Carl C. Childers

Citrus leprosis virus vectored by Brevipalpus phoenicis (Acari: Tenuipalpidae) on citrus in Brazil.

Citrus leprosis is caused by Citrus leprosis virus (CiLV) that is transmitted by mites in the genus Brevipalpus (Acari: Tenuipalpidae). This disease directly reduces production and the life span of the citrus plant. The main symptoms of the disease include lesions on fruits, leaves, and twigs or small branches, causing premature fruit drop, defoliation, and death of the twigs or branches leading to serious tree decline. Leprosis is a highly destructive disease of citrus, wherever it occurs. The Brazilian citrus industry spends over 100 million US dollars annually on acaricides to control the vector, Brevipalpus phoenicis (Geijskes). This review contains information about the history of the etiology of citrus leprosis, its geographical distribution, host range, the role of the mite vectors, viral morphology and relationships with the infected cell, and transmissibility of the virus by the mite. In addition, data on the mite-virus-plant relationship, disease damage, and strategies for controlling disease spread are presented.

Host Plants of Brevipalpus californicus, B. obovatus, and B. phoenicis (Acari: Tenuipalpidae) and their Potential Involvement in the Spread of Viral Diseases Vectored by these Mites

The family Tenuipalpidae has over 622 species in 30 genera described worldwide. A total of 928 plant species in 513 genera within 139 families are recorded hosts of one or more of the following species: Brevipalpus californicus (Banks), B. obovatus Donnadieu, and B. phoenicis (Geijskes). B. californicus has 316 plant species reported as hosts compared with 451 and 486 host plants for B. obovatus and B. phoenicis, respectively. There are 67 genera of plants within 33 families that are reported hosts of only B. californicus, 119 genera within 55 plant families that are hosts of only B. obovatus, and 118 genera of plants within 64 families that are hosts of only B. phoenicis. There are 14 genera of plants within 12 families that are hosts to both B. californicus and B. obovatus, while there are 40 genera of host plants within 26 families that are hosts for both B. californicus and B. phoenicis. A total of 70 genera of host plants within 39 families have been reported as hosts of both B. obovatus and B. phoenicis, while 77 genera of plants within 44 families have been reported as hosts of all three Brevipalpus species. Geographical differences in the three species of Brevipalpus identified on different plant species within the same genus are common.

Brevipalpus californicus, B. obovatus, B. phoenicis, and B. lewisi (Acari: Tenuipalpidae): a Review of their Biology, Feeding Injury and Economic Importance

The genus Brevipalpus includes most of the economically important species of Tenuipalpidae. Many Brevipalpus species reproduce by theletokous parthenogenesis while other species reproduce by male fertilization of female eggs. Previous researchers have determined that Brevipalpus californicus (Banks), B. obovatus Donnadieu, and B. phoenicis (Geijskes) females were haploid with two chromosomes. The life cycle and developmental times for these three species are reviewed. Longevity of each Brevipalpus species is two to three times greater than corresponding longevities of various tetranychid mites. Brevipalpus mites inject toxic saliva into fruits, leaves, stems, twigs, and bud tissues of numerous plants including citrus. Feeding injury symptoms on selected plants include: chlorosis, blistering, bronzing, or necrotic areas on leaves by one or more Brevipalpus mites. Premature leaf drop occurred on ‘Robinson’ tangerine leaves in Florida (USA). Leaf drop was observed in several sweet orange and grapefruit orchards in Texas (USA) that were heavily infested with Brevipalpus mites feeding on the twigs, leaves, and fruit. Initial circular chlorotic areas appear on both sweet orange and grapefruit varieties in association with developing populations of Brevipalpus mites in Texas. These feeding sites become progressively necrotic, darker in color, and eventually develop into irregular scab-like lesions on affected fruit. Russeting and cracking of the fruits of other plant hosts are reported. Stunting of leaves and the development of Brevipalpus galls on terminal buds were recorded on sour orange, Citrus aurantium L., seedlings heavily infested with B. californicus in an insectary. The most significant threat posed by these mites is as vectors of a potentially invasive viral disease called citrus leprosis.

Citrus leprosis and its status in Florida and Texas: past and present.

According to published reports from 1906 to 1968, leprosis nearly destroyed the Florida citrus industry prior to 1925. This was supported with photographs showing typical leprosis symptoms on citrus leaves, fruit, and twigs. Support for the past occurrence of citrus leprosis in Florida includes: (1) presence of twig lesions in affected orange blocks in addition to lesions on fruits and leaves and corresponding absence of similar lesions on grapefruit; (2) yield reduction and die-back on infected trees; and (3) spread of the disease between 1906 and 1925. Transmission electron microscopy (TEM) examination of tissue samples from leprosis-like injuries to orange and grapefruit leaves from Florida in 1997, and fruits from grapefruit and sweet orange varieties from Texas in 1999 and 2000 did not contain leprosis-like viral particles or viroplasm inclusions. In contrast, leprosis viroplasm inclusions were readily identified by TEM within green non-senescent tissues surrounding leprosis lesions in two of every three orange leaf samples and half of the fruit samples obtained from Piracicaba, Brazil. Symptoms of leprosis were not seen in any of the 24,555 orange trees examined across Florida during 2001 and 2002. The authors conclude that citrus leprosis no longer exists in Florida nor occurs in Texas citrus based on: (1) lack of leprosis symptoms on leaves, fruit, and twigs of sweet orange citrus varieties surveyed in Florida; (2) failure to find virus particles or viroplasm inclusion bodies in suspect samples from both Florida and Texas examined by TEM; (3) absence of documented reports by others on the presence of characteristic leprosis symptoms in Florida; (4) lack of its documented occurrence in dooryard trees or abandoned or minimal pesticide citrus orchard sites in Florida. In view of the serious threat to citrus in the U.S., every effort must be taken to quarantine the importation of both citrus and woody ornamental plants that serve as hosts for Brevipalpus phoenicis (Geijskes), B. californicus (Banks), and B. obovatus Donnadieu (Acari: Tenuipalpidae) from countries where citrus leprosis occurs.

Thrips feeding and oviposition injuries to economic plants, subsequent damage and host responses to infestation

Injury to various plant tissues by ovipositing Terebrantian species and feeding injuries by thrips species to pollen, flowers, fruit and leaves are characterized for different economic plants. Both the range of damage to individual economic crops and differences arising through attacks on the same plant at different stages of development are included. The range of species attacking the same plant in different parts of the world and how differences in pest status of individual thrips species on a single crop vary from one geographical area to another are presented.

Thysanoptera (Thrips) Within Citrus Orchards in Florida: Species Distribution, Relative and Seasonal Abundance Within Trees, and Species on Vines and Ground Cover Plants

Abstract Seven citrus orchards on reduced to no pesticide spray programs were sampled for Thysanoptera in central and south central Florida. Inner and outer canopy leaves, fruits, twigs, trunk scrapings, vines and ground cover plants were sampled monthly between January 1995 and January 1996. Thirty-six species of thrips were identified from 2,979 specimens collected from within citrus tree canopies and 18,266 specimens from vines and ground cover plants within the seven citrus orchards. The thrips species included seven predators [Aleurodothrips fasciapennis (Franklin), Karnyothrips flavipes (Jones), K. melaleucus (Bagnall), Leptothrips cassiae (Watson), L. macroocellatus (Watson), L. pini (Watson), and Scolothrips sexmaculatus (Pergande)] 21 plant feeding species [Anaphothrips n. sp., Arorathrips mexicanus (Crawford), Aurantothrips orchidaceous (Bagnall), Baileyothrips limbatus (Hood), Chaetanaphothrips orchidii (Moulton), Danothrips trifasciatus (Sakimura), Echinothrips americanus (Morgan), Frankliniella bispinosa (Morgan), F. cephalica (Crawford), F. fusca (Hinds), F. gossypiana (Hood), Frankliniella sp. (runneri group), Haplothrips gowdeyi (Franklin), Heliothrips haemorrhoidalis (Bouché), Leucothrips piercei (Morgan), Microcephalothrips abdominalis (Crawford), Neohydatothrips floridanus (Watson), N. portoricensis (Morgan), Pseudothrips inequalis (Beach), Scirtothrips sp., and Thrips hawaiiensis (Morgan)]; and eight fungivorous feeding species [Adraneothrips decorus (Hood), Hoplandrothrips pergandei (Hinds), Idolothripinae sp., Merothrips floridensis (Watson), M. morgani (Hood), Neurothrips magnafemoralis (Hinds), Stephanothrips occidentalis Hood and Williams, and Symphyothrips sp.]. Only F. bispinosa, C. orchidii, D. trifasciatus, and H. haemorrhoidalis have been considered economic pests on Florida citrus. Scirtothrips sp. and T. hawaiiensis were recovered in low numbers within Florida citrus orchards. Both are potential pest species to citrus and possibly other crops in Florida. The five most abundant thrips species collected within citrus tree canopies were: A. fasciapennis, F. bispinosa, C. orchidii, K. flavipes, and D. trifasciatus. In comparison, the following five thrips species were most abundant on vines or ground cover plants: F. bispinosa, H. gowdeyi, F. cephalica, M. abdominalis, and F. gossypiana. Fifty-eight species of vines or ground cover plants in 26 families were infested with one or more of 27 species of thrips.

Biology ofEuseius mesembrinus (Acari: Phytoseiidae): Life tables on ice plant pollen at different temperatures with notes on behavior and food range

Euseius mesembrinus (Dean) (Acari: Phytoseiidae) was recently reported on Florida citrus for the first time. This mite was able to develop and reproduce when fed plant pollen of Spanish needle,Bidens pilosa L. and ice plant,Malephora crocea (Jacq.) or three spider mite species (Acari: Tetranychidae) including all stages ofTetranychus urticae Koch,Eutetranychus banksi (McGregor), and larval and nymphal stages only ofPanonychus citri (McGregor).The biology ofE. mesembrinus was studied under laboratory conditions while being fed pollen ofM. crocea. The developmental time for immature stages at 18, 22, 26, and 30°C was 11.50, 7.47, 4.54, and 4.40 days, respectively. This pattern fits a log-probit model withr2=0.940. Eggs hatched, but mortality in other stages was high at 34°C. The intrinsic rate of natural increase was 0.146, 0.250, and 0.246 at 22, 26, and 30°C. The optimum temperature for this phytoseiid to develop and increase on ice plant pollen was in the range of 26 to 30°C.

Comparative residual toxicities of pesticides to the predator Agistemus industani (Acari: Stigmaeidae) on citrus in Florida.

Residual toxicities of registered and selected experimental pesticides used on citrus against Agistemus industani Gonzalez (Acari: Stigmaeidae) were compared. Pesticides considered highly toxic to A. industani were: abamectin 0.15 EC at 731 ml/ha + FC 435-66 petroleum oil at 46.8 l/ha, pyridaben 75 WP at 469 g/ha, ethion 4 EC at 7.01 l/ha + FC 435-66 petroleum oil at 46.8 l/ha, propargite 6.55 EC at 3.51 l/ha, chlorfenapyr 2 SC at 1.46 l/ha applied alone or in combination with FC 435-66 petroleum oil at 46.8 l/ha, sulphur 80 DF at 16.81 kg/ha, dicofol 4 EC at 7.01 l/ha, fenbutatin oxide 50 WP at 2.24 kg/ha, benomyl 50 WP at 2.24 kg/ha, benomyl 50 WP at 1.68 kg/ha + ferbam 76 GF at 5.60 kg/ha, ferbam 76 GF at 11.21 kg/ha, neem oil 90 EC at 46.8 l/ha, and copper hydroxide DF (40% metallic copper) at 4.48 kg metallic copper/ha + FC 435-66 petroleum oil at 46.8 l/ha. Pesticides that were moderately to slightly toxic included: copper sulphate 98% at 4.48 kg metallic copper/ha + FC 435-66 petroleum oil at 46.8 l/ha, fenbuconazole 2 F at 280 ml/ha + FC 435-66 petroleum oil at 46.8 l/ha, FC 435-66 petroleum oil applied alone at 46.8 l/ha or 23.4 l/ha, and diflubenzuron 25 WP at 1.40 kg/ha. Pesticides that were non-toxic included: fenbuconazole 2 F at 585 ml/ha, malathion 57 EC at 5.85 l/ha, FC 435-66 petroleum oil at 46.8 l/ha, carbaryl 80 S at 3.36 kg/ha, chlorpyrifos 4 EC at 4.68 l/ha, and formetanate 92 SP at 1.12 kg/ha. Understanding the toxic effects of field weathered pesticides against key predacious mite species is important for effective IPM. The results of this study provide a comparison of direct and indirect toxic effects of various pesticides to A. industani under field conditions.

First Report of Citrus leprosis virus in Panama

Citrus is a rapidly expanding fruit crop in Panama with a planted area of approximately 14,000 ha, with the crop destined for both table and juice industries for local and foreign markets. Chiriqui Province in extreme western Panama borders Costa Rica and grows 4,300 ha of citrus that consists primarily of Valencia and navel oranges with the remainder grown throughout other provinces. Some plants in commercial groves in Potrerillos and Boquete in Chiriqui Province were found with leaf (chlorotic spots or rings), stem (necrosis), and fruit (localized ringlike or depressed lesions) symptoms similar to those caused by Citrus leprosis virus (CiLV) (3). In Potrerillos, wood samples about 3 years old were identified in two of the citrus groves, indicating that the infection was established on or before 1996. The mite Brevipalpus phoenicis (Geijskes) (Acari: Tenuipalpidae) was collected in all leprosis-infected or suspected groves in both Potrerillos and Boquete. CiLV is known to be transmitted by B. obovatus Donnadieu and B. phoenicis in Argentina and Brazil, respectively (3). To confirm the presence of this virus, 20 samples (12 from Boquete [B] and 8 from Potrerillos [P]) of leaf and fruit lesions were fixed in a modified Karnovsky solution and sent to Brazil for electron microscopic examination of thin sections. In 8 samples (2 from B and 6 from P) cytopathic effects were found characterized by a dense viroplasm in the cytoplasm and short, bacilliform particles (50 to 60 × 100 to 110 nm) in the lumen of the endoplasmic reticulum, features similar to those reported by Colariccio et al. (1). In 6 samples (5 from B, and 1 from P), the cytopathic effects were similar to those observed in Orchid fleck virus (OFV)-infected cells (2), with an intranuclear, electron lucent viroplasm and short, rodlike particles (40 to 50 nm × 100 nm) either within the nucleus or in the cytoplasm, as also previously reported for a sample of CiLV in Brazil (4). The symptomatology, presence of the mite vector, characteristic cytopathic effects, and presence of virions are considered to be evidence that CiLV is present within a 100 km2 area of Potrerillos and 25 km2 of Boquete in Chiriqui Province. This is the first report of the presence of CiLV in Central America, suggesting that the virus has spread northward from South America. References: (1) A. Colariccio et al. Fitopatol. Bras. 20:208, 1995. (2) Y. Doi et al. AAB/CMI Description of Plant Viruses No. 183, 1977. (3) S. M. Garnsey and C. M. Chagas. 2000. Pages 57-58 in: Compendium of Citrus Diseases, 2nd Ed. L. W. Timmer et al, eds. APS Press, St.Paul, MN. (4) E. W. Kitajima et al. Virology 50:254, 1972.

Observations on the occurrence and feeding habits of Balaustium pulmani (Acari: Erythraeidae) in North Carolina apple orchards

Abstract Balaustium putmani Smiley was collected within and beneath apple tree canopies from late April to late August during 1975–77 in western North Carolina.