P. Larry Phelan

Chemical characterization of fruit and fungal volatiles attractive to dried-fruit beetle,Carpophilus hemipterus (L.) (Coleoptera: Nitidulidae).

The chemical basis underlying orientation to fruit and fungal odors was investigated for the dried-fruit beetle,Carpophilus hemipterus (L.). In wind-tunnel bioassays of walking and flight response from 1.8 m, beetles were attracted to odors of the yeastSaccharomyces cerevisiae on agar, aseptic banana, or banana inoculated withS. cerevisiae, although both banana substrates elicited greater response than the yeast alone. When presented in a two-choice bioassay, the yeast-inoculated banana attracted approximately twice as many beetles as did the aseptic banana. GC-MS analysis of the headspace volatiles above these odor sources revealed a somewhat more complex and concentrated volatile profile for yeast-inoculated banana than for aseptic banana. The odor from yeast on agar had fewer components, and these were present at lower concentrations than the odors of either banana substrate. By blending mineral-oil or aqueous solutions of the 18 components of inoculated-banana odor in varying concentrations, it was possible to mimic closely the headspace profile of the natural odor. This synthetic odor also elicited beetle attraction in the wind tunnel at levels comparable to the inoculated banana. Through a series of bioassays in which individual components were subtracted from or added to a synthetic odor blend, it was determined that ethyl acetate, acetaldehyde, 2-pentanol, and 3-methylbutanol comprised the simplest blend of compounds evoking full behavioral response. However, 2-methylpropanol or butanol were apparently interchangeable with 3-methylbutanol in this blend, and comparable response could also be elicited by replacing acetaldehyde with a combination of both 2-pentanone and 3-hydroxy-2-butanone. Thus, our results suggest that this generalist insect herbivore locates its hosts by a long-range response to a variety of blends of common fruit volatiles, whose concentrations are enhanced by fungi.

EVALUATION OF INDIVIDUAL COMPONENTS OF PLUM ODOR AS POTENTIAL ATTRACTANTS FOR ADULT PLUM CURCULIOS

We evaluated olfactory attraction of overwintered plum curculio (PC) adults, Conotrachelus nenuphar, to 16 individual volatile components of unripe plum odor in the laboratory using a still-air dual-choice bioassay system and in the field using baited cotton dental wicks attached to boll-weevil traps placed on the ground beneath the canopy of unsprayed apple trees. Two compounds, ethyl isovalerate and limonene, were significantly attractive in both laboratory bioassays and field experiments. In laboratory bioassays, as concentration was decreased across five orders of magnitude, a greater number of compounds elicited responses suggestive of attractancy (except at the lowest concentration). Even so, linalool, 2-hexanone, and 3-hydroxy-2-butanone were the only other compounds showing significant attractiveness in laboratory bioassays, but none of these (nor any other compounds) were significantly attractive in field assays. We suggest that the use of ethyl isovalerate and/or limonene as odor attractants offers potential to increase the efficacy of current traps for monitoring PCs immigrating into fruit orchards during spring.

Characterization of chemicals mediating ovipositional host-plant finding byAmyelois transitella females

Ovipositional host-finding in the navel orangeworm,Amyelois transitella (Walker), is brought about by an in-flight response to host odors. Wind-tunnel studies of the response of gravid females to almonds showed that this response is mediated primarily by long-chain fatty acids, particularly oleic acid and linoleic acid. Evidence for the behavioral activity of fatty acids is based on the fact that: (1) behavioral activity of almond oil was concentrated in a single liquid chromatographic fraction whose composition was predominantly long-chain fatty acids, (2) behavioral activity was lost when either almond oil or the active fraction of that oil was treated with diazomethane, (3) full activity was elicited by a selective extraction of free fatty acids from crude almond oil, and (4) upwind response by females was elicited by a blend of synthetic oleic and linoleic acids, albeit at a level less than that elicited by almond oil. Five fatty acids identified from the almond oil were: myristic acid (1%), palmitic acid (16%), stearic acid (3%), oleic acid (58%), and linoleic (22%). Attraction to various combinations of synthetic acids was observed only when oleic acid was present, and oleic acid elicited upwind flights to the source when presented alone; however, short-range responses were enhanced by the addition of linoleic acid, which elicited no long-range orientation by itself. Despite significant levels of attraction to synthetic blends, the percentage of females flying to the source was lower than that flying to acidulated almond oil, the best natural attractant tested. Thus, although longrange response may be mediated primarily by a blend of oleic and linoleic acids, additional and as yet unidentified components must also play an important role. Long-range chemically modulated host finding in this and other generalist plant feeders is discussed with respect to current models of the evolution of host finding, and it is argued that suggestions that long-range host finding should be correlated with narrowness of host utilization are logically flawed and are not supported by our current understanding of specific examples of host finding.

IDENTIFICATION OF FOOD VOLATILES ATTRACTIVE TO DUSKY SAP BEETLE, Carpophilus lugubris (COLEOPTERA: NITIDULIDAE)

The chemical mediation of host-finding was investigated for the dusky sap beetle,Carpophilus lugubris Murray. GC-MS analysis of the headspace volatiles above whole-wheat bread dough inoculated with bakers yeast, a substrate previously determined to be an effective attractant, revealed seven major components in the following order of decreasing concentration: ethanol, acetaldehyde, 2-methylpropanol, 3-methylbutanol, propanol, 2-methylbutanol, and ethyl acetate. Solutions of these seven compounds blended so as to mimic the odor of whole-wheat bread dough elicited upwind orientation from 1.8 m in a wind tunnel byC. lugubris at a level comparable to that elicited by the bread dough. A series of bioassays investigating the role of individual components from the synthetic blend determined that all seven compounds contributed to behavioral activity; however, the simplest blend evoking attraction comparable to bread dough included acetaldehyde, ethyl acetate, 2-methylpropanol, and 3-methylbutanol. Of these compounds, acetaldehyde was essential, ethyl acetate was interchangeable with ethanol or partially replaceable with propanol, and 2-methylpropanol and 3-methylbutanol were partially replaceable with a combination of the other alcohols. Headspace volatiles above aseptic or fungus-inoculated tomato, banana, sweet corn, and strawberry were also qualitatively and quantitatively analyzed. This study suggests thatC. lugubris locates its food sources by response to variable blends of common volatile constituents of plants and fungi.

Mixture models of soybean growth and herbivore performance in response to nitrogen-sulphur-phosphorous nutrient interactions

1. It is widely established that plant‐mineral nutrition is an important determinant of herbivore developmental performance and behavioural preference. Unfortunately, the specific effects of minerals on herbivory have been variable and few unifying principles have emerged. Advances in this area may be impeded in part by an experimental approach that emphasises single nutrients without regard to nutrient ratios.

Bioassay approaches to assessing behavioral responses of plum curculio adults (Coleoptera: Curculionidae) to host fruit odor.

We evaluated several approaches to developing a simple, sensitive, and reliable laboratory bioassay of responses of overwintered adult plum curculios (PCs),Conotrachelus nenuphar (Herbst), to host fruit odor or its attractive components. A high proportion of assayed PCs responded positively to odor of wild plums under no-choice, moving-air conditions in a wind tunnel and under dual-choice, still-air conditions in enclosed Petri dishes. Positive response to controls lacking host odor, however, was much greater in the wind tunnel, arguing in favor of bioassays under dual-choice conditions in still air to provide greater PC discrimination. Response to host odor (from wild plums or hexane extract of wild plums or Liberty apples) in Petri dish bioassay chambers proved greatest: (1) during the scotophase of PCs under total dark or dim red light conditions, (2) when Petri dishes were completely enclosed, (3) when PCs were starved for 24 or 48 hr, and (4) when PCs were tested within seven weeks after apple tree petal fall. Neither the sex of a PC nor the direction in which a PC was obliged to move to find the source of host odor (upward through a port in the Petri dish lid or downward through a port in the base) had a substantial effect on level of response to host odor or discrimination of host odor from a nonodorous control. We conclude that an enclosed Petri dish bioassay chamber of the type described here should be a valuable asset in the process of chemically identifying components of host fruit odor attractive to PCs.

Compounds from Host Fruit Odor Attractive to Adult Plum Curculios (Coleoptera: Curculionidae)

Three release rates of each of 30 compounds identified as components of the odor of unripe host plum or apple fruit were evaluated in field tests in 1999 for attractiveness to adult plum curculios, Conotrachelus nenuphar (Herbst). Compounds were introduced into polyethylene vials and assayed in association with boll weevil traps placed beneath infested apple trees in Ohio and Massachusetts. Results confirmed previously reported attractiveness of limonene and ethyl isovalerate to this insect. In addition, at least six other compounds showed good evidence of attractiveness (benzaldehyde, benzyl alcohol, decanal, E-2-hexenal, geranyl propionate and hexyl acetate), and five other compounds appeared worthy of further evaluation for attractiveness (2-hexanol, 1-pentanol, 2-pentanol, phenylacetaldehyde and 2-propanol). Degree of attractiveness of compounds varied according to release rate.

Micronutrient Interactions on Soybean Growth and the Developmental Performance of Three Insect Herbivores

Abstract Although the importance of plant mineral nutrition on insect herbivory has long been recognized, studies have focused almost solely on the effects of varying levels of a single nutrient. One aspect of the relationship between plant nutrition and herbivory largely ignored is the proportions among minerals. The mineral balance hypothesis postulates a plant nutritional state with optimal levels and proportions among minerals that enhances plant growth and suppresses herbivore performance. As part of a systematic series of studies to determine the optimal proportions of minerals for soybeans (Glycine max), plants were grown in hydroponic solution with different proportions of boron (B), zinc (Zn), and iron (Fe), using a D-optimal experimental design for constrained mixtures. In this design, B and Fe varied from 0 to 0.05 mM in the nutrient solutions, whereas Zn ranged from 0 to 0.01 mM. Three soybean feeders, the polyphagous soybean looper (Pseudoplusia includens [Walker]), the oligophagous Mexican bean beetle (Epilachna varivestis Mulsant), and the velvetbean caterpillar (Ancarsia gemmatalis Hübner), were fed leaves from the plants and their developmental performance was evaluated using polynomial models. For all three species, developmental performance was highest on plants grown in solutions without B. Weight gain by velvetbean caterpillar larvae, whose feeding was terminated at 6 d, showed a linear response to mineral proportion (adjusted r2 = 0.49), peaking at B:Zn:Fe = 0:20:80. Soybean looper pupal weight and larval developmental time showed predominantly quadratic responses determined primarily by B:Fe ratio (adjusted r2 = 0.33 and 0.67, respectively). Mexican bean beetle showed the most complex response to mineral proportion, with cubic models of adult weight (adjusted r2 = 0.66) and developmental time (adjusted r2 = 0.45) that indicated significant interactions among all three minerals. Soybean shoot growth was described by a reduced cubic model (adjusted r2 = 0.83), but unlike the insects, plants grew poorly in nutrient solutions lacking B. Rather, soybeans grew best at intermediate mineral proportions, and consistent with the mineral balance hypothesis, herbivores did relatively poorly on these plants. Also consistent with the hypothesis, the effect of Zn on plant growth and herbivore development was dependent on the ratio of the other two nutrients.

High light intensity: a critical factor in the wind-tunnel flight of two scarabs, the rose chafer and Japanese beetle.

We analyzed the flight of the rose chafer Macrodactylus subspinosus (F.) (Melolonthinae: Scarabaeidae) and the Japanese beetle Popillia japonica Newman (Rutelinae: Scarabaeidae) in a wind tunnel with controlled humidity, temperature, light, and airflow. The data indicate that an optimum combination of light and temperature dramatically improves their response to lures. Both species took off upwind, oriented to, and contacted the odor source well (40–60%) when light intensity was >50% of a clear day, temperature was 26–27°C, and relative humidity was 65–75%.

Arrestment of male twospotted spider mite caused by female sex pheromone

A glass slide bioassay was used to evaluate male twospotted spider mite,Tetranychus urticae Koch, arrestment caused by quiescent deutonymph extract. Males that were guarding quiescent deutonymphs prior to being tested were arrested by a 3-mm-diameter circle of quiescent deutonymph extract; nonguarding males and adult females were not arrested. Extracts of allT. urticae instars tested caused male arrestment, but mean arrestment duration was longest with quiescent deutonymph extract. Arrestment by volatile perception of pheromone and upwind orientation to point sources of extract were not observed. The mono- and sesquiterpene alcohols previously identified as components of the pheromone did not arrest males. HPLC separation of extract resulted in four active fractions; a subtractive bioassay showed that three were essential to elicit maximum male response.