Paul W. Flinn

Parasitoids and Predators

The use of insect parasitoids and predators to control stored-product insect pests has many advantages over traditional chemical controls. These natural enemies leave no harmful chemical residues. Natural enemies released in a storage facility continue to reproduce as long as hosts are available and environmental conditions are suitable. Unlike chemicals that need to be applied to a wide area, natural enemies can be released at a single location and they will find and attack pests located deep inside crevices or within a grain mass. Parasitoids and predators that attack stored-product pests are typically very small, and have a short life cycle and a high reproductive capacity. They can easily be removed from bulk grain using normal cleaning procedures before milling. In many ways the stored-product environment is favorable for biological control. Environmental conditions are generally favorable for natural enemies, and storage structures prevent these beneficial insects from leaving. Several reviews have been published on the use of insect parasitoids and predators to control stored-product insect pests (Burkholder 1981, Arbogast 1984a, b; Haines 1984, Brower 1990a, 1991a; Nilakhe and Parker 1990, Burkholder and Faustini 1991, Brower et al. 1996, Scholler et al. 1997, Adler and Scholler 1998).

Influence of temperature on the functional response of Anisopteromalus calandrae (Hymenoptera: Pteromalidae), a parasitoid of Rhyzopertha dominica (Coleoptera: Bostrichidae)

The functional response of Anisopteromalus calandrae (Howard) parasitizing 4th-instar Rhyzopertha dominica (F.) on wheat was estimated over a range of temperatures and host densities. A functional response equation was used in which a quadratic component that included temperature was substituted for handling time. The instantaneous search rate increased with increasing temperatures. The maximum rate of parasitization was 13 larvae/24 h at 30°C and 35°C. Handling time was lowest at 30°C and highest at 20°C. The ability of A. calandrae to find and parasitize R. dominica over a broad range of temperatures makes it a good candidate for natural control of stored grain pests.

Temperature-mediated functional response of Theocolax elegans (Hymenoptera: Pteromalidae) parasitizing Rhyzopertha dominica (Coleoptera: Bostrichidae) in stored wheat

The functional response of Theocolax elegans (Westwood) parasitizing the lesser grain borer, Rhyzopertha dominica (F.) was examined over a range of temperatures. A type II functional response equation was fitted to each temperature regime. The parasitization rate was highest at 301C (20 hosts per day) and was lowest at 201C (2 hosts per day). Handling time was inversely proportional to temperature, and ranged from 1.6 days at 201C to 0.05 days at 301C. Instantaneous search rate also changed with temperature. It was lowest at 201C and highest at 301C. A temperature-mediated functional response equation was fitted to the data, in which handling time was a quadratic function of temperature. The equation explained 74% of the variance in parasitization rate. Theocolax elegans has a narrower optimal temperature range than other parasitic stored-product Hymenoptera. Temperatures greater than 32.51C caused high parasitoid mortality. Published by Elsevier Science Ltd.

Augmentative releases of parasitoid wasps in stored wheat reduces insect fragments in flour.

Field studies were conducted to assess the effectiveness of the parasitoid wasp, Theocolax elegans, for reducing insect fragments in flour by suppressing populations of Rhyzopertha dominica in six bins, each containing 27 tonnes of wheat. Beetles were released into all the six bins at monthly intervals for 3 months. Parasitoid wasps were released into three of the bins, 21 days after the first beetle release. Wheat samples from the bins were milled to determine the effects of parasitoid releases on insect fragment counts in flour. In the first year of the study, after 198 days of storage, insect fragment counts were 9.4 and 31 per 50 g flour in the treatment and control bins. However, because of high variability, the means were not significantly different. New grain was used in the second year of the study, and higher numbers of beetles were released. After 131 days of storage, fragment counts averaged 56 and 487/50 g in the treatment and control bins, a reduction in the former of 89%. In the second year of the study, insect myosin in the treatment and control bins averaged 0.27 and 3.23 ng/well, a percentage reduction in the treated bin of 92%. The number of insect damaged kernels (IDK) was significantly lower in the treatment than in the control bins in both years of the study. In the first year, IDK was 6 and 15 IDK/100 g wheat in the treatment and control bins respectively, a reduction in the former of 61%. In the second year, IDK was 12 and 148 IDK/100 g wheat, in the treatment and control bins respectively, a reduction of 92%. This study showed that augmentative releases of parasitoid wasps into bins of stored wheat reduced damage to wheat kernels and the number of insect fragments in flour.

Simulation model of Rhyzopertha dominica population dynamics in concrete grain bins.

Rhyzopertha dominica is one of the most damaging insect pests in grain elevators and causes millions of dollars worth of stored grain losses annually in the USA. A simulation model was developed for predicting R. dominica population dynamics in concrete grain bins. The model used a two-dimensional representation of a cylindrical concrete bin (33 m tall 6.4 m wide), and used hourly weather data to predict changes in grain temperature. Output from the grain bin temperature and moisture module was used by the insect module to predict changes in insect density in 32 different bin regions. When compared to validation data from nine grain bins, the model accurately predicted insect vertical distribution and insect density. In December, the highest insect density was in the top center of the grain mass, and decreased steadily with increasing depth and towards the periphery of the grain mass. R. dominica attains this spatial distribution because immigration is primarily through the top of the bin, and higher populations occur in the interior of the grain mass because of warmer temperatures there. Initially, the model underestimated actual insect density in the grain bins. We increased the immigration rate by 50% and this resulted in a much better prediction of R. dominica density by the model. From 20 September to 14 December, populations of R. dominica increased from 0.1 to 3.5 insects per kg of wheat. Published by Elsevier Science Ltd.

Temporospatial distribution of the psocids Liposcelis entomophila and L. decolor (Psocoptera: Liposcelididae) in steel bins containing wheat.

ABSTRACT We studied the temporospatial distribution of psocids in steel bins containing 32.6 tonnes of wheat in 2005 and 2006 in Manhattan, KS. Psocids were sampled in the top 0.9 m of wheat using a 1.2-m open-ended trier; samples were taken from the bin center and in the four cardinal directions at 0.15 and 0.76 m from the bin wall. In addition, a 2.4-m partitioned grain trier with 16 compartments was used to sample psocids from a 2-m-diameter circle in the center of the bins and to a depth of 1.96 m. Only two species of psocids were identified in the study: Liposcelis entomophila in 2005 and L. decolor in 2006. Densities of psocids were low immediately after bins were filled in July 2005, peaked in October, dropped to almost zero in December as temperatures decreased, and remained at low levels until the study was ended in March. In 2006, densities of psocids increased gradually from August to mid-October and declined until the study was ended in early November. During the fall, psocids were more abundant at the center of the bin and at lower depths. In October to November of both years, the temperatures and moisture contents of grain in the center also were higher than that in other locations. This is the first report of temporospatial distribution of psocids in steel bins of wheat.

Aeration management for stored hard red winter wheat: simulated impact on rusty grain beetle (Coleoptera: Cucujidae) populations.

Abstract Simulation studies were conducted to determine temperature accumulations below defined thresholds and to show the impact of controlled aeration on populations of the rusty grain beetle, Cryptolestes ferrigineus (Stephens), a major secondary pest of stored wheat, Triticum aestivum (L.). Recorded data from weather stations in Texas, Oklahoma, Kansas, eastern New Mexico, and eastern Colorado (356 total) were used to determine hours of temperature accumulation below 23.9°C in June and July, 15.6°C in September and October, and 7.2°C in December. At an airflow rate of 0.0013 m3/s/m3 (0.1cubic ft 3/min/bu), which requires 120 h of temperatures below the specified threshold to complete an aeration cycle, summer cooling at 23.9°C in bulk-stored wheat could be completed throughout the hard red winter wheat zone except for extreme southern Texas. An early-autumn cooling cycle at 15.6°C could not be completed throughout most of Texas and Oklahoma before the end of September. The late-autumn cooling cycle could be completed in all states except Texas by the end of November. Five geographic regions were delineated and the times required for completion of the summer, early-autumn, and late-autumn cooling cycles within each region were estimated. Population growth of the rusty grain beetle was modeled for San Antonio, TX; Abilene, TX; Tulsa, OK; Topeka KS; and Goodland, KS, by predicting the numbers of adults in the top, outer middle, outer periphery, and the center of the bin during a 1-yr storage season. Populations of C. ferrugineus in San Antonio and Austin were predicted to exceed the Federal Grain Inspection Service (FGIS) threshold of two beetles per kilogram of wheat in all four levels of the bin during late autumn, decline during the winter, and increase the following spring. In Midland, TX, and Oklahoma City, OK, populations were predicted to exceed the threshold only in the top and outer middle of the bin, whereas populations in the Kansas locations were not predicted to exceed the threshold at any time.

Susceptibility of Lasioderma serricorne (Coleoptera: Anobiidae) life stages to elevated temperatures used during structural heat treatments.

ABSTRACT Heat treatment of food-processing facilities involves using elevated temperatures (50– 60°C for 24–36 h) for management of stored-product insects. Heat treatment is a viable alternative to the fumigant methyl bromide, which is phased out in the United States as of 2005 because of its adverse effects on the stratospheric ozone. Very little is known about responses of the cigarette beetle, Lasioderma serricorne (F.) (Coleoptera: Anobiidae), a pest associated with food-processing facilities, to elevated temperatures. Responses of L. serricorne life stages to elevated temperatures were evaluated to identify the most heat-tolerant stage. Exposure of eggs, young larvae, old larvae, and adults during heat treatment of a food-processing facility did not clearly show a life stage to be heat tolerant. In the laboratory, exposure of eggs, young larvae, old larvae, pupae, and adults at fixed times to 46, 50, and 54°C and 22% RH indicated eggs to be the most heat-tolerant stage. Time-mortality responses at each of these three temperatures showed that the time for 99% mortality (LT99) based on egg hatchability and egg-to-adult emergence was not significantly different from one another at each temperature. Egg hatchability alone can be used to determine susceptibility to elevated temperatures between 46 and 54°C. The LT99 based on egg hatchability and egg-to-adult emergence at 46°C was 605 and 598 min, respectively, and it decreased to 190 and 166 min at 50°C and 39 and 38 min at 54°C An exponential decay equation best described LT99 as a function of temperature for pooled data based on egg hatchability and egg-to-adult emergence. Our results suggest that during structural heat treatments eggs should be used in bioassays for gauging heat treatment effectiveness, because treatments aimed at controlling eggs should be able to control all other L. serricorne life stages.

Control of Stored-Product Beetles with Combinations of Protein-Rich Pea Flour and Parasitoids

Abstract Protein-rich pea flour is toxic and repellent to three major stored-grain pests: the rice weevil, Sitophilus oryzae L.; the red flour beetle, Tribolium castaneum (Herbst); and the rusty grain beetle, Cryptolestes ferrugineus (Stephens). This study found that protein-rich pea flour was not toxic to, and did not reduce the offspring of, Anisopteromalus calandrae (Howard), a parasitoid of S. oryzae, nor did it reduce offspring of Cephalonomia waterstoni (Gahan), a parasitoid of C. ferrugineus. Protein-rich pea flour was also not repellent to A. calandrae. Small-scale and large-scale tests of a combination of protein-rich pea flour and parasitoids were conducted in 2-liter jars and in barrels containing 330 kg wheat. A larger population of A. calandrae was found at a high host infestation rate (24 adults/kg for 25 d), but the parasitoid did not become established at middle and low host infestation rates (2.4; 0.24 adults/kg for 25 d). The combinations of protein-rich pea flour and parasitoids reduced populations of S. oryzae in both tests. Additional effects of protein-rich pea flour and parasitoids were found in the large-scale test. Releasing parasitoids alone reduced the populations of S. oryzae by 46% and C. ferrugineus by 49%. Treating wheat with 0.04 or 0.1% protein-rich pea flour reduced the population of S. oryzae by 26 and 79% and C. ferrugineus by 27 and 43%, respectively. Combining parasitoids with 0.04 or 0.1% protein-rich pea flour reduced S. oryzae populations by 76 and 98% and C. ferrugineus populations by 42 and 75%, respectively. At the end of the large-scale experiment, grain treated with protein-rich pea flour alone or in combination with parasitoids had better grain quality than the untreated controls.

Predicting Stored Grain Insect Population Densities Using an Electronic Probe Trap

ABSTRACT Manual sampling of insects in stored grain is a laborious and time-consuming process. Automation of grain sampling should help to increase the adoption of stored grain integrated pest management. A new commercial electronic grain probe trap (OPI Insector) has recently been marketed. We field tested OPI Insector electronic grain probes in two bins, each containing 32.6 tonnes of wheat, Triticum aestivum L., over a 2-yr period. We developed new statistical models to convert Insector catch into insects per kilogram. We compared grain sample estimates of insect density (insects per kilogram of wheat) taken near each Insector to the model-predicted insect density by using Insector counts. An existing expert system, Stored Grain Advisor Pro, was modified to automatically read the Insector database and use the appropriate model to estimate Cryptolestes ferrugineus (Stephens), Rhyzopertha dominica (F.), and Tribolium castaneum (Herbst) density from trap catch counts. Management decisions using Insector trap-catch estimates for insect density were similar to those made using grain sample estimates of insect density for most sampling dates. However, because of the similarity in size of R. dominica and T. castaneum, the software was unable to differentiate counts between these two species. In the central and southern portions of the United States, where both species frequently occur, it may be necessary to determine the proportion of each species present in the grain by manual inspection of trap catch. The combination of SGA Pro with the OPI Insector system should prove to be a useful tool for automatic monitoring of insect pests in stored grain.