Philip A. Stansly

Cultural practices for managing Bemisia tabaci and associated viral diseases

Abstract Whiteflies ( Bemisia spp.) and the viruses they vector cause extensive losses to many horticultural and agronomic crops throughout the tropics and subtropics. These losses have spurred a worldwide search for cost-effective management strategies. Cultural practices can play a significant role in integrated pest management (IPM) systems targeting whiteflies, because of their preventative nature. Yet, cultural practices have received disproportionately little attention from researchers, possibly due to the difficulty of testing by conventional methods. Practices such as crop-free periods, altering planting dates, crop rotation, and weed and crop residue disposal, perform well only if used on a regional scale and therefore are difficult to test or demonstrate experimentally. Growers may also be reluctant to adopt cultural practices such as living barriers, high planting densities, floating row covers, mulches, and trap crops, that require significant changes in conventional cropping practices. Nonetheless, we have seen adoption in recent years of some cultural practices to manage whiteflies, such as crop planning that includes host-free periods, and various forms of screened exclusion. This review focuses on research efforts, field utilization, and the potential of cultural practices to manage the whiteflies and associated viral diseases.

Incidence of invasive Diaphorina citri (Hemiptera: Psyllidae) and its introduced parasitoid Tamarixia radiata (Hymenoptera: Eulophidae) in Florida citrus.

ABSTRACT Diaphorina citri Kuwayama (Hemiptera: Psyllidae), vectors the bacterium Candidatus Liberibacter asiaticus, one of the causal organisms of the devastating citrus disease “huanglongbing” or citrus greening. In the United States, D. citri was first discovered in Florida, in 1998. Tamarixia radiata Waterston (Hymenoptera: Eulophidae) was imported from Asia and released in Florida in 1999–2001 to improve biological control of D. citri before citrus greening was detected in Florida in 2005. Florida citrus groves were surveyed during 2006 – 2007 for D. citri and T. radiata. Results showed that D. citri was established in all 28 citrus groves surveyed across 16 counties. Adult populations averaged 3.52, 1.27, and 1.66 individuals per “tap” sample at locations in the central, southwest, and eastern coastal regions, respectively. A tap sample consisted of 22- by 28-cm white paper sheet (on a clipboard) held under branches selected at random that were tapped three times. Averages of 67, 44, and 45% citrus shoots infested with psyllid eggs or nymphs were obtained in the central, southwest, and eastern coastal regions, respectively. T. radiata was recovered from fourth- and fifth-instar psyllid nymphs at 26 of the 28 locations. However, apparent parasitism rates were variable and averaged <20% during spring and summer over all locations. Incidence of parasitism increased during fall at some locations, averaging 39% in September and 56% in November in the central and southwest regions, respectively. Further efforts are warranted to enhance the biological control of D. citri and thereby reduce psyllid populations and spread of citrus greening disease.

Preplant release of Nesidiocoris tenuis and supplementary tactics for control of Tuta absoluta and Bemisa tabaci in greenhouse tomato

An early release system developed for Nesidiocoris tenuis Reuter (Heteroptera: Miridae) could provide a good control of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in tomato. Tuta absoluta and the whitefly Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) often appear simultaneously in tomato crops and this might affect control capacity. Therefore, the new approach needs to be tested in a situation with both pests present. In addition, Bacillus thuringiensis Berliner and Trichogramma achaeae Nagaraja & Nagarkatti (Hymenoptera: Trichogrammatidae) have been shown to be effective against T. absoluta and could be a supplement to N. tenuis. Two experiments were carried out to evaluate the potential of this approach and its combination with supplementary control agents against T. absoluta. In the first experiment four treatments were compared (T. absoluta, B. tabaci, T. absoluta + N. tenuis, and T. absoluta + B. tabaci + N. tenuis) and N. tenuis was able to control T. absoluta and B. tabaci either alone or together. In the second experiment, five treatments were compared: T. absoluta, T. absoluta + N. tenuis, T. absoluta + N. tenuis + T. achaeae, T. absoluta + N. tenuis + B. thuringiensis, and T. absoluta + N. tenuis + T. achaeae + B. thuringiensis. Nesidiocoris tenuis again proved capable of significantly reducing T. absoluta populations, and the implementation of additional agents did not increase its effectiveness.

CITRUS FLUSHING PATTERNS, DIAPHORINA CITRI (HEMIPTERA: PSYLLIDAE) POPULATIONS AND PARASITISM BY TAMARIXIA RADIATA (HYMENOPTERA: EULOPHIDAE) IN PUERTO RICO

Abstract Discovery of citrus greening disease or Huanglongbing in Brazil and Florida has elevated the vector psyllid, Diaphorina citri (Hemiptera: Psyllidae), to key pest status in both regions. Detected in Puerto Rico within 3 years of first detection in Florida, the psyllid appeared to be relatively scarce in the Island’s limited citrus and alternate rutaceous host, orange jasmine, Murraya paniculata. Monthly surveys were conducted at 4 locations during 2004 through 2005 to evaluate citrus flushing patterns, psyllid densities, and prevalence of parasitism by Tamarixia radiata. Although low levels of D. citri are known to be established in the high, cool areas of Adjuntas, a total lack of psyllids at the particular study location was attributed to scarcity of flush except for a short period in Feb. Greatest and most prolonged production of new flush, highest psyllid numbers, and greatest incidence of parasitism occurred at Isabela, the most coastal location and the only one with irrigated citrus. Favorable climate and irrigation resulted in prolonged availability of new foliage needed to maintain populations of psyllids and consequently its parasitoid. There, apparent parasitism of late instars was estimated to average 70% and approached 100% on 3 different occasions. Tamarixia radiata also was found parasitizing psyllid nymphs in orange jasmine at the rate of 48% and 77% at Río Piedras and San Juan, respectively, approaching 100% on 5 occasions during spring and summer. The corresponding decline in infestation during peak flush in spring and later in the year could indicate that T. radiata made important contributions to the regulation of D. citri populations at these locations. Better understanding of factors favoring high parasitism rates in Puerto Rico could lead to more effective biological control of D. citri in other citrus producing areas.

Influence of host plant and prey availability on developmental time and surviorship of Nesidiocoris tenius (Het.: Miridae)

Abstract Nesidiocoris tenuis is a zoophytophagous mirid with biological control potential. However, the relative importance of predation and herbivory for survival and development has not been clear. The bugs survived longer on tomato than on eggplant and especially sweet pepper, but could not complete development in the absence of supplemental food. Tomato also proved to be a more favorable substrate than pepper when eggs of Ephestia kuehniella were added as a food supplement. These results demonstrated that animal prey is a required dietary component for N. tenuis, and also that survival time on a strict plant diet is host plant dependent.

Toxicity and repellency of some biorational insecticides to Bemisia argentifolii on tomato plants

A mineral oil, an insecticidal soap, and a plant‐derived surfactant were compared with a broad‐spectrum pyrethroid for residual toxicity and repellency to silverleaf whitefly, Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae) on tomatoes (Lycopersicum esculentum Miller, cv. Lanai) under greenhouse and laboratory conditions. The materials tested were: Sunspray oil (a mineral oil), M‐Pede (an insecticidal soap), Nicotiana gossei extract (a sucrose ester surfactant), Garlic Barrier (repellency only), and the pyrethroid bifenthrin (Brigade 10WP), with water as a control. For toxicity studies, whiteflies were confined on leaves which had been dipped in solutions of 0.5 ×, 1 × and 2 × field rate concentrations. Insecticide residues were compared when the leaves were wet and dry. Adult mortalities were greatest with bifenthrin and Sunspray oil, followed by M‐Pede, N. gossei extract and water. Mortality from dry residue of lower rates of bifenthrin and Sunspray oil was greater than mortality from wet residues, whereas M‐Pede lost all activity upon drying. Dual and multiple choice tests for repellency were carried out in the greenhouse or laboratory by spraying plants or individual leaves to runoff with 1 × field concentrations. Bifenthrin and Sunspray oil repelled B. argentifolii adults for up to 7 and 5 days, respectively, followed by M‐Pede and extract of N. gossei, whereas Garlic Barrier was not significantly different from the water control in all tests. Numbers of whitefly eggs were significantly reduced on bifenthrin and Sunspray oil‐treated leaves, whereas egg numbers in other treatments were not different from water. Sunspray oil as a dip proved to be at least as effective as the synthetic pyrethroid for whitefly control. A multiple‐choice leaf‐wheel proved to be a useful device to quickly evaluate repellent effects of several different insecticides to whitefly.

Insecticidal activity of surfactants and oils against silverleaf whitefly (Bemisia argentifolii) nymphs (Homoptera: Aleyrodidae) on collards and tomato.

The insecticidal activities of four surfactants (Cide-kick, Silwet L-77, M-Pede and APSA- 80), a dishwashing detergent (New Day), a mineral oil (Sunspray oil), a cotton seed oil and a vegetable oil, alone or in combination, were tested against nymphs of Bemisia argentifolii Bellows & Perring on collards and tomato. Silwet L-77 was more effective (>95% mortality) than Cide-Kick or APSA-80 at rates from 0.25-1.00 g AI litre ˇ1 but caused severe phytotoxicity to tender tomato leaves at all but the lowest rate. New Day dish detergent at 2.0 ml litre ˇ1 caused mortality (95%) comparable to M-Pede insecticide soap at 10-fold greater concentration. A New Day ingredient, cocamide DEA, was con- siderably more active than the other ingredients or the commercial mixture. Additional surfactants added to Sunspray oil increased efficacy in some treatments, but not others. Toxic responses of 2nd- and 3rd- instar whiteflies to vegetable oil and cotton seed oil at 5.0 and 10.0 ml litre ˇ1 plus 0.4 g AI litre ˇ1 APSA-80 ranged from 22.1 to 79.9% and 66.3-88.7% mortality, respectively. Whitefly mortality was greater on tomato than on collard in six of seven instances when differences between host plants were significant. Our results indicate that the these surfactants and oils have good potential for controlling B argentifolii. # 2000 Society of Chemical Industry

Host Range of Tomato Mottle Virus, a New Geminivirus Infecting Tomato in Florida

A geminivirus causing mottling, upward leaf curling, and stunting was observed infecting tomatoes (Lycopersicon esculentum Mill. var. esculentum) throughout production areas of Florida since 1989; and it has been named the tomato mottle virus (TMoV). The virus was inoculated by whiteflies (Bemisia tabaci (Gennadius)) to 41 plant species representing eight families. Species of four genera became infected, three in the Solanaceae (Lycopersicon, Nicotiana, and Physalis) and one in the Fabaceae (Phaseolus)

Aggregation pheromone for the pepper weevil,Anthonomus eugenii cano (Coleoptera: Curculionidae): Identification and field activity

This study describes the identification of an aggregation pheromone for the pepper weevil,Anthonomus eugenii and field trials of a synthetic pheromone blend. Volatile collections and gas chromatography revealed the presence of six male-specific compounds. These compounds were identified using chromatographic and spectral techniques as: (Z)-2-(3,3-dimethylcyclohexylidene)ethanol, (E)-2-(3,3-dimethylcyclohexylidene)ethanol, (Z)-(3,3-dimethylcyclohexylidene)acetaldehyde, (E)-(3,3-dimethylcyclohexylidene)acetaldehyde, (E)-3,7-dimethyl-2,6-octadienoic acid (geranic acid), and (E)-3,7-dimethyl-2,6-octadien-1-ol (geraniol). The emission rates of these compounds from feeding males were determined to be about: 7.2, 4.8, 0.45, 0.30, 2.0, and 0.30µg/male/day, respectively. Sticky traps baited with a synthetic blend of these compounds captured more pepper weevils (both sexes) than did unbaited control traps or pheromone-baited boll weevil traps. Commercial and laboratory formulations of the synthetic pheromone were both attractive. However, the commercial formulation did not release geranic acid properly, and geranic acid is necessary for full activity. The pheromones of the pepper weevil and the boll weevil are compared. Improvements for increasing trap efficiency and possible uses for the pepper weevil pheromone are discussed. A convenient method for purifying geranic acid is also described.

Insecticidal Suppression of Asian Citrus Psyllid Diaphorina citri (Hemiptera: Liviidae) Vector of Huanglongbing Pathogens

Diaphorina citri vectors pathogens that cause ‘huanglongbing’ or citrus greening disease which poses a serious threat to citrus production worldwide. Vector suppression is critical to reduce disease spread. Efficacy is a main concern when choosing an insecticide. Insecticidal treatments of 49 products or 44 active ingredients (a.i) labeled or experimental were field tested between 2005–2013 as foliar sprays (250 treatments, 39 a.i) or soil applications (47 treatments, 9 a.i) to control D. citri in citrus. A combined effect of nymphal and adult suppression in response to sprays of 23 insecticides representing 9 modes of action (MoA) groups and 3 unknown MoA provided more than 90% reduction of adult D. citri over 24–68 days. Observable effects on nymphs were generally of shorter duration due to rapid maturation of flush. However, reduction of 76–100% nymphs or adults over 99–296 days was seen on young trees receiving drenches of the neonicotinoids imidacloprid, thiamethoxam or clothianidin (MoA 4A) and a novel anthranilic diamide, cyantraniliprole (MoA 28). Effective products identified for foliar sprays to control D. citri provide sufficient MoA groups for rotation to delay evolution of insecticide resistance by D. citri and other pests. However, cyantraniliprole is now the only available alternative for rotation with neonicotinoids in soil application to young trees. Sprays of up to eight of the most effective insecticides could be rotated over a year without repetition of any MoA and little or no recourse to neonicotinoids or cyantraniliprole, so important for protection of young trees. Other considerations effecting decisions of what and when to spray include prevalence of huanglongbing, pest pressure, pre-harvest intervals, overall budget, equipment availability, and conservation of beneficial arthropods. Examples of spray programs utilizing broad-spectrum and relatively selective insecticides are provided to improve vector management and may vary depending on individual or regional assessment of all factors.