Microbial vectoring capacity by internal- and external-infesting stored product insects after varying dispersal periods between novel food patches: An underestimated risk.

Understanding the ability of internal- and external-infesting stored product insects to vector microbes is important for estimating the relative risk that insects pose to postharvest commodities as they move between habitat patches and in the landscape. Thus, the aim of the current study was to evaluate and compare the microbial growth in novel food patches at different dispersal periods by different populations of Sitophilus oryzae (e.g., internal-infesting) and Lasioderma serricorne (e.g., external-infesting). Adults of both species collected from laboratory colonies or field-captured populations were either placed immediately in a novel food patch, or given a dispersal period of 24 or 72 h in a sterilized environment before entering a surrogate food patch. Vectored microbes in new food patches were imaged after 3 or 5 days of foraging, and microbial growth was processed using ImageJ while fungal species were identified through sequencing the ITS4/5 ribosomal subunit. We found that increasing dispersal time resulted in multiple-fold reductions in microbial growth surrogate food patches by L. serricorne but not S. oryzae. This was likely attributable to higher mobility by S. oryzae than L. serricorne. A total of 20 morphospecies were identified from 13 genera among the 59 sequences, with a total of 23% and 16% classified as Aspergillus and Penicillium spp. Our data suggest that there is a persistent risk of microbial contamination by both species, which has important food safety implications at food facilities.

Flight capacity and behavior of Ephestia kuehniella (Lepidoptera: Pyralidae) in response to kairomonal and pheromonal stimuli.

Flight behavior is an important component to understand in the context of pest management. However, because of their small size, little is known about the flight capacity of most stored-product insects, and when a flight has been assessed, it usually consists of a propensity for initiating flight. Despite a priori expectations of the importance of flight for moths, there are no data about the flight capacity and little on the flight behavior of the Mediterranean flour moth, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). As a result, the objective of the current study was to (i) characterize the baseline flight capacity of E. kuehniella and (ii) determine how flight capacity is affected by the presence of kairomonal, pheromonal, or no stimuli. We found adult E. kuehniella flew a mean of 24-34 km in a 24-h period, and the distance flown per bout increased from 91 to 207 m in the presence of pheromones but decreased to 41 m when food was nearby compared to a negative control. The total number of flight bouts was 1.6-fold higher in the presence of pheromone compared to the negative control, but E. kuehniella flew significantly slower with pheromone and food cues present, suggesting they may be exhibiting an optimal foraging strategy. Our data on flight capacity results in qualitatively and quantitatively different conclusions about flight than those conclusions formed if only flight initiation is considered. Overall, this novel information is useful for understanding the spread within facilities and in the landscape (between facilities), as well as parameterizing ecological modeling.

Efficacy of the Fumigants Propylene Oxide and Ethyl Formate to Control Two Pest Species of Dry-Cured Hams.

The ham mite Tyrophagus putrescentiae and the red-legged ham beetle Necrobia rufipes are harmful pests to several high-valued stored products. The regulatory phase-out of the fumigant methyl bromide necessitates the search for alternative fumigants. Propylene oxide (PPO) and ethyl formate (EF) were therefore evaluated in the laboratory for controlling these pests of dry-cured hams. Concentration-mortality studies at 25 °C of PPO and EF found that the mobile stages of the mites were very susceptible to low concentrations of 10 mg/L and less of each gas, while mite eggs were very tolerant and required 20 mg/L for PPO and 80 mg/L of EF for 100% mortality. Mixed life stage cultures of mites and beetles were treated for 24 h with either PPO or EF at 1× and 2× the estimated 99% lethal doses and confirmed effectiveness for controlling simulated pest populations. The sorptive properties of each gas in chambers with ham pieces, dog food kibbles, or fish meal were minimal for a reduction in mite toxicity when compared to treatments in empty chambers. There was no evidence that any desorbed gas occurred at a level toxic to mite eggs in any of the fumigated commodities. These fumigation studies with ham pests support further work with PPO and EF on any changes in the sensory quality of dry-cured hams for human taste and for commercial-scale fumigations toward regulatory approval.

Attraction, mobility, and preference by Lasioderma serricorne (Coleoptera: Ptinidae) to microbially-mediated volatile emissions by two species of fungi in stored grain.

Insects and microbes are known to interact in a variety of ways at food facilities, compounding damage. However, little research has explicated how specific common fungal species affect the behavior of the cosmopolitan secondary stored product pest, Lasioderma serricorne. Enhanced knowledge about attraction to microbially-produced volatile organic compounds (MVOCs) may be used to manipulate insect behavior. Aspergillus flavus and Fusarium verticillioides are two common, widespread pre- and postharvest fungi on small cereals that produce aflatoxins and fumonisins, respectively, while directly competing with each other for nutrients. Our goals were to (1) characterize the volatile emissions from grain inoculated by A. flavus or F. verticillioides derived from the cuticle of L. serricorne compared to uninoculated and sanitized grain, and (2) understand how MVOCs from each fungal species affects mobility, attraction, and preference by L. serricorne. Headspace collection revealed that the F. verticillioides- and A. flavus-inoculated grain produced significantly different volatiles compared to sanitized grain or the positive control. Changes in MVOC emissions affected close-range foraging during an Ethovision movement assay, with a greater frequency of entering and spending time in a small zone with kernels inoculated with A. flavus compared to other treatments. In the release-recapture assay, MVOCs were found to be attractive to L. serricorne at longer distances in commercial pitfall traps. There was no preference shown among semiochemical stimuli in a still-air, four-way olfactometer. Overall, our study suggests that MVOCs are important for close- and long-range orientation of L. serricorne during foraging, and that MVOCs may have the potential for inclusion in behaviorally-based tactics for this species.