Disruption of semiochemical-mediated movement by the immature Trogoderma variabile Baillon and Trogoderma inclusum Le Conte (Coleoptera: Dermestidae) after exposure to long-lasting insecticide-incorporated netting.

BACKGROUND: Highly mobile stored product insects may be able to readily orient in response to food cues and pheromones to attack durable commodities at each link of the postharvest supply chain. A 0.4% deltamethrin-incorporated long-lasting insecticide-incorporated netting (LLIN) is a successful novel preventative integrated pest management (IPM) tactic to intercept dispersing insects after harvest. However, it is unknown whether exposure to LLIN may affect olfaction and orientation to important semiochemicals by immature stored product dermestids, therefore the aim of this study was to assess whether exposure to LLIN disrupts the normal olfactory and chemotactic behavior of warehouse beetle, Trogoderma variabile Ballion (Coleoptera: Dermestidae), and the larger cabinet beetle, T. inclusum Le Conte (Coleoptera: Dermestidae), larval movement in the presence of important semiochemicals, including food kairomones (e.g., flour) and pheromones, e.g., (Z)-14-methyl-8-hexadecenal. RESULTS: The distance moved by the larval population of T. variabile was reduced by 64% after 24-h exposure to LLIN compared to control netting but not immediately after exposure, while T. inclusum larvae movement was reduced by 50% after 24-h exposure to LLIN compared to the control netting. Generally, the olfaction and orientation of larval dermestids were affected after exposure to LLIN compared to control netting. There were species-linked differences in effects on olfaction after the insects were exposed to LLIN. CONCLUSION: Our study suggests the use of LLIN may enhance the effectiveness of other concurrent behaviorally-based strategies such as mating disruption when used as part of a comprehensive IPM program in the postharvest environment. © 2023 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Evaluation of Hermetic Storage Bags for the Preservation of Yellow Maize in Poultry Farms in Dormaa Ahenkro, Ghana.

Using low-quality maize, resulting from insect pests and fungal attack, for formulating feed reduces chicken performance. This study evaluated the effectiveness of hermetic storage bags to keep insect pest and mycotoxin levels in check in yellow maize. The study was conducted in storehouses at three poultry farms in Dormaa Ahenkro, Bono Region, Ghana. The experiment was set up in a Randomized Complete Block Design with ZeroFly® Hermetic (ZFH), Purdue Improved Crop Storage (PICS), and Polypropylene (PP) bags as treatments. In each treatment, twelve 50 kg samples of untreated maize were each put in 100 kg capacity bags. Two bags in each treatment were destructively sampled monthly for 6 months. The number of insects was significantly higher in the PP bag (161.00 ± 4.25), compared to the PICS and ZFH bags: 7.00 ± 0.29 and 4.50 ± 0.76, respectively. The PICS and ZFH bags had less insect damage and lower weight loss than the PP bags. Aflatoxin and fumonisin levels were below the recommended safe thresholds of 15 ppb and 4 ppm, respectively, in all the bags. With the exception of ash, proximate analyses were higher for all variables in the PICS and ZFH bags. The study showed that PICS and ZFH bags conserved maize quality better than the PP bag.

Importance of Sanitation for Stored-Product Pest Management.

Sanitation is essential for the cost-effective pest management of stored-product insects. The Food, Drug and Cosmetic Act of 1938 led to the Food and Drug Administration (FDA) tightening regulatory standards, and many local surveys, courses and conferences were organized to prepare the industry for these new regulations. Sanitation removes insects and residual food, which may also provide shelter for insects, with heat treatments and insecticide applications. The number of insects removed by cleaning may be reduced as the number of available hiding places increases. Decreased sanitation negatively affects the efficacy of most other pest management practices, with means of 1.3- to 17-fold decreases in efficacy. The majority of studies quantifying the efficacy of sanitation have been performed on the farm storage of grain, but some studies have been conducted for grain elevators, food processing, and the marketing system. Results ranged from no effect of sanitation alone to very effective alone or with other methods. Sanitation can also reduce insect infestation prior to harvest. Some cost-benefit analyses have been conducted for sanitation.

Mobility of Phosphine-Susceptible and -Resistant Rhyzopertha dominica (Coleoptera: Bostrichidae) and Tribolium castaneum (Coleoptera: Tenebrionidae) After Exposure to Controlled Release Materials With Existing and Novel Active Ingredients.

There is interest in developing controlled release materials (CRMs) with novel modes of action to improve resistance management. Long-lasting insecticide-incorporated netting (LLIN) with deltamethrin has been effectively used against stored-product pests. Here, we evaluated the efficacy of different CRMs (LLIN or packaging) with each of four active ingredients (AI) (deltamethrin, permethrin, indoxacarb, and dinotefuran) and compared them to control CRMs in reducing movement and increasing mortality of phosphine-susceptible and -resistant Rhyzopertha dominica and Tribolium castaneum. Adults were exposed for 0.5, 2, or 60 min, and movement was assessed immediately or after 24, or 168 h using video-tracking and Ethovision software. We recorded total distance and velocity traveled by adults. Finally, we tested higher rates of each AI on surrogate netting material (e.g., standardized-sized cheesecloth) and varied exposure time to obtain median lethal time (LT50) for each compound and susceptibility. Exposure to LLIN with deltamethrin significantly reduced the movement of both species compared to the other CRMs regardless of their susceptibility to phosphine. Deltamethrin was the most effective AI for both species, while dinotefuran and indoxacarb were the least effective for R. dominica and T. castaneum adults, respectively. Most AIs resulted in appreciable and approximately equivalent mortality at higher concentrations among phosphine-susceptible and -resistant strains. Our results demonstrate that CRMs can be an additional approach to combat phosphine-resistant populations of stored product insects around food facilities. Other compounds such as permethrin, dinotefuran, and indoxacarb are also effective against phosphine-resistant populations of these key stored product insects except indoxacarb for T. castaneum.

Biology and trapping of stable flies (Diptera: Muscidae) developing in pineapple residues (Ananas comosus) in Costa Rica.

Pineapple production in Costa Rica increased nearly 300-fold during the last 30 yr, and >40,000 hectares of land are currently dedicated to this crop. At the end of the pineapple cropping cycle, plants are chopped and residues incorporated into the soil in preparation for replanting. Associated with increased pineapple production has been a large increase in stable fly, Stomoxys calcitrans (L.), populations. Stable flies are attracted to, and oviposit in, the decomposing, chopped pineapple residues. In conjunction with chemical control of developing larvae, adult trapping is an important control strategy. In this study, four blue-black fabric traps, Nzi, Vavoua, Model H, and Ngu, were compared with a white sticky trap currently used for stable fly control in Costa Rica. Overall, the white sticky trap caught the highest number of stable flies, followed by the Nzi, Vavoua, Model H, and Ngu. Collections on the white sticky trap increased 16 d after residues were chopped; coinciding with the expected emergence of flies developing in the pineapple residues. During this same time period, collections in the blue-black fabric traps decreased. Sex ratio decreased from >7:1 (females:males) 3-7 d after chopping to 1:1 at 24-28 d. White sticky, Nzi and Vavoua traps collected similar numbers of colonizing flies 3-7 d after residues were chopped. However, white sticky traps collected more flies once emergence from the pineapple residues began. Although white sticky traps collected more flies than fabric traps, they remain labor intensive and environmentally unsound because of their disposable and nonbiodegradable nature.

Synergistic manipulations of plant and insect defences.

BACKGROUND: It has been demonstrated previously that cis-jasmone acts as an elicitor of plant defence mechanism(s) by inducing secondary metabolism. It has also been demonstrated that temporal synergism can result in hypersensitive insect pests due to the inhibition of metabolic enzymes. RESULTS: Laboratory bioassays demonstrated that pre-exposure of insects by piperonyl butoxide followed by cis-jasmone treatment of crops, reduced Aphis gossypii on cotton by 80% and Myzus persicae on sweet pepper by 90%. By microencapsulating the cis-jasmone and combining with piperonyl butoxide, Bemisia tabaci on tomatoes was reduced by 99%. A field trial with microencapsulated cis-jasmone combined with piperonyl butoxide resulted in a comparable reduction of whitefly egg numbers to that given by the registered rate of imidacloprid, with efficacy of 89% and 93%, respectively. CONCLUSIONS: If insect defence enzymes are compromised by piperonyl butoxide whilst plant defence is primed by cis-jasmone, there are possibilities of an insecticide-free method of controlling insect pests. The success seems largely dependent upon the toxicity of the plants' secondary chemistry.

Increase in susceptibility to insecticides with aging of wild Anopheles gambiae mosquitoes from Côte d'Ivoire.

BACKGROUND: Appropriate monitoring of vector insecticide susceptibility is required to provide the rationale for optimal insecticide selection in vector control programs. METHODS: In order to assess the influence of mosquito age on susceptibility to various insecticides, field-collected larvae of An. gambiae s.l. from Tiassalé were reared to adults. Females aged 1, 2, 3, 5 and 10 days were exposed to 5 insecticides (deltamethrin, permethrin, DDT, malathion and propoxur) using WHO susceptibility test kits. Outcome measures included the LT50 (exposure time required to achieve 50% knockdown), the RR (resistance ratio, i.e. a calculation of how much more resistant the wild population is compared with a standard susceptible strain) and the mortality rate following 1 hour exposure, for each insecticide and each mosquito age group. RESULTS: There was a positive correlation between the rate of knockdown and mortality for all the age groups and for all insecticides tested. For deltamethrin, the RR50 was highest for 2 day old and lowest for 10 day old individuals. Overall, mortality was lowest for 2 and 3 day old individuals and significantly higher for 10 day old individuals (P < 0.05). With permethrin, the RR50 was highest for 1 to 3 day old individuals and lowest for 10 day old individuals and mortality was lowest for 1 to 3 day old individuals, intermediate for 5 day old and highest for 10 day old individuals. DDT did not display any knockdown effect and mortality was low for all mosquito age groups (<7%). With malathion, the RR50 was low (1.54 - 2.77) and mortality was high (>93%) for all age groups. With propoxur, no knockdown effect was observed for 1, 2 and 3 day old individuals and a very low level of mortality was observed (< 4%), which was significantly higher for 5 and 10 day old individuals (30%, P < 0.01). CONCLUSION: Results indicate that for An. gambiae s.l. adults derived from wild-collected larvae, there was an influence of age on insecticide susceptibility status, with younger individuals (1 to 3 days old) more resistant than older mosquitoes. This indicates that the use of 1 - 2 day old mosquitoes in susceptibility assays as recommended by the WHO should facilitate detection of resistance at the stage where the highest rate of the resistance phenotype is present.

Can piperonyl butoxide enhance the efficacy of pyrethroids against pyrethroid-resistant Aedes aegypti?

BACKGROUND: Pyrethroid resistance can be considered the main threat to the continued control of many mosquito vectors of disease. Piperonyl butoxide (PBO) has been used as a synergist to help increase the efficacy of certain insecticides. This enhancement stems from its ability to inhibit two major metabolic enzyme systems, P450s and non-specific esterases, and to enhance cuticular penetration of the insecticide. OBJECTIVE: To compare the mortality of a characterized resistant Aedes aegypti strain, Nha Trang, from Vietnam and the susceptible laboratory strain Bora Bora on netting with the pyrethroid deltamethrin (DM) alone and in combination with PBO. METHODS: Resistance mechanisms were characterized using molecular and bioassay techniques; standard PCR was used to test for the kdr target site mutation. Potential genes conferring metabolic resistance to DM were identified with microarray analysis using the Ae. aegypti 'detox chip'. These data were analysed alongside results from WHO susceptibility tests. P450, CYP9J32, was significantly overexpressed in the DM-resistant strain compared with the susceptible Bora Bora strain. Another five genes involved with oxidative stress responses in mosquitoes were also significantly overexpressed. The Nha Trang strain was homozygous for two kdr mutations. WHO cone bioassays were used to investigate mortality with incorporated DM-treated nets with and without PBO. PBO used in combination with DM resulted in higher mortality than DM alone. CONCLUSION: Synergists may have an important role to play in the future design of vector control products in an era when alternatives to pyrethroids are scarce.

An analogue of piperonyl butoxide facilitates the characterisation of metabolic resistance.

BACKGROUND: Previous work has demonstrated that piperonyl butoxide (PBO) not only inhibits microsomal oxidases but also resistance-associated esterases. The ability to inhibit both major metabolic resistance enzymes makes it an ideal synergist to enhance xenobiotics but negates the ability to differentiate which enzyme group is responsible for conferring resistance. RESULTS: This study examines an analogue that retains the ability to inhibit esterases but is restricted in its ability to act on microsomal oxidases, thus allowing an informed decision on resistance enzymes to be made when used in conjunction with the parent molecule. CONCLUSION: Using examples of resistant insects with well-characterised resistance mechanisms, a combination of PBO and analogue allows identification of the metabolic mechanism responsible for conferring resistance. The relative potency of PBO as both an esterase inhibitor and an oxidase inhibitor is also discussed.

A novel assay reveals the blockade of esterases by piperonyl butoxide.

BACKGROUND: Conventional in vitro assays sometimes fail to reveal esterase inhibition by piperonyl butoxide (PBO), although synergism studies suggest loss of esterase-mediated sequestration of insecticide does take place. A new in vitro assay has been devised that routinely reveals binding between PBO and these esterases. RESULTS: The new 'esterase interference' assay detects the blockade of resistance-associated esterases in a species, Myzus persicae Sülzer, where this has not previously been seen. The assay also demonstrates directly the protective effect esterases may confer to target sites of insecticides. CONCLUSION: The new assay reveals esterase blockade by PBO and thus has the potential to be used as a high-throughput screening method for other potential synergists.

Temporal synergism can enhance carbamate and neonicotinoid insecticidal activity against resistant crop pests.

BACKGROUND: Piperonyl butoxide (PBO) effectively synergises synthetic pyrethroids, rendering even very resistant insect pests susceptible, provided a temporal element is included between exposure to synergist and insecticide. This concept is now applied to carbamates and neonicotinoids. RESULTS: A microencapsulated formulation of PBO and pirimicarb reduced the resistance factor in a clone of Myzus persicae (Sulzer) from >19 000- to 100-fold and in Aphis gossypii (Glover) from >48 000- to 30-fold. Similar results were obtained for a strain of Bemisia tabaci Gennadius resistant to imidacloprid and acetamiprid, although a second resistant strain did not exhibit such a dramatic reduction, presumably owing to the presence of target-site insensitivity and the absence of metabolic resistance. Synergism was also observed in laboratory susceptible insects, suggesting that, even when detoxification is not enhanced, there is degradation of insecticides by the background enzymes. Use of an analogue of PBO, which inhibits esterases but has reduced potency against microsomal oxidases, suggests that acetamiprid resistance in whiteflies is largely oxidase based. CONCLUSION: Temporal synergism can effectively enhance the activity of carbamates and neonicotinoids against resistant insect pests. Although the extent of this enhancement is dependent upon the resistance mechanisms present, inhibition of background enzymes can confer increased sensitivity against target-site resistance as well as increased metabolism. .

Temporal synergism by microencapsulation of piperonyl butoxide and alpha-cypermethrin overcomes insecticide resistance in crop pests.

A microencapsulated formulation that gives a burst release of piperonyl butoxide (PBO) several hours before a burst release of a conventional pyrethroid can effectively overcome metabolic resistance in Bemisia tabaci Gennadius, Helicoverpa armigera (Hübner), Aphis gossypii Glover and Myzus persicae Sulzer. This increase in efficacy against resistant pests was reflected in a field trial against B. tabaci on cotton, eliminating the need for two treatments. The ratio between the active insecticide and the synergist was found to be crucial in reducing resistance factors.