Semi-field Trials Research Articles

Edible Plant Extracts against Aedes aegypti and Validation of a Piper nigrum L. Ethanolic Extract as a Natural Insecticide.

The Aedes aegypti mosquito significantly impacts public health, with vector control remaining the most efficient means of reducing the number of arboviral disease cases. This study screened the larvicidal and pupicidal activity of common edible plant extracts. Piper nigrum L. (black pepper) extract production was optimized using accelerated solvent extraction (ASE) and validated following regulatory requirements using HPLC-PDA analytical methodology to quantify its major component-piperine. Larvicidal activity was determined for the standardized P. nigrum fruit ethanol extract (LC50 1.1 µg/mL) and piperine standard (LC50 19.0 µg/mL). Furthermore, 9-day residual activity was determined for the extract (4 µg/mL) and piperine (60 µg/mL), with daily piperine quantification. Semi-field trials of solid extract formulations demonstrated 24-day activity against Ae. aegypti larvae. Thus, the standardized P. nigrum extract emerges as a potential candidate for insecticide development to control the arboviral vector.

Efficacy of Conventional and Organic Insecticides against Scaphoideus titanus: Field and Semi-Field Trials

Scaphoideus titanus is the main vector of phytoplasmas associated with Flavescence dorée (FD), one of the most serious threats to viticulture in many European countries. To minimize the spread of this disease, mandatory control measures against S. titanus were decided in Europe. In the 1990s, the repeated application of insecticides (mainly organophosphates) proved to be an effective measure to control the vector and the related disease in north-eastern Italy. These insecticides and most of the neonicotinoids were recently banned from European viticulture. Serious FD issues detected in the recent years in northern Italy could be related to the use of less effective insecticides. Trials aimed at evaluating the efficacy of the most used conventional and organic insecticides in the control of S. titanus have been performed in semi-field and field conditions to test this hypothesis. In efficacy trials, carried out in four vineyards, etofenprox and deltamethrin proved to be the best conventional insecticides, while pyrethrins were the most impactful among organic insecticides. Insecticide residual activity was evaluated in semi-field and field conditions. Acrinathrin showed the most significant residual effects in both conditions. In semi-field trials, most of the pyrethroids were associated with good results in terms of residual activity. However, these effects declined in field conditions, probably due to high temperatures. Organic insecticides showed poor results in terms of residual efficacy. Implications of these results in the context of Integrated Pest Management in conventional and organic viticulture are discussed.

Integrated Biological and Chemical Control against the Maize Late Wilt Agent Magnaporthiopsis maydis

Today’s fungal plant disease control efforts tend towards environmentally friendly and reduced chemical applications. While traditional broad-spectrum fungicides provide efficient protection to many field crops, they pose a risk to the soil’s beneficial microflora and a potential health hazard. Moreover, their intensive use often evokes the appearance of resistant pathogens. On the other hand, biocontrol agents such as Trichoderma spp. provide a green solution but often cannot shield the plants from aggressive disease outbreaks. Integrated biological and chemical disease control can combine the benefits of both methods while reducing their drawbacks. In the current study, such a bio-chemo approach was developed and evaluated for the first time against the maize late wilt pathogen, Magnaporthiopsis maydis. Combinations of four Trichoderma species and Azoxystrobin were tested, starting with an in vitro seed assay, then a growth room sprouts trial, and finally a semi-field, full-season pot experiment. In the plates assay, all four Trichoderma species, Trichoderma sp. O.Y. (T14707), T. longibrachiatum (T7407), T. asperellum (P1) and T. asperelloides (T203), grew (but with some delay) in the presence of Azoxystrobin minimal inhibition concentration (0.005 mg/L). The latter two species provided high protection to sprouts in the growth room and to potted plants throughout a full season in a semi-field open-enclosure trial. At harvest, the P1 and T203 bio-shielding exhibited the best parameters (statistically significant) in plant growth promotion, yield increase and late wilt protection (up to 29% health recovery and 94% pathogen suppression tracked by real-time PCR). When applied alone, the Azoxystrobin treatment provided minor (insignificant) protection. Adding this fungicide to Trichoderma spp. resulted in similar (statistically equal) results to their sole application. Still, the fact that Azoxystrobin is harmless to the beneficial Trichoderma species over a complete semi-field condition is a great opening stage for carrying out follow-up studies validating the integrated control in a commercial field situation challenged with acute disease stress.

Attractant Activity of Host-Related Chemical Blends on the Poultry Red Mite at Different Spatial Scales

Many blood-feeding arthropods use volatile organic compounds (VOCs) to detect their vertebrate hosts. The role of chemical interactions in mediating the behavior of hematophagous insects and ticks has been investigated before but remains poorly understood in hematophagous mesostigmatic mites. The poultry red mite Dermanyssus gallinae is an obligatory blood-sucking mesostigmatic mite that feeds on birds and causes damage in poultry farms. We characterized the attractive response of D. gallinae to candidate VOCs previously reported from the odor emitted by living hens. We performed in-vitro choice-test bioassays as well as semi-field and field trials using baited and unbaited traps, in the presence and absence of hens. Among different tested combinations of VOCs, a blend of 5 VOCs (mix1.0) was significantly attractive to our reference population of D. gallinae in vitro, whereas the same individual compounds tested alone were not attractive. Ammonia was attractive on its own and increased the mix1.0 attractiveness. The attractiveness of mix1.0 was confirmed at 'natural' spatial scales in the absence of hens both at the lab and on the farm that provided the reference population. The presence of hens inhibited the mix1.0 attractiveness. The attractive power of mix1.0 was not found in other farms. This research is an important step to advance our understanding of host-parasite interactions in hematophagous mesostigmatic mites and paves the way for developing alternative control tools against D. gallinae by interfering with chemical interactions. Moreover, it underlines the importance of assessing kairomonal activity on different pest populations when developing attract-and-kill systems.

Long-term storage does not affect the infectivity of entomopathogenic nematodes on insect hosts.

Entomopathogenic nematodes (EPNs) are effective biopesticides used in insect control. There are several formulations of entomopathogenic nematodes which are commercially available, but their popularity is low because the requirement of periodic release of stored entomopathogenic nematodes in field has reduced infectivity and is a constraint in large-scale repeated application of entomopathogenic nematodes in field. So, in order to overcome this impediment, the current study focuses on storage of entomopathogenic nematodes for a longer period of time using encapsulating beads. In this study, three EPNs, namely, Steinernema carpocapsae, Steinernema monticolum, and Rhabditis blumi, were encapsulated with Arabic gum and sodium alginate gel beads at different concentrations. Bio-efficacy of stored EPNs at different concentrations (50, 100, 200, 500, and 1000 infective juveniles (IJs)) in varying time intervals of 3, 6, 9, and 12weeks were tested against Culex quinquefasciatus larvae. The results show that, after 3weeks of storage, these entomopathogenic nematode species showed survival up to 96%, and in 12-week storage, survival rate was 50%. The virulence of the progeny that emerged from these stored entomopathogenic nematodes was similar to the fresh infective juveniles. The results of the present study show that Arabic gum-sodium alginate combination is a promising approach toward storing entomopathogenic nematodes. Furthermore, semi-field trials showed 70-90% larval mortality at a concentration of 3000 IJs (encapsulated and stored entomopathogenic nematodes in S. monticolum, S. carpocapsae, and R. blumi) on C. quinquefasciatus larvae. KEY POINTS: • Increased survival of stored EPNs (S. carpocapsae, S. monticolum, and R. blumi) in encapsulated gel using Arabic gum, sodium alginate, and yeast cells was assessed. • The efficacy was greater in stored EPNs at different concentrations from 3 to 12 weeks. • Semi-field trials of stored encapsulated EPNs are efficient in mosquito larval control.

Control of spotted wing drosophila (Drosophila suzukii) in sweet cherry and raspberry using bait sprays

Spotted wing drosophila (Drosophila suzukii Matsumura) is a major pest of fruit crops with global significance. Effective control is reliant on uniformly spraying insecticides on all crop foliage. To encourage pest attraction and ingestion of insecticides, phagostimulant baits can be employed in ‘attract and kill’ strategies. In semi-field trials, we compared (1) full-field foliar sprays of two insecticides spinosad and cyantraniliprole, with (2) reduced [40%] and (3) low [4%] rates of the insecticides to control D. suzukii and reduce insecticide residues in fruit in sweet cherry and raspberry. The low rates of the insecticides were also combined with baits, (4) Combi-protec, a proprietary mixture of plant extracts, proteins and sugars and (5) molasses; treatment (6) was an untreated control. In both crops, when combined with baits, low rates of insecticides gave comparable control of D. suzukii in fruits compared with the full-rate sprays in most cases, and D. suzukii was significantly lower in these treatments compared with the untreated controls. Crop spray coverage was eight and thirty times higher in the full-rate applications compared with the bait and low-rate sprays, in raspberry and cherry, respectively. The reduction in applied insecticide was achieved by lower concentrations and volumes and a narrower band spray applied across the middle of the crop canopy. Spinosad and cyantraniliprole residues were detected in cherries taken from trees sprayed with full-rate applications but not in fruit from trees given the low rates of insecticides with bait. This study demonstrates that bait sprays can be effectively employed on crops with complex canopies for D. suzukii control.

Exploring plant volatile-mediated interactions between native and introduced plants and insects

In invasion scenarios, native and introduced species co-occur creating new interactions and modifying existing ones. Many plant–plant and plant–insect interactions are mediated by volatile organic compounds (VOCs), however, these have seldom been studied in an invasion context. To fill this knowledge gap, we explored some interactions mediated by VOCs between native and introduced plants and insects in a New Zealand system. We investigated whether a native plant, Leptospermum scoparium (mānuka), changes its volatile profile when grown adjacent to two European introduced plants, Calluna vulgaris (heather) and Cytisus scoparius (Scotch broom), in a semi-field trial using potted plants without above- or below-ground physical contact. We also investigated the influence of plant cues on the host-searching behaviour of two beetles, the native Pyronota festiva (mānuka beetle), and the introduced biocontrol agent Lochmaea suturalis (heather beetle), by offering them their host-plant and non-host volatiles versus clean air, and their combination in a Y-tube olfactometer. As a follow-up, we performed preference/feeding tests in Petri dishes with fresh plant material. Results of the semi-field experiment show a significant reduction in green leaf volatiles, sesquiterpenes and total volatile emissions by mānuka plants neighbouring heather. In the Y-tube assays, the native beetle P. festiva performed poorly in discriminating between host and non-host plants based on plant volatile cues only. However, it performed relatively well in the Petri dish tests, where other cues (i.e., visual, gustatory or tactile) were present. In contrast, the introduced beetle L. suturalis showed high host-specificity in both Y-tube and Petri dish assays. This study illustrates the importance of VOCs in mediating interactions between introduced and native species, suggesting that invasive plants can disrupt native plants’ communication and affect the host-searching behaviour of native insects. It also reinforces the relevance of regular host testing on introduced weed biocontrol agents to avoid unwanted host shifts or host-range expansion.

Development and evaluation of an efficient and real-time monitoring system for the vector mosquitoes, Aedes albopictus and Culex quinquefasciatus.

BackgroundThe surveillance of vector mosquitoes is essential for prevention and control of mosquito-borne diseases. In this study, we developed an internet-based vector mosquito monitor, MS-300, and evaluated its efficiency for the capture of the important vector mosquitoes, Aedes albopictus and Culex quinquefasciatus, in laboratory and field trials.Methodology/Principal findingsThe linear sizes of adult Ae. albopictus and Cx. quinquefasciatus were measured and an infrared window was designed based on these data. A device to specifically attract these two species and automatically transmit the number of captured mosquitoes to the internet was developed. The efficiency of the device in capturing the two species was tested in laboratory, semi-field and open field trials. The efficiency results for MS-300 for catching and identifying Ae. albopictus in laboratory mosquito-net cages were 98.5% and 99.3%, and 95.8% and 98.6%, respectively, for Cx. quinquefasciatus. In a wire-gauze screened house in semi-field trials, the efficiencies of MS-300 baited with a lure in catching Ae. albopictus and Cx. quinquefasciatus were 54.2% and 51.3%, respectively, which were significantly higher than 4% and 4.2% without the lure. The real-time monitoring data revealed two daily activity peaks for Ae. albopictus (8:00–10:00 and 17:00–19:00), and one peak for Cx. quinquefasciatus (20:00–24:00). During a 98-day surveillance trial in the field, totals of 1,118 Ae. albopictus and 2,302 Cx. quinquefasciatus were captured by MS-300. There is a close correlation between the number of captured mosquitoes and the temperature in the field, and a positive correlation in the species composition of the captured samples among the mosquitoes using MS-300, BioGents Sentinel traps and human landing catches.Conclusions/SignificanceThe data support the conclusion that MS-300 can specifically and efficiently capture Ae. albopictus and Cx. quinquefasciatus, and monitor their density automatically in real-time. Therefore, MS-300 has potential for use as a surveillance tool for prevention and control of vector mosquitoes.

Evaluation of Nanoemulsion of Eucalyptus globulus Oil as Potent Botanical Larvicide against Malaria Vector, Anopheles stephensi and West Nile Vector, Culex pipiens Under Laboratory and Semi-Field Conditions.

Due to undesired environmental impact of insecticides as well as resistant of vectors to them, the development of organic and natural insecticides has been more considered. In the current study, we developed nanoemulsion of eucalyptus and investigated lavicidal activity of it against malaria vector, Anopheles stephensi and Culex pipiens under laboratory as well as semi-field conditions. An optimized nanoemulsion was prepared by mixing Eucalyptus oil, Tween 80 and ethanol at ratio of 1:2:1.5 in distilled water, then, stirred for 20 minutes at room temperature. The product was then used for bioassay tests against 3-4th instar larvae of Anopheles stephensi as well as Culex pipiens. Furthermore, a semi-field trial was carried out to evaluate larvicidal activity of nanoemulsion of eucalyptus. Nanoemulsion of eucalyptus showed significantly high lavicidal activity comparing with bulk eucalyptus essential oil. The LC50 and LC90 value of nanoemulsion against An. stephensi were 111.0 and 180.8 ppm respectively and 29.5 and 73.7 ppm for Cx. pipiens, respectively. In the semi field condition, the Nanoemulsion of eucalyptus decreased 1-2nd instar larval density of Culicines and Anophelines to 90.1% and 85.2%, respectively. The nano formulation of eucalyptus oil showed high larvicidal activity. Therefore, nanoemulsion of eucalyptus oil can be used as an eco-friendly larvicide against mosquitoes.

Anti-mosquito properties of Pelargonium roseum (Geraniaceae) and Juniperus virginiana (Cupressaceae) essential oils against dominant malaria vectors in Africa

BackgroundMore than 90% of malaria cases occur in Africa where the disease is transmitted by Anopheles gambiae and Anopheles arabiensis. This study evaluated the anti-mosquito properties of Juniperus virginiana (JVO) and Pelargonium roseum (PRO) essential oils (EOs) against larvae and adults of An. gambiae sensu lato (s.l.) from East Africa in laboratory and semi-field conditions.MethodsEOs was extracted from the aerial green parts of Asian herbs by hydrodistillation. Their constituents were characterized by gas chromatography-mass spectrometry (GC-MS). Larvicidal activities of JVO, PRO, and PRO components [citronellol (CO), linalool (LO), and geraniol (GO)] were investigated against An. gambiae sensu stricto (s.s.). The percentage of knockdown effects and mortality rates of all oils were also evaluated in the adults of susceptible An. gambiae s.s. and permethrin-resistant An. arabiensis.ResultsGC-MS analyses identified major constituents of JVO (sabinene, dl-limonene, β-myrcene, bornyl acetate, and terpinen-4-ol) and PRO (citronellol, citronellyl formate, L-menthone, linalool, and geraniol). Oils showed higher larvicidal activity in the laboratory than semi-field trials. The LC50 values for JVO/PRO were computed as 10.82–2.89/7.13–0.9 ppm and 10.75–9.06/13.63–8.98 ppm in laboratory and semi-field environments, respectively at exposure time of 24–72 h. The percentage of knockdown effects of the oils were also greater in An. gambiae s.s. than in An. arabiensis. Filter papers impregnated with JVO (100 ppm) and PRO (25 ppm) displayed 100% mortality rates for An. gambiae s.s. and 3.75% and 90% mortality rates, for An. arabiensis populations, respectively. Each component of CO, LO, and GO exhibited 98.13%, 97.81%, and 87.5%, respectively, and a mixture of the PRO components indicated 94.69% adult mortality to permethrin-resistant An. arabiensis.ConclusionsThe findings of this study show that PRO and its main constituents, compared to JVO, have higher anti-mosquito properties in terms of larvicidal, knockdown, and mortality when applied against susceptible laboratory and resistant wild populations of An. gambiae s.l. Consequently, these oils have the potential for the development of new, efficient, safe, and affordable agents for mosquito control.

The effects of a naturalized weed, Lepidium virginicum, on the development and behaviors of the diamondback moth and its natural enemies in Hawaii

Weeds can play numerous important roles in pest suppression in agroecosystems. These include influencing the host searching behaviors of herbivorous pests and their natural enemies and providing shelter and alternative food sources for predators and parasitoids. Virginia pepperweed, Lepidium virginicum, is a widespread naturalized weed in Hawaii and can often be found in and around agricultural fields. It is a member of the Brassicaceae family and is a known host plant of the diamondback moth (DBM), Plutella xylostella. In this study, we found that DBM preferentially oviposit on L. virginicum (vegetative stage) when presented with a choice of cabbage. Using laboratory and semi-field trials, we investigated the responses of the natural enemies of DBM to the vegetative stage of L. virginicum and cabbage infested with DBM larvae. When DBM-infested plants were placed in the field for 48 h, more spiders and parasitized DBM larvae were recovered from the L. virginicum than from cabbage. In laboratory choice experiments, we demonstrated that the dominant DBM parasitoid species in Hawaii (Cotesia vestalis) oviposited in more host larvae on L. virginicum compared to cabbage, though this had no particular benefit for parasitoid development (adult size and sex ratio). Our findings suggest that the presence of L. virginicum in cabbage agroecosystems could be beneficial by serving to divert DBM oviposition away from cabbage and promoting predator and parasitoid populations.

Appraising the role of anti-thermal activity of beta-cyclodextrin on selective insecticides against Thrips tabaci (Thysanoptera: Thripidae)

Abstract Evaluation studies investigated the leverage effects of beta-cyclodextrin (β-CD) on the long-termed toxicity of cypermethrin 25% EC, sulfoxaflor 24% SC, acetamiprid 20% SL and chlorfenapyr 24% SC against adults of Thrips tabaci laboratory strain (Thysanoptera: Thripidae) (Lindeman, 1889) from 8 up to 40 °C. Laboratory studies showed no toxicity for β-CD alone at all tested concentrations. Concentrations of β-CD at 1.25 and 2.50 gm L−1 had potent leverage effects on the LC50s of cypermethrin within 30–35 °C and sulfuxoflor at 40 °C. β-CD at 0.5 gm L−1 had no leverage effect on tested insecticides. All the tested concentrations of β-CD decreased the toxicity of acetamiprid. Semi-field trials (≥28 °C) along 12 days declared that β-CD (equivalent to 1.25 gm L−1) increased the overall mean mortality percentages of 0.5 FRs of cypermethrin (73.08%) and sulfoxaflor (54.74%) compared to their 0.5 FRs alone of 63.70 and 44.30%, respectively in season 2020. While in season 2021, only cypermethrin at 0.5 FR + β-CD (74.45%) surpassed its 0.5FR (61.83%). Lethal times (LT50) values in semi-field trials showed a prolonged residual toxicity periods for the 0.5 FRs of cypermethrin + β-CD (8.58 days) and sulfoxaflor + β-CD (4.80 days) compared to their 0.5 FRs of 6.65 and 3.24 days, respectively in season, 2020. Furthermore, LT50 values of the 0.5 FRs of cypermethrin + β-CD (9.02 days) and sulfoxaflor + β-CD (7.34 days) exceeded their 0.5 FRs of 6.24 and 4.07 days, respectively in 2021. Thus β-CD could realize leverage efficacy and longer-termed toxicity for cypermethrin and sulfoxaflor in high temperatures.

Chemical Compounds Emitted from Mentha spicata Repel Aromia bungii Females.

Simple SummaryAromia bungii (Faldermann) (Coleoptera: Cerambycidae) is a serious wood borer of stone fruit trees. Native to parts of Asia and Russia, this beetle recently invaded Germany, Italy, and Japan, causing enormous economic losses. Repellents are effective and sustainable control methods of insect pests. In this study, we identified the A. bungii female-repellency ingredients from Mentha spicata: myrcene, (S)-(+)-carvone, (E)-β-caryophyllene, and borneol, as well as their recommended quantities for use. These results contribute to research on repellents that prevent infestation and damage caused by A. bungii.Aromia bungii (Coleoptera: Cerambycidae) is an economically important wood-boring insect pest of stone fruit trees, particularly Prunus persica, in China. It has entered Japan and several European countries as an invasive species in recent years. It is difficult to control because of the cryptic feeding behaviour of larvae beneath the bark. Identification of repellent constituents from non-host plants has potential for use in management strategies against this beetle. Mentha spicata is cultivated extensively in Hebei Province (China) as a medicinal plant. Firstly, antennal responses of female A. bungii to M. spicata volatiles were evaluated by coupled gas chromatography-electroantennograms (GC-EAD), and then the EAD-active components were tested in semi-field trials. The results showed that A. bungii females were significantly repelled by myrcene, (S)-(+)-carvone, (E)-β-caryophyllene, and borneol compared with the control. The presence of myrcene (100 µL; 90% purity), (S)-(+)-carvone (200 µL; 96% purity), (E)-β-caryophyllene (500 µL; 98.5% purity), and borneol (800 µL; 80% purity) significantly reduced the perching rates of A. bungii females on both peach logs and leaves. Considering cost and commercial availability, we suggest that myrcene, (S)-(+)-carvone, and (E)-β-caryophyllene could be promising repellents against A. bungii females in the field.

Half Friend, Half Enemy? Comparative Phytophagy between Two Dicyphini Species (Hemiptera: Miridae).

Simple SummaryOmnivorous predators, such as some mirids, are important biological control agents in several vegetable crops since they are generalists and can survive in the crop in the absence of prey. Nesidiocoris tenuis is a mirid used worldwide and its phytophagy is well known, which is not the case for the Palearctic Dicyphus cerastii. To use the latter in biological control it is crucial to evaluate the damage it causes to plants. We compared these two mirid species, under laboratory and semi-field conditions, regarding the damage they caused to plants and fruit, and their location on the plant versus on the fruit. Both species produced plant damage (scar punctures on leaves and necrotic patches on petioles) and caused flower abortion, at a similar level, however, only N. tenuis produced necrotic rings. Overall, N. tenuis females produced more damage to tomato fruit than D. cerastii. There was an increased frequency of D. cerastii females found on the plants over time, which did not happen with N. tenuis. Our results suggested that although D. cerastii caused less damage to tomato fruit than N. tenuis, it did feed on the fruit and could cause floral abortion, which requires field evaluation and caution in its use.Despite their importance as biological control agents, zoophytophagous dicyphine mirids can produce economically important damage. We evaluated the phytophagy and potential impact on tomato plants of Dicyphus cerastii and Nesidiocoris tenuis. We developed a study in three parts: (i) a semi-field trial to characterize the type of plant damage produced by these species on caged tomato plants; (ii) a laboratory experiment to assess the effect of fruit ripeness, mirid age, and prey availability on feeding injuries on fruit; and (iii) a laboratory assay to compare the position of both species on either fruit or plants, over time. Both species produced plant damage, however, although both species produced scar punctures on leaves and necrotic patches on petioles, only N. tenuis produced necrotic rings. Both species caused flower abortion at a similar level. Overall, N. tenuis females produced more damage to tomato fruit than D. cerastii. There was an increased frequency of D. cerastii females found on the plants over time, which did not happen with N. tenuis. Our results suggested that, although D. cerastii caused less damage to fruit than N. tenuis, it still fed on them and could cause floral abortion, which requires field evaluation and caution in its use in biological control strategies.

Lab-scale characterization and semi-field trials of Wolbachia Strain wAlbB in a Taiwan Wolbachia introgressed Ae. aegypti strain.

Dengue fever is one of the most severe viral diseases transmitted by Aedes mosquitoes, with traditional approaches of disease control proving insufficient to prevent significant disease burden. Release of Wolbachia-transinfected mosquitoes offers a promising alternative control methodologies; Wolbachia-transinfected female Aedes aegypti demonstrate reduced dengue virus transmission, whilst Wolbachia-transinfected males cause zygotic lethality when crossed with uninfected females, providing a method for suppressing mosquito populations. Although highly promising, the delicate nature of population control strategies and differences between local species populations means that controlled releases of Wolbachia-transinfected mosquitoes cannot be performed without extensive testing on specific local Ae. aegypti populations. In order to investigate the potential for using Wolbachia to suppress local Ae. aegypti populations in Taiwan, we performed lab-based and semi-field fitness trials. We first transinfected the Wolbachia strain wAlbB into a local Ae. aegypti population (wAlbB-Tw) and found no significant changes in lifespan, fecundity and fertility when compared to controls. In the laboratory, we found that as the proportion of released male mosquitoes carrying Wolbachia was increased, population suppression could reach up to 100%. Equivalent experiments in semi-field experiments found suppression rates of up to 70%. The release of different ratios of wAlbB-Tw males in the semi-field system provided an estimate of the optimal size of male releases. Our results indicate that wAlbB-Tw has significant potential for use in vector control strategies aimed at Ae. aegypti population suppression in Taiwan. Open field release trials are now necessary to confirm that wAlbB-Tw mediated suppression is feasible in natural environments.

Integrated control of Aedes albopictus in Southwest Germany supported by the Sterile Insect Technique

BackgroundThe invasive species Aedes albopictus, commonly known as the Asian tiger mosquito, has undergone extreme range expansion by means of steady introductions as blind passengers in vehicles traveling from the Mediterranean to south-west Germany. The more than 25 established populations in the State of Baden-Württemberg, Palatine and Hesse (south-west Germany) have become a major nuisance and public health threat. Aedes albopictus deserves special attention as a vector of arboviruses, including dengue, chikungunya and Zika viruses. In Germany, Ae. albopictus control programs are implemented by local communities under the auspices of health departments and regulatory offices.MethodsThe control strategy comprised three pillars: (i) community participation (CP) based on the elimination of breeding sites or improved environmental sanitation, using fizzy tablets based on Bacillus thuringiensis israelensis (fizzy Bti tablets; Culinex® Tab plus); (ii) door-to-door (DtD) control by trained staff through the application of high doses of a water-dispersible Bti granular formulation (Vectobac® WG) aimed at achieving a long-lasting killing effect; and (iii) implementation of the sterile insect technique (SIT) to eliminate remaining Ae. albopictus populations. Prior to initiating large-scale city-wide treatments on a routine basis, the efficacy of the three elements was evaluated in laboratory and semi-field trials. Special emphasis was given to the mass release of sterile Ae. albopictus males.ResultsMore than 60% of the local residents actively participated in the first pillar (CP) of the large-scale control program. The most effective element of the program was found to be the DtD intervention, including the application of Vectobac® WG (3000 ITU/mg) to potential breeding sites (10 g per rainwater container, maximum of 200 l = maximum of approx. 150,000 ITU/l, and 2.5 g per container < 50 l) with a persistence of at least 3 weeks. In Ludwigshafen, larval source management resulted in a Container Index for Ae. albopictus of < 1% in 2020 compared to 10.9% in 2019. The mean number of Aedes eggs per ovitrap per 2 weeks was 4.4 in Ludwigshafen, 18.2 in Metzgergrün (Freiburg) (SIT area) and 22.4 in the control area in Gartenstadt (Freiburg). The strong reduction of the Ae. albopictus population by Bti application was followed by weekly releases of 1013 (Ludwigshafen) and 2320 (Freiburg) sterile Ae. albopictus males per hectare from May until October, resulting in a high percentage of sterile eggs. In the trial areas of Ludwigshafen and Frieburg, egg sterility reached 84.7 ± 12.5% and 62.7 ± 25.8%, respectively; in comparison, the natural sterility in the control area was 14.6 ± 7.3%. The field results were in line with data obtained in cage tests under laboratory conditions where sterility rates were 87.5 ± 9.2% after wild females mated with sterile males; in comparison, the sterility of eggs laid by females mated with unirradiated males was only 3.3 ± 2.8%. The overall egg sterility of about 84% in Ludwigshafen indicates that our goal to almost eradicate the Ae. albopictus population could be achieved. The time for inspection and treatment of a single property ranged from 19 to 26 min depending on the experience of the team and costs 6–8 euros per property.ConclusionsIt is shown that an integrated control program based on a strict monitoring scheme can be most effective when it comprises three components, namely CP, DtD intervention that includes long-lasting Bti-larviciding to strongly reduce Ae. albopictus populations and SIT to reduce the remaining Ae. albopictus population to a minimum or even to eradicate it. The combined use of Bti and SIT is the most effective and selective tool against Ae. albopictus, one of the most dangerous mosquito vector species.Graphical

Novel pyriproxyfen based treatment for Aedes breeding control through a long-lasting formulation: Laboratory and field trials in Western Maharashtra, India.

There is a need to evaluate novel techniques for dengue control in India. Several formulations of pyriproxyfen have been assessed for efficacy and duration of action. Pyriproxyfen is also used as a microencapsulated ready-to-use formulation against the Aedes vector. We evaluated a novel pyriproxyfen-based microencapsulated formulation. This slow-release, ready-to-use aqueous spray is a larvicidal formulation, and we assessed its efficacy and residual action through laboratory and semi-field trials against Aedes immature stages. The study was carried out as per the guidelines for laboratory and field/small-scale field testing of mosquito larvicides by the World Health Organization. The evaluation was conducted in laboratory and semi-field conditions from August to December 2018. We tested the novel formulation on three materials (plastic, ceramic, and enamel) in the laboratory for its action as an antilarval. Four containers of each kind were sprayed with the formulation and kept as replicates. Four controls were used in the laboratory trials - 120 larvae (third instar) were introduced in the replicates and the controls each. Readings were taken daily till complete adult emergence or larval and pupal mortality. In the semi-field trials, we applied this formulation to the inside of desert coolers and observed larvicidal and pupicidal activity over five months. Data is presented in numbers and percentages, along with mean and standard deviation. Adult emergence and Emergence Inhibition was calculated. There was 100% adult emergence inhibition amongst the exposed larvae in the treated containers in the laboratory trials. In the untreated controls, adult emergence ranged from 80-95% in all types of containers. In the semifield trials, Inhibition Emergence was 100% in the treated desert coolers during the five months of the study period. This advancement in insecticide formulation technology promises to make dengue control more effective and efficient.

Laboratory and semi-field evaluation of the efficacy of Bacillus thuringiensis var. israelensis (Bactivec®) and Bacillus sphaericus (Griselesf®) for control of mosquito vectors in northeastern Tanzania

Bacterial larvicides Bacillus thuringiensis var. israelensis (Bti) and Bacillus sphaericus (Bs) have been used extensively for mosquito control. However, their efficacy varies greatly mainly due to factors related to target mosquitoes, larval habitat conditions, and inherent larvicide properties. We evaluated the efficacy of Bti (Bactivec®) and Bs (Griselesf®) for control of Anopheles gambiae complex, Culex quinquefasciatus and Aedes aegypti larvae under laboratory and semi-field conditions in northeastern Tanzania. Laboratory bioassays were conducted with five to six different concentrations of Bti and Bs, replicated four times and the experiment repeated on three different days. Larvae mortality was recorded at 24 or 48 h after the application of larvicide and subjected to Probit analysis. Laboratory bioassays were followed by semi-field trials to establish initial and residual activity of Bti and Bs. Semi-field trials were conducted in artificial larval habitats in the open sunlit ground and in “mosquito spheres”. These artificial larval habitats were colonized with mosquito larvae, treated with Bti and Bs, and the impact of treatments on mosquito larvae was monitored daily. Lethal concentration values that caused 50% and 95% mortalities of test larvae (LC50 and LC95) showed that An. gambiae complex and Cx. quinquefasciatus tested were highly susceptible to Bti and Bs under laboratory conditions. Likewise, larvae of Ae. aegypti were highly susceptible to Bti, with LC95 value as low as 0.052 mg/l. However, Ae. aegypti larvae were not susceptible to Bs under practical doses of laboratory settings. In semi-field trials, all treatment dosages for Bti provided 91.0–100% larval mortality within 24 h whereas Bs resulted in 96.8–100% larval mortality within the same time-frame. Bs had a more prolonged residual activity, with pupal reductions range of 55.7–100% for 9 days at all application rates while the corresponding pupal reduction with Bti was 15.4–100% for 5 days. Due to the low residual activity of Bti and Bs tested, weekly application at a maximum label rate would be appropriate to reduce mosquito larvae in natural larval habitats. Based on laboratory findings, Bs product tested would not be recommended for use in the control of Ae. aegypti.

Insecticide Efficacy Against Trimen’s False Tiger Moth, Agoma trimenii (Lepidoptera: Agaristidae)

Trimen’s false tiger moth, Agoma trimenii (Lepidoptera: Agaristidae), has developed pest status in vineyardsin the Northern Cape and Groblersdal areas of South Africa, and an integrated pest management system isrequired. The objective of this study was to test the susceptibility of A. trimenii larvae to three commercialproducts (Delegate®WG, Steward®150 EC and three doses of DiPel® DF). Bioassay tests using all threeproducts, and semi-field trials to test the potential of DiPel® DF against A. trimenii larvae, applied at differentwater volumes (50 g/1 000 L/ha and 50 g/1 430 L/ha) were performed. The residual activity of DiPel® DF,when applied at different water volumes, was investigated daily. Delegate® WG, Steward®150 EC and therecommended dose of DiPel® DF showed 100% larval mortality within seven days. Delegate® WG and therecommended dose of DiPel® DF proved to be the fastest acting products. The product label recommendeddose of DiPel® DF (0.25 g/500 mL distilled water) proved the most effective dose (in comparison to halvedand doubled dosages) and showed 100% mortality five days after application. Increasing the water volumeper ha of a spray application of DiPel® DF for the same application area, showed no significant increasein larval mortality. A reduction in insecticidal activity for DiPel® DF applied at both water volumes wasseen between leaves picked four days after spraying and leaves picked five days after spraying, and nomortality was observed after day 6. To help improve efficacy, attention should be given to increasing spraycoverage and residual activity of DiPel® DF, as well as using all tested products within an integrated pestmanagement system.

Residual toxicity of selected insecticides on Aphis gossypii and their safety limits on honeybees

AbstractEvaluation studies were carried out to simulate realistic field exposures of sulfoxaflor and flonicamid againstAphis gossypiiat foraging time ofApis mellifera. Semi-field trials of field rates of sulfoxaflor and flonicamid againstA. gossypiilaboratory strain at 48 h of exposure had equipollent overall mean of mortality of 62.50 and 63.50%, respectively in season of 2020, likewise 60.50 and 62.50%, respectively in season of 2021. Lethal time values (LT1) had ranges of 51.33–32.46 days for sulfoxaflor and 49.00–39.55 days for flonicamid. Laboratory trials on foraging honeybees (∼21 days old) at 5 h of exposure showed an excellence for sulfoxaflor (5.00%) in overall mean of mortality compared to flonicamid (2.75%) in season of 2020. Likewise, sulfoxaflor (4.75%) surpassed flonicamid (2.75%) in season of 2021. The highest LT1s on honeybees for sulfoxaflor and flonicamid reached 27.45 and 10.94 days, respectively. International Organization for Biological Control classified both insecticides to be harmless on honeybees. Survival foraging bees exposed to LD50s of the tested insecticides had malformed digestive tracts gradually vanished along week of exposure. Suggestions for foliar spray stoppages prior to flowering period were mentioned for both insecticides.