Joseph K. Peterson

Quantification of electroantennogram responses of the primary rhinaria ofAcyrthosiphon pisum (Harris) to C4-C8 primary alcohols and aldehydes

Electroantennograms (EAGs) of the distal and proximal primary rhinaria (DPR and PPR, respectively) were recorded from excised antennae of alate virginoparous pea aphids,Acyrthosiphon pisum (Harris) (Homoptera: Aphididae). Primary unsaturated alcohols and aldehydes with varying carbon length (C4–C8) were used as volatile stimuli. EAGs were recorded for a series of source concentrations from the DPR and PPR separately through the use of sectional electroantennography. A logistic equation was fitted to the source concentration-response data. Differences in relative EAG response of the DPR and PPR to the alcohols and aldehydes were analyzed by deriving five parameters from this logistic equation. These parameters relate to particular characteristics of sigmoid curves: the saturation (maximum) EAG response (Rs), the concentration for which the relative EAG response is ½Rs (CR50), the stimulus response range (SR0.9), the threshold concentration (CR1), and the EAG response area (AR). Of these parameters, the EAG response area showed the largest separation between EAG responses of the DPR and PPR to the two homologous groups and between compounds with varying carbon chain lengths. The DPR was significantly more responsive to alcohols than to aldehydes, while the reverse was true for the PPR, indicating a basic difference between the two primary rhinaria. The highest overall responses were elicited by 1-hexanol, hexanal, and heptanal.

Squash leaf glandular trichome volatiles: Identification and influence on behavior of female pickleworm moth [Diaphania nitidalis (Stoll.)] (Lepidoptera: Pyralidae)

Fourteen volatile compounds occurring in leaf trichomes of yellow squash (Cucurbita pepo L. cv. Early Prolific Straightneck) were identified. These compounds accounted for 83.5% of the volatile matrix. Ubiquitous constituents of the epidermis (myristic, palmitic, and stearic acids,n-tricosane, andn-pentacosane) accounted for 73.7%; these compounds were not bioassayed. The volatileso-,m-, andp-xylene, toluene, 2-heptanone, (R)-(+)- and (S)-(−)-limonene, and germacrene D were tested for their influence on attraction and oviposition by the pickleworm moth (Diaphania nitidalis Stoll.). No single compound, except germacrene D, was attractive. (R)-(+)-Limonene and 2-heptanone were weakly repellent. Mixtures of the highly volatile fractions were as attractive as volatiles emanating from whole, intact leaves. Oviposition levels on treated artificial sites corresponded with levels of visitation. Oviposition was significantly stimulated by “whole-leaf” volatiles, and (S)-(−)-limonene caused a slight but significant reduction.

Isolation of substance from sweet potato (Ipomoea batatas) periderm tissue that inhibits seed germination

Chromatographic procedures were used to isolate inhibitors of seed germination from sweet potato root periderm tissue. The inhibitory activity of all fractions was monitored using a proso millet seed germination bioassay. A single HPLC peak, representing approximately 1.2% of the periderm dry weight, accounted for most of the inhibitory activity. The active fraction was labile in methanolic solution. Further fractionation of this peak by HPLC methods was not successful. In vitro seed germination dose-response relationships were established for the peak. The various seed species exhibited an extremely wide range of sensitivity. The I50 values were 0.16, 0.013 and 0.011 mg/ml for redroot pigweed, velvetleaf, and proso millet, respectively. Tall morning glory was not inhibited by any concentration tested.

Internal bacteria in the Chrysomelidae

The exiguous attention given thus far to the occurrence and biology of internal bacteria or other microorganisms in the Chrysomelidae, is surprising. The family is represented by a large number of species (perhaps 60,000–70,000, Jolivet et al. 1988) and many carry considerable economic importance such as the Colorado potato beetle, [Leptinotarsa decemlineata (Say)], the asparagus beetle [Criocerus asparagi (L.)], several members of the genus Diabrotica and many others. The considerable damage caused by the phytophagous Chrysomelidae as well as possible vectoring of plant pathogens warrants increased efforts toward the study of bacterial associations. Also, the role of an insect’s internal microbiota in the metabolism of chemical pesticides has hardly been considered. To quote Steinhaus (1955): Theoretically altering an insect’s environment in such a way as to destroy its symbiote or cause the symbiote to become pathogenic offers a possible method of biological control of certain pests’. Although such an approach does not seem practical, it is not impossible (Brooks, 1963). Recent scientific advances in molecular genetics and chemical ecology may increase attention given to the microecology of the Chrysomelidae.

INFLUENCE OF DROUGHT STRESS ON SWEETPOTATO RESISTANCE TO SWEETPOTATO WEEVIL, CYLAS FORMICARIUS (COLEOPTERA: APOINIDAE), AND STORAGE ROOT CHEMISTRY

Abstract The effect of drought stress on the resistance of sweetpotato roots to sweetpotato weevil (SPW), Cylas formicarius (Fab.), was studied in 1997 and 1998 in two genotypes (“Beauregard” and “Excel”) with different SPW susceptibility. Storage roots produced under drought or normal conditions were tested for adult feeding, oviposition, larval survival and pupal weight in the laboratory under no-choice and free-choice test conditions. The levels of sweetpotato resin glycoside and caffeic acid in the periderm tissue of the roots were also determined. Drought-stressed roots received significantly more SPW eggs under no-choice and free-choice conditions and more feeding punctures under free-choice conditions than non-stressed roots in 1997. Larval survival rate was significantly lower on drought-stressed roots. A significant drought effect on feeding, oviposition and larval survival was absent in 1998. Drought stress had no effect on sweetpotato resin glycosides content in both years, but significantly reduced the content of caffeic acid in 1997. Genotype had a significant effect on SPW feeding in 1997 and on feeding and oviposition in 1998 under free-choice test conditions, where Beauregard was preferred for both feeding and oviposition. Beauregard also supported a significantly higher larval survival rate compared with Excel. Resin glycosides or caffeic acid contents were similar for the two genotypes in 1997, while higher level of resin glycosides was detected in Excel than in Beauregard in 1998. The interaction between drought stress and genotype was significant for adult feeding under free-choice conditions and for larval survival, indicating a different response between the two genotypes.

Chemical Factors involved in Selection of Host Plant for Oviposition by the Pickleworm Moth (Lepidoptera: Pyralidae)

Studies with caged gravid females of the pickleworm, [Diaphania nitidalis (Stoll.)], revealed that leaves of yellow squash (Curcurbita pepo L.) contain small (MW <1000), non-volatile and highly polar amphoteric compounds which stimulate oviposition on artificial sites. Several compounds, extracted from paper chromatograms, caused moderate stimulation of oviposition. When these extracts were recombined, the mixture proved highly active. Addition of whole leaf volatiles to the active water-soluble fraction increased oviposition. The whole leaf volatiles mixture could be substituted with volatiles originating from leaf glandular trichomes. Index Words. Lepidoptera, Diaphania nitidalis, oviposition, host plant, squash, Curcurbita pepo, trichomes, volatiles.

Isolation and Structural Identification of Sucrose Esters from Corn Spurrey (Spergula arvensis); Inhibition of Seed Germination

Polar as well as nonpolar extracts of Spergula arvensis (corn spurrey) were shown to cause inhibition of seed germination. The polar methylene chloride extracts were subjected to solvent partitioning and separations by a combination of silicic acid and Sephadex LH-20 column chromatography. All chromatographic fractions were monitored by a proso-millet seed germination assay, which resulted in the isolation of a group of sucrose esters (SE). The identity of the ester acids was determined by gas chromatography (GC) of their butyl esters. Further characterization of the SE by GC-mass spectrometry of their trimethylsilyl derivatives showed the presence of four different SE groups with two to seven acyl groups attached to sucrose. The SE isomers in greatest abundance contained either octanoic or dodecanoic acid along with two smaller branched-chain acids (butanoic and pentanoic acids). All four SE groups were inhibitory to seed germination. This is the first report of SE outside the family Solanaceae.