P. F. Lamb

Cultivar preferences of ovipositing wheat stem sawflies as influenced by the amount of volatile attractant

ABSTRACT The wheat stem sawfly, Cephus cinctus Norton, causes severe losses in wheat grown in the northern Great Plains. Much of the affected area is planted in monoculture with wheat, Triticum aestivum L., grown in large fields alternating yearly between crop and no-till fallow. The crop and fallow fields are adjacent. This cropping landscape creates pronounced edge effects of sawfly infestations and may be amenable to trap cropping using existing agricultural practices. The behavioral preference for two wheat varieties was assessed in the context of developing trap crops for this insect. In field nurseries, stem lodging assessments indicated that the cultivar ‘Conan’ was infrequently damaged, whereas ‘Reeder’ was often heavily damaged. In laboratory choice and no-choice tests, ‘Reeder’ was significantly preferred by ovipositing wheat stem sawfly females. These two cultivars did not differ significantly in height or developmental stage, factors known to impact sawfly preference. Although Conan received fewer eggs than Reeder in no-choice tests, oviposition was further reduced in choice tests, indicating that females clearly preferred Reeder. In field trials where the overall dimensions of the spatial structure in choice tests was varied, females always selected Reeder over Conan in alternating block, row, and interseeded planting scenarios. Reeder releases greater amounts of the attractive compound, (Z)-3-hexenyl acetate than Conan but is similar to Conan for three other known, behaviorally active volatile compounds. The results are discussed in terms of cultivar selection for large scale trap crop experiments for the wheat stem sawfly.

Using Agronomic Traits and Semiochemical Production in Winter Wheat Cultivars to Identify Suitable Trap Crops for the Wheat Stem Sawfly

Abstract Trap crops are a plausible control strategy for the wheat stem sawfly (WSS), Cephus cinctus Norton (Hymenoptera: Cephidae), especially in alternate wheat—fallow cropping systems. Identifying the most suitable winter wheat (Triticum aestivum L., Poaceae) cultivars is necessary to further improve the effectiveness of winter wheat trap crops. We compared cultivars suitable for cultivation in Montana to identify those that exhibit the greatest potential as trap crops. To accomplish this we used nine winter wheat cultivars to analyze plant characteristics that influence the oviposition behavior of the WSS: stem height, stem diameter, rate of plant development, and emission of the WSS attractant (Z)-3-hexenyl acetate. Data on sawfly-induced stem cutting collected from these cultivars in field nurseries were analyzed to evaluate the potential of each cultivar to attract sawflies. Based on these criteria, five cultivars with good potential as trap crops are ‘Norstar’, ‘Neeley’, ‘Morgan’, ‘Rampart’, and ‘BigSky’. More data from laboratory preference tests and detailed measurement of semiochemical production from these cultivars are required for selecting optimal cultivars for trap-cropping.

Characterization of Resistance to Cephus cinctus (Hymenoptera: Cephidae) in Barley Germplasm

Abstract Most barley cultivars have some degree of resistance to the wheat stem sawfly (WSS), Cephus cinctus Norton (Hymenoptera: Cephidae). Damage caused by WSS is currently observed in fields of barley grown in the Northern Great Plains, but the impact of WSS damage among cultivars due to genetic differences within the barley germplasm is not known. Specifically, little is known about the mechanisms underlying WSS resistance in barley. We characterized WSS resistance in a subset of the spring barley CAP (Coordinated Agricultural Project) germplasm panel containing 193 current and historically important breeding lines from six North American breeding programs. Panel lines were grown in WSS infested fields for two consecutive years. Lines were characterized for stem solidness, stem cutting, WSS infestation (antixenosis), larval mortality (antibiosis), and parasitism (indirect plant defense). Variation in resistance to WSS in barley was compared to observations made for solid-stemmed resistant and hollow-stemmed susceptible wheat lines. Results indicate that both antibiosis and antixenosis are involved in the resistance of barley to the WSS, but antibiosis seems to be more prevalent. Almost all of the barley lines had greater larval mortality than the hollow-stemmed wheat lines, and only a few barley lines had mortality as low as that observed in the solid-stemmed wheat line. Since barley lines lack solid stems, it is apparent that barley has a different form of antibiosis. Our results provide information for use of barley in rotation to control the WSS and may provide a basis for identification of new approaches for improving WSS resistance in wheat.