Do temperature, relative humidity and interspecific competition alter the population size and the damage potential of stored-product insect pests? A hierarchical multilevel modeling approach

The premises of stored agricultural products and food consists of a complex ecosystem in which several pests can seriously affect the quality and quantity of the products. In this study we utilize a 4-level hierarchical linear multilevel model in order to assess the effect of temperature, relative humidity (RH) and interspecific competition on the population size and damage potential of the larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrychidae) and the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae). As RH was increased, we observed higher percentage of live insects, while increased levels of temperature significantly decreased the percentage of live insects. The combination of R. dominica and P. truncatus lead to reduction of the percentages of live insects in comparison to single species treatments. However, P. truncatus is more damaging than R. dominica in maize, based on the proportion of damaged kernels which were infested by each insect species. We expect our results to have bearing in the management of these species

(Quasi)-binomial vs. Gaussian models to evaluate thiamethoxam, pirimiphos-methyl, alpha-cypermethrin and deltamethrin on different types of storage bag materials against Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) and Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae)

The Mediterranean flour moth, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) and the confused flour beetle, Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae) are worldwide spread and notorious organisms of numerous stored-products. Both species are dangerous for bagged commodities as penetrators and invaders. The aim of the current study was to examine the efficacy of thiamethoxam, pirimiphos-methyl, alpha-cypermethrin, and deltamethrin, against E. kuehniella and T. confusum larvae, on different types of storage bag materials, i.e., woven propylene, biaxially oriented polypropylene and kraft paper through a (quasi)-binomial modeling approach. The type of the tested storage bag material did not affect the mortality rates of both species when treated with the tested insecticides. Thiamethoxam and pirimiphos-methyl showed statistically significant higher mortality rates on E. kuehniella and T. confusum (beta coefficient = 0.141; p-value < 0.05) compared to alpha-cypermethrin and deltamethrin. In addition, T. confusum exhibited significantly higher mortality rate in comparison to E. kuehniella. Our results also showed that the tested doses and surface treatments had a significant effect on the mortality E. kuehniella and T. confusum larvae. Significantly higher mortality rates were recorded when larvae were exposed on bag materials having both surfaces treated or on the single treated surface than when they were exposed on the untreated surface. Our findings can be useful towards an effective management strategy against stored-product insect pests

Chemical composition and broad-spectrum insecticidal activity of the flower essential oil from an ancient sicilian food plant, ridolfia segetum

Several species of the family Apiaceae are aromatic herbs that produce essential oils usable on an industrial scale for pharmaceutical, cosmetic, and food purposes. In particular, some essential oils, such as green insecticides for example, may replace synthetic insecticides, keeping most of their efficacy and avoiding environmental pollution or human poisoning. In the present study, we explored the insecticidal potential of Ridolfia segetum (L.) Moris essential oil (EO) against three different pests: Culex quinquefasciatus Say, Musca domestica L., and Spodoptera littoralis (Boisduval). For this purpose, the EO was obtained by hydrodistillation of flowers and its composition was achieved by gas chromatography/flame ionization detection (GC/FID) and gas chromatography/mass spectrometry (GC/MS). This EO was rich in α-phellandrene (49.3%), β-phellandrene (9.2%), terpinolene (20.7%), and piperitenone oxide (5.9%). Concerning the mosquitocidal efficacy, the EO showed noteworthy toxicity against C. quinquefasciatus 3rd instar larvae, with a LC50 = 27.1 µL L−1 and LC90 = 42.5 µL L−1. Regarding M. domestica, a different toxicity of the R. segetum EO was found on male and female flies, calculating LD50 values of 10.5 and 50.8 µg adult−1, respectively. The EO was also toxic to S. littoralis 3rd instar larvae, achieving LD50 and LD90 values of 37.9 and 99.6 µg larva−1, respectively. Overall, this flower EO, extracted from a traditional Sicilian food plant, merits further investigation for the development of green insecticide formulations to be used in real world conditions, pending a careful assessment of non-target toxicity on beneficial organisms

Human N-acetyltransferase 2 (NAT2) gene variability in Brazilian populations from different geographical areas

Introduction: Several polymorphisms altering the NAT2 activity have already been identified. The geographical distribution of NAT2 variants has been extensively studied and has been demonstrated to vary significantly among different ethnic population. Here, we describe the genetic variability of human N-acetyltransferase 2 (NAT2) gene and the predominant genotype-deduced acetylation profiles of Brazilians.Methods: A total of 964 individuals, from five geographical different regions, were genotyped for NAT2 by sequencing the entire coding exon.Results: Twenty-three previously described NAT2 single nucleotide polymorphisms (SNPs) were identified, including the seven most common ones globally (c.191G&gt;A, c.282C&gt;T, c.341T&gt;C, c.481C&gt;T, c.590G&gt;A, c.803A&gt;G and c.857G&gt;A). The main allelic groups were NAT2*5 (36%) and NAT2*6 (18.2%), followed to the reference allele NAT2*4 (20.4%). Combined into genotypes, the most prevalent allelic groups were NAT2*5/*5 (14.6%), NAT2*5/*6 (11.9%) and NAT2*6/*6 (6.2%). The genotype deduced NAT2 slow acetylation phenotype was predominant but showed significant variability between geographical regions. The prevalence of slow acetylation phenotype was higher in the Northeast, North and Midwest (51.3%, 45.5% and 41.5%, respectively) of the country. In the Southeast, the intermediate acetylation phenotype was the most prevalent (40.3%) and, in the South, the prevalence of rapid acetylation phenotype was significantly higher (36.7%), when compared to other Brazilian states (p &lt; 0.0001). Comparison of the predicted acetylation profile among regions showed homogeneity among the North and Northeast but was significantly different when compared to the Southeast (p = 0.0396). The Southern region was significantly different from all other regions (p &lt; 0.0001).Discussion: This study contributes not only to current knowledge of the NAT2 population genetic diversity in different geographical regions of Brazil, but also to the reconstruction of a more accurate phenotypic picture of NAT2 acetylator profiles in those regions

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 (&lt;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

Invader competition with local competitors: displacement or coexistence among the Invasive Khapra Beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae), and two other major Stored-Grain Beetles?

Local potential competitor species are important determinants of the invasibility of an environment even when widely recognized invasive species are concerned since it may compromise its establishment. Thus, the outcome of the direct competition among the invasive khapra beetle, Trogoderma granarium, and the cosmopolitan species lesser grain borer, Rhyzopertha dominica and rice weevil, Sitophilus oryzae, and thus the likelihood of establishment of T. granarium under their co-occurrence, was here explored in paddy rice and wheat, at temperatures between 25 and 35∘C and through 200 days of storage. Insect infestations were higher in wheat rather than in paddy rice. Trogoderma granarium was unable to displace any of the competing species under two and three-species competition experiments retaining lower adult population than both local competitors at the lowest temperature level. Rhyzopertha dominica prevailed in paddy rice, while S. oryzae prevailed in wheat. Paradoxically, T. granarium adults retained low population growth but contributed more for the total frass production and grain loss, much more than that recorded for R. dominica. Nonetheless, T. granarium larvae exhibited high population numbers 130 days after the introduction of the parental individuals. At higher temperature levels (30 and 35∘C) the numbers of T. granarium larvae were extremely high even after 65 days, while the numbers of the other two species rapidly declined. Interestingly, the simultaneous presence of R. dominica and S. oryzae was beneficial for the population growth of T. granarium. Consequently, T. granarium has the ability to outperform other primary stored-product insects at high temperatures, while its presence at low temperatures remains for long periods apparently unaffected by other co-occurring species. Hence, T. granarium, in wheat, is able to outcompete other major species of stored-product insects at elevated temperatures, while at 25∘C this species can maintain low numbers of individuals for long periods, which can rapidly produce population outbursts when the prevailing conditions are suitable for its development

Functional Asymmetries Routing the Mating Behavior of the Rusty Grain Beetle, Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae)

The rusty grain beetle, Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae), is a serious secondary pest of stored and processed food commodities. In the present study, we investigated the lateralization of males during courtship and mating, attempting to understand if it can be linked with a high likelihood of successful copulation. Most males exhibited left-biased (41%) approaches towards females, and turned 180&deg; to their left, with 37% mating success. Right-biased males (i.e., approaching from the right and then turning 180&deg;) were fewer than left-biased ones; 26% out of 34% managed to copulate with females. Only 9% out of 13% and 7% out of 11% of the back side- and front side-approaching males succeeded in mating, respectively. Directional asymmetries in approaching a potential mate, as well as the laterality of side-biased turning 180&deg;, significantly affected male copulation success, with left-biased males achieving higher mating success if compared to right-biased males. Copula duration was significantly lower for left-biased-approaching males (1668.0 s) over the others (i.e., 1808.1, 1767.9 and 1746.9 for right-biased, front and back side-males, respectively). Left-biased males performed shorter copulation attempts and copula compared to right-biased males. Overall, our study adds basic knowledge to the lateralized behavioral displays during courtship and copula of C. ferrugineus

Using multilevel models to explore the impact of abiotic and biotic conditions on the efficacy of pirimiphos-methyl against Tenebrio molitor L.

In this study, we utilized a hierarchical multilevel modeling approach to test the hypothesis that the activity of the organophosphate insecticide pirimiphos-methyl against the cosmopolitan serious secondary pest of stored products, the yellow mealworm, Tenebrio molitor (Coleoptera: Tenebrionidae), is affected by temperature, relative humidity (RH), and developmental stage (adults, small larvae, large larvae). Our results showed that as temperature increased from 20 to 25 °C, the observed mortality of T. molitor was significantly higher. Furthermore, mortality at 25 °C did not significantly differ from that of 30 °C. An ultimate increase at 35 °C resulted in the highest mortality rate of T. molitor. However, an increase of RH from 55 to 75% adversely affected the efficacy of pirimiphos-methyl. In our study, it is also shown that the insect developmental stage is a critical feature of pirimiphos-methyl efficacy. Tenebrio molitor adults exhibited significantly higher mortality than larvae. In addition, small larvae showed significantly higher mortality than large larvae. Thus, adult is the most susceptible developmental stage of T. molitor to pirimiphos-methyl treatment. Our results could be useful tools for the management of T. molitor by indicating the optimum combination of temperature and RH that favors the insecticidal treatment against this species. In addition, we expect that the percentage of developmental stages in a whole population of T. molitor affects the insecticidal efficacy of pirimiphos-methyl

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