Insecticide Sprays Research Articles

Impact of Chemical Insecticide Application on Beneficial Insects in Maize.

The European corn borer (ECB) (Ostrinia nubilalis Hübner) and to a lesser extent the western corn rootworm (Diabrotica virgifera virgifera LeConte) are a threat to maize in the Po Valley (Northern Italy), and their control can require insecticide applications. The results of a study to evaluate the effects of insecticide sprays on the beneficial insect Trichogramma brassicae (Hymenoptera: Trichogrammatidae) and aphid predators are reported. A three-year research project was carried out in two Study Areas, in Lombardy. In area 1, crop rotation was a common practice, while in area 2 repeated maize crop was practiced. The natural trend of ECB egg masses attacked by T. brassicae was affected and parasitism rates were reduced as a result of insecticide exposure (chlorpyriphos methyl, cypermethrin, alphacypermethrine). Repeated maize crop and insecticides spraying increased the abundance of the aphid population and negatively affected the aphid predator community, which mainly included ladybirds, hoverflies, true bugs and lacewings. The predator community was dominated by hoverflies in sprayed fields managed according to repeated maize crop protocols, whereas ladybirds and Orius spp. dominated in maize fields managed according to crop rotation protocols. Crop rotation protocols help to prevent ECB outbreaks; when the risk of exceeding the economic threshold limit is high, and this may be the case when maize is cultivated for seeds or for horticultural crops such as sweet corn, inundative release of T. brassicae and/or microbial control (i.e., use of Bacillus thuringiensis preparations) can integrate natural biocontrol, and provide a valuable alternative to chemical insecticides.

Evaluation of Botanicals against Rice Case Worm Parapoynx stagnalis Zeller. (Lepidoptera: Pyralidae)

Rice, Oryza sativa L. is the staple food of two thirds of world population. Several insect pests are reported to cause damage to rice crop. Rice case worm, unlike other lepidopteran rice pests, have an aquatic larval period and hence depends on dissolved oxygen in the water drop it carries in its case, made from rice leaf. Application of insecticide spray, does not give much control of this pest. No botanicals are yet reported as effective against this pest. In the present study, six botanicals were tested on rice case worm under laboratory and field conditions. Of the six plants, Anamirta cocculus gave promising results at five percent concentration followed by Glyricida sepium under both field and laboratory conditions.

Integrated Pest Management Strategies for Fruitfly (Bactrocera cucurbitae) in Bittergourd (Bactrocera cucurbitae)

The present study was conducted to evaluate the effects of Integrated Pest Management practices against bitter gourd fruit fly in Tiruvallur District, Tamil Nadu, India. The demonstration was conducted at farmer’s fields in two village viz., Kilambakkam and Periya kilambakkam of the district Tiruvallur during Kharif season 2018 and 2019. The front line demonstration was consisted of IPM (Field sanitation, fruit fly baits, Installation of fruit fly traps and spraying of neem oil 3%) and Non –IPM practices (Spraying of chemical insecticides). When compared to non-IPM fields, IPM techniques with fruit fly traps (with cue lure) attracted a large number of fruit flies, resulting in a 64 percent reduction in fruitfly infestation and a 3-4 times higher yield. The use of pheromone traps instead of insecticides to control fruit flies results in significant cost savings and pesticide-free bitter gourd output.Results indicated average fruit yield of 12.80 t/ha, an increase of 55.29% increase in yield over farmers practice as well as a net income of Rs.1,62,700/-. Reduction in cost of cultivation due to less investment for plant protection aspects has been recorded

An analytically tractable, age-structured model of the impact of vector control on mosquito-transmitted infections.

Vector control is a vital tool utilised by malaria control and elimination programmes worldwide, and as such it is important that we can accurately quantify the expected public health impact of these methods. There are very few previous models that consider vector-control-induced changes in the age-structure of the vector population and the resulting impact on transmission. We analytically derive the steady-state solution of a novel age-structured deterministic compartmental model describing the mosquito feeding cycle, with mosquito age represented discretely by parity-the number of cycles (or successful bloodmeals) completed. Our key model output comprises an explicit, analytically tractable solution that can be used to directly quantify key transmission statistics, such as the effective reproductive ratio under control, Rc, and investigate the age-structured impact of vector control. Application of this model reinforces current knowledge that adult-acting interventions, such as indoor residual spraying of insecticides (IRS) or long-lasting insecticidal nets (LLINs), can be highly effective at reducing transmission, due to the dual effects of repelling and killing mosquitoes. We also demonstrate how larval measures can be implemented in addition to adult-acting measures to reduce Rc and mitigate the impact of waning insecticidal efficacy, as well as how mid-ranges of LLIN coverage are likely to experience the largest effect of reduced net integrity on transmission. We conclude that whilst well-maintained adult-acting vector control measures are substantially more effective than larval-based interventions, incorporating larval control in existing LLIN or IRS programmes could substantially reduce transmission and help mitigate any waning effects of adult-acting measures.

Development and Characterization of a Contact-Charging Electrostatic Spray UAV System

Utilizing agricultural UAVs for pesticide and insecticide spraying is an effective measure for plant protection. However, achieving effective coverage on the back side of target is often challenging. To address this issue, this study combined a contact-charging spraying system with a UAV to develop an electrostatic plant protection UAV system. Upon activating the electrostatic component, strong electrostatic effects were observed at the nozzle, altering the distribution of the liquid flow; the distribution within the liquid flow became more homogeneous, while the edge regions experienced electrostatic repulsion, leading to changes in droplet size and an increase in droplet density. In the central area, droplet size reduced from 159 μm to 135 μm, while in the edge area, it changed from no value to 120 μm. During field tests using the UAV, the results showed an increase of 1.0 m in effective spray width (at a flight height of 4.0 m), indicating that the charges and propellor wind field contributed to the diffusion of droplets towards the edges. Additionally, the droplet density increased by an average of 19.7 droplets/cm2, and the overall deposition increased by 0.12 μL/cm2, resulting in an approximate three-fold increase compared to conventional spray, which aids in insect control and reduces pesticide usage.

Laboratory Bioassays to Study the Efficacy of Diamides against Leucinodes orbonalis (Guenee) of Brinjal

This study was undertaken with the objectives to investigate the toxicity of insecticides against larval stage of L. orbonalis in the laboratory. Management stratagies of the pest requires frequent spraying of chemical insecticides. Due to continuous spraying of insecticides L. orbonalis had developed a resistance to different insecticides that are urgently needed to test new molecules. In this bioassay, seven insecticides such as Cyantraniliprole 10OD, chlorantraniliprole 18.5SC, flubendiamide 480SC thiodicarb 75WP, methomyl 40SP, cartap hydrochloride and profenophos 50EC belonging to different insecticides groups were tested against L. orbonalis in the laboratory. In this bioassay larval mortality showed increasing trend with maximum percent mortality observed at 72HAT. All the treatments were found significantly superior over UTC. Among the seven insecticides tested against L. orbonalis, three diamides were found to be significantly superior. Cyantraniliprole 10OD recorded significantly highest percent larval mortality (97.26%), followed by chlorantraniliprole 18.5SC (94.14%) flubendiamide 480SC (88.45%), thiodicarb 75WP (77.53%), methomyl 40SP (71.50%), cartap hydrochloride 50SP (68.04%) and profenophos 50EC (65.88%). It is suggested that diamides may be used for the control of L. orbonalis.

Effects of insecticide spray drift on arthropod prey resources of birds in grasslands in Minnesota

AbstractSoybean aphid (Aphis glycines) insecticides are used throughout the Upper Midwest and Great Plains regions of North America, including the farmland region of Minnesota, USA, to combat insect pests. These broad‐spectrum, foliar spray insecticides have the potential to drift beyond target fields into nearby grassland cover where birds and other insectivores forage. Arthropods serve important roles in grassland ecology and are susceptible to mortality and sublethal effects from exposure to these pesticides. Our objective was to assess effects of soybean aphid insecticides on grassland arthropods, especially those that are important in grassland bird diets. We measured the abundance, consumable biomass, and family richness of insects and spiders in grasslands adjacent to soybean fields in an agricultural landscape. Soybean fields were treated with chlorpyrifos and lambda‐cyhalothrin, which were the 2 most common foliar pesticides used to control soybean aphids in Minnesota. We compared measures at focal sites to samples collected at reference sites adjacent to corn fields not sprayed for aphids during 3 periods in mid‐to‐late summer: 1–3 days before spraying, 3–5 days post‐spraying, and 19–21 days post‐spraying. The abundance of arthropods in focal grasslands was lower 3–5 days after pesticide applications. Coleoptera family richness at focal sites was also lower than at reference sites 3–5 days after pesticide applications. These measures 19–21 days after application were similar to pre‐spraying levels, indicating that arthropod populations rebounded during this period. Measures of consumable dry biomass, bird prey abundance, bird prey biomass, family richness of Araneae, family richness of Hemiptera, and family richness of Orthoptera were not different between focal and reference sites after spraying. Our results reveal that reductions in arthropod food abundance for grassland birds are associated with pesticide applications up to 5 days after spraying. We suggest that natural resource managers factor proximity to row crop fields and susceptibility to pesticide drift into decisions about where to add grassland cover to landscapes.

Compatibility Studies on Selective Insecticides, Fungicides and Water-Soluble Fertilizer Mixtures in Soybean

In present context, there is a demand for combination spray of insecticides and fungicides to manage both insect pests and diseases simultaneously in a crop season. However, tank mixing of incompatible combinations can reduce the effectiveness of the chemicals, cause phytotoxicity or development of insecticide resistance in pests. Hence, a laboratory experiment was conducted at Agricultural Research Station (UAS, Dharwad), Sankeshwar, Karnataka to study the physical, chemical and phytotoxic compatibility of selective insecticides, fungicides and water-soluble fertilizer mixtures at their recommended dose in soybean by jar compatibility method. Out of eighteen different combinations tested emamectin benzoate 5 SG (0.3 g l-1) in combination with propiconazole 25 EC (1 ml l-1) and 19:19:19 (N:P:K @ 5 g l-1), as well as lambda cyhalothrin 4.6 + chlorantraniliprole 9.3 ZC (0.4 ml l-1) in combination with propiconazole 25 EC (1 ml l-1) and 19:19:19 (5 g l-1) exhibited sedimentation levels of 1 ml l-1 which was less than the limits of 2 ml 100 ml-1 as specified in 1973 by Indian Standard Institute. The pH of agrochemicals both alone and combinations in all solutions test ranged from 6.02 to 8.39 and none of the solutions found extremely acidic nor alkaline. No phytotoxic symptoms were observed in combination treatments at 5 and 10 days after spraying. All test combinations were physically, chemically and biologically compatible hence, tank mixing of these chemicals can be recommended in soybean for managing of insect pest and diseases.

Mass trapping of the diamondback moth (Plutella xylostella L.) by a combination of its sex pheromone and allyl isothiocyanate in cabbage fields in southern Vietnam.

A lure composed of (Z)-11-hexadecenal, (Z)-11-hexadecenyl acetate, and (Z)-11-hexadecen-1-ol at a ratio of 5 : 5 : 1 at a dose of 0.01 mg was optimal for the attraction of the Vietnamese strain of the diamondback moth (DBM). The combination of the sex pheromone with a plant volatile, allyl isothiocyanate, significantly increased the attraction of the pheromone trap. Females were also attracted, but they were only about 2% of all moths captured. In plots with 120-130 traps per ha, mass trapping with the combined lures reduced the DBM larval densities in cabbage fields as effectively as the spraying of insecticides 6 to 8 times. The weekly trap catches indicated that DBM adult densities in the mass-trapping fields were low until 28 days after transplantation, and then were kept to a modest increase until day 49. This field study also shows that the trap catches were well correlated with the DBM larval densities.

Field evaluation of whorl application of sand mixed or spray insecticides against Spodoptera frugiperda (Lepidoptera: Noctuidae) on yield of maize

BackgroundSpodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), the fall armyworm (FAW), has recently invaded Egypt and poses serious threats to maize farmers as it causes huge economic costs and yield losses. Selection of efficient insecticides and appropriate methods of application can be a problem to control this pest.MethodsTwo-year field studies to effectiveness of whorl application (sand mixed or spray) of seven insecticides comprising new insecticides generations with conventional insecticides from different groups at maximum recommended dosage field rate against FAW on yield of maize was evaluated in maize fields at El-Qualubia Governorate, Egypt.ResultsIn plots treated with insecticide mixed in sand, all tested insecticides recorded a significant decrease in FAW larvae with significantly higher yields than those treated with spraying or untreated plots. However, among tested insecticides in both applications, chlorantraniliprole was found to be the most effective followed by emamectin benzoate and spinosad and these insecticides gave better control FAW with higher yield than conventional insecticides tested. In this context, the highest decrease in FAW density was recorded in plots treated with chlorantraniliprole mixed in sand or sprayed (93.69% for 2021; 91.59% for 2022) and (84.74% for 2021; 85.78% for 2022), respectively, as well as a significantly high yield. However, lambda-cyhalothrin recorded the highest density of FAW (33.86% for 2021; 32.72% for 2022) in the treated plots with spraying with lowest significant yield during the 2021 and 2022 seasons in the treated plots with spraying by 8.98 and 8.00%, respectively, increase over control plots.ConclusionsThese results indicate that insecticides mixed in sand application are more efficacious against FAW larvae along with yield increase than spraying.

Pea leaf weevil, Sitona lineatus (L.) (Coleoptera: Curculionidae), adult feeding preference and larval development on pulse crop varieties in Montana.

Montana accounts for approximately 45% of US dry pea production and the pea leaf weevil (PLW; Sitona lineatus (L.)) is the most common insect pest in this region. After crop emergence adult PLW feed on the foliage to mature and subsequently mate, and the soil-dwelling larvae feed and develop on the nitrogen-fixing root nodules. Producers commonly apply prophylactic insecticide treatments to the seed at planting as well as one or two post-emergent insecticide sprays to control PLW damage. To develop alternative management strategies based on integrated pest management (IPM), this field study evaluated pulse crops grown in Montana for adult feeding preference and larval development. Ten different field pea varieties, along with two faba bean, lentil and chickpea varieties, were evaluated during the 2020 and 2021 field seasons at the Montana State University Arthur H. Post Agronomy Farm. Significant PLW pest pressure was observed within the research plots during both experimental years. Field pea and faba bean were preferred by the foliage feeding adult stage, with all but one variety averaging 39.2 to 86.3 average notches per plant. The pea variety Lifter was significantly preferred over all other comparisons, averaging 142.4 and 95.0 notches per plant in 2020 and 2021, respectively. Adult PLW feeding on lentil and chickpea was minimal, averaging 3.3 to 8.2 and 0.5 to 1.6 notches per plant, respectively. Numbers of larvae were highest on the roots of pea varieties, a known reproductive host, and almost nil on lentil and chickpea roots. Faba bean is also known as reproductive host, but, unexpectedly, larval populations were also low on the two faba bean varieties. The results from this study provide some limited evidence for alternative IPM strategies for field peas based on host plant tolerance or resistance within the range of varieties tested. Adult preference and larval development of PLW varied between the different pulse crops with field peas and faba beans being the most susceptible and lentils and chickpeas being the least susceptible. Host plant resistance against PLW could provide more sustainable IPM approaches in the future. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Assessing organophosphate insecticide retention in muscle tissues of juvenile common carp fish under acute toxicity tests

Organophosphate insecticide spray poses potential threat of contamination of environmental components their accumulation in aquatic organisms. Although various physiological deficits associated with their exposure in fishes are documented, yet their retention in their edible muscle tissues has been poorly studied. In this context, the study was undertaken to ascertain the bioaccumulation of two organophosphate insecticide compounds (dimethoate and chlorpyrifos) in the muscles of juvenile Cyprinus carpio. The study could provide insight into the risks to human health associated with consuming contaminated fish flesh. The fishes exposed to various concentrations of dimethoate and chlorpyrifos in-vivo for 96 to ascertain the uptake and retention of these insecticides in the muscle. Results indicated that fish muscles accumulated the residues at all the concentrations with the recovery of 2.99% (0.032 ppm) of dimethoate exposed to LC50 concentrations. In contrast, the chlorpyrifos residues were found Below the Detection Level (BDL) in the fishes exposed to LC50 concentrations. The percentage bioaccumulation of dimethoate in fish muscle was 88.10%, and that of chlorpyrifos was BDL. The bio-concentration factor was dose-dependent and increased with increasing doses of both insecticides. The study invites attention to human health risk assessment in the regions where contaminated fish are consumed without scientific supervision.

Compatibility of Metarhizium sp. (M201-NL strain) in Insecticide and Herbicide Mixtures

Field application of Metarhizium to control Oryctes rhinoceros in oil palm plantations may be overlapped with pesticides (insecticide and herbicide) spray. These chemicals may harm the fungus leading to poor virulence. This paper, however, shows that Metarhizium sp. M201-NL strain may react differently against some pesticides tested using poisoning media method. In the first experiment, the growth of mycelium of the Metarhizium sp. was observed in plated media mixed with insecticide. The highest mycelium radial growth was Fipronil 0.15 % (51.9 mm) which was not significantly different compared to the control, without insecticide (52.2 mm). However, suppression of growth of mycelium was observed in other insecticides. The radial growth of mycelium was significantly lower compared to the control if either Ethiprol, Lambdha cyhalothrin or Acephate was applied at 14 DAI. The second separate experiment involved herbicides. It was found that some herbicides did not inhibit the radial growth of mycelium. These include Metsulfuron-methyl 0.098 % (84.0 mm), Metsulfuron-methyl 0.19 % (82.75 mm), Glyphosate 19.6 % (82.5 mm), Glyphosate 9.8 % (81.6 mm) and Metsulfuron-methyl 0.39 % (80.37 mm) which were not significantly different compared to control, without herbicide (86.12 mm) at 21 DAI. In contrast, the growth of mycelium was significantly retarded when Paraquat, Triclopyr, Glyphosate, and 2.4-D was applied separately. Further study was undertaken to observe sporulation and virulence (bioassay) of the treated mycelium. The sporulations of mycelium treated with Fipronil 0.15 % or Metsulfuron-methyl of different concentrations were not statistically different to control. Similar results were also shown from bioassay. The infection rates of O. rhinoceros larva treated with mixtures of Metarhizium sp. spores with either Fipronil or Metsulfuron-methyl were insignificantly different compared to the control.

Impact of 4% Deltamethrin-Impregnated Dog Collars on the Incidence of Human Visceral Leishmaniasis: A Community Intervention Trial in Brazil.

In Brazil, human visceral leishmaniasis (HVL) is caused by the protozoan parasite Leishmania infantum, primarily transmitted by the sand fly Lutzomyia longipalpis, with dogs acting as the main urban reservoir. This study aims to evaluate the effectiveness of 4% deltamethrin-impregnated dog collars (DMC) on HVL incidence. This is a community intervention study carried out from 2012 to 2015 in the municipalities of Araguaína, State of Tocantins, and Montes Claros, State of Minas Gerais, Brazil. Two areas in each were randomly allocated to either (1) culling seropositive dogs + residual insecticide spraying (control area-CA) or (2) culling seropositive dogs + residual insecticide spraying + DMC fitted to dogs every six months for two years (intervention area-IA). Cases of HVL (n = 1202) occurring from 2008 to 2020 were identified from the Brazilian Reportable Diseases Information System and georeferenced to the control and intervention areas. The HVL cases from 2008 to 2012 were considered as occurring in the "pre-intervention" period. Those cases from 2013 to 2016 and from 2017 to 2020 were regarded as occurring in the "intervention" and "post-intervention" periods, respectively. We used a mixed-effects Poisson regression model to estimate the effectiveness of the intervention, comparing the changes from the pre-intervention period to the intervention and post-intervention periods in the control and intervention areas. In Araguaína, there was a statistically significant reduction in the incidence of HVL in both the control and intervention areas, comparing both the intervention and post-intervention periods with the pre-intervention period. The intervention with DMC was significantly associated with a reduction in HVL when comparing the intervention and pre-intervention periods, yielding an effectiveness estimate of the DMC of 27% (IC95% 1-46%, p = 0.045). No differences were observed when comparing the pre- and post-intervention periods (p = 0.827). In Montes Claros, cases reduced in both the control and intervention areas from the pre-intervention period to the intervention period (p = 0.913). In the post-intervention period, the incidence increased in the control area, while cases continued to decrease in the DMC area (p = 0.188). The use of DMC was associated with a reduction of 27% in the incidence of HVL during the period of DMC delivery, indicating that DMC is effective as an additional strategy for controlling visceral leishmaniasis in Brazil. However, no significant reduction associated with DMC was detected after the intervention period, suggesting that a control program based on the large-scale deployment of DMC might have to be maintained for more extended periods without interruption.

Seasonal prevalence of the invasive rusty-spotted longhorn beetle, Apriona swainsoni (Coleoptera: Cerambycidae), adults in Fukushima Prefecture, Japan

AbstractInvasive longhorn beetles are serious pests of tree stands worldwide. The rusty-spotted longhorn beetle, Apriona swainsoni (Hope) (Coleoptera: Cerambycidae: Lamiinae), is native to continental Asia, where it is a significant pest of legume trees. Its invasion into non-native ranges and damage to the local legume tree, Maackia amurensis, were first reported from Fukushima Prefecture, Japan, in 2021. This study investigated the biology of A. swainsoni in relation to adult emergence in Japan. Preliminary observations confirmed that A. swainsoni larvae create planned emergence holes on the host surface in late May. By exploiting these planned emergence holes, the adult emergence period was investigated in a field promenade of M. amurensis during the summer of 2022 and 2023. The researchers plugged the holes and recorded plug removal, resulting in the observation of 60 and 227 putative emergence events in respective years, with the majority occurring in early to mid-July. Further, during the summer of 2022, a periodic field survey of adult emergence was conducted, obtaining eight adults. Furthermore, a supplementary survey using infested logs maintained in a field cage demonstrated that the emergence period does not differ between sexes and the male-to-female ratio is one:one. Our results suggest that control efforts to suppress A. swainsoni adults in the field, such as insecticide spraying, should be prioritized in the relatively short, peak emergence period. This work indicates that the plug survey is useful for detecting the emergence period.

Mathematical Modelling of Malaria Transmission Dynamics with Optimal Control Strategies in Kebri Dehar District, Somali Regional State, Ethiopia

Malaria is an infectious disease caused by the Plasmodium parasite and transmitted between humans through bites of female anopheles mosquito. In this study, we present a mathematical model of malaria transmission dynamics with optimal control. We estimated the basic reproduction number for the infected cases in Kebri Dehar district from September 2011 - June 2015 E.C is . The parameters of the model are estimated by using the confirmed malaria cases of Kebri Dehar district, Ethiopia. We formulated the model for malaria and present its dynamics in details. Initially, we present the basic mathematical results and then show briefly the stability results for the model. Further, we formulate an optimal control problem with control functions and obtain the optimal control characterization. The optimal control problem is solved numerically and the results comprised of controls system for different strategies. The controls such as prevention, treatment and insecticide could use the best role in the disease eradication from the community. Our results suggest that the prevention of humans from the mosquitoes, treatment of infected humans and the insecticide spray on mosquitoes can significantly reduce the infection of malaria and may reduce further spread of infection in the community.

Biophysical factors and agronomic practices associated with Fusarium ear rot and fumonisin contamination of maize in multiple agroecosystems in Ethiopia

AbstractIn Ethiopia, Fusarium ear rot (FER) reduces yield, quality, and safety of maize and negatively impacts the economics of maize growers. However, there is almost no published information on geographic distribution, severity, or causal agents of FER in Ethiopia or levels of preharvest fumonisin contamination, biophysical factors, and agronomic practices associated with FER. Therefore, we surveyed 480 agricultural fields located in 10 Ethiopian zones to assess the incidence and severity of FER as well as agricultural practices and biophysical factors associated with each field. We also determined the concentration of fumonisin in samples taken from the fields. Results revealed that FER was prevalent with varied disease intensity and yield loss levels among the assessed zones. The highest percent severity index (PSI) was recorded in Mirab Wellega (33.2%), with a correspondingly maximum estimated mean grain yield loss of 13.6%, while the minimum disease severity 11.3% and yield loss 5.4% were recorded from the Ilubabor zone. Fumonisins (FB1, FB2, FB3, and FB4) were detected in 98% of the samples, and the levels ranged from 5 to 7517 μg kg−1 (mean, 540 μg kg−1 and median 82.4 μg kg−1). The mean fumonisin contamination of 1524.4, 1316.8, 744.5, and 742.6 μg kg−1 was recorded for Mirab Welega, Misraq Wellega, Assosa, and Hawassa zones, respectively. In total, about 11.3% of the maize samples exceeded the maximum tolerable total fumonisin limit set by the European Union in maize flour (>1000 μg kg−1) and are not suitable for human consumption. Disease severity highly significantly (p < 0.0001) correlated with biophysical factors such as insect infestation (r = 0.60, p < 0.0001) and weed infestation (r = 0.64, p < 0.0001) and agronomic practices such as nitrogen phosphorus sulfur fertilizer application rate (r = −0.39, p < 0.0001) and insecticide spray frequency (r = −0.55, p < 0.0001). Other agronomic practices such as earlier or later sowing date and inter‐cropping systems significantly reduced (p < 0.001) FER incidence, PSI, and the associated grain yield loss. There was significant (p < 0.0001) variation among maize cultivars currently under production in reaction against FER disease intensity. Moreover, the result of the present study attests a strong positive association (p < 0.001) between disease intensity and maize fumonisin concentrations. Generally, the study revealed a wider distribution of FER and fumonisin contamination of maize in the southwest major maize‐growing belts of Ethiopia. Thus, appropriate integrated pre‐harvest ear rot management strategies including the use of resistant cultivars and suitable agronomic practices are recommended for the management of FER and the associated mycotoxins in Ethiopia.

Mathematical Modelling of Host-Pest Interaction in the Presence of Insecticides and Resistance: A Case of Fall Armyworm

Several pest management programs have been developed to control rising agricultural pest populations. However, the challenge of rapid evolution and pest resistance towards control measures continues to cause high production losses to maize farmers in Africa. Few models have attempted to address the issue of fall armyworm (FAW) but have barely incorporated the effect of insecticide resistance. Models with resistance would help predict the dynamics of the FAW population, thus mitigating losses. The main objectives of this work were to develop, analyze, and numerically simulate a susceptible-infected deterministic mathematical model expressing the FAW-maize interaction and population dynamics under insecticidal sprays and resistance FAW larvae. Three model steady states are established. Their local stability is conducted using either the eigenvalue or the Routh–Hurwitz stability criteria, and their global stability is analyzed using either the Castillo–Chavez, Perron eigenvector, or the Lyapunov methods. An expression for the basic reproduction number R0, together with the sensitivity analysis of its parameter values, is provided. Numerical analysis is conducted on various model parameter values. The results established all the model steady states to be locally and globally asymptotically stable at R0≤1. Also, resistance ω increased the infection rates by increasing the FAW larvae survival rate λ and reducing the insecticidal efficacy δR and δN. This work informs the agriculturists and policymakers on pest control with the best ways to use insecticides to minimize pest resistance and enhance efficacy in production. Pest control measures should be modified to lower the FAW survival rate and all model parameters contributing to resistance formation by FAW larvae to minimize FAW-host interaction, thus reducing crop damage.

Cost–Benefit Analysis of Monitoring Insect Pests and Aerial Spraying of Insecticides: The Case of Protecting Pine Forests against Dendrolimus pini in Brandenburg (Germany)

Monitoring of insect pests and aerial spraying of insecticides have proven to be effective in protecting forests against needle-feeding insect pests. However, the literature on the economic viability of insect monitoring and aerial spraying of insecticides is scant. This research conducts a cost–benefit analysis of monitoring insect pests and use of insecticides for 5600 ha of managed pine forests. The case studied is the mass outbreak of the pine tree lappet moth (Dendrolimus pini L.) in Brandenburg (Germany) in 2014. Costs were estimated based on information from standardized questionnaires and semi-structured expert interviews. Benefits were analyzed by comparing the loss of revenue due to D. pini with the costs of insect monitoring and insecticide spraying in two scenarios of pine production (with protection vs. without protection). The results show that monitoring D. pini and aerial spraying of insecticides are economically beneficial to forest owners. The total net present value (NPV) of protection was about EUR 1965 ha−1 at a discount rate of 0% and the benefit–cost ratio (BCR) was about 22.14. NPVs and BCRs per hectare were highest for protecting stands with high site index and stands in the age class of 20–39 years. Sensitivity analyses revealed that NPV results are more sensitive to changes in timber prices than to changes in protection costs. The authors conclude that monitoring insect pests and aerial spraying of insecticides are economically viable options to protect forests against needle-feeding insect pests.

Pressure from insect-resistant maize on protected butterflies and moths.

Intensification in agriculture affects many insect species, including butterflies. Insect-resistant crops, such as Bt (Bacillus thuringiensis) maize, which produces a toxin active against Lepidoptera, are an alternative to insecticide sprays. Genetically modified crops are regulated in most countries and require an environmental risk assessment. In the European Union, such assessments include the use of simulation models to predict the effects on nontarget Lepidoptera (NTL). To support the assessment of protected NTL, we extended an individual-based, stochastic, spatially explicit mathematical model (LepiX) to include a wider range of exposure scenarios, a species-sensitivity distribution, and an option for repeated exposure of individuals. We applied the model to transgenic maize DAS-1507, which expresses a high concentration of Bt toxin in pollen that may be consumed by NTL larvae on their host plants nearby. Even in the most conservative scenario without repeated exposure, mortality estimates for highly sensitive species ranged from 41% to 6% at distances of 10-1000 m from the nearest maize field. Repeated exposure can cause additional mortality and thus is relevant for the overall risk assessment. Uncertainties in both exposure and ecotoxicity estimates strongly influenced the predicted mortalities. Care should be taken to include these uncertainties in the model scenarios used for decision-making. In accordance with other modeling results, our simulations demonstrated that mean mortality may not be safe for protected species. With its high pollen expression, DAS-1507 maize may pose risks to sensitive and protected butterfly and moth species that may be difficult to manage. High expression of Bt toxin in pollen is unnecessary for controlling target pests. Consequently, we suggest that Bt maize with high pollen expression not be cultivated in regions where protected butterflies are to be conserved.