Integrating long-lasting insecticide netting tactics into integrated pest management programs for food facilities

We have completed three primary research objectives included below with the methods involved:

Obj. 1: Evaluating the use of insecticide netting in bulk storage to decrease phosphine fumigation in food facilities.

Methods: For obj. 1, we used three 110 metric tons (MT) capacity grain bins to assess whether miniature grain silos (e.g., 2-gallons buckets) filled with wheat and protected with α-cypermethrin (0.34%)-based long lasting insecticide-incorporated netting (LLIN) (BASF) can reduce phosphine fumigations and pest infestation compared to those protected by untreated netting, or no netting. In each grain bin, 60 miniature silos with small openings were filled with 500 g of clean wheat with 20% cracked wheat. Miniature silos were protected by LLIN (0.3% α-cypermethrin, Carifend®, BASF), positive control (without insecticide), or negative control (no netting). Half of each treatment was randomly assigned to phosphine fumigation treatment, while the remainder were not fumigated. After grain deployment, a total of 300 insects of our three target species were released in each grain bin, supplemented by naturally occurring insects. Monthly samples of 100 g of grain from four silos from each treatment in four blocks from three-grain bins were taken between June and October for two years. During each monthly sample, the number of insects, and their life stages were recorded. Grain quality measures were also evaluated.  We determined whether phosphine fumigation could be reduced with the use of LLIN over the season. Half of the miniature silos in a bin were fumigated or left unfumigated, based on a conservative US Federal Grain Inspection Services (FGIS) defect guidelines of 2 whole insects or 16 insect-damaged kernels per 100 g. Once fumigation was triggered, affected buckets were moved to a dedicated fumigation-designated grain bin in a 50-bushel drum, and magnesium phosphide tablets were added. The concentration of phosphine were monitored in real-time with a Centaur wireless sensor, and typically reached 700-2500 ppm.

Obj. 2. Leverage ongoing residual contact insecticide use by pairing with insecticide netting deployment to reduce overall inputs at food facilities

Methods: For Obj. 2, the experimental arena consisted of a 63 × 15.5 × 9.5 cm L: W:H metal frame. This arena also contained four square blocks of concrete measuring 15.24 × 15.24 × 1.5 cm L: W:H to create a testing platform that mimics the surface of a food facility. The concrete was prepared by first mixing tap water and Rockite cement mix in a large water pitcher. The tap water was added to the dry Rockite mixture and combined until a thick-paste consistency was achieved. The slurry was poured into a 1.1 L volume silicone square mould (15.24 × 15.24 × 4.57 cm L: W:H). The slurry was poured 1.5 cm thick. The cement concrete squares were left to dry and solidify at room temperature for 2–3 days. Cement squares were modular and new ones were used with each replicate performed for the assay.

We assessed whether LLIN (0.34% alpha-cypermethrin, BASF) may enhance the effects of residual contact insecticides such as Centanyl EC (Central Life Sciences), active ingredient (a.i.) deltamethrin and Evergreen (McLaughlin Gormley King Co.), a.i. natural pyrethrins against the red flour beetle, Tribolium castaneum and lesser grain borer, Rhyzopertha dominica. We used the following six treatments: (1) untreated controls with netting identical to LLIN but lacking insecticide and/or concrete sprayed only with distilled water, (2) LLIN only (Carifend net, 0.34% alpha-cypermethrin, BASF Corp., Ludwigshafen, Germany) applied near the insect release point (15.24 × 15.24 cm; same size strip of the net were used for whole experiment), (3) deltamethrin only applied near the insect release position, (4) pyrethrins only applied near the insect release position, (5) a strip of the LLIN and deltamethrin (LLIN laid sequentially directly before the insecticide to intercept immigrating insects) and (6) a strip of the LLIN material and pyrethrins (LLIN laid sequentially directly before the insecticide to intercept immigrating insects). For each replicate, 30 mixed-sex adult insects were released at the far end of the testing platform opposite the food source. After a 48-h dispersal period, we counted the number of insects on each concrete square. The condition of the adults was checked under the dissecting microscope and rated as alive, affected, or dead. Those that were classified as dead were completely immobile. We collected the food source by removing the flour or wheat. Subsequently, the commodity was gently sieved using two sieves, making sure no eggs were harmed during the process and all food dust and detritus was transferred to progeny production containers. All the adults were removed from the commodity and the commodity was retained for 6 weeks at 27.5°C, 65% RH, and 14:10 (L:D) h photoperiod in environmental chambers to evaluate progeny production. There were 5–6 replications for each treatment and species combination.

Obj. 3. Model stored product insect population-level response to LLIN to determine long-term effects of usage on stored product pests

Methods: We modeled the overall efficacy of LLIN on preventing establishment and growth of T. castaneum using a stage-based model with the package popbio in R software. There were four life stages: eggs, larvae, pupae, and adults. Survivorship, fecundity, and transition information for each stage were derived from the literature. A sensitivity analysis was performed to determine which stage can be targeted to most greatly affect the population growth after exposure to LLIN. In addition, a mortality function based on empirical data with LLIN collected in the laboratory on T. castaneum will be implemented. We parameterized based on documented fecundity reductions from the literature after exposure to LLIN.