Joe Funderburk

Predation of Frankliniella occidentalis (Thysanoptera: Thripidae) in Field Peppers by Orius insidiosus (Hemiptera: Anthocoridae)

Abstract Natural enemies have not been shown previously to play a significant role in regulating thrips in field crops. Most thrips are r-selected with population attributes that are believed to result in thrips outstripping the capacity of natural enemies to regulate thrips populations. In replicated field experiments conducted in 1995, insecticide applications to peppers were observed to increase rather than decrease populations of Frankliniella spp. thrips in flowers. We conducted experiments in 1996 and 1997 to determine if this phenomenon resulted from exclusion of predators. Species of thrips abundant in the pepper flowers were Frankliniella occidentalis (Pergande), F. tritici (Fitch), and F. bispinosa (Morgan). The only common predator in the flowers was Orius insidiosus (Say). Different treatments of biological and synthetic insecticides were used which altered the population densities of prey and predator. Covariate analyses over time were used each year to separate insecticide and predator effects on thrips populations. The predator significantly suppressed populations of all three thrips species. F. occidentalis and F. tritici reproduced in pepper flowers, but most of the larval thrips in untreated plots were F. occidentalis. Near extinction of F. occidentalis adults and larvae occurred within days after predator:prey ratios reached 1:40. Exclusion of the predator with synthetic insecticides resulted in continued abundance of thrips. We conclude that O. insidious was an effective predator that suppressed populations of Frankliniella spp. in field peppers during a period when thrips were rapidly colonizing and developing in the flowers. Species of Orius are abundant predators nearly worldwide, and the role of density dependence in regulation of thrips populations should be reevaluated.

Population Dynamics of Frankliniella spp. and Tomato Spotted Wilt Incidence as Influenced by Cultural Management Tactics in Tomato

Abstract We investigated the effects of ultraviolet (UV)-reflective mulch and two rates of nitrogen fertilization on populations of Frankliniella spp. thrips and on the incidence of tomato spotted wilt in field-grown tomato in northern Florida. The higher of the two soil nitrogen fertilizer treatments significantly increased populations of Frankliniella occidentalis (Pergande), whereas mulch reflectance significantly decreased populations of F. occidentalis. Populations of Frankliniella tritici (Fitch) were decreased only by UV-reflective mulch. Decreased thrips populations in UV-reflective mulch plots were probably due to disruptions in host-finding behavior. Increased thrips populations in tomatoes treated with the higher nitrogen fertilization rate were probably due in part to increased nutrients available in flowers. Incidence of tomato spotted wilt was significantly decreased in tomatoes grown on UV-reflective mulch, whereas disease incidence was significantly greater in increased nitrogen-fertilized plots. This research reveals that cultural practices resulted in up to 45% reduction in the numbers of vector and nonvector species of flower thrips and up to 50% reduction in tomato spotted wilt.

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.

Population abundance and movement of Frankliniella species and Orius insidiosus in field pepper

1 A recent study revealed the capacity of the Orius insidiosus to suppress populations of Frankliniella spp. in field pepper during the spring when thrips are rapidly colonizing and reproducing. In this study, population abundance in pepper during spring, summer, and autumn was determined to understand better predator/prey dynamics under local conditions. Local movement between pepper flowers also was quantified to examine how population attributes of the predator allow suppression of rapidly moving populations of prey.

Competitive exclusion of a worldwide invasive pest by a native. Quantifying competition between two phytophagous insects on two host plant species

1. High competitive ability is believed to be an important characteristic of invasive species. Many animal studies have compared the competitive ability of invasive species with a native species that is being displaced, but few have looked at systems where an invasive species has failed to establish itself. These types of studies are important to determine if competition is relevant not only to invading species but also to the biotic resistance of a community. 2. The thrips species F. occidentalis is a highly invasive pest that has spread from its original range (the western states of the USA) to a worldwide distribution. Despite this, F. occidentalis is largely absent or occurs in low numbers in the eastern states of the USA, where the native F. tritici dominates. It is possible that F. tritici is competitively excluding F. occidentalis from this region. 3. Larval competition between these two thrips species was tested on two known plant hosts, Capsicum annuum (a crop plant), and Raphanus raphanistrum (an invasive weed), using a response surface design with number of larvae surviving as the response variable. The response surface design allowed competition models to be fit to data using maximum likelihood estimation, thus generating quantitative values for interspecific competition. 4. On both plant hosts, the native F. tritici did not experience significant interspecific competition from the invasive F. occidentalis. In contrast, F. occidentalis did experience significant interspecific competition from F. tritici. Competition from F. tritici larvae on F. occidentalis larvae was estimated to be 1.72 times (on C. annuum) and 1.76 times (on R. raphanistrum) the effect of intraspecific competition. The invasive F. occidentalis appears to be competitively excluded by the native F. tritici. 5. This study confirms the importance of competition in the biotic resistance of a community and is one of the few animal studies to not only test for competition in an apparently resistant ecosystem but also to quantify the level of interspecific competition between two animal species.

Annual Cycles of Frankliniella spp. (Thysanoptera: Thripidae) Thrips Abundance on North Florida Uncultivated Reproductive Hosts: Predicting Possible Sources of Pest Outbreaks

Abstract Frankliniella spp. (Thysanoptera: Thripidae) thrips damage a variety of crops, feed on a broad range of hosts, and often migrate into cropping systems from adjacent vegetation. To determine potential sources of Frankliniella spp. thrips on crops, annual cycles of abundance of Frankliniella occidentalis (Pergande), Frankliniella fusca (Hinds), Frankliniella bispinosa (Morgan), and Frankliniella tritici (Fitch) were evaluated on seven common, uncultivated reproductive hosts. These hosts included Raphanus raphanistrum L., Rubus trivialis Michx., Rubus cuneifolius Pursh., Vicia sativa L., Trifolium repens L., Solidago canadensis L. and Chenopodium ambrosioides L. Thrips were collected from R. cuneifolius, and T. repens in the spring, R. raphanistrum in the summer, and C. ambrosioides and S. canadensis in the fall. The most common Frankliniella species on every plant species was F. tritici, and a fifth species, Pseudothrips inequalis (Beach), was collected in the fall on C. ambrosioides and S. canadensis. All thrips species were highly aggregated in the flowers or flower racemes, rather than leaves or fruit, and they were generally only collected from flowering plants. R. raphanistrum supported large populations, and they may be an important link for thrips between spring and fall. In addition, it may be an essentially enemy free host, as only one O. insidiosus, an important thrips predator, was collected from this host. S. canadensis also supported large thrips populations in the fall, and it may be a source of thrips migrating into crops the following spring. Controlling thrips on these hosts in their respective seasons may limit the number migrating into cropping systems.

Management of the Western Flower Thrips (Thysanoptera: Thripidae) in Fruiting Vegetables

ABSTRACT Feeding by the western flower thrips, Frankliniella occidentalis (Pergande), causes damage to the fruits of vegetables, and the species is the key vector of Tomato spotted wilt virus. Frankliniella tritici (Fitch) and Frankliniella bispinosa (Morgan) are not pests of fruiting vegetables. Both species compete with F. occidentalis. Effective management of F. occidentalis in pepper integrates conservation of natural populations of the predator, Orius insidiosus (Say), with the use of reduced-risk insecticides such as spinetoram for the control of western flower thrips and other pests. Naturally occurring O. insidiosus are very effective predators and their effectiveness is predictable based on the number of the predator relative to the number of thrips prey. Populations of F. occidentalis resurge when natural enemies and competing thrips are killed. Some insecticides especially pyrethroids have beneficial effects on the development and reproduction of F. occidentalis. The predator O. insidiosus does not prefer tomato, and numbers remain too low in fields to suppress thrips. Tomato growers primarily rely on the use of ultra-violet reflective mulch combined, if needed, with the use of effective insecticides. Additional management efforts are needed in the future to manage F. occidentalis and other difficult pests in space and time. Management of the pepper weevil (Anthonomus eugenii Cano) is proving a challenge to pepper growers in central and southern Florida trying at the same time to manage F. occidentalis. Growers need to emphasize sanitation and other cultural tactics over the use of broad-spectrum insecticides that kill O. insidiosus and induce F. occidentalis in other ways. The identification of thrips in scouting programs also is critical as the use of broad-spectrum insecticides against populations of the non-pest flower thrips is inducing F. occidentalis to pest status.

Predation by Orius insidiosus (Heteroptera: Anthocoridae) on Life Stages and Species of Frankliniella Flower Thrips (Thysanoptera: Thripidae) in Pepper Flowers

Abstract We compared predation of Orius insidiosus (Say) on adult and second instars of Frankliniella occidentalis (Pergande) and on adults of F. occidentalis and F. tritici (Fitch) in arenas with pepper flowers. Also, we compared the dispersal of these thrips in the presence and absence of the predator. For each experiment, two densities of thrips (10 and 20 total thrips) and two time exposures (10 and 34 h) were tested. Second instars were more likely to move from the flower where they were released than were F. occidentalis adults. F. tritici dispersed more than F. occidentalis. The presence of the predator enhanced movement by thrips from flowers in which they were released. Despite differences in prey movement, O. insidiosus successfully preyed on all types of prey that were offered. However, O. insidiosus appeared to deal differently with each type of prey. Predation of both larvae and adults was most likely to occur inside flowers. In trials with adults and second instars of F. occidentalis, larvae were significantly more vulnerable to predation than were adults. F. tritici, the more active species, may have been vulnerable to predation because of higher rates of encounter with the predator; however, O. insidiosus may have had greater attack success against the less active F. occidentalis. The ability of O. insidiosus to prey successfully on different life stages and species of thrips in complex environments indicates that it is an efficient predator of thrips and an important biological control agent.

Differential predation by the generalist predator Orius insidiosus on congeneric species of thrips that vary in size and behavior

We investigated interactions between the generalist predator Orius insidiosus (Say) (Heteroptera: Anthocoridae) and two species of thrips prey, Frankliniella bispinosa (Morgan) and Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), and interspecific differences in morphology and behavior between these prey species that could contribute to differences in predation by O. insidiosus. Frankliniella occidentalis is significantly larger than F. bispinosa. Frankliniella bispinosa has greater mobility compared with F. occidentalis. When O. insidiosus was offered either F. bispinosa or F. occidentalis as prey in single species trials, there were no significant differences in the number of prey captured. However, O. insidiosus had significantly more encounters with F. bispinosa than with F. occidentalis. In arenas with equal numbers of both species, O. insidiosus encountered and captured F. occidentalis more than F. bispinosa. In large arenas with two pepper plants (Capsicum annuum L.), O. insidiosus preyed on more F. occidentalis than on F. bispinosa. These results indicate that O. insidiosus can prey on both thrips species, but that it preferentially captures F. occidentalis. The greater locomotion and movement of F. bispinosa, perhaps combined with its smaller size, allow it to evade predation by O. insidiosus better than F. occidentalis. Consequently, the observed preference of O. insidiosus for F. occidentalis is not exclusively a function of active selection by the predator but also could arise from inherent differences among prey. We propose this differential predation as a mechanism contributing to observed differences in the temporal dynamics of these species in pepper fields.

Infection of Frankliniella fusca (Thysanoptera: Thripidae) in Peanut by the Parasitic Nematode Thripinema fuscum (Tylenchidae: Allantonematidae)

Abstract Frankliniella fusca (Hinds) is a species of thrips that is a pest of peanuts and an important vector of tomato spotted wilt virus. In previous research, populations of thrips declined in peanut during midseason for unexplained reasons. Nematodes in the genus Thripinema are parasites of thrips that render infected females sterile. A new species, T. fuscum Tipping & Nguyen, was recently described as a parasite of F. fusca in peanut. In 1997 and 1998, the temporal changes in percent parasitism of F. fusca in plots of peanuts were determined. Parasitism of adult female thrips increased from an estimated 1% on seedling peanut each year to a maximum of 68% later in the 1997 growing season and 38% in the 1998 growing season. Treatments of several insecticides for control of thrips reduced percent parasitism of the females on most sample dates in 1997, but parasitism was not significantly affected in 1998. Estimates of the numbers of F. fusca in the flowers and terminal buds of peanuts declined each year as parasitism increased. The very high levels of parasitism in 1997 were associated with near extinction of larval populations of thrips during midseason. As a result, the spread of tomato spotted wilt virus by this vector species was reduced. Thus, T. fuscum may be an important natural enemy of F. fusca responsible for suppression of populations of thrips in peanut.