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5 Male Flight and Mate Location

5 Male Flight and Mate Location

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14



Semiochemicals in Mealybugs



male’s body axis is maintained almost vertical

during flight. The main purpose of the eyes would

be to monitor the presence of females in conjuction with pheromones.

Unlike neotenic adult females, male mealybugs are active fliers, do not feed, and they live

only a few days. The response of males of different ages to a synthetic pheromone and virgin

females was tested. In the petri dish bioassay,

class I males (up to 10 h after eclosion) and less

than 20 % of class II males (10–29 h after eclosion) responded to the pheromone or virgin

females. On the other hand, most of class III

males (29 or more hours after eclosion) showed a

clear response. After eclosion, most P. citri males

need to complete a period of sexual maturation of

at least 30 h before they can respond to the sex

pheromone and mate. Without mating, the maximal lifespan of males was approximately 5 days

and 50 % of males lived only up to 4.4 days

(25.0 ± 0.5 °C). Most P. citri males have less than

3 days to find a receptive female and mate with

her. However, since P. citri males only fly within a

period of approximately 4 h after sunrise, the total

effective time available for mate location by flight

is only less than 12 h (da Silva et al. 2009a, b, c).



14.6



Identification/Isolation

of Pheromones



Using sophisticated analytical and bioassay

instruments such as gas chromatography–mass

spectral detector (GCMS), gas chromatography

electroantennogram detector (GCEAD), vibrational circular dichroism (VCD) spectroscopy,

and nuclear magnetic resonance (NMR) spectroscopy, the sex pheromones of some economically important species of mealybugs have been

identified and synthesized. These include the

Comstock mealybug Pseudococcus comstocki

(Negishi et al. 1980b), citrus mealybug

Planococcus citri (Bierl-Leonhardt et al. 1981),

vine mealybug Planococcus ficus Signoret

(Hinkens et al. 2001), citriculus mealybug

Pseudococcus cryptus Hempel (Arai et al. 2003),

pink hibiscus mealybug Maconellicoccus hirsutus (Green) (Zhang et al. 2004), obscure mealy-



177



bug Pseudococcus viburni (Millar et al. 2005b),

grape mealybug Pseudococcus maritimus

(Ehrhorn) (Figadère et al. 2007), passionvine

mealybug Planococcus minor (Maskell) (Ho

et al. 2007), Japanese mealybug Planococcus

kraunhiae (Kuwana) (Sugie et al. 2008), longtailed mealybug Pseudococcus longispinus

(Millar et al. 2009), Madeira mealybug,

Phenacoccus madeirensis Green (Ho et al. 2009),

citrophilous mealybug Planococcus calceolariae

(Maskell) (El-Sayed et al. 2010) and Dysmicoccus

grassii Leonardi (de Alfonso et al. 2012).

All known mealybug pheromones are monoterpenoid esters, mostly of simple acids.

However, most of them are irregular non-headto-tail monoterpenoids, with unusual connections

of two isoprene units (Millar and Midland 2007).

The majority of naturally occurring isoprenoid

compounds that have been identified have

1´–4,head-to-tail linkages between isoprenoid

units, whereas most irregular terpenoids with

non-head-to-tail linkages have been found in

members of the plant family Asteraceae (Rivera

et al. 2001). Non-head-to-tail isoprenoid compounds are produced in three biosynthetic reactions, that is, cyclopropanation, branching, and

cyclobutanations (Thulasiram et al. 2008). Millar

and Midland (2007) suggested that terpenoid biosynthetic pathways in mealybugs are distinctly

different from the typical terpenoid pathways

found in other organisms, representing a variety

of enzymes that can catalyze cyclizations and

rearrangements. On this basis, and considering

that mealybug endosymbionts are believed to be

important to the nitrogen and sterol requirements

of their hosts and may play a role in physiological processes such as resistance to microbial

pathogens or detoxification of plant secondary

compounds, we tend to speculate that these

enzymes may originate, at least in part, from

mealybug endosymbionts. Thus, for example, a

variety of symbionts associated with bark beetles

are capable of producing compounds that are

used as pheromones. Spectroscopically, pheromones have been isolated and identified from

several species of mealybugs. A list of pheromones identified for several species is given in

Table 14.1.



Planococcus citri (Risso)



Planococcus minor

(Maskell)

Planococcus ficus

(Signoret)



Pseudococcus comstocki

(Kuwana)



4



5



7



6



Phenacoccus madeirensis

Green



3



Sl. No. Species

1

Crisicoccus matsumotoi

(Siraiwa)

2

Maconellicoccus hirsutus

(Green)



R-3-acetoxy,2,6-dimethyl-1,5,-heptadiene

2,6-dimethyl-1,5-heptadien-3-yl acetate



S-lavandulol and (S)-(+)-lavandyl senecioate



E-2-isopropyl-5-methyl-2-hexadienyl acetate







Zhang and Nie (2005)



Hinkens et al. (2001);

Zada et al. (2001);

Zada et al. (2003)

Negishi et al. (1980b)

Bichina et al (1982)



Ho et al. (2007)



Bierl-Leonhardt et al.

(1981, 1982)



Ujita and Saeki (2008); Zada and Dunkelblum (2006);

Zada and Harel (2004); Zada et al. (2003), Millar et al.

(2002), Hinkens et al. (2001)

McCullough et al. (1991); Baeckstroem and Li (1990);

Kang and Park (1990); Skatteboel and Stenstroem (1989);

Larcheveque and Petit (1989); Fall et al. (1986);

Baeckstrom et al. (1984); Nakagawa and Mori (1984);

Bierl-Leonhardt et al. (1982); Mori and Ueda (1981);

Uchida et al. (1981)



Kukovinets et al. (2006); Zada et al. (2004); Passaro and

Webster (2004); Chibiryaev et al. (1991); Odinokov et al.

(1991); Serebryakov et al. (1986); Wolk et al. (1986);

Odinokov et al. (1984a, b); Carlsen and Odden (1984);

Bierl-Leonhardt et al. (1981)

Millar (2008); Ho et al. (2007)







Zhang et al. (2004); Zhang and Nie (2005)



Zhang et al. (2004)



Trans-1R,3R-chrysanthemyl (R)-2-methyl

butanoate and (R) lavandulyl (R) methyl

butanoate (93:1)

(R)-2-isopropenyl-5-methyl-4-hexenyl

(S)-2-methylbutanoate [common name is

(R)-lavandulyl (S)-2-methylbutanoate] and

[(R)-2,2-dimethyl-3-(1-methylethylidene)

cyclobutyl]methyl (S)-2-methylbutanoate

[which we refer to as (R)-maconelliyl

(S)-2-methylbutanoate

Trans (1R,3R)-chrysanthemyl (R)-2-methylbutanoate and (R)

lavandyly(R-methylbutanoate

(+)-(1R)-cis-2,2,-dimethyl 3-isopropenyl

cyclobutane methanol acetate (1R,3R)

3-isopropenyl-2,2-dimethyl cyclobutane

methyl acetate

Ho et al. (2009)



Synthesis references

Tabata et al. (2012)



Identification reference

Tabata et al. (2012)



Chemical identified

3-methyl-3-butenyl-5-methyl-hexanoate



Table 14.1 Pheromone compounds identified from different species of mealybugs



178

N. Bakthavatsalam



15



14



13



12



11



10



9



Pseudococcus viburni

(Signoret)

Pseudococcus kraunhiae

(Kuwana)

Pseudococcus longispinus

(Targioni Tozzetti

Planococcus minor

(Maskell)

Dysmicoccus grassii

Leonardi



Pseudococcus

calceolariae (Maskell)

Pseudococcus maritimus

(Ehrhorn)



Sl. No. Species

8

Pseudococcus cryptus

Hempel



(−)-(R)-lavandulyl propionate and acetate



(1R,2R,3S)-(2,3,4,4-tetramethyl cyclopentyl)methyl acetate

2-isopropylidene-5-methyl-4-hexen-1-yl

butyrate

2-(1,5,5-trimethylcyclopent-2-en-1-yl)ethyl

acetate

2-isopropyl-5-methyl-2,4-hexadienyl acetate



(R, R)-trans-(3,4,5,5-tetramethyl cyclopent-2en-1-yl) methyl 2-methyl propanoate



Chemical identified

(1R3R)-3-isopropenyl-2-2dimethmylcyclobutylmethyl-3-methyl-3butenoate

Chrysamthemyl 2-acetoxy-3-methylbutanoate





Millar et al. (2009)

Ho et al. (2007)





Millar et al. (2009)

Ho et al. (2007)

de Alfonso et al. (2012)



Figadère et al. (2007)



Hashimoto et al. (2008); Millar and Midland (2007)



Unelius et al. (2011); El-Sayed et al. (2010)



Synthesis references

Nakahata et al. (2003)



Sugie et al. (2008)



Millar et al. (2005b)



Unelius et al. (2011);

El-Sayed et al. (2010)

Figadère et al. (2007)



Identification reference

Arai et al. (2003)



14

Semiochemicals in Mealybugs

179



N. Bakthavatsalam



180



14.6.1 Planococcus citri



14.6.3 Planococcus kraunhiae



In Italy, the sex pheromone released by females

of Planococcus citri was extracted from unmated

females by ethanol, diethyl ether, or petroleum

ether. Extracts in ethanol, diethyl ether, or petroleum ether placed on filter paper or hydrophilized

poly(methyl methacrylate) discs elicited high

attraction and pairing responses in the males

(Rotundo and Tremblay 1976, 1982). P. citri

pheromone is a cyclobutane compound.



A sex pheromone component of the Japanese

mealybug, Planococcus kraunhiae was isolated

and identified. A crude extract of the pheromone

obtained by airborne collection was first fractionated with Florisil column chromatography. The

active fraction was further purified by HPLC, and

an active component was isolated by preparative

GC. The purified compound was determined

to be 2-isopropylidene-5-methyl-4-hexen-1-yl

butyrate by GC–MS and NMR analyses showing

the attraction activity to adult males of P.

kraunhiae in the field (Sugie et al. 2008).



14.6.2 Pseudococcus calceolariae

Headspace volatiles collected from virgin

females of the citrophilous mealybug, Ps. calceolariae, containing the main female-specific

compound is identified as [2,2-dimethyl-3-(2methylprop-1-enyl)cyclopropyl]methyl 2-acetoxy-3-methylbutanoate

(chrysanthemyl

2-acetoxy-3-methylbutanoate). The other two

compounds are identified as [2,2-dimethyl-3-(2methylprop-1-enyl)cyclopropyl]methanol (chrysanthemol) and [2,2-dimethyl-3-(2-methylprop

-1-enyl)cyclopropyl]methyl 2-hydroxy-3-methylbutanoate (chrysanthemyl 2-hydroxy-3-methyl

butanoate). Traps baited with 100 μg and 1,000

μg indicated that 100 μg of chrysanthemyl 2-acetoxy-3-methylbutanoate captured 4- and 20-fold

more males than traps baited with virgin females

(El-Sayed et al. 2010). The absolute configuration of the sex pheromone of Pseudococcus

calceolariae was determined to be (1R,3R)-[2,2dimethyl-3-(2-methylprop-1-enyl)cyclopropyl]

methyl (R)-2-acetoxy-3-methylbutanoate NMR,

derivatization reactions, chiral GCMS, and comparison with synthetic chiral reference compounds were used to determine the absolute

configuration of this compound. Traps baited

with 1,000 μg of the pheromone compound

caught 367 times more males than traps baited

with virgin females. A mixture of stereoisomers

of pheromones can be used for field trapping

without adverse effects on trap catches (Unelius

et al. 2011).



14.6.4 Planococcus ficus

The existence of pheromones was detected in the

females of mealybugs Planococcus ficus

(Signoret) by Rotundo and Tremblay (1982). The

sex pheromone of Planococcus ficus has been

identified as a single component, (S)-lavandulyl

senecioate (LS) 2a. Males were equally attracted

to either (S)-2a or racemic 2a, indicating that the

unnatural enantiomer does not inhibit male behavioral responses. Female mealybugs also produced

(S)-lavandulyl, but mixtures of racemic 1 with

racemic 2a were less attractive to male mealybugs

than racemic 2a alone. In field trials, lures loaded

with 100 μg doses of racemic 2a attracted males

for at least 12 weeks (Millar et al. 2005a).



14.6.5 Phenacoccus madeirensis

Two compounds in Ph. madeirensis Green were

identified as trans-1R, 3R-chrysanthemyl (R)-2methyl butanoate and (R) lavandulyl (R)-methyl

butanoate in a ratio of 3:1. The structures of two

pheromones differ significantly.



14.6.6 Pseudococcus comstocki

Pseudococcus comstocki pheromone is an aliphatic

acetate. The sex pheromone produced by females

of the Ps. comstocki Kuwana, was isolated and



14



Semiochemicals in Mealybugs



identified as 2,6-dimethyl-3-acetoxy-1,5-heptadiene. Synthetic pheromone showed a potent

activity in laboratory bioassay and field test

(Negishi et al. 1980b).



14.6.7 Pseudococcus maritimus

In Pseudococcus maritimus (Ehrhorn), an irregular non-head-to-tail monoterpenoid was identified as (R,R)-1-trans 3,4,5,5,-tetramethyl

cyclopenta-2-en-1-yl) methyl-2-methyl propionoate (Figadere et al. 2007) and Zou et al.

(2010) observed that racemic mixture of transalphanecrodyl isobutyrate is more attractive than

(RR) or (SS) enantiomers.



181



Captures of male M. hirsutus showed that pheromone with the naturally occurring (R)-maconelliyl

(S)-2-methylbutanoate and (R)-lavandulyl (S)-2methylbutanoate [R-S configuration] was most

attractive and that pheromone with the unnatural

S-S configuration was less attractive. An inhibitory effect was observed when R-R and S-R were

combined with naturally occurring R-S blend.

Thus, S configuration on the acid moiety elicits

attraction, whereas the R configuration induces

inhibition. However, the attractive activity shows

some degree of tolerance toward chirality change

in the alcohol portion of the pheromone molecules

(Zhang et al. 2006).



14.6.11 Planococcus minor

14.6.8 Pseudococcus longispinus

The sex pheromone of the long-tailed mealybug

Ps. longispinus, identified as 2-(1,5,5-trimethylc

yclopent-2-en-1-yl)ethyl acetate, represents the

first example of a new monoterpenoid skeleton.

A [2,3]-sigmatropic rearrangement was used in a

key step during construction of the sterically congested tetra alkyl cyclopentene framework

(Millar et al. 2009).



14.6.9 Crisicoccus matsumotoi

Most of the mealybug pheromones are carboxyl

esters of monoterpene alcohols; however, a hemiterpene pheromone (3)-methyl-3-butenyl 5 methylhexanoate was identified from Crisicoccus

matsumotoi (Siraiva) (Tabata et al. 2012).



14.6.10 Maconellicoccus hirsutus

The two chiral centers in the sex pheromone of

pink hibiscus mealybug, Maconellicoccus hirsutus, could elicit different male responses. The chiral center in the acid moiety of the pheromone

seemed to be more critical than the alcohol portion

of the pheromone molecule for attractiveness.



The sex pheromone of the mealybug, Planococcus

minor, was isolated by fractionation of crude

pheromone extract obtained by aeration of virgin

females. The pheromone was identified as the

irregular

terpenoid,

2-isopropyl-5-methyl2,4-hexadienyl acetate, by mass spectrometry,

microchemical tests, and (1)H NMR spectroscopy. The stereochemistry of the pheromone was

assigned as (E) by comparison with synthetic

standards of known geometry. The compound

was highly attractive to males in laboratory bioassays, whereas the (Z)-isomer appeared to

antagonize attraction (Ho et al. 2007).



14.6.12 Pseudococcus viburni

The sex pheromone of the obscure mealybug, Ps.

viburni, consists of (1R*,2R*,3S*)-(2,3,4,4tetramethylcyclopentyl)methyl acetate, the first

example of a new monoterpenoid structural motif

in which the two isoprene units forming the carbon skeleton are joined by 2′–2 and 3′–4 connections rather than the usual 1′–4 head-to-tail

connections. This highly irregular terpenoid

structure, and the irregular terpenoid structures of

related mealybug species, suggests that these

insects may have unique terpenoid biosynthetic

pathways (Millar et al. 2005b).



N. Bakthavatsalam



182



14.6.13 Dysmicoccus grassii

In Dysmicoccus grassii, a main pest of Canary

Islands banana, the principal components

(−)-(R)-lavandulyl propionate and acetate in a

6:1 ratio were identified by volatile collection

and GC–MS analysis from aeration of virgin

females. (R)-lavandulyl propionate induced a

stronger attractive effect when compared with

(R)-lavandulyl acetate (de Alfonso et al. 2012).

Although the males of several mealybug species are attracted to the females, sex pheromones

are yet to be identified (e.g., Phenacoccus herreni

(Cox&Williams)).



14.7



Synthesis of Pheromones/

Pheromone Production



14.7.1 Pheromone Production

Pheromones must be isolated, identified, and

synthesized before any basic or practical studies

can be performed. Entomologists and chemists

must cooperate closely in order to achieve these

goals. Despite the availability of modern analytical equipment, the identification of natural

mealybug sex pheromones remains a difficult

and laborious task. Mealybugs are small or tiny

insects that release minute quantities of pheromone; therefore large numbers must be reared,

and often tedious separation of virgin females

must be done to collect sufficient amounts of

pheromone for isolation and identification. Males

having a short lifespan of at most a few days are

required for bioassay, either by attraction tests or

by GC–EAG (gas chromatography electroantennography). All known mealybug pheromones are

monoterpenoid esters, mostly of simple acids.

Unlike moth sex pheromones, the mealybug

pheromones are not homologous compounds;

their structures vary significantly, and three types

of structures have been found so far: open chain

esters, cyclobutane derivatives, and cyclopentane

rings. All mealybug pheromones, except the Pl.

minor and Pl. kraunhiae pheromones, are chiral

compounds. Generally, enantioselective synthesis of chiral compounds is much more compli-



cated and expensive than that of racemic

compounds but, fortunately, racemic pheromones

can be used because the unnatural stereoisomers

have no behavioral effect and, therefore, are

benign (Zada et al. 2008). A unique case is the

pheromone of M. hirsutus; it contains a chiral

acid function that must have the correct chirality

for biological activity (Zhang and Amalin 2005;

Zhang et al. 2006). The passionvine mealybug is

strongly inhibited by the (Z)-stereoisomer of its

pheromone, suggesting that this compound may

be the pheromone of a related sympatric species

(Millar 2008). Unlike moths and beetles, which

are generally sensitive to isomers (structural and

chemical) of their pheromone components,

mealybugs are less sensitive to stereoisomers. In

practice, this means that the use of mixture of isomers of the pheromone will be effective for controlling most of the mealybug pheromones.

Moreover, mealybugs are responsive to small

amounts (doses of about 1 mg) of the pheromones (Millar et al. 2005b; Zhang and Amalin

2005; Sugie et al. 2008), so that potentially it is

possible to achieve pheromone-based control at

relatively low costs. Not all the mealybug sex

pheromones are commercially available. In fact,

most of them, except for those of the citrus

mealybug and the vine mealybug, are synthesized only for research in small (milligram)

quantities. The citrus mealybug pheromone, for

example, which has a rather complex structure,

has been synthesized via a variety of routes, but it

still is not available in large quantities (hundreds

of grams) required for mating disruption. At

present, only commercial lures for monitoring

are available. Because of the worldwide economic importance of the mealybugs, there is a

need to improve the efficiency of pheromone

synthesis and to make the pheromone available

for control application. A series of analogs of this

pheromone was prepared, in order to find a less

expensive attractant (Liu et al. 1995; Dunkelblum

et al. 1987), but most of them were insufficiently

attractive, except for a homologue in which a

cyclobutaneethanol moiety replaced the cyclobutanemethanol moiety in the natural pheromone.

The homologue displayed about 40 % attractiveness as compared with the pheromone, and in



14



Semiochemicals in Mealybugs



some field tests it was as active as the latter

(Dunkelblum et al. 1987). The advantage of the

homolog is that its synthesis is easier and less

expensive than that of the pheromone. Some

pheromone analogs of the Comstock mealybug,

Pseudococcus comstocki Kuwana, were also synthesized and tested in the field (Uchida et al.

1981; Bierl-Leonhardt et al. 1982). 2,6-dimethyl1,5-heptadien-3-yl acetate and three of its analogues of the sex pheromone of Pseudococcus

comstocki (Kuw.), a pest of agricultural crops

including apple and pear, were synthesized and

evaluated for their attractiveness to males. All

four compounds were found to be the effective

attractants for the insect, but the synthetic sex

pheromone showed a two- to seven fold higher

activity than the analogues (Uchida et al. 1981).



14.7.2 Synthesis of Pheromones

Through modifications of acetoxy group, several

pheromone analogues were synthesized for

different species of mealybugs. A synthetic

pheromone would provide a much more economical, convenient, and useful survey tool. Synthesis

of pheromone compounds of Pl. minor, Pl. citri,

and Ps. viburni was done successfully (Millar

2008; Ho et al. 2007; Kukovinets et al. 2006;

Millar and Midland 2007).



14.7.2.1 Planococcus citri

The mealybug sex pheromones that have been

identified generally are complex molecules,

which are relatively difficult to synthesize on a

large scale. Nevertheless, because male mealybugs are so exquisitely sensitive to the pheromone, with lures containing only a few

micrograms remaining active for at least several

months under field conditions, widespread use of

pheromone-baited traps for monitoring mealybugs is economically feasible. For example, 1 g

of racemic pheromone is sufficient to prepare

50,000 lures or more @20 μg per lure.

In Pl. citri, (1R,3R)-3-isopropenyl-2,2dimethylcyclobutanemethyl acetate (C12H20O2)

was identified, and a simple synthesis path was

developed in Israel, and the synthesized material



183



(1R cis-3-isopropenyl-2-2-dimthyl cyclobutane

methyl acetate) was found to attract males effectively (Dunkelblum et al. 1986). Alcohol analogue

(1R-cis)-3-isopropenyl-2-2dimethycyclobuanemethal) was an effective

attractant to P. citri, and homologue (1R-cis)-3isopropeny-2,2 dimethyl cyclobutane ethylacetate

at 2,000 μg per dispenser was equal to 500 μg

pheromone (Dunkelblum et al. 1986). Analogue

of pheromone of P. citri, (+)-(1R)-cis-2-2dimethyl-3-isopropenyl cyclobutano methanol

acetate was synthesized using starting material cispinoic acid or cis-pinonic aldehyde, which were

obtained from cheap α-pinene and conversion of

the pinonic derivatives to pinononic derivatives

was achieved through Hundsdiecker reaction.

Pinononyl aldehyde was used for synthesis of

pheromone through Wittig reaction (Dunkelblum

et al. 2002). Structural analogue of (+) cis(1R)-(3)-isopropenyl-2-2-dimethyl cyclobutane

methyl acetate, the sex pheromone of P. citri, was

synthesized and field-tested in grapefruit orchards

and the most active analogue was (+)-(cis-(1R)2-(3-iso-propenyl-2-dimethyl cyclobutane ethyl

acetate (Dunkelblum et al. 1987).



14.7.2.2 Maconellicoccus hirsutus

The sex pheromone of M. hirsutus, Maconelliol,

was synthesized in steps from Alpha pinene, and

the key step was the dehydration of steps 5–7

through the intermediate 6 (Zhang et al. 2004).

14.7.2.3



Pseudococcus viburni



An improved diastereoselective synthesis of

(1R*,2R*,3S*)-1-acetoxymethyl-2,3,4,4tetramethylcyclopentane 1, the sex pheromone of

Pseudococcus viburni, was described and the key

step was diastereoselective catalytic hydrogenation of the tetrasubstituted double bond in

2,3,4,4-tetramethyl-cyclopent-2-enone 4 to give

the thermodynamically less favored cis-2,3,4,4tetramethyl-cyclopentanone 3a (Zou and Millar

2011). The pheromone of P. viburni was also synthesized from pentalactone (Hajare et al. 2010).

In the obscure mealybug Ps. viburni,

2,3,4,4-tetramethylcyclopentyl)methyl acetate

was identified as the sex pheromone. The active

compound has a number of isomers, and all were



N. Bakthavatsalam



184



made to conclusively verify the identity of the

insect-produced compound. An efficient synthesis of the active compound, capable of being

scaled up to produce multigram quantities, was

then developed. The pheromone was field-tested

in California vineyards and nurseries, and by collaborators in South America and New Zealand.

The pheromone is extraordinarily active, with

lures loaded with sub-milligram quantities

remaining attractive to male mealybugs for several months. In South Africa, The sex pheromone

for P. viburni was recently identified and synthesized in South Africa. There was a positive and

significant relationship between the fruit infestation and number of P. viburni adult males caught

in pheromone-baited traps (r2 = 0.454, P < 0.001)

in pome orchards. The action threshold level was

estimated to be 2.5 male P. viburni caught per

trap per fortnight at an economic threshold of 2

% fruit infestation. This monitoring method was

less labor-intensive, more accurate, and quicker

than the current visual sampling and monitoring

techniques (Mudavanhu et al. 2011).



traps baited with virgin females. A mixture of

stereoisomers of the pheromone compound can

be used for field trapping without adverse effects

on trap catch (Unelius et al. 2011).



14.7.2.5 Pseudococcus longispinus

A single compound was unique to the headspace

of the sexually mature female Ps. longispinus.

The first reported synthesis involves a polyphosphoric acid-mediated cyclization of isobutyl

2-butenoate. The cyclopentenone was then converted into the allylstannane after being reduced.

A short and efficient synthesis of the mealybug

pheromone was developed from readily available

iodoketone with an overall yield of 21 %. The

pheromone has been shown to have extremely

high biological activity; in lures, just 25 μg of the

racemic pheromone can attract males for more

than 3 months (Bakonyi 2012). The synthesis

of a recently identified and highly active sex

pheromone of Ps. longispinus, was reported by

Kurhade et al. (2013).

14.7.2.6



14.7.2.4 Pseudococcus calceolariae

Traps baited with 100–1,000 μg of racemic chrysanthemyl 2-acetoxy-3-methylbutanoate captured 4–20-fold more males than traps baited

with virgin females. In Chile, a single dose of

100 μg was known to capture 1,171 males,

whereas none were captured in control traps. An

isomeric mixture of synthetic 3 proved to be

highly attractive to male mealybugs in the field in

New Zealand and in Chile. Male mealybugs were

highly attracted to the racemic material and this

will greatly facilitate the development of the

pheromone for monitoring and control of this

pest, because racemic 3 can be readily synthesized from commercially available intermediates

(El-Sayed et al. 2010). This activity of 1R,3R)[2,2-dimethyl-3-(2-methylprop-1-enyl)cyclopropyl]methyl (R)-2-acetoxy-3-methylbutanoate in

Pseudococcus calceolariae was further confirmed

by testing synthetic stereoisomers of the compound as lures in traps for adult male mealybugs.

Traps baited with 1,000 μg of the pheromone

compound caught 36 times more males than



Pseudococcus comstocki



The

synthesis

of

the

acetate

of

2,6-dimethylhepta-1,5-dien-3-ol—the sex pheromone of the Comstock bug—has been carried out

by condensing isobutenyl lithium with

3,4-epoxy-2-methylbut-1-ene and acetylating

the 2,6-dimethylhepta-1,5-dien-3-ol formed. The

overall yield of pheromone was 46 % (Ishchenko

et al. 1989). The synthesis of racemic versions of

pheromones of Ps. comstocki was done through

reductive lithiation of allyl phenyl thioesters

followed by transmetallation, producing allylmetallics, which react selectively with carbonyl

compounds at the most on least-substituted terminus and the latter results in cis-olefin

(McCullough et al. 1991).



14.8



Commercial Development

of Pheromones



Currently, of these seven pheromones, only the

vine mealybug Pl. ficus pheromone is commercially available, but Millar is working to transfer



14



Semiochemicals in Mealybugs



the manufacturing technology to companies that

produce pheromone products. None of the pheromones are protected by patents; therefore, all are

freely available for the commercial development.

Companies also need to know that there is a substantial market for these products, so growers

should communicate their needs to company representatives to expedite the entry of mealybug

pheromone traps into the market place.

Chemist Aijun Zhang in Beltsville, MD,

developed the pheromone of M. hirsutus, which

mimics the female mealybug’s scent, according

to a news release. South Carolina Scientific Inc.,

of Columbia, SC, will market the chemical. The

sex pheromone, placed inside sticky traps, effectively monitors and traps male mealybug. By luring males to traps, the pheromone would provide

a much more useful detection tool. Relatively

high concentrations of the pheromone repel

males away from the source, disrupting mating.

However, natural enemies of the mealybug are

not attracted to the scent, so biological control

would not be compromised (http://www.thegrower.com/news/firm_to_market_pink_mealybug_

pheromone_117886474.html#sthash.

2KIGfvcv.dpuf). Commercial lures of Ps. longispinus and Ps. maritimus also became available

from Suterra LLC (Bend, OR) in 2010.



14.9



185



• Place the rubber septum containing the pheromone (lure) inside the trap on top of the sticky

coating on the bottom panel.



14.9.1.2 Trap Placement

• Tie the trap to the plant at 2–3 feet above

ground level. Traps baited with virgin

Pseudococcus comstocki females, placed in

Ps. comstocki-infested fruitless mulberry

trees about 9 ft above ground level, had

caught an average of 225 Ps. comstocki

males compared with 6 ft by each of the

other traps (Moreno et al. 1972). Make sure

leaves and shoots are not obstructing the

entrance into the trap. Do not hang it too low

or too high in the canopy.

• Place the trap at the center of the block for

surveying the largest area possible.

14.9.1.3 Labeling Traps

• Label the trap with the block name and

row number, where the trap was placed

and the dates it was set out in the field and

removed.

• Label the outer side of the trap with the following information: date of placement (DOP),

vineyard and block name, row and vine number, and lure (L) type. When you remove the

trap, write the date of removal (R). Use a permanent marker.



Traps



Pheromone traps can attract the mealybugs

within one-quarter mile from the trap site.



14.9.1 Trapping Guidelines

14.9.1.1 Trap Assembly

• Obtain or purchase a red Delta trap, preferably

with a white sticky bottom panel for ease of

viewing mealybugs.

• Assemble the trap by folding in the side edges

to reduce the size of the openings.



14.9.1.4 Trap Density

• Place one trap per hectare or one per smaller

orchard.

14.9.1.5 Trapping Season

• Placement of traps based on the information

gathered on the seasonal activity more

closely in the locality. In California, placement of traps begins in late March to June

(depending on region) and trapping is continued through October or until the first rain

in vineyards.



186



14.9.1.6 Checking Traps

• Check traps every 2 weeks for the presence of

mealybugs on the sticky surface.

14.9.1.7 Trap Replacement

• Replace the trap when it becomes soiled.

• Lures are effective for a maximum of 8 weeks.

If no male mealybugs are found, new pheromone

lures can be placed into old traps. Do not forget to re-label the new trap and note when new

lures are placed in the trap.



14.9.2 Types of Traps

Multi-season plastic Delta traps are used for

monitoring and mass trapping the mealybugs.

These Delta traps areresistant to severe weather

conditions. They are very easy to assemble and

collapse flat for storage. Hwang and Chu (1987a)

developed an effective, cylindrical, and transparent plastic trap (diameter 8 cm and length 8 cm)

with white sticky card (8 × 12.5 cm) inserted at

the bottom, and traps placed at 100 cm and above

caught more than 50 % of males. Commercially

developed traps with more surface such as green

Delta, Pherocon IIB, and Pherocon V captured

more males than other traps (Vitullo et al. 2007).

Delta sticky traps, baited with 50 or 200 μg of LS

were used to determine the daily flight pattern

and the seasonal flight activity including vine

plant infestation for P. ficus (Zada et al. 2008). A

method is described for handling sticky trap

cards and evaluating catches, using the sex pheromones of Planococcus citri and Pseudococcus

comstocki (Fargerlund and Moreno 1974). In

USA and Japan, 2,6-dimethyl-1,5-heptadien-3-yl

acetate was identified in Ps. comstocki and a synthetic material was prepared in the Moldavian

area of the USSR. The sticky traps proved very

successful in attracting and catching male mealy-



N. Bakthavatsalam



bugs in mulberry ecosystem (Bichina et al. 1982).

Pheromone-baited traps with larger trapping surfaces (green Delta, Pherocon IIB, and Pherocon

V) captured more males of Maconellicoccus hirsutus per trap than those with smaller surfaces

(Jackson and Storgard Thinline), and fewest

males were captured by Storgard Thinline traps.

However, Jackson traps captured as many or

more males per square centimeter of trapping

surface than those with larger surfaces, and the

time required to count males in Jackson traps was

significantly less than in green Delta, Pherocon

IIB, and Pherocon V traps. Although all trap

designs accumulated some debris and nontarget

insects, it was rated as light to moderate for all

designs. The Jackson trap is most suitable for

monitoring M. hirsutus populations. In addition,

unlike the other traps evaluated, which must be

replaced entirely or inspected in the field and

then redeployed, only the sticky liners of Jackson

traps require replacement, enhancing the efficiency of trap servicing (Vitullo et al. 2007).

Adhesive traps, baited with virgin females of

Maconellicoccus hirsutus and placed on hibiscus, captured more males than did unbaited traps

(Serrano et al. 2001).

The color of the pheromone trap influenced

the numbers of males of Pseudococcus comstocki

(Kuw.) caught. Multi-season plastic Delta traps

are available in red and white. Generally, yellow

traps with sticky surfaces were effective in trapping males. Pheromone traps baited with green

Delta, Pheroxin IIB, and Pherocon V trapped

more males in Maconellicoccus hirsutus.

Moreover, Jackson traps captured more adults

per square centimeter (Vitullo et al. 2007). The

color

preference

was

red = dark

green = black > green > yellow > white. According

to Hwang and Chu (1987a, b), red color sticky

cards are the most attractive to the males of

Planococcus citri.



14



Semiochemicals in Mealybugs



Triangular tent-shaped



Yellow trap



14.10 Pheromone-Based

Management Tactics

Sex pheromones of insects, including mealybugs,

are natural compounds emitted by virgin females

in order to attract conspecific males for mating.

The sex pheromones are effective in extremely

small quantities; they are nontoxic and can be

applied in various ways. Unlike pesticides, these

chemicals are species specific and do not affect

beneficial insects. The behavioral impacts of the

semiochemicals are limited to the target pest

organisms. The potential of mealybug sex pheromones as an alternative and ecologically friendly

means for monitoring and control is important

and promising. Sex pheromones are used in lures

for monitoring, for detection of outbreaks, and

for population management. Monitoring systems

provide vital information for the timing of insecticide applications. Population levels can be

reduced or controlled by mass trapping, mating

disruption, or lure and kill. The success of these

methods depends on the availability of the pheromone, and on an appropriate formulation and

deployment. In contrast to the extensive use of

sex pheromones in controlling beetle and moth

pests, sex pheromones are yet to be used to a

great extent in controlling the mealybugs.



14.10.1



Monitoring



Sampling is a key element of mealybug management, because of the need for real-time information on the mealybug population and the potential



187



Yellow traps



damage. Monitoring for mealybug infestation is

quite labor intensive as mealybugs are often

located in the protected areas of plants like bark

crevices and leaf axils. Pheromone traps may be

used as an early warning tool for grape growers

to monitor mealybug activity and to detect the

initial establishment of mealybug colonies. The

traps are baited with female mealybug pheromone impregnated in a rubber lure. The traps are

placed within the vine canopy to attract winged

male mealybugs. When the mealybug population

is small, using a sex pheromone trap to attract

winged males is far more efficient than trying to

search vines over a large area for hidden females.

The male mealybugs can fly about one-half mile,

and it can be wind-blown much further. Mealybug

monitoring methods involve examination of specific plant parts for live individuals, and detection

of honeydew, sooty mold, or ant activity (Franco

et al. 2004a, b; Millar et al. 2005a). Sampling

procedures have been developed for several

mealybug species and various crops, such as the

citrus mealybug, Pl. citri (Martinez-Ferrer et al.

2006), the grape mealybug, Ps. maritimus

(Geiger and Daane 2001), or the sugarcane

mealybug, S. sacchari (Allsopp 1991; Debarro

1991). However, the cryptic occurrences of

mealybugs as well as their typical clumped spatial distribution (Allsopp 1991; Martinez-Ferrer

et al. 2006; Nestel et al. 1995) make monitoring

laborious and often impracticable. Population

estimates based on the level of male capture in

pheromone-baited traps are considered more

convenient (Millar et al. 2005a). Much work has

been done to optimize these sampling methods,



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