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2 The Origin of Mealybug Pest Status

2 The Origin of Mealybug Pest Status

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120



These were subdivided by Franco et al. (2004)

as follows:

1. Recent invasion by exotic mealybug species

(a) Lack of control by natural enemies

2. Application of non-selective pesticides

(a) Mortality differences between pests and

their natural enemies

(b) Indirect effects of pesticides on natural

enemies, for example, elimination of their

prey

(c) Effects on predator and parasitoid host

interactions

(d) Trophobiosis – positive indirect effects of

pesticides on pests, mediated through

changes in the host plant

(e) Hormoligosis – positive direct effects of

pesticides on pests

(f) Effects of pesticides on insect behavior

(g) Effects of pesticides on interspecific competition among phytophagous species of

different taxa

3. Effect of environmental factors (tritrophic interactions: host-plant/mealybug/natural enemy)

(a) Host-plant susceptibility and/or hostplant characteristics

(b) Water stress

(c) Nitrogen fertilization

(d) Weather

(e) Mealybug defences, for example,

encapsulation

(f) Mealybug refuges from natural enemies

• Spatial refuge (cryptic behavior), for

example, under the bark and on roots

• Temporal refuge: ant interactions

• Other factors that may affect natural enemies, for example, intraguild predation

and interference, hyperparasitoids

Cause 1 is well documented with regard to

mealybug outbreaks and is mainly driven by the

combination of host susceptibility and absence of

natural enemies in the invaded region (Ben-Dov

1994; Blumberg et al. 1999; Muniappan et al.

2006; Nakahira and Arakawa 2006; Roltsch et al.

2006; Williams and Granara de Willink 1992).

The use of non-selective pesticides (Cause 2)

may lead to resurgence and secondary outbreaks.



M. Mani and C. Shivaraju



The mechanisms involved in these two types of

outbreaks were discussed by Hardin et al. (1995),

and studied by Franco et al. (2004) with regard to

the mealybug pests of citrus. Environmental factors (Cause 3) may also directly and indirectly

affect the tritrophic interactions that develop

between mealybugs, their host plants and their

natural enemies, thereby initiating mealybug outbreaks. Several mechanisms may be involved.

Host-plant characteristics may favour or be detrimental to the development, reproduction and survival of mealybugs (Boavida and Neuenschwander

1995; Calatayud et al. 1994b; Leru and Tertuliano

1993; Nassar 2007; Tertuliano et al. 1993;

Wysoki et al. 1977; Yang and Sadof 1995). The

resistance mechanisms of the host plant may

become involved in both the fixation (antixenosis) and the development of the mealybug (antibiosis) (Tertuliano et al. 1993). Tertuliano and

Leru (1992) concluded that the different levels of

resistance to the cassava mealybug, P. manhioti,

which were observed in different varieties of cassava, were not associated with the concentrations

of amino acids or sugars, with the ratios between

these concentrations, or with the compositions of

amino acids obtained from leaf extracts. The

identification and assay of cyanogenic and phenolic compounds in the phloem sap of cassava

and the honeydew of the cassava mealybug were

carried out by Calatayud et al. (1994a). Yang and

Sadof (1995) showed that variegation in Coleus

blumei could increase the abundance of the citrus

mealybug, P. citri. Sadof et al. (2003) found that

the life-history characteristics of P. citri on

Coleus blumei were not correlated with total

amino acids and sucrose contents in stem exudates, but were correlated negatively with the

proportions of shikimic acid precursors and positively with those of other nonessential amino

acids. Host-plant characteristics can also influence the performance of the natural enemies of

mealybugs (Serrano and Lapointe 2002; Souissi

and Leru 1997; Yang and Sadof 1997). Waterstressed plants may favour the population

increases of mealybugs (Calatayud et al. 2002;

Gutierrez et al. 1993; Lunderstadt 1998).

Mealybug life-history parameters/damage

may also be influenced by the levels of nitrogen



9



Damage



fertilization and leaf nitrogen concentration; high

nitrogen concentrations were shown to lead to

enhanced performance of the citrus mealybug, P.

citri (Hogendorp et al. 2006). The antibiotic

resistance of two varieties of cassava mealybug

increased with the addition of nitrogen (Leru

et al. 1994). Survival of immature sugarcane

mealybugs, S. sacchari, increased to a maximum

at a soluble nitrogen concentration of 320 mg L−1

in sugarcane, and decreased at higher levels,

whereas mealybug size increased with increasing

nitrogen concentration over the whole tested

range (Rae and Jones 1992). Weather conditions,

especially temperature and relative humidity, are

major ecological factors that affect both mealybugs and their natural enemies (Chong and

Oetting 2007; Gutierrez et al. 1993, 2008a;

Nakahira and Arakawa 2006). Encapsulation

may adversely affect the degree of biological

control exerted by mealybug parasitoids, as it

may either prevent the establishment of exotic

parasitoids in new regions or reduce parasitoid

efficacy (Blumberg 1997). The cryptic behavior

and tending of mealybugs by ants may, respectively, originate spatial and temporal refuges

from natural enemies. Several other factors may

affect mealybugs’ natural enemies, which include

intraguild predation and interference (Chong and

Oetting 2007), and hyperparasitoids (Moore and

Cross 1992).



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M. Mani and C. Shivaraju

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Coleus blumei. Environ Entomol 26:978–982



Mealybugs as Vectors



10



R. Selvarajan, V. Balasubramanian,

and B. Padmanaban



Mealybugs are well-known sap-sucking insects

which transmit plant viruses. They are omnipresent, polyphagous, can cause more damage as

pests and are less uncommon as virus vectors.

The feeding behavior of these vectors has profound ecological and evolutionary implications

for the viruses they transmit, as the acquisition

and inoculation of viruses occurs during vector

feeding. In most cases, there is an intimate relationship between the virus and its vector, and no

transmissions occur without the insects feeding

in a specific manner. This feeding behavior often

causes considerable economic loss to agriculture

through direct damage to crops and via virus

transmission (Golino et al. 2002; Miiler et al.

2002). They are considered pests as they feed on

the plant juices of economically important crop

plants, and also act as vectors for several plant

viral diseases. The transmission of the plant virus

species belonging to Caulimoviridae and

Closteroviridae by different species of mealybugs is furnished in detail in this chapter.



R. Selvarajan (*) • V. Balasubramanian

National Research Centre for Banana,

Tiruchirapalli 620 102, India

e-mail: selvarajanr@gmail.com

B. Padmanaban

ICAR-National Research Centre for Banana,

Tiruchirappalli 620 102, India



10.1



Feeding Behaviour

of Mealybugs



Mealybugs are found in moist and warm climates. They are less mobile on plants than other

groups of vectors, such as aphids and leaf hoppers, a feature that makes them relatively inefficient as virus vectors. They spread from one plant

to another when in contact with them, and crawling nymphs move more readily than adults. Adult

females can be extremely polyphagous and feed

by sucking on plant sap. The stylet pathway to

the phloem is intercellular and contains several

intracellular punctures (Calatayud et al. 1994).

These bugs have less control over fine stylet

movements than aphids and produce fewer

(8–20/h) and longer intracellular punctures (20 s)

along the entire route to the phloem (Calatayud

et al. 1994; Cid and Fereres 2010). Mealybugs

rarely produce brief probes; they often reach the

phloem after a single probe, and it takes a relatively long time to reach the phloem. Some mealy

bugs are unable to tap into the phloem sieve elements even after a period of 20 h, but most are

able to reach the phloem in 1–6 h (Calatayud

et al. 1994; Cid and Fereres 2010). Mealybug stylets are exceedingly long and are coiled within

their body when they are not feeding.

This unique morphology of their mouth may

explain the propensity of mealybugs to make a

single stylet insertion and their inability to reach

the phloem quickly, as is seen with other

hemipterans. Once in the phloem, the mealybugs



© Springer India 2016

M. Mani, C. Shivaraju (eds.), Mealybugs and their Management in Agricultural

and Horticultural crops, DOI 10.1007/978-81-322-2677-2_10



123



R. Selvarajan et al.



124



may continue to feed from the same sieve tube

for several days. Xylem ingestion is also a predominant feeding behavior for some mealybug

species (Calatayud et al. 1994; Cid and Fereres

2010).



aphid transmitted viruses; apparently, the virus is

carried on or near the stylets of the mealybug.



10.2



10.3.1 Viruses of Caulimoviridae



Types of Transmission



Mealybugs are phloem feeders, and a minimum

inoculation time of 15 min is needed for successful transmission. The virus persists through the

moult, and for 2–3 days in starved or feeding vectors. All mealybug-transmitted viruses appear to

have a semi-persistent mode of transmission

based on retention times; however, the Grapevine

leafroll-associated virus 3 (GLRaV-3) was found

in the salivary glands of its mealybug vector,

suggesting a circulative mode of transmission

(Cid et al. 2007). Mealybug-transmitted viruses

appear to have a high rate of acquisition and a

low rate of inoculation (Cid and Fereres 2010).

Ants that tend to carry the mealybugs may move

them from one plant to another (Sether et al.

1998), and occasionally, long-distance dispersal

by wind may also occur. An important factor

contributing to the slow rate of spread is that

newly infected trees are not infective for some

weeks, or even months, and the virus may not

become fully systemic in large trees for at least 1

year. Temperature-mediated mealybug activity

may be an important variable in transmission

efficiency, and the virus spread can occur through

the airborne dispersal of young, GLRaV-3infected crawlers (Cabaleiro and Segura 1997).

Cacao swollen shoot virus (CSSV) is transmitted

in a semi-persistent mode, meaning that the virus

is taken up into the vector's circulatory system

but does not replicate within it (Dzahini-Obiatey

et al. 2010). The feeding period required for the

acquisition of the virus is a minimum of 20 min,

but optimally 2–4 days (Posnette and Robertson

1950). Once acquired, the virus can be transmitted within 15 min, but optimal transmission

occurs 2–10 h after acquisition. No transmission

of the virus occurs through the mealybug eggs.

The relationship between the CSSV and mealybugs has some similarities to the non- persistent



10.3



Plant Viruses Transmitted

by Mealybugs



Nineteen species of mealybugs belonging to 13

genera are known to occur on Musaceae (Watson

and Kubiriba 2005). The Banana streak virus

(BSVs) (Fig. 10.1a) is transmitted by Planococcus

citri (Risso) and Saccharicoccus sacchari

(Cockerell), both of which colonize bananas

(Lockhart et al. 1992). Sugarcane bacilliform

virus (SCBV) is serologically related to BSVs

(Lockhart and Autrey 1988), and is reported to be

transmitted from sugarcane to banana by

Saccharicoccus sacchari (Cockerell) (Lockhart

and Olszewski 1993). Experimental transmission

of BSV’s has also been demonstrated with the

pink pineapple mealybug Dysmicoccus brevipes

(Cockerell) (Kubiriba et al. 2001) and

Pseudococcus comstocki (Kuwana) (Su 1998).

Ferrisia virgata (striped mealybug) (Fig. 10.1b)

has been found to be able to transmit the Banana

streak Mysore Virus (BSMYV) from banana to

banana (Selvarajan et al. 2006). Meyer et al.

(2008) reported that the transmission of activated

episomal Banana streak OL virus (BSOLV) to

cv. Williams banana (Musa sp.) by three mealy

bug species, viz. Dysmicoccus brevipes,

Planococcus citri and P. ficus.

Planococcus citri transmitted episomal

BSOLV and the Banana streak GF virus

(BSGFV) from tissue-culture derived plants of

FHIA-4 to cv. Williams plants. Using FHIA-TC

10 as the donor plant for transmission, the vector

transmitted a 100 % episomal BSOLV to

Williams’s plants after 3 months, and the numbers of mealybugs feeding on individual recipient plants during the inoculation access period

(IAP) ranged from 2 to 25 (Meyer et al. 2008).

Episomal BSVs were transmitted by D. brevipes.

At 3 months post transmission, the virus was

detected and symptoms had appeared. Due to the

reluctance of the mealybugs to move to Musa spp.,



10



a



Mealybugs as Vectors



125



b



c



d



e



f



g



h



i



j



Fig. 10.1 (a) Electron micrograph of BSV; (b) Ferrisia

virgata feeding on banana; (c) Pink pineapple mealybug,

Dysmicoccus brevipes; (d) Gray pineapple mealybug, D.

neobrevipes; (e) Electron micrograph of GLRaV; (f)



Electron micrograph of GVB; (g) Vine mealybug; (h)

Symptoms of BSV in banana; (i) GLRaV infected grapevine; (j) Symptoms of mealybug wilt of pineapple



the low numbers survived the inoculation access

period; the virus was transmitted from the TC-5

to the William banana. However, no episomal

BSGFV could be transmitted by D. brevipes from

the FH-4 donor to the recipient plants (Meyer



et al. 2008). The fact that none of the mealybug

species were able to transmit integrated BSOLV

from the FHIA-4 to Williams proves that the integrated form of BSV is not likely to be transmitted

by mealybugs; even highly efficient mealybugs



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