Short-term spatial dispersion patterns between the larger grain borer and the maize weevil in grain columns.

The invasive larger grain borer (Prostephanus truncatus) and the maize weevil (Sitophilus zeamais) co-occur in many regions of the world. While competition between these 2 species has been studied extensively, there is little information on spatial dispersion patterns in bulk storage of grain. To evaluate potential overlap in realized niche, we evaluated the short-term spatial dispersion behavior of P. truncatus and S. zeamais in monolayers of maize alone or together for 1 day compared to 7 days. We evaluated competition under three different densities, namely 10-20, 75-150, and 150-300 insects/kg for P. truncatus and S. zeamais. The monolayers were equally divided into 24 zones to track location the abundance of insects and damage to maize. We found that both species generally aggregated together and were correlated to the same location as heterospecifics. After 1 day, most of the insects for both species were near the top of the monolayer, but by 7 days, most individuals were at the bottom of the monolayers. In monolayers, when alone, P. truncatus created a clear path of destruction to the bottom of the monolayer, but when S. zeamais was present, damage was lessened and shifted upwards in the grain column. In an olfactometer assay, P. truncatus preferred maize odors, while S. zeamais exhibited no preference among maize, conspecifics, and heterospecifics. In evaluating relative emissions, each of these treatments emitted unique odors but with significant overlap. These data may improve targeting of chemical control tactics by identifying the position of these insects in the grain mass.

The behavioral response to the putative necromones from dead Tribolium castaneum (Coleoptera: Tenebrionidae) in traps by conspecifics as a function of density and time since capture.

Long-term trapping programs of stored product pests provide information for timely and accurate pest management. Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) is a highly successful external-infesting grain pest and is frequently monitored using a commercial pitfall trap that combines pheromonal and kairomonal stimuli. However, an often overlooked component of lure-based traps is the potential for the volatile plume to change over time as individuals are captured. These now-dead insects may then release necromones altering the captures of conspecifics. In this study, we evaluated changes in (i) the behavior of T. castaneum and (ii) the relative change in volatiles over time since dead insects were added and among different densities of dead conspecifics in a commercially available kairomone oil. We used multiple behavior assays, including wind tunnel, release-recapture, and 2-way olfactometer, and performed chemical analyses via headspace collection and gas chromatography coupled with mass spectrometry. Tribolium castaneum response to the kairomone lure was not consistent among assays of density of conspecifics between 4 and 40 adults after 24 or 96 h, or time of seeding over 1-96 h or 8-11 days prior. Tested strains collected in 2012 and 2019 ruled out strain-specific differences. Oil batch effects were also ruled out as a factor contributing to the response of T. castaneum. The relative volatile composition was generally stable among the treatments despite using different seeding densities and seeding times. Given that attraction and relative volatile composition were generally unaffected by prior captures, long-term monitoring programs may be robust in their interpretability over time.

Efficacy of deltamethrin and pirimiphos-methyl in proportionally layer-treated maize against the larger grain borer and the maize weevil.

Two insecticides (deltamethrin and pirimiphos-methyl) were evaluated in laboratory assays as grain protectants when applied as a total percentage of a maize mass to control adult Prostephanus truncatus and Sitophilus zeamais. All experiments were conducted at the University of Thessaly in Greece at 30°C and 65% RH under continuous darkness. Either insecticide was applied to 20 g of maize placed in a vial or to the upper one half, one fourth, or one-eighth layer of the maize, then insects were either added to the vials before or after the maize in a completely randomized block design CRBD with n = 9 replicates. Mortality, progeny production, and insect damaged kernels (IDK) were then evaluated for each vial. Insect introduction method (before or after) did not have any impact on any of the variables. Mortality was nearly 100% for all treatments for both insecticides for P. truncatus. Subsequently, progeny production and the number of insect damaged kernels were very low or zero for P. truncatus. Mortality of S. zeamais remained low across layer treatments for deltamethrin. However, S. zeamais was easily controlled by pirimiphos-methyl. The results of this laboratory study show that while deltamethrin and pirimiphos-methyl have some effectiveness as a layer treatment on a column of maize, efficacy will be dependent on the target species, and the depth of the treated layer, as well as the location on which the insects are present.

Microbial Volatile Organic Compounds from Tempered and Incubated Grain Mediate Attraction by a Primary but Not Secondary Stored Product Insect Pest in Wheat.

There has been a dearth of research elucidating the behavioral effect of microbially-produced volatile organic compounds on insects in postharvest agriculture. Demonstrating attraction to MVOC's by stored product insects would provide an additional source of unique behaviorally-relevant stimuli to protect postharvest commodities at food facilities. Here, we assessed the behavioral response of a primary (Rhyzopertha dominica) and secondary (Tribolium castaneum) grain pest to bouquets of volatiles produced by whole wheat that were untempered, or tempered to 12%, 15%, or 19% grain moisture and incubated for 9, 18, or 27 days. We hypothesized that MVOC's may be more important for the secondary feeder because they signal that otherwise unusable, intact grains have become susceptible by weakening of the bran. However, contrary to our expectations, we found that the primary feeder, R. dominica, but not T. castaneum was attracted to MVOC's in a wind tunnel experiment, and in a release-recapture assay using commercial traps baited with grain treatments. Increasing grain moisture resulted in elevated grain damage detected by near-infrared spectroscopy and resulted in small but significant differences in the blend of volatiles emitted by treatments detected by gas chromatography coupled with mass spectrometry (GC-MS). In sequencing the microbial community on the grain, we found a diversity of fungi, suggesting that an assemblage was responsible for emissions. We conclude that R. dominica is attracted to a broader suite of MVOC's than T. castaneum, and that our work highlights the importance of understanding insect-microbe interactions in the postharvest agricultural supply chain.

Synergisms in Science: Climate Change and Integrated Pest Management Through the Lens of Communication-2019 Student Debates.

Every year, the Student Debates Subcommittee (SDS) of the Student Affairs Committee (SAC) for the annual Entomological Society of America (ESA) meeting organizes the Student Debates. This year, the SAC selected topics based on their synergistic effect or ability to ignite exponential positive change when addressed as a whole. For the 2019 Student Debates, the SAC SDS identified these topic areas for teams to debate and unbiased introduction speakers to address: 1) how to better communicate science to engage the public, particularly in the area of integrated pest management (IPM), 2) the influential impacts of climate change on agriculturally and medically relevant insect pests, and 3) sustainable agriculture techniques that promote the use of IPM to promote food security. Three unbiased introduction speakers gave a foundation for our audience to understand each debate topic, while each of six debate teams provided a strong case to support their stance or perspective on a topic. Debate teams submitted for a competitive spot for the annual ESA Student Debates and trained for the better part of a year to showcase their talents in presenting logical arguments for a particular topic. Both the debate teams and unbiased introduction speakers provided their insight toward a better understanding of the complexities of each topic and established a foundation to delve further into the topics of science advocacy and communication, climate change, and the many facets of integrated pest management.

Temperature-Mediated Competition Between the Invasive Larger Grain Borer (Coleoptera: Bostrichidae) and the Cosmopolitan Maize Weevil (Coleoptera: Curculionidae).

Interspecific competition between agricultural pests may affect the species that can establish, and may also affect food production. Prostephanus truncatus (Horn), the larger grain borer, is endemic to Central America, but invaded Africa with disastrous consequences for maize production. Its main competitor is Sitophilus zeamais Motschulsky, the maize weevil, which is cosmopolitan. These insects co-occur in many regions of the world and both are threats to maize. However, the impact of competition between these two species is not well-understood, nor is its effect on grain quality or potential to limit P. truncatus invasion in new areas. The aims of our study were to evaluate the outcome of interspecific competition between P. truncatus and S. zeamais at four different temperatures on a fixed quantity of grain, and determine effects on progeny production, grain damage, and mold growth. We found that coexistence may be possible at a range of 25-30°C, but mixed colonies experienced a direct competitive cost compared to single-species colonies. Prostephanus truncatus performed better at warmer temperatures, while S. zeamais favored cooler temperatures. The majority of grain damage was the result of P. truncatus activity as opposed to S. zeamais. Finally, mold growth was greater where both species were present, and species of mold that produce aflatoxin were identified. Although there are an increasing number of areas where both of these species occur, our results suggest P. truncatus will be capable of destroying much more maize in a shorter period compared to S. zeamais at temperatures greater than 25°C.

Cumulative oxygen consumption during development of two postharvest insect pests: Callosobruchus maculatus Fabricius and Plodia interpunctella Hübner.

Insect pests such as Callosobruchus maculatus Fabricius and Plodia interpunctella Hübner cause substantial losses to grain during postharvest storage. In the last few years, hermetic storage technologies have been successfully used by smallholder farmers in Africa and Asia to protect their harvested grain against insect pests. Hermetic technologies owe much of their effectiveness to restricting oxygen availability to insects confined in the containers. There is a need to better understand the biology of specific storage insect pests and their responses to hypoxia. We employed a novel and non-invasive analytical technology, the OxySense 5250i, to measure oxygen levels in closed containers, and evaluated its effectiveness in measuring the total oxygen consumption of two insect pests during their development: C. maculatus and P. interpunctella. The total amount of oxygen consumed by C. maculatus during its larval development period determined with the OxySense apparatus was not different from that previously recorded using another instrument, the Mocon Pac Check 325 gas analyzer. Using the OxySense 5250i, we found that P. interpunctella consumes nearly three times as much oxygen per insect over its larval-to-adult developmental period compared to C. maculatus. Information on the lifetime oxygen consumption of insects provides relevant information to the effectiveness and ability of hermetic technologies to protect stored products against insect pests.