Postharvest Pests Research Articles

Biocontrol of Maize Weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), in Maize over a Six-Month Storage Period.

Food security is contingent upon increasing crop yields but also upon reducing crop losses to post-harvest pests and diseases. Weevils are particularly important agents of post-harvest losses in grain crops. A long-term evaluation of a biocontrol agent, Beauveria bassiana Strain MS-8, at a single dose of 2 × 109 conidia kg-1 of grain was formulated in kaolin as a carrier at levels of 1, 2, 3, and 4 g kg-1 of grain and screened against the maize weevil, Sitophilus zeamais. After six months, the application of B. bassiana Strain MS-8 at all levels of kaolin significantly reduced the maize weevil populations compared to the untreated control (UTC). The best control of maize weevil was observed in the first 4 months after application. Strain MS-8 applied in a kaolin level of 1 g kg-1 performed the best, resulting in the lowest number of live weevils (36 insects/500 g of maize grain), the lowest level of grain damage (14.0%), and the least weight loss (7.0%). In the UTC the number of live insects was 340 insects/500 g of maize grain, the level of grain damage was 68.0%, and weight loss was 51.0%.

Yield and Post-Harvest Pest Status of Some White Yam (Dioscorea rotundata Poir.) Landraces in Uyo Southeastern Nigeria

Field experiment was conducted at National Cereals Research Institute (NCRI),Uyo out- Station in 2012 and 2013 to evaluated yield and post-harvest pest status of some yam landraces in Nigeria. The experiment was laid out in a randomized complete block design (RCBD), replicated thrice. Treatments were eight white yam landraces; Nwopoko, Obiotorugo, Offala, Hambakwashe, Aloshi, Udeanyi, Pepa and Eteme and one improved yam cultivar TDr 89/02665. Data obtained from yield and pest severity were subjected to analysis of variance. Result showed that Hambakwase produced significant tuber yield of 31.10 and 33.01 t/ha in 2012 and 2013, respectively. Obioturugo produced 28.18 and 28.02 t/ha, respectively. Eteme produced the least tuber yield of 16.23 and 15.33 t/ha. Udanyi had significant higher number of rotten tubers per plot at harvest; 2.41 and 2.08 in both years. At 3 months in storage, Offala had significant dry rot of 1.73 and 2.01, followed by 1.61 and 0.91 dry rot tubers per plot, recorded in Aloshi. Number of wet rot tubers per plot as influenced by white yam landraces at 3 months storage varied significantly different (p<0.05). Udanyi had significant higher number of wet tuber rot; 4.30 and 3.22 in 2012 and 2013. Presence of mealy bug infestation were seen Offala, Aloshi,Udanyi and Eteme in 2012. In 2013, Offala, Udanyi, Eteme and TDr 89/02665 had mealy bug infestation. .Among the yam landraces, scale insects were observed in the following; Obioturugo, Hambakwase and Udanyi in 2012 while in 2013, Obioturugo, Udanyi and Eteme had presence of scale insect in tubers at 3 months storage. This study therefore recommended Hambakwase and Nwopok for high tuber yield, less susceptible to rot, beetle and termite attack. Also, these promising yam landraces showed be incorporated into yam breeding programme in Nigeria.

Efficacy and sorption of sulfur dioxide as a fumigant for control of navel orangeworm (Amyelois transitella) on stored pistachios

Sulfur dioxide (SO2) fumigation was evaluated for postharvest control of navel orangeworm (NOW), Amyelois transitella, on stored pistachios in a laboratory study. Sorption of SO2 on pistachios were measured at 5, 15, and 25 °C. Because of rapid sorption of SO2 on pistachios after SO2 injection, 3 h short fumigations were used to determine effective treatments against NOW eggs, larvae, and pupae. SO2 fumigation was effective against all of the life stages tested. However, large larvae in infested pistachios were most tolerant and eggs were most susceptible to SO2 fumigation. Smaller larvae were more susceptible to SO2 fumigation than larger larvae. Complete controls of eggs, larvae, and pupae were achieved in 3 h fumigations with 0.2, 2.0, and 1.0% SO2, respectively. Large SO2 fumigation trials each with 4.5 kg pistachios were conducted in a 19.8L chamber and complete control of 6th instar larvae were achieved in 3 h fumigation with about 1.6–1.8% SO2 at ambient temperatures of 18–21 °C. The results showed that SO2 fumigation has potential to control NOW on stored pistachios as well as to control other postharvest pests on stored products.

Control of Rice Powder Pest Sitophilus oryzae L. with Entomopathogenic Fungus Metarhizium anisopliae (Metch.).

<b>Background and Objective:</b> Rice is one of the most important staple foods in the world, especially on the Asian Continent. Postharvest pests can reduce the quality and quantity of rice by up to 25%. Control using pathogenic microbes is the best choice in controlling postharvest pests in general and <i>Sitophilus oryzae</i> rice powder pests in particular. Research has been carried out to know the effect of dosage concentrations of pathogenic cultures and LC<sub>50</sub> values of pathogenic <i>Metarhizium anisopliae</i> cultures on the control of <i>S. oryzae</i> rice powder pest. <b>Materials and Methods:</b> The concentration dose of the pathogenic culture of <i>M. anisopliae</i> acted as a treatment. The test insect population for each treatment was 25 imagos. The study of the effect of dose concentration of <i>M. anisopliae</i> culture on the mortality of <i>S. oryzae</i> imago used analysis of variance. Determination of the effective concentration of LC<sub>50</sub> using probit analysis. <b>Results:</b> The higher the concentration of the pathogenic culture of <i>M. anisopliae</i>, the higher the mortality of the adult rice powder pest <i>S. oryzae</i>. The highest mortality of rice powder pest <i>S. oryzae</i> occurred at a dose of 50% concentration of the pathogen <i>M. anisopliae</i> culture, namely 89.33%, followed by a concentration of 40% with a mortality of 72.0%, a concentration of 30% with a mortality of 57.33%, a concentration of 20% with a mortality of 13.33% and the lowest dose concentration of 10% with a mortality of 1.33%. <b>Conclusion:</b> The effective concentration dose (LC<sub>50</sub>) of the pathogenic culture of <i>M. anisopliae</i> in controlling the rice powder pest <i>S. oryzae</i> was 31.88%.

INSECTICIDAL ACTIVITY OF OCIMUM BASILICUM ESSENTIAL OIL AND OF ITS MAJOR CONSTITUENTS, LINALOOL AND ESTRAGOLE, AGAINST CALLOSOBRUCHUS MACULATUS (COLEOPTERA: CHRYSOMELIDAE)

Callosobruchus maculatus (Fabricius, 1775) (Coleoptera: Chrysomelidae) is the main post-harvest pest of Vigna unguiculata. The objective was to evaluate the fumigant activity of Ocimum basilicum essential oil and its major components linalool and estragole, on C. maculatus, through the evaluation of toxicity, oviposition inhibition, instantaneous rate of population growth (ri) and insect development. The experimental units were composed of 0.8 L flasks treated with concentrations of 1.2 to 3.6 μL L-1 of O. basilicum essential oil, linalool, and estragole, applied on filter paper discs with a microsyringe. Each treatment had four replicates with adult insects exposed for 48 h. C. maculatus development rate was evaluated through a daily count o emerged adults. Oviposition was evaluated at the concentrations (LC50, LC25, LC10, and LC1). The LC50 and LC95 of O. basilicum essencial oil, linalool, and estragole were 1.79 and 4.36 μL L-1 of air, 1.68 and 3.35 μL L-1 of air, and 1.51 and 2.87 μL L-1 air, respectively. The increase in essential oil concentrations reduced the ri, rate of development, oviposition and number of eggs of C. maculatus, thus having potential to control this pest.

Insecticidal activity of the Mentha arvensis L. essential oil on stored grain pest Callosobruchus maculatus F.

Stored grain insect pests are becoming the foremost threat for reducing nutritional quality and quantity of grains in the storages worldwide. The pulse beetle, Callosobruchus maculatus F. is one the most serious post-harvest pest threat to stored legumes in tropical and subtropical regions. Today, for their control using eco-friendly and sustainable methods over the traditional chemical control are very crucial. In our study, an attempt was made to find the potency of the essential oil by two physical methods to control the beetle by using a common pulse grain – Vigna radiata L. (green gram). The repellency, fumigant and contact toxicity of the essential oil extracted from Mentha arvensis L. were checked by direct and indirect methods. Indirect method showed better results as the oil had prevented the pest from feeding on the grains. The Mentha arvensis essential oil was further screened for its chemical constituents by the technique of Gas Chromatography. The essential oil had high content of Menthol along with other constituents such as l-Menthone, Isomenthone, Menthol acetate, D-Limonene. Menthol which could all be responsible for the essential oil’s significant insecticidal property against Callosobruchus maculatus.

Identification of Resistance to the Corn Weevil (Sitophilus zeamais M.) in Mexican Maize Races (Zea mays L.)

Sitophilus zeamais (Motsch.) (Coleoptera: Curculionidae) has a global distribution and is one of the most important post-harvest pests of maize (Zea mays L.). Some Mexican maize races could be a novel source of resistance against S. zeamais to improve commercial maize, generating lines, varieties, and hybrids with resistance to the pest. These are original races from the center of origin of maize and have been exposed to selection pressure from S. zeamais and other pests for thousands of years, which probably resulted in some type of resistance. We studied the resistance of Mexican maize races to S. zeamais focusing on antixenosis, antibiosis, and tolerance. Antibiosis reduces the survival and reproduction of the insect or prolongs the time between generations, whereas antixenosis reduces the rate of initial and successive accumulation of the insect population. Obligate-antibiosis and free-choice bioassays were performed, and in those experiments, resistance traits and the consumption by S. zeamais were measured. The most resistant accession showed high adult mortality and fewer adults in the 1st generation, where the number of emerged adults is an ideal trait to evaluate the level of maize resistance to the pest. Net consumption (in grams) is the most economically important trait because it indicates the gross amount lost in a store, while yield losses (percentage of consumption) allow for studying tolerance. The type of endosperm did have an influence on the resistance/tolerance to S. zeamais. The flint varieties showed significantly higher mortality of adults before entering the seed, a lower quantity of emerged adults of the first generation in the obligate-antibiosis bioassay, and lower net consumption and percentage in both bioassays. In general, the varieties of the races Cristalino de Chihuahua, Apachito, and Azul showed high levels of resistance, with the Cristalino-079 (flint) and Azul (floury) accessions also being tolerant, and low levels of consumption by S. zeamais. Both could be used in breeding programs to reduce losses caused by S. zeamais.

Post-Harvest Insect Pests and Their Management Practices for Major Food and Export Crops in East Africa: An Ethiopian Case Study.

Ethiopian subsistence farmers traditionally store their grain harvests, leaving them open to storage pests and fungi that can cause contamination of major staple crops. Applying the most effective strategy requires a precise understanding of the insect species, infestation rates, storage losses, and storage conditions in the various types of farmers' grain stores. This study did a complete literature analysis on post-harvest pest and management measures with a focus on Ethiopia. The most frequent insect pests of stored cereals in this study were weevils (Sitophilus spp.), the lesser grain borer (Rhyzopertha dominica), rust-red flour beetle (Tribolium sp.), sawtoothed grain beetle (Oryzaephilus sp.), grain beetle (Cryptolestes spp.), Indian meal moth (Plodia interpunctella), and Angoumois grain moth (Sitotroga cerealella). Flour beetles (Tribolium spp.), sawtoothed beetles (Oryzaephilus sp.), flat grain beetles (Cryptolestes pusillus), and some moths have been identified as common stored product pests of stored oil seed, while bruchid beetles (Callosobruchus chinensis) and the moths were reported for pulses. Additionally, the storage pests in Ethiopia under varied conditions caused storage losses of 9-64.5%, 13-95%, 36.9-51.9%, and 2-94.7% in maize, sorghum, chickpeas, and sesame, respectively. To reduce the losses incurred, preventative measures can be taken before infestations or as soon as infestations are discovered. A variety of pest population monitoring systems for harvested products and retailers have been developed and recommended. In this context, reducing post-harvest grain losses is an urgent concern for improving food accessibility and availability for many smallholder farmers in Ethiopia and ensuring the nation's long-term food security.

A potential role of nitric oxide in postharvest pest control: A review

Novel methods of stored-product pest control are essential to greater success against a wide variety of pest species worldwide, especially in tropical regions. Modern methods such as ozonation and organic pesticides have ensured grain preservation without loss of quality and without the accumulation of residues; these properties are considered fundamental to food safety. Thereby, nitric oxide (NO) is a newly discovered fumigant that has shown the potential to control stored product pests. It has also been described as a substitute for phosphine and sulfuryl fluoride. In this regard, NO has the potential to become an alternative method of postharvest pest control, primarily due to its high pest mortality rate from a broader range of pests and products. However, research is needed to reduce the impact of NO on food quality due to the high reactive power of NO. Potentially toxic residues, such as the primary forms of NO oxidation, NO2− and NO3−, can accumulate in treated products and damage consumers' health. Further research is needed into the possible use of NO fumigation as an alternative practice in controlling stored grain pests.

Sitotroga cerealella-resistant mexican maize races (Zea mays L.), new sources of resistance for commercial maize breeding

Sitotroga cerealella (Oliv.) (Lepidoptera: Gelechiidae) is one of the most important post-harvest pests of maize Zea mays L. Some Mexican maize races (Z. mays) could be a novel source of resistance against S. cerealella to improve commercial maize varieties, lines and hybrids. We studied the resistance of Mexican maize races, recollected at Chihuahua State to S. cerealella. We focused on antibiosis and tolerance of maize to S. cerealella. Cristalino-079 maize race shows low level of consumption in grams and percentage, increased larvae mortality before to entering the seed. In addition, Cristalino-079 reduced first adult’s generation and show the largest biological cycle. Due to the small number of emerged adults, there was very little grain weight loss in resistant maize race. The compound that causes high mortality of larvae before to entering the grain is in the pericarp of resistant maize races. The compound that causes longest development time is in the endosperm and embryo. Cristalino-079 show the better level of resistance to S. cerealella infestation in almost all traits studied and this can be used as source of resistance for maize breeding.

Characterization of Microbial Communities from the Alimentary Canal of Typhaea stercorea (L.) (Coleoptera: Mycetophagidae).

Simple SummaryHairy fungus beetle, Typhaea stercorea, is a secondary post-harvest pest of stored grains that thrives by feeding on mytoxigenic fungi. Bacterial communities residing in the alimentary canal of most insects contribute to their host’s development. While there are many examples, little is known about the role of bacterial communities in the alimentary canal of T. stercorea. The objectives of this study were to (1) characterize the microbial communities residing in T. stercorea and (2) compare the microbial compositions of field-collected and laboratory-reared populations. In this study, we were able to identify bacterial communities that possess mycolytic properties and track mark changes in the microbiota profiles associated with development. The genus Pseudomonas was enriched in T. stercorea larvae compared to adults. Furthermore, field-collected T. sterocrea adults had a lower species richness than both larva and adult laboratory-reared T. sterocrea. Moreover, the gut microbial compositions of field-collected and laboratory-reared populations were vastly different. Overall, our results suggest that the environment and physiology can shift the microbial composition in the alimentary canal of T. stercorea.The gut microbiomes of symbiotic insects typically mediate essential functions lacking in their hosts. Here, we describe the composition of microbes residing in the alimentary canal of the hairy fungus beetle, Typhaea stercorea (L.), at various life stages. This beetle is a post-harvest pest of stored grains that feeds on fungi and serves as a vector of mycotoxigenic fungi. It has been reported that the bacterial communities found in most insects’ alimentary canals contribute to nutrition, immune defenses, and protection from pathogens. Hence, bacterial symbionts may play a key role in the digestive system of T. stercorea. Using 16S rRNA amplicon sequencing, we examined the microbiota of T. stercorea. We found no difference in bacterial species richness between larvae and adults, but there were compositional differences across life stages (PERMANOVA:pseudo-F(8,2) = 8.22; p = 0.026). The three most abundant bacteria found in the alimentary canal of the larvae and adults included Pseudomonas (47.67% and 0.21%, respectively), an unspecified genus of the Enterobacteriaceae family (46.60 % and 90.97%, respectively), and Enterobacter (3.89% and 5.75%, respectively). Furthermore, Pseudomonas spp. are the predominant bacteria in the larval stage. Our data indicated that field-collected T. stercorea tended to have lower species richness than laboratory-reared beetles (Shannon: H = 5.72; p = 0.057). Furthermore, the microbial communities of laboratory-reared insects resembled one another, whereas field-collected adults exhibited variability (PERMANOVA:pseudo-F(10,3) = 4.41; p = 0.006). We provide evidence that the environment and physiology can shift the microbial composition in the alimentary canal of T. stercorea.

Effects of Long-Term Low Oxygen Storage Treatment on Survival of Rice Weevil (Sitophilus oryzae) and Confused Flour Beetle (Tribolium confusum).

There is a need for alternative treatments for postharvest pests on stored products. In this study, 45-d long-term controlled atmosphere (CA) treatments with 3, 5, 6.5, and 8% O2 were studied to determine effects on survival and development of rice weevil (Sitophilus oryzae) and confused flour beetle (Tribolium confusum) eggs and susceptibility of different life stages to a 14-d 5% O2 treatment. Low oxygen treatments were effective against S. oryzae and T. confusum. The 45-d CA treatments with 6.5, 5, and 3% O2 resulted in 0.26, 0.004, and 0% survival rates from egg to adult respectively for S. oryzae and 6.51, 0.14, and 0% survival rates from egg to later stages respectively for T. confusum. For both species, eggs were more susceptible to low oxygen treatment than larvae or pupae. A 14-d CA treatment with 5% O2 resulted in 4.9 and 3.3% survival of eggs of S. oryzae and T. confusum, respectively, as compared with over 50% survival of larvae and pupae for both species. S. oryzae adults, however, were very susceptible to low oxygen treatment and 14-d exposure to 5% O2 atmosphere resulted in zero survival. In contrast, the 14-d exposure to 5% O2 atmosphere resulted in over 94% survival for T. confusum adults. This study suggested there were considerable differences between stored product insects in susceptibility to low oxygen treatment and that long-term CA storage treatments with a low oxygen level of ≤6.5 and ≤5% have potential in controlling S. oryzae and T. confusum, respectively.

Small Animals, Big Impact? Early Farmers and Pre- and Post-Harvest Pests from the Middle Neolithic Site of Les Bagnoles in the South-East of France (L'Isle-sur-la-Sorgue, Vaucluse, Provence-Alpes-Côte-d'Azur).

Simple SummaryArchaeological excavations at Les Bagnoles (SE France) unearthed three Middle Neolithic water wells (4250–3700 cal B.C.) whose waterlogged conditions allowed the preservation of organic remains, notably a large number of rodent and beetle species. The evaluation of these results in the context of an open-air farming site raised the question of whether these species could have posed a threat to both the field plants and crops stored at the Middle Neolithic settlement. The findings of this study suggest that the native wood mouse was probably one of the first unwanted inhabitants of human settlements in Europe prior to the appearance of the invasive house mouse during the Bronze Age. The analysis also advances the argument that the storage pest grain weevil played a role in the clear shift in the crop spectrum from naked to glume wheat around 4000 B.C., as glume wheats are less vulnerable to its infestation. Moreover, the current study demonstrates that investigating insects and rodents from archaeological sites is key to grasping the challenges of the competitive relationship between Neolithic farming communities and pests.Pests appear to have accompanied humans and their crops since the beginning of farming. Nevertheless, their study is only rarely integrated into research on farming in prehistory. An assemblage of invertebrates and small mammals was recovered from the waterlogged layers of three wells at the Middle Neolithic site (4250–3700 cal B.C.) of Les Bagnoles (SE France). The microfaunal remains were retrieved from sediment samples by wet sieving (wash-over technique). The most common among the rodents is the wood mouse. The assemblage also consists of insect remains of grain weevil, seed beetle, and corn ground beetle. The different finds not only offer data on the role of insect and rodent pests in the Neolithic but on the possible strategies adopted by the early farming communities in the western Mediterranean in response to pest infestation. The findings appear to confirm the hypothesis that the wood mouse was a commensal and storage pest in settlements long before the arrival of the invasive house mouse during the Bronze Age. The presence of the main storage pest, the grain weevil, suggests a long-term grain storage issue at Les Bagnoles. The combination of the results of the site’s archaeobotanical findings with those of other sites in the western Mediterranean suggests that the shift from naked to glume wheat around 4000 B.C. may also stem from a reaction to the problem of grain weevil infestation.

Phytochemical compositions and insecticidal efficacy of four agro-waste used as biological control of cowpea beetle, Callosobruchus maculatus (Fab.) [Coleoptera: Bruchidae

BackgroundThe cowpea bruchid, Callosobruchus maculatus is the major postharvest insect pest of cowpea seeds in storage. This had led to huge losses and quality deterioration of stored cowpea seeds that serve as poor man’s meat in lieu of expensive meat source in developing countries. This research was carried out to evaluate the bioefficacy of rice husk, maize cob, groundnut, and cowpea pods against C. maculatus in the laboratory. Adult insect mortality, eggs laid, adult emergence, damaged seeds, weight loss and beetle perforation index (BPI) were evaluated. Phytochemicals of the wastes were investigated.ResultsThe result showed that the agricultural wastes contained alkaloids (1.56–2.77 mg/g), saponin (1.51–3.38 mg/g), phytate (7.00–17.76 mg/g), oxalate (0.32–1.13 mg/g). All agricultural wastes showed a high mortality effect on C. maculatus, and their effects increased as the exposure time and concentration/ dosage increased. Beetle mortality was highest in cowpea pod with 80% mortality for powder after 3 and 4 days when applied at 0.5 g/20 g cowpea seed. This showed that cowpea pod powder has the greatest insecticidal activity while the least was observed in maize cob powder (73.33%). Fewer adults emerged with maize cob having the least emergence when applied at 0.2–0.5 g dosage. Extracts of all agricultural wastes tested against C. maculatus were able to affect 70–100% mortality after 4 days of application at concentration 0.5 ml with cowpea pod extract causing 100% mortality of beetle after 4 days of application. The calculated lethal dose (LD50 and LD90) and concentrations (LC50 and LC90) of wastes powders and extracts cowpea pod was observed to have the lowest lethal dose while maize cob wastes were the highest across all period of exposure.ConclusionBase on the results obtained, cowpea pod waste was the most toxic in biocontrol of C. maculatus.

Essential Oil Coating: Mediterranean Culinary Plants as Grain Protectants against Larvae and Adults of Tribolium castaneum and Trogoderma granarium.

Simple SummaryThe protection of stored agricultural products has been established as a global priority serving both food safety and security. Toxicity and residual issues of synthetic insecticides shifted the research focus towards natural pest control agents. In this context, six edible plants were selected for the conduction of a novel bioprospecting effort aiming to identify potential control agents against the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and the khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae). The proposed bioprospecting effort aims to identify the chemodiversity of essential oils (EOs) and exploit the potential of EO-based microemulsion (ME) coating as alternative tools for the management of the tested stored-product insects and the concomitant postharvest losses. Elevated toxicity was recorded against T. castaneum larvae and T. granarium adults. The fact that these EO-based MEs originate from culinary plants renders them safe for human consumption. The present study pioneers the utilization of EO-based MEs as grain protectants in the form of grain coating.Postharvest agricultural losses constitute a major food security risk. In contrast, postharvest protection is strongly linked with food safety. The present study aims to develop novel postharvest protection tools through a bioprospecting protocol utilizing edible essential oils (EOs) as grain coatings. For this purpose, six Mediterranean culinary plants were selected for evaluation. The EOs of juniper, Juniperus phoenicea L. (Pinales: Cupressaceae), marjoram, Origanum majorana L. (Lamiales: Lamiaceae), oregano, Origanum vulgare ssp. hirtum (Link) A.Terracc. (Lamiales: Lamiaceae), bay laurel, Laurus nobilis L. (Laurales: Lauraceae) and tarhan, Echinophora tenuifolia ssp. sibthorpiana (Guss.) Tutin (Apiales: Apiaceae) were retrieved through steam distillation, while lemon, Citrus limon (L.) Osbeck (Sapindales: Rutaceae) EO was retrieved through cold press extraction. All EOs were formulated to microemulsions (MEs) and applied uniformly as a coating on wheat against larvae and adults of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and Trogoderma granarium Everts (Coleoptera: Dermestidae). All EO-based MEs have been evaluated for the first time as grain coatings. They caused moderate to high mortality to T. castaneum larvae (67.8–93.3% 14 days post-exposure) and T. granarium adults (70.0–87.8% after 7 days of exposure). Citrus limon, O. majorana and E. tenuifolia ssp. sibthorpiana EO-based MEs were the most efficient against T. castaneum larvae, by exhibiting 93.3%, 91.1% and 90.0% mortality 14 days post-exposure, respectively. Origanum majorana, L. nobilis and J. phoenicea EO-based MEs were the most efficient against T. granarium adults, exhibiting 87.8%, 84.4% and 83.3% mortality after 7 days of exposure, respectively. These results indicate that EO-based ME coating is a potent tool against the tested postharvest pests.

Germination and Agronomic Traits of Phaseolus vulgaris L. Beans Sprayed with Trichoderma Strains and Attacked by Acanthoscelides obtectus

Acanthoscelides obtectus, one of the world’s most important post-harvest pests, attacks wild and cultivated common beans (Phaseolus vulgaris L.). Four Trichoderma strains, Trichoderma arundinaceum IBT 40,837 (=Ta37), a wild-type strain producer of trichothecene harzianum A (HA); two transformed strains of Ta37, Ta37-17.139 (Δtri17) and Ta37-23.74 (Δtri23); and T. brevicompactum IBT 40,841 (=Tb41), a wild-type strain producer of the trichothecene trichodermin, were evaluated to determine the effect of these compounds on the virulence of A. obtectus and the effect of these strains on the seed’s capacity of germination and on the agronomic traits of the plants grown from these seeds. Treatments of bean seeds with different Trichoderma strains provided varying survival rates in A. obtectus adults, so life survival of insects after Tb41 strain application was reduced to 15 days. Δtri17 and Tb41 strains sprayed on P. vulgaris beans resulted in low weight losses (1.21 and 1.55%, respectively). In spite of the low germination percentage of beans treated with Δtri23 strain (lower than the germination percentages of the rest of the fungal strains applied), this treatment encouraged a greater Wet Weight of Aerial Part of the plants grown from both damaged and undamaged beans. High germination rates of Ta37 and Δtri17 strains (higher than with the rest of treatments), did not turn into a greater Wet Weight Aerial Part and Wet Weight of Root System in the future plants developed. Linear regression between the number of exit holes and the wet weight aerial part on the one hand, and between the number of exit holes and the wet weight root system on the other, showed interaction, so Δtri23 and Tb41 strains behaved differently in comparison to their respective control treatments. The number of exit holes of beans treated with Δtri23 or Tb41 was negatively correlated with both the wet weight aerial part and the wet weight root system in P. vulgaris plants. Δtri23 sprayed on undamaged beans caused the greatest Wet Weight Aerial Part and wet weight root system in plants. Due to the good results obtained by Δtri23 and Tb41 strains in this work, more studies for A. obtectus control, P. vulgaris plant growth and trichothecenes production by these strains should be explored, in order to advance in the knowledge of how these fungi could be used in the field crop, together with the application of management strategies to mitigate risks for farmers and to minimize environmental contamination.

Essential Oil-Based Nano-Biopesticides: Formulation and Bioactivity against the Confused Flour Beetle Tribolium confusum

Post-harvest pest control can rely on few approved pesticides and tools; hence, there is a rising interest in new sustainable, eco-friendly approaches. In this study, eight commercial essential oils (EOs) (anise Pimpinella anisum, artemisia Artemisia vulgaris, fennel Foenicum vulgare, garlic Allium sativum, lavender Lavandula angustifolia, mint Mentha piperita, rosemary Rosmarinus officinalis, and sage Salvia officinalis) were selected for their bioactivity and commercial availability, and then formulated in nano-emulsions. Repellency and acute toxicity of the developed nano-formulations were tested against a key stored product pest, Tribolium confusum (Coleoptera: Tenebrionidae). All the developed nano-emulsions presented optimal physical characteristics (droplet dimension = 95.01–144.30 nm; PDI = 0.146–0.248). All the formulations were repellent over time tested against adult beetles, in area preference bioassays. The best repellent was the anise EO-based formulation (RC50 = 0.033 mg). Mortality values from cold aerosol trials showed that the majority of tested EOs caused immediate acute toxicity, and garlic EO nano-emulsion caused the highest mortality of T. confusum adults (LC50 = 0.486 mg/L of air). EO-based nano-insecticides, used as cold aerosol and gel, are promising control methods against stored product pests, which can be integrated and combined with other sustainable biorational approaches.

Trehalose and proline failed to enhance cold tolerance of the cowpea weevil, Callosobruchus maculatus (F.) (Col.: Bruchidae)

The cowpea weevil, Callosobruchus maculatus (F.) (Col.: Bruchidae) is a cosmopolitan field-to-store pest ranked as the major post-harvest pest of cowpea in tropical regions. The cold tolerance of an insect species can vary as a result of abiotic features including food resources. In this study, C. maculatus larvae were fed with proline and trehalose (10, 20, and 40 mmol) treated cowpea seeds to determine the effects of these potential cryoprotectants on the supercooling (SCP) and cold hardiness of the upcoming adult beetles. The SCPs of the control, proline-fed and trehalose-fed adults non-significantly changed from −18.2 °C for the control to −17.2 °C for trehalose-fed adults. The cold hardiness (24 h at 0, -5.0, −7.5, −10.0, and −12.5 °C) of the adults was almost the same for control and treatments. Median lethal times (LT50; lethal time for 50% mortality) were 6.3, 6.0, and 5.4 h, respectively. Moreover, feeding the larvae with proline and trehalose-treated seeds did not affect the proline and trehalose contents of the adult beetles. Our results showed that C. maculatus could not tolerate subzero temperatures well above their SCP, indicating that this species might be a chill-susceptible insect.

Anisole is an environmentally friendly fumigant for postharvest pest control

Plant essential oils have demonstrated insecticidal effects but not many are as effective as currently used fumigants. We evaluated anisole, a volatile compound extracted from aniseed, for control of four insect pests including adult rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), granary weevil, Sitophilus granarius (L.) (Coleoptera: Curculionidae), and confused flour beetle, Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae), and a fresh produce product pest, western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), in the laboratory tests. Anisole fumigations were effective against all four pests. At a dose of 100 μL/L, anisole fumigation completely controlled S. granarius and S. oryzae in 24 and 16 h, respectively. At a dose of 150 μL/L, complete control of the two weevils was achieved in 16 and 8 h, respectively. T. confusum was completely controlled in 16 and 8 h with anisole fumigations at 400 μL/L and 600 μL/L respectively. F. occidentalis was 100% controlled in 8 and 6 h treatments with anisole at doses of 150 μL/L and 300 μL/L, respectively. The median lethal times (LT50) of anisole fumigation at 50 μL/L were 0.6 and 0.5 h for S. granarius and S. oryzae, respectively. LT50 for T. confusum at 600 μL/L was 2.9 h. In a 16 h confirmatory test in a mini silo, anisole fumigation achieved 100% control of rice weevil at different depth of stored corn. This study demonstrated that anisole fumigation was effective against insects. Therefore, anisole fumigation has potential as an environmentally friendly, alternative fumigant for postharvest pest control.

Disparate genetic variants associated with distinct components of cowpea resistance to the seed beetle Callosobruchus maculatus.

Polygenic genome-wide association mapping identified two regions of the cowpea genome associated with different components of resistance to its major post-harvest pest, the seed beetle Callosobruchus maculatus. Cowpea (Vigna unguiculata) is an important grain and fodder crop in arid and semi-arid regions of Africa, Asia, and South America, where the cowpea seed beetle, Callosobruchus maculatus, is a serious post-harvest pest. Development of cultivars resistant to C. maculatus population growth in storage could increase grain yield and quality and reduce reliance on insecticides. Here, we use a MAGIC (multi-parent, advanced-generation intercross) population of cowpea consisting of 305 recombinant inbred lines (RILs) to identify genetic variants associated with resistance to seed beetles. Because inferences regarding the genetic basis of resistance may depend on the source of the pest or the assay protocol, we used two divergent geographic populations of C. maculatus and two complementary assays to measure several aspects of resistance. Using polygenic genome-wide association mapping models, we found that the cowpea RILs harbor substantial additive-genetic variation for most resistance measures. Variation in several components of resistance, including larval development time and survival, was largely explained by one or several linked loci on chromosome 5. A second region on chromosome 8 explained increased seed resistance via the induction of early-exiting larvae. Neither of these regions contained genes previously associated with resistance to insects that infest grain legumes. We found some evidence of gene-gene interactions affecting resistance, but epistasis did not contribute substantially to resistance variation in this mapping population. The combination of mostly high heritabilities and a relatively consistent and simple genetic architecture increases the feasibility of breeding for enhanced resistance to C. maculatus.