Insecticidal potency of mixtures of plant powders and Actellic SuperTM (Pirimiphos-methyl + Permethrin) on Callosobruchus chinensis F. and Sitophilus zeamais Motch

Insect pests still cause substantial quantitative and qualitative grain loss ranging from 20 to 100% in small holder farming systems in tropical countries. Synthetic pesticides are recommended as stop gap measures for the management of stored product insect pests. However, their application has not been fully exploited in small scale farming due to environmental, health, and economic concerns. As a result, new researches have shifted focus to exploiting pesticidal plants as alternatives to synthetic pesticides. Therefore, the current study evaluated mixtures of plant powders and reduced amount of Actellic superTM (pirimiphos-methyl + permethrin) as alternative insecticide formulation against Callosobruchus chinensis and Sitophilus zeamais. Green grams and wheat grains were mixed with a mixture of plant powders in the ratios of 1:1, 1:3 and 1:9 to obtain four rates (0.0, 2.0, 6.0 and 10%w/w). Grains and plant powders were also mixed with reduced amount (10, 25, and 50 %) of recommended rate of Actellic SuperTM to obtain dosages as above. Twenty unsexed adults, 1-5 day old S. zeamais and C. chinensis were introduced into treated grains. The mixture of C. lusitanica: T. vogelii powders in the ratios of 1:1, 1:3 and 1:9 caused mortality in C. chinensis of 55, 95 and 85%, respectively. At the same ratio, E. saligna: L. camara mixture produced mortality in S. zeamais of 77, 82, and 85% respectively. In mixture of C. lusitanica and T. vogelii and reduced amount of Actellic SuperTM by 50% the mortality of C. chinensis was 85 and 80 % respectively. Similarly, E. saligna and L. camara and reduced amount of Actellic SuperTM by 50% caused a mortality of S. zeamais of 48 and 97% respectively. The application of plant powders and reduced amounts of synthetic insecticide has the potential to be applied in stored product pest control

Entomotoxic effects of synthesized aluminum oxide nanoparticles against Sitophilus oryzae and their toxicological effects on albino rats

Recently, nanoparticles are emerging as a potential alternative to synthetic pesticides for protection against stored-product insect pests, such as the rice weevil Sitophilus oryzae; however, the toxic effects of nanoparticles on nontarget organisms are not yet understood. Therefore, we investigated the insecticidal effects of synthesized aluminum oxide nanoparticles (Al2O3-NPs) on S. oryzae, as well as their potential toxicity in albino rats. S. oryzae mortality increased as the period of Al2O3-NP exposure increased; 100% mortality was reached at 8000 mg Al2O3-NPs/kg of wheat grain after 7 days of exposure. After 60 days of exposure, all tested Al2O3-NPs concentrations (1000, 2000, 4000, and 8000 mg/kg grain) significantly reduced the number of S. oryzae offspring in a dose-dependent manner. In albino rats, exposure to the LC90 of Al2O3-NPs in a treated diet caused a significant decrease in total body weight and an increase in liver weight in a subacute toxicity test. Moreover, Al2O3-NP treatment elevated the levels of alanine aminotransferase, aspartate aminotransferase, and creatinine in exposed rats relative to control rats, while the uric acid levels of treated rats decreased. Histopathological analysis also revealed various hepatic and renal lesions in treated rats. In summary, although Al2O3-NPs have insecticidal effects, they also have hazardous toxicological effects on rats. Therefore, if Al2O3-NPs are used in the current powder form to protect stored products, they may cause adverse effects to workers and consumers. Further research will be required to develop new nanoformulations with increased safety and potency before these nanoparticles can be used in stored-product pest control.

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.

Influence of Temperature and Photoperiod on the Fecundity of Habrobracon hebetor Say (Hymenoptera: Braconidae) and on the Paralysis of Host Larvae, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae)

Studies were carried out in the laboratory to understand the optimum environmental conditions at which the ectoparasitoid, Habrobracon hebetor Say (Hymenoptera: Braconidae), can paralyze and lay eggs when reared on the larvae of the stored product pest, Plodia interpunctella Hübner (Lepidoptera: Pyralidae). At the four temperatures investigated (20, 25, 30, and 35 °C), optimum temperatures for oviposition were found to be 25 and 30 °C, while 35 °C was the least favorable temperature. No significant differences were found between the percentages of diapausing and non-diapausing larvae paralyzed by the wasp at the temperatures of 20, 25, 30, 35 °C within 5 days. However, in another experiment that investigated the effect of photoperiods at different temperatures that included 15, 19 and 28 °C, the number of paralyzed larvae was highly reduced at low temperatures (15 °C) but photoperiods had no significant impact on the number of host larvae paralyzed. In addition, observations at short time intervals also showed that lower temperatures slowed down host larvae paralysis. The results suggest that H. hebetor can paralyze host larvae of P. interpunctella more efficiently and deposit more eggs at temperatures within the range of 20–30 °C.

Behavioral and Antennal Responses of Tribolium confusum to Varronia globosa Essential Oil and Its Main Constituents: Perspective for Their Use as Repellent

Essential oils of aromatic plants represent an alternative to classical pest control with synthetic chemicals. They are especially promising for the alternative control of stored product pest insects. Here, we tested behavioral and electrophysiological responses of the stored product pest Tribolium confusum, to the essential oil of a Brazilian indigenous plant, Varronia globosa, collected in the Caatinga ecosystem. We analyzed the essential oil by GC-MS, tested the effects of the entire oil and its major components on the behavior of individual beetles in a four-way olfactometer, and investigated responses to these stimuli in electroantennogram recordings (EAG). We could identify 25 constituents in the essential oil of V. globosa, with anethole, caryophyllene and spathulenole as main components. The oil and its main component anethole had repellent effects already at low doses, whereas caryophyllene had only a repellent effect at a high dose. In addition, the essential oil abolished the attractive effect of the T. confusum aggregation pheromone. EAG recordings revealed dose-dependent responses to the individual components and increasing responses to the blend and even more to the entire oil. Our study reveals the potential of anethole and the essential oil of V. globosa in the management of stored product pests.

Susceptibility of Tribolium castaneum (Coleoptera: Tenebrionidae) to the Fumigation of Two Essential Satureja Oils: Optimization and Modeling

Due to the numerous side effects of synthetic pesticides, including environmental pollution, threats to human health, harmful effects on non-target organisms and pest resistance, the use of alternative healthy, available and efficient agents in pest management strategies is necessary. In this paper, the susceptibility of the cosmopolitan, polyphagous, stored-product pest Tribolium castaneum (red flour beetle) to the fumigation of the essential oils of two important medicinal and food additive plants, Satureja hortensis and S. intermedia, was investigated. The insecticidal properties of the essential oils were modeled and optimized using response surface methodology. It was found that a maximum significant mortality of 94.72% and 92.97% could be achieved within 72 h with the applications of 55.15 µL/L of S. hortensis (with the linear model) and 58.82 µL/L of S. intermedia (with the quadratic model), respectively. There were insecticidal terpenes and phenylpropanoids in both essential oils, including thymol (50.8%), carvacrol (11.2%) and p-cymene (13.4%), in the S. intermedia and estragole (68.0%) and methyl eugenol (5.6%) in the S. hortensis. It was suggested that the essential oils of S. hortensis and S. intermedia could be offered as promising pesticidal agents against T. castaneum for further studies in the management of such pests instead of detrimental synthetic pesticides.

Volatile Infochemicals from Rhyzopertha dominica Larvae and Larval Feces Involved in Theocolax elegans Host Habitat Location

The development of biologically based approaches for stored product pest control is needed to reduce chemical inputs. Bioassays were performed to investigate host habitat location in the trophic interaction durum wheat/Rhyzopertha dominica/Theocolax elegans. GC-MS analyses were carried out to identify some chemical compounds produced by the host-related substrates. Choice and no-choice experiments demonstrated that female parasitoids were poorly attracted to intact kernels with respect to the infested substrates. Furthermore, T. elegans females performed longer residence time on infested wheat, and they generally displayed a short-term like fidelity for this cue, remaining on it during the whole observation. Infested wheat emitted one chemical (fenchone), which is possibly linked to host larvae presence, while the feces produced by host larvae emitted some other characteristic compounds. Results demonstrated that the presence of host larvae is a key factor for T. elegans host habitat location, considering that the attractiveness of the undamaged wheat is irrelevant. Furthermore, parasitoid females tended to stay on attractive cues, limiting the risk of contamination of other commodities. Biological control tools may be useful to improve the efficiency of pest management programs, but their application should be carefully evaluated.

Organic anion-transporting polypeptides are involved in the elimination of insecticides from the red flour beetle, Tribolium castaneum

Organic anion-transporting polypeptides (OATPs) are integral membrane transporters that mediate cellular uptake of a broad range of substrates in humans. The functions of OATPs in insects are less well investigated and only poorly understood. A large number of compounds potentially toxic to insects are organic anions that include secondary plant and insecticide-derived metabolites. Some insect OATP genes are expressed in metabolic, neuroprotective and excreting tissues, and they are co-expressed together with genes known to be involved in detoxification and excretion. Therefore, a role in the elimination of insecticides has been proposed for OATPs, but experimental proof was pending. The aim of this study was to identify OATPs that affect tolerance to insecticides in the red flour beetle, Tribolium castaneum, a genomic model species and stored product pest. We determined expression profiles of TcOATP genes in different tissues and developmental stages and analyzed RNAi phenotypes. We found that some TcOATP genes had particularly high transcript levels in relevant tissues and that knockdown of TcOATP4-C1 led to sever developmental defects during larval–pupal molt. Then, we exposed the larvae to different chemically unrelated insecticides and analyzed transcript levels and mortalities. Some genes were specifically upregulated in response to insecticide treatment, and mortalities observed after administering certain insecticides were significantly increased when specific TcOATPs were silenced. By applying systemic RNAi in T. castaneum, we provide first evidence that OATPs are involved in the elimination of insecticides and hence may contribute to insecticide resistance, which becomes an increasingly serious problem in agriculture and forestry. Graphic abstract

Insecticidal Activity of 25 Essential Oils on the Stored Product Pest, Sitophilus granarius

The granary weevil Sitophilus granarius is a stored product pest found worldwide. Environmental damages, human health issues and the emergence of resistance are driving scientists to seeks alternatives to synthetic insecticides for its control. With low mammal toxicity and low persistence, essential oils are more and more being considered a potential alternative. In this study, we compare the toxicity of 25 essential oils, representing a large array of chemical compositions, on adult granary weevils. Bioassays indicated that Allium sativum was the most toxic essential oil, with the lowest calculated lethal concentration 90 (LC90) both after 24 h and 7 days. Gaultheria procumbens, Mentha arvensis and Eucalyptus dives oils appeared to have a good potential in terms of toxicity/cost ratio for further development of a plant-derived biocide. Low influence of exposure time was observed for most of essential oils. The methodology developed here offers the possibility to test a large array of essential oils in the same experimental bioassay and in a standardized way. It is a first step to the development of new biocide for alternative management strategies of stored product pests.

Amplitude of circadian rhythms becomes weaken in the north, but there is no cline in the period of rhythm in a beetle

Many species show rhythmicity in activity, from the timing of flowering in plants to that of foraging behavior in animals. The free-running periods and amplitude (sometimes called strength or power) of circadian rhythms are often used as indicators of biological clocks. Many reports have shown that these traits are highly geographically variable, and interestingly, they often show latitudinal or longitudinal clines. In many cases, the higher the latitude is, the longer the free-running circadian period (i.e., period of rhythm) in insects and plants. However, reports of positive correlations between latitude or longitude and circadian rhythm traits, including free-running periods, the power of the rhythm and locomotor activity, are limited to certain taxonomic groups. Therefore, we collected a cosmopolitan stored-product pest species, the red flour beetle Tribolium castaneum, in various parts of Japan and examined its rhythm traits, including the power and period of the rhythm, which were calculated from locomotor activity. The analysis revealed that the power was significantly lower for beetles collected in northern areas than southern areas in Japan. However, it is worth noting that the period of circadian rhythm did not show any clines; specifically, it did not vary among the sampling sites, despite the very large sample size (n = 1585). We discuss why these cline trends were observed in T. castaneum.