Proceediuqe of the 7th International Working Conference on Stored-product Protection. - Volume 2 Decrease in population size of Rhyzopertha dominica (Coleoptera: Bostrichidae ) at two temperatures in different wheat cultivars by the parasitoid Theocolax elegans (Hymenoptera: Pteromalidae) * Michael D. Toews", Gernt W. Cuperus, and Thomas W. Phillips Abstract mcreased mterest m usmg entomophagous insects, such as A laboratory study was conducted to examine the role of the the parasitoid Theocolox elegans (Westwood) parasitoid Theccolax elegans in decreasing quantity of F1 (Hymenoptera: Pteromahdae ) , m managing pests such as Rhyzopertha dominica progeny. Expenments were Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae ). conducted at two temperatures, 27.0 and 34.0°C, and in Rhyzopertha domuiica IS one of the most damaging and frve divergent cultivars of U. S wheat. Wheat stored in abundant pests of stored gram m the southern Umted States (Cuperus et al. 1986, Vela-Coiffier et al. 1997). ThIS glass Jars was infested with R. domuuca for four days and then the parental generation was removed wlule the progeny msect feeds m gram both as a larva and as an adult. were allowed to complete their life cycle Theocolax Detection of the species ISdifficult because larvae and adults tend to remain hidden inside the kernel (Fargo et al. 1989, elegans were released into half of the Jars and their progeny Vela-Coiffier et al. 1997). Females feed extensively and were allowed to develop. Adult progeny of pest and then lay eggs singly or in small clusters extenor to the parasitoid were collected and analyzed to access efficacy of kernels (Golebiowska 1969). The first instar then bores into the parasitoid at suppressing Its host. the kernel where It continues feeding on the endosperm, Increased suppression of the pest was detected at the molting 3 - 5 times before pupation The complete hfe cycle lower temperature when compared with the upper takes approximately 25 days at 34.0°C (BIrch and Snowball temperature. More parasitoids completed their life cycle at 1945, Howe 1950) Optimal developmental temperatures for the lower temperature, thus mcreasmg the potential for this species are 32.0 to 35. O°C (White 1995) but control m future generations. Analysis of interactions among development can be slowed by cooling the temperature of the the three trophic levels indicated that wheat cultivars did not gram (Howe 1950) significantly enhance the reproductive capacity of the Theocolax elegans IS a sohtary ectoparasrtoid that parasitoid. parasitizes beetle larvae within the kernel Sharifi (1972) provided an extensive list of possible hosts of T elegans. Potential SItes for oviposition are determined through mechanical detection using the antennae (Van Den Assem Introduction and Kuenen 1958) Dunng oviposition, the female inserts an egg into the kernel placmg it on the exterior body surface of the host larva. The larva of the parasrtoid continues to Biological control is an Important part of integrated pest develop extenor to the pest larva while both are still management (IPM) methods for stored grain. Parasitoids confined within the kernel. Theocolox elegans can complete and predators occur naturally m bulk stored grain facilrties one generation m approximately 25 days at 25. O°C (Van (Nilakhe and Parker 1990, Vela de Garza 1993, Gates 1995) Den Assem and Kuenen 1958). The developmental time for and are known to attack most msect pests of stored gram T. elegans is approximately one-half that of ItS hosts (Flmn (Hagstrum and Flinn 1992). In 1992 the U. S Food and et al. 1996). After emergence, the adult parasitoid bores Drug Admmistration (Anonymous 1992) exempted benefICial out of the kernel. msects from tolerance standards m stored gram. This has Few studies have been conducted utIhzmg augmentation of T elegarus to suppress R. dominica populations. Fhnn et 1Oklahoma State UruversIty, Department of Entomology and Plant al (1996) conducted expenments m steel gram bms m Pathology, 127 Noble Research Center, StIllwater, Oklahoma 74078 whIch thIS parasitOld speCIes was able to suppress R -3033 USA dominica populatIOns m excess of 90 % for two years * MDT WIll be presentIng trus paper compared to the unparaslhzed group In addItion, R 1231 Proceedrnqs of the 7th lnternatumal Worktng Conference on Stored-product Protection - Yolume 2 dominica populations were suppressed well below the existing infestations Gram was then cleaned by multiple Federal Grain Inspection Service (FGIS) standard of two passages over a seed cleaner (Clipper model M2B, Bluffton hve insects per kg for the' sample' grade designauon. Flmn Agncultural Industnal Corp , Bluffton, Indiana) and then (1998) also demonstrated that augmentative releases of T tempered to 13 ± 0.5 % moisture by either adding water or elegans were more efficacious when coupled with lower by ambient drying Whole wheat flour was added to each temperatures sample of wheat at a rate of one percent by weight to Ecologists use the term trophic or feedmg level to stimulate oviposition by R. donuruca . Wheat moisture delmeate an organism's place m the food cham (Lmdeman contents were determined using the ASAE standard dry 1942) The management system of concern m this paper weight method (Society of Agncultural Engineers 1996). includes the wheat cultrvar as the first trophic level, R Experiments were conducted WIth 75.0 ± 1.0 g of wheat dommica as the second, and finally T elegans as the tlurd in 0 2366 liter round glass cannmg jars. Forty, 2 - 3 week trophic level. Interactions among these three trophic levels old unsexed R dominica adults, from OSU stock cultures are collectively termed 'tntrophlc mteractIons' An reared on the hard red winter cultrvar '2163' , were added Important consideration among tntrophic mteractions IS that to each jar for a four-day oviposrtional penod All Jars were members of the first and third trophic levels may act m a kept at 30.0 ± O. 5°C in an environmental chamber mutuahstic manner (Pnce 1986) Starks et al. (1972) (Percrval-Scienufic Corp., Model 1-35 LVL) durmg the studied relationships in a cereal field crop ecosystem and mitial oviposrtional penod m order to begin With an quantified Important observations pertinent to other approximately equal number of eggs in each jar. Followmg ecosystems Of primary concern m their study and several the ovipositional penod, gram was gently sieved over a 1.40 others was the concept that the pnmary trophic level, I E. mm standard dockage SIeve. Beetles were collected below the host plant of the herbivore, could influence development that SIeveon a 0.21082 mm SIevewhile the dust fell through and survivorship of a carnivorous species at the third tropluc both SIeves to be collected m a bottom pan. Wheat and dust level (Starks et al. 1972, Reed et al 1991, 1992, 1993, were returned to the jars for the duration of the expenment. Reitz and Trumble 1996). A second Important aspect of Ventilation was permitted through filter paper held m place these studies was that activIty of parasitOids at the thIrd by the cannmg nng. Samples were mamtamed at eIther trophIC level can mfluence the extent of feedmg damage to 27.0 ± 0 .5°C or 34.0 ± 0 .YC and 70 ± 5% rho Completely the plant speCIes Fmally, biOlogIcalcontrol and host plant dark condItions were utilIzed throughout the expenment resIstance can be hIghly compatible m the development of Hygrothermographs were mamtamed mSIde each successful pest management programs (Salto et al. 1982). envIronmental chamber to momtor any changes m Objectives of thISstudy were to (1) evaluate the effects of temperature or humIdIty wheat cultIvar, temperature, and the parasitOid T elegans, Expenments were conducted m a splIt plot arrangement m on the number of adult R dommica progeny, (2) WhICh the mam plot was temperature, arranged m a determme percent suppreSSIon of adult R. donnmca completely randomIzed deSIgn, whIle the subplot treatments progeny due to T elegans, (3) compare the abIlIty of T. were cultIvar and presence of the parasitOId, arranged m a elegans to complete ItS lIfe cycle under the mfluence of the randomIzed complete block. Subplot treatments were dIfferent temperatures. blocked across the envIronmental chambers from left to nght because an earlier umformlty tnal mdlcated dIfferences m a Materials and Methods chamber Each envIronmental chamber represented one applIcation of 'temperature' while subplot treatments were FIve cultIvars of wheat (Tntwum aestz1mm 1.) were each replIcated four times wlthm each chamber. The procured from commercial seed producers and vanous expenmental umt at the subplot level m thISexpenment was foundation seed stocks across the Umted States. Wheat a jar of wheat mfested WIthR donumca. Wlthm a subplot cultIvars represented dIvergent genetIc lmeage and replIcatiOneach wheat cultivar was represented two times, resistance to common field pathogens and msects. Selections once m the absence of the parasltoid and once WIth the mcluded the hard red wmter cultivar '2163' (Oklahoma parasitOid present. Each expenment mcluded two Foundation Seed Stocks, Inc , Stillwater), soft red wheats replIcations of temperature (two chambers at each 'Coker 916' (NovartIs Seeds, Inc., Bay, Arkansas) and expenmental temperature), eIght replIcations of each 'WakefIeld' (Arkansas Agncultural Expenment Station, cuItIvar WIth parasltOids per temperature, and eIght FayettevIlle), the durum wheat 'Mumch' (North Dakota replIcations of each cultIvar WIthout parasitOids. Seedstocks Project, Fargo) and a whIte spnng wheat, TIme of beetle and parasitOid mtroductIon and removal , WawawaI' (Washington State Crop Improvement times are summanzed m Table 1. All adult T elegans were AsSOCiation,Pullman) Followmg receIpt wheat samples less than three days old when released mto the gram. were frozen for one week to elImmate the poSSIbIlItyof ParasitOidswere reared m stock colomes on R donunica m 1232 Proceedwgs of the 7th lnternational Workzng Conference on Stored-product Proteciuni - Yoiume 2 '2163' wheat FIve male and 10 female parasitoids were expenmental temperatures were estimated With a degree released at each release time.