Aleurodicus dispersus
(whitefly)

Aleurodicus dispersus is of Neotropical origin, and is native to Central America and the Caribbean region. It is naturally found in Central and South America, the Caribbean and southern Florida, USA. It has been present in the Canary Islands since 1962. During the 1970s it began a rapid expansion of its range. It established in Hawaii in 1978 (Paulson and Kumashiro, 1985). It was first reported in the Philippines in 1982, and during the 1980s it spread throughout the islands of the Pacific (Waterhouse and Norris, 1989). Since then, it has been reported in India, Sri Lanka, Africa, Indonesia, Thailand, Taiwan and northern Australia (Martin, 1990; Wijesekera and Kudagamage, 1990; Kajita et al., 1991; Akinlosotu et al., 1993; Wen et al., 1994b; Palaniswami et al., 1995; Carver and Reid, 1996). More recently, it has been reported in Unguja Island Tanzania, Sao Tome and Principe, Senegal and Seychelles (Hazell et al., 2008; EPPO, 2014).

The distribution map includes records based on specimens of A. dispersus from the collection in the Natural History Museum (London, UK): dates of collection are noted in the list of countries.

Aleurodicus dispersus presents a serious phytosanitary risk to tropical and subtropical areas on the edges of its current range. Quarantine areas have been declared in Queensland, Australia. The movement of plants, plant material and fruits out of quarantine areas can only proceed after official inspections (Lambkin, 1998). The spread of A. dispersus on citrus is of particular concern, in Australia, Mexico and other countries. A. dispersus is quarantine pest for Iran (Cheraghian, 2015). Only the climatic limitations will ultimately determine the final distribution of this highly invasive and polyphagous pest. It has not stopped moving yet. A. dispersus will remain on the alert list in Spain (EPPO, 2005).

It appears unlikely that it could establish outdoors in most parts of the EPPO region. However, it may present a risk for the warmest parts of southern Europe, where many of its host plants are grown (citrus, avocado, palms, tomato, aubergine etc.). It may also present a risk for ornamentals or vegetable crops grown under glasshouse conditions (EPPO, 2006). The risk would be associated with movement of leaves (that are used to make traditional food dishes in the Pacific). In the last 25 years, A. dispersus has been shown to be a highly invasive pest in the Pacific and elsewhere. There are few Pacific Island countries that have not reported its presence. Failing to abide by strict quarantine procedures may lead to new areas becoming infested with whiteflies. It is not known to be a vector of any plant viruses.

Aleurodicus dispersus is highly polyphagous, being common on a wide range of different families. Russell (1965) recorded it from 38 genera in 27 plant families in Florida, USA.

In Taiwan, Wen et al. (1994b) listed 144 species of host plant, in 64 families, with host range varying with season. In Indonesia, Kajita et al. (1991) reported A. dispersus attacking 22 plants in 14 families, including ornamentals, shade and fruit trees and annual crops. In India, Boopathi (2013) listed 147 host plant in 53 families. In Kerala, India, Prathapan (1996) listed 72 host plants, ranked by intensity of infestation.

In addition to the hosts listed, Diospyros philippinensis, Elaeocarpus serratus, Heliotropium indicum, Ixeris oldhami, Laguncularia racemosa, Melaleuca leucadendron [Melaleuca leucadendra], Peristeria spp., Pterocarpus spp., Rhus semialata [Rhus chinensis], Sagittaria trifolia and Sideroxylon ferrugineum are also secondary hosts of A. dispersus. In India, Boopathi (2013) recorded 56 host plants as a new host of A. dispersus out of 147 host plants.

Reproductive Biology

The common name of A. dispersus, the spiralling whitefly, is derived from its characteristic egg-laying pattern, although other species of aleurodicine whitefly also lay eggs in spiral patterns (Martin, 1990). Females, collected in the field in Sri Lanka and studied in the laboratory, each laid 14-26 eggs in a loose spiral on the underside of leaves. Eggs hatched after 7-10 days, the first and second larval instars lasted for 6-9 days in total, the third instar for 5-13 days and the fourth (pupae) 5-16 days. Adults lived for about 2 weeks (Wijesekera and Kudagamage, 1990). Boopathi (2013) described adult longevity ranging from 11.0 to 15.4 days. Adult longevity was greater on Gossypium hirsutum (15.1 days) and Manihot esculenta (14.4 days), compared to a shorter duration on Capsicum annuum (chilli) (11.0 days).

Physiology and Phenology

The immature stages of A. dispersus are found on the lower leaf surface of host plants. The leaf structure of the host plant appears to affect feeding preference (Wen et al., 1994a). The larval stages and adults feed by sucking phloem sap from leaves. Copious honeydew is excreted which coats surrounding surfaces and often develops a layer of sooty mould when colonies are poorly controlled.

Wen et al. (1994b) described the effects of temperature on development rate and fecundity. Adults were active between 12.3-32.3°C and maximum female fecundity occurred at 25°C. A. dispersus populations were found all year round in southern Taiwan, building up rapidly in October, reaching a peak in November and then declining gradually after December. The developmental time (from oviposition to eclosion) of the pest at 25°C on poinsettia, canna, guavas (Psidium guajava) and pawpaws (Carica papaya) was 26.1, 25.0, 29.4 and 26.1 days; immature mortality was 26.9, 24.5, 33.3 and 27.8%; and fecundity was 65.2, 35.8, 51.3 and 58.0 eggs per female, respectively (Wen et al., 1996). Boopathi (2013) described the highest incubation period (8.3 days), first instar (6.1 days), second instar (6.2 days), third instar (7.0 days), fourth instar (7.4 days), total nymphal period (26.7 days), pupal period (2.7 days) and adult longevity (17.6 days) were recorded on cassava at 25°C as compared to other two temperatures viz., 30 and 35°C. The total developmental period (39.8 days) was also highest at 25°C. The highest and lowest percent adult emergence was at 25°C (90.3) and 35°C (82.8), respectively. A temperature of 30°C (28.3/female) produed the highest number of eggs by a female. The highest egg hatchability was at 25°C (93.9%) (Boopathi, 2013).

Females begin laying eggs within a few days of emergence and continue to lay throughout their lifetime. The rate of population growth can be rapid. In one experiment, 20 pairs produced 1549 individuals in 37 days (Waterhouse and Norris, 1989). Unmated females produce only male progeny, while mated females produce a mixture of male and female progeny. Adults are most active in the morning, but mate in the afternoon (Waterhouse and Norris, 1989). Boopathi (2013) reported that fecundity showed greater variations among different host plants. The highest and least number of eggs laid per female was in M. esculenta (28.5) and M. alba (13.1), respectively.

Environmental Requirements

In the USA, A. dispersus is limited to southern coastal areas in Florida where mild winter temperatures occur. Extreme mortality occurs at low temperatures (below 10°C), which limits the northward spread of A. dispersus in the Americas (Cherry, 1979).

Manzano et al. (1995) described the biology of A. dispersus in the Canary Islands. In Karnataka, India, Aishwariya et al. (2007) studied the biology of A. dispersus on guava during the winter, summer and wet seasons. Boopathi (2013) described the biology of A. dispersus in Tamil Nadu, India on ten different host plants and also studied the effect of temperature on the biology of A. dispersus on cassava and eggplant (Solanum melongena).

Aleurodicus dispersus is recorded as being frequently parasitized in Florida, USA (Russell, 1965). The common parasitoids of A. dispersus on banana in Costa Rica were described by Blanco-Metzler and Laprade (1998). Gerling (1990) presented a short key for parasitoids of whiteflies. Clausen (1934) listed natural enemies of Aleyrodidae in tropical Asia, although A. dispersus was probably not present in Asia at that time. Ramani et al. (2002) and Boopathi (2013) listed natural enemies of A. dispersus in India.

Encarsia haitiensis was believed to be host-specific on A. dispersus (Waterhouse and Norris, 1989); however, E. haitiensis as a parasitoid of A. dispersus is based on a misidentification. The species widely reported in published papers as E. haitiensis or E. near haitiensis is in fact an undescribed species closely related to E. hispida, which also attacks A. dispersus (Polaszek et al., 2004). Boopathi (2013) described the morphometry and parasitization level of E. guadeloupae and E. sp. nr. meritoria. Hernandez-Suarez et al. (2003) reported E. hispida and E. guadeloupae affecting A. dispersus in the Canary Islands. In India, E. guadeloupae and E. sp. nr. meritoria were the most abundant parasitoids of A. dispersus on cassava (Manihot esculenta) (Boopathi 2013).

Paulson and Kumashiro (1985) described natural enemies of A. dispersus in Hawaii. Kumashiro et al. (1983) described the introduction of two parasitoids and several coccinellids into Hawaii for the biological control of A. dispersus, of which Nephaspis oculatus (N. amnicola) was the most effective coccinellid predator. Boopathi (2013) and Boopathi et al. (2016) described the predatory potential and life history of Mallada astur, M. desjardinsi, C. zastrowi sillemi, Cybocephalus spp., Cryptolaemus montrouzieri and A. puttarudriahi.Yoshida and Mau (1985) described the life history and feeding behaviour of N. oculatus. Although N. oculatus has a wide prey range in laboratory studies, in the field, it shows a strong preference for whiteflies. However, it is only effective as a natural enemy within high prey densities. In contrast, E. haitiensis is most effective when whitefly populations are low (Kumashiro et al., 1983). Boopathi (2013) and Boopathi et al (2017) studied the effect of insecticides on natural enemies of A. dispersus in cassava and eggplant (Solanum melongena).

When A. dispersus are abundant they are conspicuous on leaves due to the white flocculence that covers their bodies (Russell, 1965). They are found on the undersides of leaves, often associated with sticky honeydew and sometimes sooty mould growth.

A. dispersus were found in significantly higher numbers in the upper canopy than in the middle and the lower canopy on guava (Shah Alam et al., 1997).

The white spiral pattern of eggs and white, fluffy wax, which covers the immature stages and adults on the underside of the leaves, is conspicuous and distinctive. Note that other species of whitefly also lay eggs in a spiral pattern.

Russell (1965) described A. dispersus in comparison with the closely related A. coccolobae and A. flavus. Identification is on the basis of distinctive compound and simple pores in the pupal stage. It should be noted that other members of this genus, mostly native to the Neotropical region, also lay their eggs in spiral patterns like A. dispersus. Reliable identification requires microscopic study of slide-mounted pupal cases.

Martin et al. (1997) provided keys to enable adults and puparia of A. dispersus to be distinguished from the newly introduced crop pest Lecanoideus floccissimus sp. nov. in the Canary Islands. Comprehensive microscopic analysis is required to accurately identify whitefly species.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Biological Control

Aleurodicus dispersus was first recorded in Hawaii in 1978, after which it spread rapidly. Its pest status on guavas (Psidium guajava) stimulated a successful biological control programme (Kumashiro et al., 1983; Beardsley, 1993). The introduction and establishment of the coccinellid beetle Nephaspis oculatus (N. amnicola) and the parasitoid Encarsia haitiensis successfully controlled A. dispersus on guavas in highland and lowland areas of Honolulu, Hawaii. In 1980-1981, peak population densities of A. dispersus were reduced by 79% in the lowlands and 98.8% in the highlands. Rainfall, temperature and previously established predators, particularly Allograpta obliqua, probably also contributed to the reduction of A. dispersus populations (Kumashiro et al., 1983). Mallada astur and Cybocephalus spp. were found to be the most efficient predator in reducing the population of A. dispersus in India (Boopathi, 2013). Inundative releases of Cryptolaemus montrouzieri and M. astur against A. dispersus had only in temporary reduction of the whiteflies during 1998-1999 in Karnataka (Mani et al., 2001).

Since the biological control of A. dispersus in Hawaii, there have been further successes on Pacific Islands; for a review see Waterhouse and Norris (1989). In each case, E. haitiensis was successful, aided by one or more of the introduced coccinellids.

A biological programme in tropical Africa was described by Neuenschwander (1996), in which two exotic hymenopterous parasitoids were introduced. These helped control A. dispersus populations, with indigenous coccinellids playing a minor role. A. dispersus was observed in Benin for the first time in 1993, along with the parasitoids E. haitiensis and E. guadeloupae, which were thought to have been accidentally introduced. Between 1993 and 1996, these parasitoids helped control A. dispersus populations on guava (D'Almeida et al., 1998). E. haitiensis has been successfully introduced into Queensland, as part of the biological control of A. dispersus in Australia (Lambkin, 1998). In India, E. guadeloupae was found to be the most effective parasitoid in the reduction of A. dispersus population on cassava (Manihot esculenta) and eggplant (Solanum melongena; Boopathi, 2013) and Boopathi et al. (2015a, b) evaluated the entomopathogenic fungi Beauveria bassiana, Metarhizium anisopliae, Lecanicillium lecanii and Isaria fumosorosea [Cordyceps fumosorosea] were tested for their efficacy in managing the A. dispersus on cassava and eggplant in India. The fungi I. fumosorosea [C. fumosorosea] and L. lecanii exhibited promising levels of control (>70% mortality). L. lecanii at 1.33 x 10⁷ and Verticel at 7.5 g/l were found to be most effective against A. dispersus at 7, 15 and 21 days after spraying (Mallappanavar, 2000).

 

Chemical Control

Kajita et al. (1991) described some insecticides effective against A. dispersus on soyabeans in Indonesia. However, because the whitefly has such a wide host-plant range and insecticides also impact natural enemies, chemical control is usually considered impractical and uneconomic in the long-term (Kajita et al., 1991; Lambkin, 1998). In India, Boopathi et al. (2017) described several insecticides against A. dispersus on cassava and eggplant. Acephate and triazophos were effective in controlling A. dispersus population (>90% reduction) on cassava and recorded higher tuber yield. Laprade and Cerdas (1998) evaluated insecticide treatments on banana farms in Costa Rica. Dilute aqueous solutions of soaps and detergents have also provided effective control in smallholdings, in conjunction with pruning and mulching, the latter to counter moisture loss by plants due to infestation (Anon., 1980). Chlorpyriphos at 0.04% was found to effective against A. dispersus (Dubey and Sundararaj, 2004). Contact insecticides like malathion and carbaryl at 0.10% were also found effective against young nymphs (Ragumoorthy and Kempraj, 1996). Dichlorvos 0.08% was found toxic to various stages of spiralling whitefly (Mariam, 1999).

In India, tobacco extract, neem oil, fish oil, rosin soap and detergent solution in addition to several insecticides have been found effective (Ranjith et al., 1996; Mariam, 1999; Muralikrishna, 1999; Geetha, 2000; Boopathi, 2013). Alim et al. (2017) described the toxicity of eight plant extracts and their mixtures used as insecticides in South Asian countries such as Bangladesh, India and Nepal. The highest mortality (100%) of adults was recorded for neem (ethanol) extract (500 mg/L) at 6 h after topical spray. Neem (ethanol) extract mixed with crown flower (acetone), oleander (acetone), or sweet sop (ethanol) (in the ratio of 1:1, 1:2 and 1:3 for each plant extract) showed synergism. Boopathi (2013) evaluated some botanicals on cassava and eggplant in India. The neem seed kernel extract (NSKE) 5% and azadirachtin 5.0% produced the highest mortality of A. dispersus population on eggplant and cassava.

Monitoring and Surveillance

Light traps are an appropriate tool for monitoring. A simple method for trapping large number of A. dispersus with light traps coated with vaseline was suggested by Srinivasan and Mohanasundaram (1997). Fluorescent light smeared with castor oil attracted and trapped large number of adults (Mariam, 1999). Maximum adults were attracted and caught in yellow colour sticky trap (Geetha, 2000). Boopathi (2013) described the sticky traps for attracting A. dispersus on cassava (Manihot esculenta) and eggplant (Solanum melongena). More number of adults were attracted to traps placed below crop canopy level in all the coloured sticky traps. Descending order in attraction of A. dispersus to different coloured sticky traps were yellow, transparent, red, orange, black, green, white and blue (Boopathi, 2013).

03/10/2017 Update by:

Dr T. Boopathi, ICAR Research Complex for NEH Region, Mizoram, India