Antifungal Activity of Benzoquinones Produced by Tribolium castaneum in Maize-Associated Fungi.

Tribolium castaneum (Herbst) adults produce 1,4-benzoquinone (BQ), methyl-1,4-benzoquinone (MBQ), and ethyl-1,4-benzoquinone (EBQ). These components are chemical defenses used as repellents and irritants, and BQ has a negative impact on the growth of some fungal species. In this work, the inhibitory and/or lethal effects of these benzoquinones on the development of six fungi identified in maize, namely Aspergillus flavus, A. fumigatus, A. niger, Fusarium sp., Penicillium sp., and Trichoderma sp., were evaluated. Ten-day-long disk diffusion trials were performed using benzoquinones. The experiments simulated the activity of BQ (B1) or "EBQ + MBQ" (B2) released by 40-day-old insect adults (n = 200), considering a total average release of 45 µg per adult. Inhibition halos imposed by benzoquinones on fungal growth showed a significant effect when compared with the controls (water and solvent). Mycelial growth was decreased for all fungi, with the level of response depending on the fungal species. B1 and B2 displayed an inhibitory effect against all fungi, but Trichoderma sp. and A. niger showed rapid recoveries. B2 showed a lethal effect on Penicillium sp. The inhibitory and lethal activities of benzoquinones released by T. castaneum adults may contribute to regulate fungal growth, and understanding their interaction is important to develop innovative control strategies.

Drivers of Post-Harvest Aflatoxin Contamination: Evidence Gathered from Knowledge Disparities and Field Surveys of Maize Farmers in the Rift Valley Region of Kenya.

Maize-dependent populations in sub-Saharan Africa are continually exposed to aflatoxin poisoning owing to their regular consumption of this dietetic cereal. Being a staple in Kenyan households, consumption of maize-based meals is done almost daily, thereby exposing consumers to aflatoxicoses. This study assessed awareness levels, knowledge disparities, and perceptions regarding aflatoxin contamination at the post-harvest phase among farmers in the Rift Valley Region of Kenya. Households were randomly selected using a geographical positioning system (GPS) overlay of the agro-ecological zones within Uasin Gishu and Elgeyo Marakwet counties. Face-to-face interviews were conducted in 212 smallholder and large-scale farms. The study documented the demographic profiles of farmers and knowledge, awareness, and perceptions of aflatoxin contamination using a pre-designed structured questionnaire. Most farmers were familiar with aflatoxins and the adverse effects they present to health (61.32%). Almost all the farmers (94.37%) were aware of storage molds and food-spoilage fungi. However, few farmers adopted good post-harvest practices (PHPs), such as avoiding premature harvests (49.8%), using well-ventilated storage spaces (44.6%), grain sorting (30.5%), proper drying of maize (17.8%), and using hermetic bags for storage (30.5%). Conclusively, intensified farmer education is required to train farmers on good PHPs to protect their maize from aflatoxigenic fungi and aflatoxin accumulation.

Evaluation of Two Formulations of Chlorantraniliprole as Maize Protectants for the Management of Prostephanus truncatus (Horn) (Coleoptera: Bostrychidae).

The larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrychidae) is one of the most destructive insect pests of stored maize and dried tubers of cassava, and a wood-boring species. In the present study, we examined two chlorantraniliprole formulations, WG (wettable granule) with 350 g/kg active ingredient (a.i.) and SC (suspension concentrate) with 200 g/L a.i., as maize protectants against P. truncatus adults. Chlorantraniliprole formulations were applied as solutions at 0.01, 0.1, 1 and 10 ppm, and tested at 20, 25 and 30 °C. Both formulations performed similarly. After 7 days of exposure, the overall mortality provided by both formulations was very low (<17%). Seven days later, mortality was remarkably increased on maize treated with 1 and 10 ppm at 25 and 30 °C for both formulations. The highest mortality was noted in chlorantraniliprole WG, at 10 ppm and 30 °C (98.9%), followed by chlorantraniliprole SC (96.1%), at the same dose and temperature. WG formulation was more effective at 10 ppm and 25 °C (92.8%) than SC formulation (89.4%). No progeny production was noted on maize treated with the WG formulation at 20 and 30 °C. The SC formulation caused complete offspring suppression at 10 ppm at all three tested temperatures. The results of the present work indicate that chlorantraniliprole is an effective compound with a high insecticidal activity against T. truncatus on stored maize that depends on temperature, dose and exposure interval. The fact that chlorantraniliprole is a broad-spectrum insecticide, exhibiting low toxicity to mammals and beneficial arthropods, could be a valuable management tool in storage facilities.

Insecticidal effect and impact of fitness of three diatomaceous earths on different maize hybrids for the eco-friendly control of the invasive stored-product pest Prostephanus truncatus (Horn).

Diatomaceous earths (DEs) are able to successfully protect grain commodities from noxious stored-product insect and mite infestations; however, their effectiveness may be moderated by the grain hybrid or variety they are applied to. There is a gap of information on the comparison of the efficacy of different DEs when are applied on different maize hybrids against Prostephanus truncatus (Horn). Therefore, here we tested three commercially available DEs (DEA-P at 75 and 150 ppm, Protect-It at 500 ppm, and PyriSec at 500 ppm) on five different maize hybrids (Calaria, Doxa, Rio Grande, Sisco, and Studio) for the control of P. truncatus adults in terms of mortality (at 7 and 14 days), progeny production, properties of the infested maize hybrids (number and weight of kernels with or without holes, number of holes per kernel) and the adherence level of the tested DEs to the kernels. DEA-P was very effective at 75 ppm while a considerable proportion of the exposed P. truncatus adults was still alive after 14 days of exposure on all maize hybrids treated with 500 ppm of Protect-It or PyriSec, even though it was 3.3 times higher than the maximal application tested dose of DEA-P. Apart from parental mortality, DEA-P was able to reduce P. truncatus progeny production in all hybrids contrary to Protect-It or PyriSec. The adherence ratios were always higher for DEA-P than Protect-It or PyriSec to all maize hybrids. The highest numbers of kernels (or weight of kernels) without holes were noticed after their treatment with DEA-P. Doxa and Sisco performed better than Calaria, Rio Grande, or Studio based on the differences found concerning the numbers of kernels without holes at treatments with DEA-P and Protect-It. Overall, the findings of our study indicate the high potentiality of DEA-P as protectant of different maize hybrids to P. truncatus infestations at low doses, a fact that could help the eco-friendly management of this noxious species in the stored-product environment.

Resistance of maize cultivars to Sitophilus zeamais (Coleoptera: Curculionidae) / Resistência de cultivares de milho a Sitophilus zeamais (Coleoptera: Curculionidae)

Five Zea mays cultivars (BRS Caatingueiro, BRS Gorutuba, BRS Sertanejo, BRS Asa Branca and BR 106) were evaluated considering their effect on the nutrition of the maize weevil Sitophilus zeamais, by analysis of total protein in adult fed with these cultivars and for the presence of lectins and trypsin inhibitors in grains. In addition, free-choice and no-choice assays were performed to investigate the resistance of grains of the Z. mays cultivars to an attack by S. zeamais. The BR 106 cultivar showed the lowest susceptibility index, followed by BRS Caatingueiro, BRS Asa Branca, BRS Sertanejo and BRS Gorutuba. The number of emerged adults in the Z. mays cultivars ranged from 213.17 to 74.0, and the lowest number of insects was recorded for the BR 106 cultivar. The insects were able to feed on grains of all cultivars, but the BR 106 cultivar showed the least reduction in dried biomass. Lectins were detected in extracts from BR 106, BRS Asa Branca, BRS Sertanejo and BRS Gorutuba, and the highest activity was shown by BR 106. The lowest protein assimilation was detected in the insects from treatments with BRS Asa Branca. The extracts from all cultivars were able to inhibit the activity of bovine trypsin, but this effect was not related to the resistance degree of Z. mays cultivars. The results suggest the resistance of BR 160 to the attack of S. zeamais, as well as indicating that the presence of lectin in the grains is the cause of this resistance.(AU)

Foram avaliadas cinco cultivares de Zea mays (BRS Caatingueiro, BRS Gorutuba, BRS Sertanejo, BRS Asa Branca e BR 106) e seu efeito na nutrição do gorgulho-do-milho Sitophilus zeamais, por meio da análise de proteína total em adultos alimentados com esses cultivares e a presença de lectinas e inibidores da tripsina nos grãos. Além disso, foram realizados ensaios com e sem chance de escolha para investigar a resistência dos cultivares de Z. mays ao ataque de S. zeamais. O cultivar BR 106 apresentou o menor índice de susceptibilidade, seguido por BRS Caatingueiro, BRS Asa Branca, BRS Sertanejo e BRS Gorutuba. O número de adultos emergidos nos cultivares de Z. mays variou de 213,17 a 74,0, e o menor número de insetos foi registrado para o cultivar BR 106. Os insetos foram capazes de se alimentar de todos os cultivares, no entanto, o BR 106 mostrou a menor redução na biomassa seca. As lectinas foram detectadas em extratos de BR 106, BRS Asa Branca, BRS Sertanejo e BRS Gorutuba, e a maior atividade foi demonstrada pela BR 106. A menor assimilação de proteína foi detectada nos insetos que se alimentaram com BRS Asa Branca. Os extratos de todos os cultivares foram capazes de inibir a atividade da tripsina bovina, mas esse efeito não está correlacionado ao grau de resistência dos cultivares de Z. mays. Os resultados sugerem a resistência da BR 160 ao ataque de S. zeamais, além de indicar que a presença de lectina nos grãos é a causa dessa resistência.(AU)

Insecticide resistance and size assortative mating in females of the maize weevil (Sitophilus zeamais).

BACKGROUND: Random mating is a common assumption in studies of insecticide resistance evolution, but seldom tested despite its potential consequences. Therefore, the existing evidence of female choice and insecticide resistance in populations of the maize weevil (Sitophilus zeamais), a key pest of stored cereals, led to the assessment of mating preferences and their association with insecticide resistance in this species. RESULTS: Mixed lines of a maize weevil colony were established from field-collected populations, which after 5 months of natural breeding were selected for deltamethrin resistance for five generations, reaching over 100-fold resistance. Mating preference was significantly based on the partner size, measured as body mass (χ2 = 5.83, df = 1, P = 0.016). Susceptible females preferred heavier males for mating (χ2 = 5.83, df = 1, P = 0.015), a trait that was more frequently associated with deltamethrin resistance (χ2 = 7.38, df = 1, P = 0.007). Deltamethrin resistance compromised daily fertility, although the reduced offspring production observed in matings between susceptible females and resistant males was negligible. CONCLUSION: Susceptible female weevils prefer larger (and heavier) males to mate, a trait associated with deltamethrin resistance, favouring the maintenance and spread of the resistant phenotype in the population. © 2016 Society of Chemical Industry.