Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2002
Publication Date: 6/1/2003
Citation: GILES, K.L., JONES, D.B., ROYER, T.A., ELLIOTT, N.C., KINDLER, D. DEVELOPMENT OF A SAMPLING PLAN IN WINTER WHEAT THAT ESTIMATES CEREAL APHID PARASITISM LEVELS AND PREDICTS POPULATION SUPPRESSION. JOURNAL OF ECONOMIC ENTOMOLOGY. 2003. v. 96(3): p. 975-982. Interpretive Summary: The cereal aphids are serious insect pests of wheat that cause extensive monetary losses to wheat growers in the Southern Plains. Certain parasitic wasps lay their eggs in cereal aphids, which subsequently hatch into larvae that kill the aphid. These parasites are capable of controlling cereal aphids in a wheat field biologically, but control does not always occur, and sampling methods are required to assess the likelihood of successful biological control. A relationship between the proportion of cereal aphids parasitized and the proportion of tillers with a mummified aphid (an aphid that has been killed by a parasitic wasp) was determined in numerous wheat fields in Oklahoma. Based on this study it was determined that when 10% or more of wheat stems in a sample had one or more mummies, effective biological control was predicted to occur. We monitored cereal aphid populations in 16-25 winter wheat fields over the growing season during two years and assessed whether cereal aphid infestations increased above or were maintained below levels at which they would be expected to cause economic injury to wheat fields. Results of this validation study revealed that aphid infestations exceeded the economic injury level in only one field when it was predicted to remain below. The sampling scheme developed during the study allowed us to quickly and accurately classify fields as to whether the cereal aphid infestation would be controlled biologically by parasitic wasps or not. Based on our results, we believe that simultaneous use of cereal aphid and parasitic wasp sampling schemes will be efficient and useful tools for consultants and producers in the Southern Plains and will decrease the number of unnecessary insecticide applications.
Technical Abstract: From 1998 to 2001, the relationship between the proportion of cereal aphids parasitized (Pp) and the proportion of tillers with > 0 mummified aphids (Ptm) was estimated on 57 occasions in fields of hard red winter wheat located in central and western Oklahoma. Both original (57 fields) and validation data (34 fields; 1998-2002) revealed that when Ptm > 0.1, Pp always exceeded the recommended parasitism threshold of 0.2. Based on these findings, upper (Ptm1) and lower (Ptm0) decision threshold proportions were set at 0.1 and 0.05, respectively. We monitored cereal aphid populations in 16-25 winter wheat fields over time, and based on the upper and lower decision threshold proportions (Ptm1=0.1, Ptm0=0.05), predicted whether aphid intensities (# per tiller) would increase above or be maintained below selected economic thresholds (3, 9, and 15 aphids per tiller). Results of this validation study revealed that aphid intensity exceeded an economic threshold in only one field when predicted to remain below; Ptm > 0.1 but aphid intensity reached a maximum of 4 aphids per tiller. The sampling plan developed during this study allowed us to quickly classify Ptm, and independent of initial cereal aphid intensities, very accurately predict suppression of populations by parasitoids. Sequential sampling stop lines based on sequential probability ratio tests for classifying proportions were calculated for Ptm1=0.1 and Ptm0=0.05. The average sample number required to classify Ptm as above 0.1 or below 0.05 ranged from 130 (Ptm = 0.075) to less than 25 (Ptm > 0.20). Based on the results of this study, we believe that simultaneous use of aphid and parasitoid sampling plans will be efficient and useful tools for consultants and producers in the southern plains and decrease the number of unnecessary insecticide applications.