frugiperda deposited about two times more eggs on -Si than on +Si maize. The mortality of neonate S. frugiperda larvae was about sixfold higher in +Si compared to -Si plants, even though they consumed similar leaf area on both treatments. Although there were no mortality differences, Si supplementation also impacted third-instar larvae that gained about twofold less weight than those fed on -Si maize. In olfactometer assays, O. insidiosus was not attracted to volatiles of uninfested maize plants with or without Si supplementation, but it was attracted to those emitted by fall armyworm-infested plants, irrespective of whether plants received Si supplementation. However, when the flower bug could choose between the volatiles released from -Si and +Si fall armyworm-infested plants, it preferentially oriented to +Si fall armyworm-infested plant. Our results show that Si supplementation in maize may deter fall armyworm colonization because of greater direct defences and attractiveness of HIPVs to the flower bug.

Assuntos

RESUMO

Resistance to insect pests can be found in several native, landrace plants and can be an important alternative to conventional control methods. Diabrotica speciosa (Germar) (Coleoptera: Chrysomelidae) larvae are important maize (Zea mays L.) (Cyperales: Poaceae) root pests and finding native resistance in landraces would greatly contribute to maize-breeding programs aimed at controlling this pest. This study investigated whether the growth, survival, oviposition rhythm, fecundity, and fertility of D. speciosa are negatively influenced by specific maize landraces, and the existence of any morphological barriers in the roots that may correlate with plant resistance to the larval attack. Nineteen genotypes (17 landraces and 2 cultivars) were screened for antibiosis in assays that were conducted in the laboratory using seedling maize plants where the development time, longevity, weight, total survival, and sex ratio of adults were evaluated. Out of nineteen genotypes, eight were selected according to their resistance levels for an additional rearing study evaluating oviposition and fecundity. Landrace Pérola and cultivar SCS 154-Fortuna were classified as resistant because they increased the maturation period from larva to adult and decreased survivorship; and the landrace Palha Roxa was also classified as resistant for showing a lower fertility rate than other landraces. Resistant landraces that were infested by D. speciosa larvae showed greater amounts of some morphological barriers comparing with uninfested plants. The landraces classified as resistant may be considered in future plant-breeding programs, aiming to develop resistant maize cultivars to D. speciosa larval attack.

Assuntos

RESUMO

This study aimed to evaluate some factors that influence the expression of antixenosis in soybean genotypes against Anticarsia gemmatalis Hübner and Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae). Free-choice and no-choice feeding assays were performed with the resistant soybean genotype IAC 100 and the susceptible genotype BRSGO 8360 using A. gemmatalis and S. frugiperda larvae. The following factors that may affect expression of resistance were evaluated: one larva versus two larvae per leaf disc; use of larvae without prior feeding suspension versus larvae starved for 3 h prior to the assay; leaf discs versus entire leaflets; upper part versus lower part of the plant; and, vegetative versus reproductive growth stages. The level of resistance exhibited by the genotype IAC 100 was high enough to not be obscured by the effects of all factors assayed in the present study upon the feeding preference of A. gemmatalis and S. frugiperda larvae. However, our results demonstrate the importance of knowing the optimal conditions for conducting an assay for evaluating resistance of genotypes for specialist and generalist insect species. Utilization of two larvae of A. gemmatalis per leaf disc, not starved before the assays, with leaf discs from the upper part of plants at the reproductive growth stage provided better discrimination of differences in antixenosis expression in soybean genotypes. For S. frugiperda, use of one larva per leaf disc, not starved before the assays, with leaf discs from the lower part of plants at the reproductive growth stage gave more satisfactory results for feeding preference tests.

Assuntos

RESUMO

The present study aimed to identify common bean (Phaseolus vulgaris L.) cultivars less susceptible to Caliothrips phaseoli (Hood) in different growing seasons, to evaluate whether climatic conditions influence plant resistance to C. phaseoli infestation, and to investigate the preferred plant part for insect feeding. Eighteen common bean cultivars were evaluated in the winter season, and 19 cultivars were assessed in the rainy and dry seasons, under field conditions in the municipality of Jaboticabal, state of São Paulo, Brazil. Infestation of C. phaseoli nymphs in the upper and lower parts of the beans plants was recorded at weekly intervals from 25 days after plant emergence (DAE) to 60 DAE. In the winter season, the cultivars 'IAC Galante,' 'IAC Centauro,' 'IAC Carioca Eté,' and 'IAC Formoso' had significantly lower number of thrips than the cultivar 'IAC Diplomata.' In the rainy season, the cultivars 'IAC Harmonia' and 'IPR Siriri' had the lowest thrips infestation, differing from the cultivars 'BRS Pontal' and 'IAC Una.' The bean cultivars were equally susceptible to C. phaseoli in the dry season. The results suggest that C. phaseoli nymphs prefer to infest leaves of the lower part of bean plants, like most generalist herbivorous insects. In the winter and dry seasons, the highest thrips infestation was observed at 60 DAE, while in the rainy season, it was recorded from 32 to 46 DAE. Overall, C. phaseoli infestation on bean cultivars was not influenced by either temperature, relative humidity, or rainfall.

Assuntos