Steven Arthurs

Evaluation of the nematodes Steinernema feltiae and Thripinema nicklewoodi as biological control agents of western flower thrips Frankliniella occidentalis infesting chrysanthemum

Abstract In greenhouse studies, we evaluated a commercial formulation of the entomopathogenic nematode Steinernema feltiae and the inoculative release of the thrips-parasitic nematode Thripinema nicklewoodi against western flower thrips (WFT), Frankliniella occidentalis Pergande infesting potted chrysanthemums. Foliar sprays of S. feltiae applied at 1.25–2.5×103 IJ mL−1 and 1000 – 2000 L ha−1 at 3-day intervals alone (targeting feeding stages) or in combination with soil applications (simultaneously treating non-feeding stages in the soil at the same rates) decreased but did not provide adequate control of thrips in flowering plants artificially infested with a dense population. Similar nematode treatments applied for four to five applications at 6-day intervals in two batches of initially clean chrysanthemums failed to prevent unacceptable damage to flowers and leaves from a dense natural infestation within the greenhouse. Although some IJ survived up to 48 h within flowers and flower buds, few nematode-infected thrips (larvae and adults) were recovered. In studies with T. nicklewoodi (which is not amenable for mass production), the inoculative releases of two parasitized hosts per plant enabled the nematode to become established within existing WFT populations under greenhouse conditions. However, relatively poor transmission and slow speed of kill (nematode primarily suppresses populations through host sterilization) prevented low level inoculations being effective over a single crop cycle. Further studies showed that transmission of T. nicklewoodi persisted for nine host generations, infected up to 83% of adult thrips and provided long-term suppression of discrete caged populations, but only after uneconomically high thrips densities had been reached.

In vivo Rearing of Thripinema nicklewoodi (Tylenchida: Allantonematidae) and Prospects as a Biological Control Agent of Frankliniella occidentalis (Thysanoptera: Thripidae)

Abstract Methods are described for the in vivo production of the nematode Thripinema nicklewoodi (Siddiqi), an obligate parasite and potential biological control agent of western flower thrips Frankliniella occidentalis (Pergande). Nematode infection is not lethal but causes sterilization of adult female hosts. Both fertilization and horizontal transmission of T. nicklewoodi is achieved in 1.5-ml microcentrifuge tubes (infection arenas), in the presence of 100% humidity, a temporary food source and preferably a damp substrate. Following exposure to infection arenas, F. occidentalis are reared on excised bean leaves Phaseolus vulgaris (L.) in polypropylene containers for 2 wk at 25°C to allow the reproduction and development of a single generation of nematodes within infected hosts’s abdominal cavity. To identify infected hosts after this incubation period, thrips are isolated in microcentrifuge tubes and monitored for free-living nematodes being released along with frass. Infected thrips are reintroduced back into infection arenas to inoculate further thrips to maintain the culture. We documented the output of the rearing procedure using a standard method and following simple manipulation of several individual parameters of the infection technique. The standard method was the most efficient, and resulted in an increased (output/input) ratio of infected thrips of ≈2; i.e., the number of infected thrips approximately doubles each generation. Monitoring infected thrips revealed that nematodes were first released between 12–14 d postinfection and for an average of 7.9 d at 25°C; highlighting the potential to reuse infective thrips between infection arenas. The possibility of using T. nicklewoodi as an inoculative agent against F. occidentalis infesting floricultural crops is discussed.

Thrips Parasitic Nematode Thripinema nicklewoodi (Tylenchida: Allantonematidae) Reduces Feeding, Reproductive Fitness, and Tospovirus Transmission by Its Host, Frankliniella occidentalis (Thysanoptera: Thripidae)

Abstract The parasitic nematode Thripinema nicklewoodi is a potential inoculative biological control agent of the western flower thrips, Frankliniella occidentalis. Laboratory studies were undertaken to assess the effect of T. nicklewoodi infection on: 1) host feeding, 2) host fecundity, and 3) viral competency of F. occidentalis coinfected with a tospovirus. Individual thrips infected with nematodes as larvae and maintained on leaf discs in microcentrifuge vials showed a reduced feeding throughout the adult life span. This per capita reduction in feeding by parasitized individuals contributed to a total reduction in feeding of 87% on chrysanthemum petals and 91% on bean foliage relative to uninfected thrips. Parasitism also reduced the longevity of adult thrips by 3–5 d, although the preadult developmental time was unaffected. In a separate study, thrips infected with nematodes as larvae became reproductively sterile and appeared to have a reduced vector competency for tomato spotted wilt virus (TSWV). Thrips larvae were inoculated with both TSWV and nematodes in a factorial design, and adults were subsequently exposed to a petunia leaf disc assay to test for fecundity and virus transmission using enzyme-linked immunosorbent assay (ELISA). No eggs were recovered from thrips infected with nematodes, and dissections revealed that their embryos remained fully degenerate, which was not observed among healthy thrips. Although the proportion of thrips testing positive to a TSWV nonstructural protein (indicating systemic virus acquisition) was statistically similar between treatments, fewer viruliferous F. occidentalis coinfected with T. nicklewoodi became virus transmitters. Moreover, the per capita frequency of virus transmission among nematode-infected thrips was reduced by ≈50% relative to nematode-free thrips. Our results suggest that T. nicklewoodi may help prevent thrips outbreaks and reduce direct feeding damage and secondary virus spread during the prelethal period of infection.

Effect of temperature on infection, development and reproduction of the parasitic nematode Thripinema nicklewoodi in Frankliniella occidentalis

The parasitic nematodeThripinema nicklewoodi Siddiqi (Tylenchida:Allantonematidae) is currently underinvestigation for use in inoculative releasestrategies against western flower thrips (WFT),Frankliniella occidentalis Pergande(Thysanoptera: Thripidae) infesting greenhousefloricultural crops. The aim was to determinewhether temperatures within greenhouses wouldpermit the establishment of T.nicklewoodi. The abilities of T.nicklewoodi to infect, develop and reproducein WFT were assessed under a range of constantand fluctuating temperatures in the laboratory.At constant temperatures, T. nicklewoodiinfected WFT over the range of 1–30 °C,although the temperature-related infectionprofile followed an asymmetric distributionaround an optimum ∼20 °C (∼80%infection). The lower and upper thresholds forT. nicklewoodi in vivo development andreproduction were higher than for infection, at10 °C and 35 °C, respectively.Climate data recorded over 1999–2000 in acommercial greenhouse (Texas) revealed atemperature range of ∼15 °C to∼31 °C from early March through mid June,when WFT were most abundant. While low(nighttime) greenhouse temperatures areconducive for T. nicklewoodi, upperdaytime temperatures are close to the upperthreshold for infection and may reducereproductive output. However, fluctuatingtemperature bioassays in the laboratorydemonstrated that T. nicklewoodimaintained separately at the upper thresholdtemperatures for infection (30 °C) anddevelopment (35 °C) readily infected anddeveloped in WFT when they were allowedintermittent (10 h daily) exposure to apermissive temperature in the range10–20 °C. Drawing on the results, thediurnal temperature-fluctuations of variousgreenhouses growing ornamentals would permitthe establishment of T. nicklewoodi.

Flight Activity and Field Infestation Relationships for Coffee Berry Borer in Commercial Coffee Plantations in Kona and Kau Districts, Hawaii

Abstract The coffee berry borer (CBB), Hypothenemus hampei Ferrari (Coleoptera: Curculionidae: Scolytinae) is a recent invader to Hawaii.To date, limited information regarding the seasonal phenology of this pest on the islands limits the implementation of integrated control strategies. As part of a coffee farmer training program, we monitored CBB flight activity in 15 coffee plantations (Kona and Kau Districts) over 10 mo with methanol-ethanol (3:1 ratio) baited traps. Concurrently, we quantified CBB infestation and penetration rates inside developing coffee berries through the end of harvest. Approximately 1 million CBB were captured, with the highest activity (e.g., >500 CBB/trap/wk) in December through February, coinciding with end of main regional harvesting periods. Relatively high activity (>250 CBB/trap/wk) was also observed during berry development, in May and June (Kona) and June and July (Kau). Field infestation rates were higher overall in Kau (9.6 ± 1.1%) compared with coffee plantations in Kona (4.7 ± 0.4%). Linear regression investigated relationships between CBB trap data and berry infestation rates. Trap catch data generally correlated better with the proportion of shallow entries (AB position) compared with deeper penetrations (CD position) or total infestation. Pearson correlation coefficients based on different parameters (i.e., region, altitude, and berry phenology) revealed positive and mostly significant correlations between these variables (R values 0.410 to 0.837). Timing peak flight activity of CBB with insecticide applications will help coffee growers improve pest control.The ability of trap data to calculate reliable economic (action) thresholds for the CBB is discussed.

Microbial biopesticides for invertebrate pests and their markets in the United States

Microbial pesticides based on bacteria, fungi and viruses or their bioactive compounds have long been developed as alternatives for synthetic pesticides to control invertebrate pests. However, concern for environmental and human health from excessive reliance on chemical pesticides, changes in residue standards, and increased demand for organically grown produce has contributed to a considerable growth in their use in recent years. There are currently 356 registered biopesticide active ingredients in the U.S., including 57 species and/or strains of microbes or their derivatives, labelled for use against pestiferous insects, mites and nematodes. Strains of Bacillus thuringiensis for Lepidoptera remain the most popular products, but newer bacterial strains and their metabolites have been developed against a wider range of arthropods for use on fruit, vegetable and ornamental crops. Currently, ten fungal species/strains are registered against thrips, whiteflies, aphids, or other sucking pests and plant parasitic nematodes in greenhouse, nursery and field crops, while five nucleopolyhedroviruses and three granuloviruses are registered for Lepidoptera in field and greenhouse grown vegetables and ornamentals, tree fruit and nuts, forestry, and stored products. Many of these products are organic listed and most have 4 h or less reentry and no pre-harvest restrictions. Investment by multinational companies, advances in screening, industrial fermentation and storage of new microorganisms, are increasing the market share for microbials. Here, we summarize the market for microbial-based pesticides labelled for invertebrates in the U.S. We cover current uses and recent advances that further advance their use in additional markets in the coming decades.

Phenotype responses to abiotic stresses, asexual reproduction and virulence among isolates of the entomopathogenic fungus Cordyceps javanica (Hypocreales: Cordycipitaceae)

Selecting entomopathogenic fungal isolates with resilience to environmental stresses, optimal mass production characteristics, and with high virulence to target pests favors the development of mycopesticides. A case in point, Cordyceps (= Isaria) javanica has been extensively investigated for non-chemical control of whiteflies worldwide. We phylogenetically characterized 11 native C. javanica isolates from Northeastern and Central Brazil. These isolates were screened for tolerance to heat-shock, UV-B radiation, osmotic and oxidative stresses, as well as conidial production on cereal grain and insecticidal activity against the whitefly Bemisia tabaci (MEAM 1) in the laboratory. All isolates were pathogenic to whiteflies and significant (3-fold) differences in median lethal concentration were observed among isolates. Furthermore, pronounced differences among isolates were found for stress factors and conidial production. Using principal component analysis, our results highlighted three major clusters formed by isolates (i) resistant to osmotic and oxidative stress, (ii) resilient to UV-B, and (iii) with high virulence, conidial production and heat tolerance. Overall, isolate CG1228 performed best based on multi-stress resistance, mass production and virulence attributes in the laboratory. This study highlights the importance of exploring natural variation in entomopathogenic fungi for selection of appropriate isolates for effective biocontrol of insect pests coupled with mass production characteristics and abiotic stress tolerances.

Microbial insecticides in Iran: History, current status, challenges and perspective

Biological control programs with arthropods have been in practice in Iran since the 1930s. However, development and registration of microbial biopesticides is much more recent. Currently, about 15 biopesticide products are registered or pending registration for commercial use on various crops. Products based on Bacillus thuringiensis subsp. kurstaki are most widely sold for lepidopteran pest control, followed by B. thuringiensis subsp. isralensis against dipteran pests in vector control programs. Additionally, mycoinsecticides based on Lecanicillium lecanii and Beauveria bassiana, against various arthropod pests, and a mycofungicide based on Trichoderma harzianum for controlling soilborne diseases are also registered. In Iran, the national Plant Protection Organization (PPO) manages regulation of microbial pesticides and the Pesticide Supervision Board within the PPO oversees registration of all pesticides. Currently, two Iranian companies produce microbial pesticides and two more companies are approved to start production in the near future. We review the history of microbial control of arthropod pests in Iran with examples of sustainable agricultural practices, the current status of the market and registration procedures for microbial pesticides, along with the challenges and opportunities for the advancement of microbial control in Iran.

Comparison of Frankliniella fusca and Frankliniella occidentalis (Thysanoptera: Thripidae) as Vectors for a Peanut Strain of Tomato Spotted Wilt Orthotospovirus

Abstract Tomato spotted wilt orthotospovirus (TSWV) is a major disease in peanut, Arachis hypogaea L., across peanut producing regions of the United States and elsewhere. Two thrips, Frankliniella fusca Hinds and Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), are considered important vectors of TSWV in peanut in the Southeast. We compared the efficiency of acquisition (by larvae) and transmission (adults) of both thrips species for TSWV (Texas peanut-strain) to leaf disks of peanut (Florunner), as well as to Impatiens walleriana Hook. f. (Dwarf White Baby) and Petunia hybrida Juss. ‘Fire Chief’ using double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). Both species were competent TSWV vectors in peanut and Impatiens, although F. fusca was the more efficient vector overall, i.e., virus acquisition and transmission rates for F. fusca averaged over several bioassays were 51.7 and 26.6%, respectively, compared with 20.0 and 15.3% for F. occidentalis. Neither species effectively transmitted this TSWV strain to Petunia (i.e., ≤3.6% transmission). We found statistically similar virus acquisition and transmission rates between both sexes for each species. We also detected no differences in TSWV-acquisition and transmission frequency between macropterous and brachypterous (short-wing) forms of F. fusca collected from a field population in south Texas. DAS-ELISA failed to detect low levels of TSWV in a few thrips that subsequently proved to be competent vectors.