Heather J. McAuslane

Within-Plant Distribution of Frankliniella species (Thysanoptera: Thripidae) and Orius insidiosus (Heteroptera: Anthocoridae) in Field Pepper

Abstract We evaluated the within-plant distribution of Frankliniella spp. and the predator Orius insidiosus (Say) in pepper (Capsicum anuum L.), over a range of field conditions, and we conducted behavioral experiments to examine the time budgets of F. occidentalis (Pergande) and F. tritici (Fitch) females on pepper plant parts. In the field experiments Frankliniella species composition varied by season and location. Still, all populations of thrips and O. insidiosus in untreated and insecticide-treated pepper were highly concentrated in the flowers, with 82–99% of individuals of each taxa found in flowers. This preference for flowers was corroborated by laboratory-choice experiments. Adult females of F. occidentalis and F. tritici showed a strong preference for pepper flowers over leaves and buds. In laboratory observations, females of F. occidentalis spent 3.6× as much time on flowers as on all other plant parts, and females of F. tritici spent over 6.3× as much time on flowers as on all other plant parts. Therefore, the concentration of these thrips in flowers appears to be behaviorally based and not an artifact of insecticide applications or sampling. Using estimates of populations from flowers of field pepper is sufficient for understanding the local dynamics of Frankliniella spp. and the predator O. insidiosus, and for estimating the benefits of biological control in scouting programs based on predator to prey ratios.

Systemic induction of terpenoid aldehydes in cotton pigment glands by feeding of larval Spodoptera exigua

Pigment glands in cotton contain terpenoid aldehydes that are toxic and deterrent to feeding of several generalist lepidopteran insects. We hypothesized that previously observed systemically induced feeding deterrence may be associated with pigment glands. We conducted experiments to determine the dynamics and chemical nature of inducible feeding deterrents in leaves of cotton, Gossypium hirsutum L, to larvae of the beet armyworm, Spodoptera exigua. Production and/or filling of pigment glands was influenced by physiological age of Deltapine 90 cotton plants. In undamaged plants, successively formed leaves contained more pigment glands, up to the seventh or eighth true-leaf developmental stage. Feeding choice tests conducted one or seven days after initial feeding damage revealed that third instars of S. exigua consumed more of the two youngest leaves from control cotton plants than from plants whose two oldest leaves had been fed on previously for 24 hr by S. exigua. The preference for leaves from control plants was significant one day after initial damage and highly significant seven days after damage. Consumption of mature foliage (leaf immediately above initially damaged leaves) from control plants and damaged plants did not differ. More pigment glands were counted on the youngest leaf of damaged plants than on the youngest leaf of control plants one day after initial damage. HPLC analysis revealed greater amounts of hemigossypolone, heliocides 1 and 2 (H1 and H2), and total terpenoid aldehydes per gland in young foliage of damaged plants than control plants one day after initial injury. By seven days after initial injury, greater quantities of hemigossypolone and all heliocides except H4 were detected in young foliage from damaged plants compared to control plants. Concentrations of H1 per gland in young leaves from damaged plants increased the most of all terpenoid aldehydes measured (3.4× the amount found in leaves from control plants). Mature leaves from damaged plants did not contain more terpenoid aldehydes than mature leaves from control plants. We suggest that systemically induced feeding deterrence to S. exigua in young leaves of glanded cotton was due to increased amounts of terpenoid aldehydes in pigment glands.

SYSTEMIC INDUCTION OF ALLELOCHEMICALS IN GLANDED AND GLANDLESS ISOGENIC COTTON BY Spodoptera exigua FEEDING

Induction of systemic resistance to feeding of beet armyworm, Spodoptera exigua, was investigated in two isogenic lines of Stoneville 213 cotton, Gossypium hirsutum, that differed in the presence of pigment glands. In laboratory bioassays, larvae strongly preferred to feed on glandless cotton plants when presented a choice between undamaged terminal leaves of undamaged glanded and glandless plants. Feeding damage inflicted by S. exigua larvae on the two oldest leaves of glanded plants seven days prior to feeding bioassays caused larvae to prefer by 33-fold the undamaged terminal foliage from undamaged plants compared to that from damaged plants. Feeding damage on glandless plants caused only a 2.6-fold greater preference for terminal foliage from undamaged plants over foliage from previously damaged plants. Extracts of terminal foliage from glanded cotton damaged seven days earlier had significantly greater quantities of terpenoid aldehydes (hemigossypolone, gossypol, and heliocides) than did foliage from undamaged glanded plants. Terpenoid aldehydes were undetectable in extracts of both undamaged and previously damaged glandless plants. The profile of volatile compounds collected from the headspace of mechanically damaged terminal leaves of undamaged glanded and glandless plants differed. Both cotton isolines released large quantities of lipoxygenase products (hexenyl alcohols, acetates, and butyrates), but glandless plants released only small amounts of mono- and sesquiterpenes compared to glanded plants. Glandless plants damaged seven days prior to volatile collection released significantly greater quantities of lipoxygenase products, β-ocimene, and α- and β-farnesene than did undamaged glandless plants. Previously damaged glanded plants released significantly greater quantities of all mono- and sesquiterpenes and hexenyl acetates and butyrates, but not alcohols. The relative importance of volatile compounds versus terpenoid aldehydes in induced feeding deterrence in cotton to S. exigua larvae is still unclear.

Accumulation of terpenoid phytoalexins in maize roots is associated with drought tolerance.

Maize (Zea mays) production, which is of global agro-economic importance, is largely limited by herbivore pests, pathogens and environmental conditions, such as drought. Zealexins and kauralexins belong to two recently identified families of acidic terpenoid phytoalexins in maize that mediate defence against both pathogen and insect attacks in aboveground tissues. However, little is known about their function in belowground organs and their potential to counter abiotic stress. In this study, we show that zealexins and kauralexins accumulate in roots in response to both biotic and abiotic stress including, Diabrotica balteata herbivory, Fusarium verticillioides infection, drought and high salinity. We find that the quantity of drought-induced phytoalexins is positively correlated with the root-to-shoot ratio of different maize varieties, and further demonstrate that mutant an2 plants deficient in kauralexin production are more sensitive to drought. The induction of phytoalexins in response to drought is root specific and does not influence phytoalexin levels aboveground; however, the accumulation of phytoalexins in one tissue may influence the induction capacity of other tissues.

Pepper Weevil Attraction to Volatiles from Host and Nonhost Plants

ABSTRACT The location of wild and cultivated host plants by pepper weevil (Anthonomus eugenii Cano) may be aided by visual cues, the male-produced aggregation pheromone, herbivore-induced, or constitutive host plant volatiles. The attractiveness of constitutive plant volatiles to pioneer weevils is important in understanding, and perhaps controlling, dispersal of this insect between wild and cultivated hosts. Ten-day-old male and 2- and 10-day-old female weevils were tested in short-range Y-tube assays. Ten-day-old male and female weevils were attracted to the volatiles released by whole plants of three known oviposition hosts, ‘Jalapeno’ pepper, American black nightshade, and eggplant, as well as tomato, a congener, which supports feeding but not oviposition. Two-day-old females were attracted to all plants tested, including lima bean, an unrelated, nonhost plant. Fruit volatiles from all three hosts and flower volatiles from nightshade and eggplant were also attractive. In choice tests, weevils showed different preferences for the oviposition hosts, depending on age and sex. Upwind response of 10-day-old male and female weevils to host plant volatiles was also tested in long-range wind tunnel assays. Weevils responded to pepper, nightshade, and eggplant volatiles by moving upwind. There was no difference in the observed upwind response of the weevils to the three host plants under no-choice conditions. Reproductively mature pepper weevils can detect, orient to, and discriminate between the volatile plumes of host plants in the absence of visual cues, conspecific feeding damage, or the presence of their aggregation pheromone.

Effect of Silver Reflective Mulch and a Summer Squash Trap Crop on Densities of Immature Bemisia argentifolii (Homoptera: Aleyrodidae) on Organic Bean

Abstract Polyethylene mulch with a reflective silver stripe and a yellow summer squash, Cucurbita pepo L., trap crop were tested alone and in combination as tactics to reduce densities of Bemisia argentifolii Bellows & Perring eggs and nymphs, and incidence of bean golden mosaic geminivirus on snap bean, Phaseolus vulgaris L. Egg densities were consistently higher on squash than on bean, but egg densities and virus incidence were not lower on bean grown with squash than on bean grown in monoculture. Silver reflective mulch reduced egg densities compared with bean grown on bare ground during the first week after crop emergence for 2 of the 3 yr that the study was conducted. However, egg suppression by silver mulch was not enhanced by the presence of a squash trap crop when both tactics were combined. The obstacles to suppressing B. argentifolii through the use of trap crops are discussed.

Influence of previous herbivory on behavior and development of Spodoptera exigua larvae on glanded and glandless cotton.

We examined the influence of previous herbivore injury on the feeding behavior, survival and development of larval beet armyworm, Spodoptera exigua Hübner (Lepidoptera: Noctuidae), on glanded and glandless ‘Stoneville 213’ cotton, Gossypium hirsutum L. In a greenhouse study, neonate S. exigua placed on the terminal foliage of glanded cotton plants moved down the plant to feed on older leaves. The location of feeding was more concentrated towards the bottom of the plant on previously damaged plants than on undamaged control plants. In contrast, larval feeding on glandless plants was evenly distributed within the plant and no difference in distribution was noted on plants that had sustained previous herbivore injury when compared to undamaged plants. In a laboratory study, where larvae were offered one type of foliage in a no‐choice situation, survival on young or mature leaves from glanded or glandless plants, with or without previous herbivore injury, did not differ significantly. However, pupae of larvae reared on young leaves of damaged glanded cotton weighed significantly less than pupae from larvae fed all other diets. Pupae from larvae fed young leaves of control glandless plants weighed significantly more than pupae from all other diets. Similar trends were observed in adult weights. In addition, time to pupation and time to adult emergence were significantly longer for larvae fed young leaves from damaged glanded plants compared to all other diets. The experiments reported here link larval feeding behavior of S. exigua to performance. Larval feeding preferences changed following induction of systemic defense such that food choice was optimized for growth.

Attraction of pepper weevil to volatiles from damaged pepper plants

Pioneer herbivorous insects may find their host plants through a combination of visual and constitutive host‐plant volatile cues, but once a site has been colonized, feeding damage changes the quantity and quality of plant volatiles released, potentially altering the behavior of conspecifics who detect them. Previous work on the pepper weevil, Anthonomus eugenii Cano (Coleoptera: Curculionidae), demonstrated that this insect can detect and orient to constitutive host plant volatiles released from pepper [Capsicum annuum L. (Solanaceae)]. Here we investigated the response of the weevil to whole plants and headspace collections of plants damaged by conspecifics. Mated weevils preferred damaged flowering as well as damaged fruiting plants over undamaged plants in a Y‐tube olfactometer. They also preferred volatiles from flowering and fruiting plants with actively feeding weevils over plants with old feeding damage. Both sexes preferred volatiles from fruiting plants with actively feeding weevils over flowering plants with actively feeding weevils. Females preferred plants with 48 h of prior feeding damage over plants subjected to weevil feeding for only 1 h, whereas males showed no preference. When attraction to male‐ and female‐inflicted feeding damage was compared in the Y‐tube, males and females showed no significant preference. Wind tunnel plant assays and four‐choice olfactometer assays using headspace volatiles confirmed the attraction of weevils to active feeding damage on fruiting plants. In a final four‐choice olfactometer assay using headspace collections, we tested the attraction of mated males and virgin and mated females to male and female feeding damage. In these headspace volatile assays, mated females again showed no preference for male feeding; however, virgin females and males preferred the headspace volatiles of plants fed on by males, which contained the male aggregation pheromone in addition to plant volatiles. The potential for using plant volatile lures to improve pepper weevil monitoring and management is discussed.

Role of Leaf Sheath Lignification and Anatomy in Resistance Against Southern Chinch Bug (Hemiptera: Blissidae) in St. Augustinegrass

ABSTRACT Southern chinch bug, Blissus insularis Barber (Hemiptera: Blissidae), is the most serious insect pest of St. Augustinegrass Stenotaphrum secundatum (Walter) Kuntze, a common lawngrass grown in southeastern U.S. states. Host plant resistance to southern chinch bug has been identified in the polyploid St. Augustinegrass‘FX-10′ and the diploid ‘Captiva’. The objective of this research was to identify possible physical mechanism(s) explaining chinch bug resistance in these cultivars. We studied the distribution of chinch bug salivary sheaths in the preferred tissue for feeding (the axillary shoot) of the two resistant cultivars and two susceptible cultivars, paired for ploidy (‘Floratam’, polyploid, and Palmetto, diploid). We also investigated the potential role of axillary shoot lignification and anatomy in chinch bug resistance. Salivary sheaths were more abundant on the outermost leaf sheath of axillary shoots of resistant cultivars compared with susceptible cultivars. In contrast, fewer salivary sheaths reached the innermost meristematic tissue in the axillary shoots of resistant St. Augustinegrass cultivars than in the two susceptible cultivars. The polyploid cultivars FX-10 and Floratam had higher total lignin in axillary shoots compared with the diploid cultivars Captiva and Palmetto. However, total lignin content was not correlated with resistance to southern chinch bug. Light microscopic studies found no differences in epidermal layer thickness among resistant and susceptible St. Augustinegrass cultivars. However, transmission electron microscopic studies revealed that the cell walls of the sclerenchyma cells around the vascular bundle of southern chinch bug-resistant FX-10 and Captiva were significantly thicker than the cell walls in susceptible Floratam and Palmetto. Our research suggests that the thick-walled sclerenchyma cells around the vascular bundle play a role in southern chinch bug resistance in St. Augustinegrass, possibly by reducing stylet penetration to the vascular tissue.

Influence of Bemisia argentifolii (Homoptera: Aleyrodidae) Infestation and Squash Silverleaf Disorder on Zucchini Seedling Growth

Abstract We investigated the effect of different levels of infestation by whiteflies, Bemisia argentifolii Bellows & Perring, on the growth and pigment concentrations of seedlings of zucchini, Cucurbita pepo L., that differed in their tolerance to squash silverleaf disorder. Genetically similar sister lines that were either tolerant (ZUC76-SLR) or susceptible (ZUC61) to silverleaf disorder exhibited reduced plant height, internode length, plant dry weight, and petiole length in response to whitefly feeding. Similar plant growth responses to whitefly feeding were observed despite that the foliage of ZUC61 silvered severely, whereas the foliage of ZUC76-SLR showed no silvering in a greenhouse experiment conducted in the spring and showed only minimal silvering in a similar greenhouse experiment conducted in the fall. In plants of both sister lines infested with 50 pairs of whiteflies and their progeny, petioles, but not the leaf blades, of uninfested leaves had reduced chlorophyll content. In another experiment, two different genetic sources of tolerance to silverleaf disorder (ZUC33-SLR/PMR and ZUC76-SLR) and a commercial silverleaf-susceptible zucchini hybrid (‘Zucchini Elite’) responded similarly to whitefly feeding, except the tolerant genotypes did not exhibit leaf silvering. All genotypes, silverleaf tolerant or not, had reduced dry weight, plant height, and internode length that became more pronounced as whitefly infestation increased. All genotypes had reduced levels of chlorophylls and carotenoids in uninfested young leaf blades and petioles from infested plants. Petioles, however, were more affected by feeding than leaf blades, showing a 66% reduction in chlorophylls a+b and carotenoids at the lowest infestation level (30 pairs of whitefly and their progeny), whereas pigments in leaf blades declined more slowly in response to whitefly feeding density, averaging 14–15% less at the highest infestation level (90 pairs of whitefly and their progeny). We conclude that tolerance to silverleaf disorder does not prevent stunting in zucchini seedlings nor does it protect against the systemic loss of photosynthetic and protoprotectant pigments induced by feeding of B. argentifolii whiteflies.