Life Stages of
California Red Scale
and Its Parasitoids
Lisa D. Forster
Robert F Luck
and Elizabeth E. Grafton-Cardwe ll
C
ALI F OR N IA RED SCALE, Aonidiella auranlii
(Mask.) (fig. 1), is a major pest or citrus that
growers have traditionally controlled with
insecticides. Populations or California reel scale devel-
oped resistance to organophosphate and carbamate
insecticides in South Africa, Australia and lsrael in the
1970s and in California in the 1990s, and these broad
spectrum insecticides are losing their effectiveness. An
alternate appro ach Lo chemical control or California red
scale is augmentative biological control as part or an
integrated pest managemem-(IPM) approach. Growers
can release the insectary-reared parasitoid wasp Aphy tis
me/inus DeBach from February through November to
augment the native Aphy tis populations that attack and
redu ce armored scale populations. This approach can
Figure 2 . Inve rted female scale with crawlers
Figur e 1. Scale infes ted fruit
suppress armored scale densities below economic injury
levels. In years when biological control is less effective,
selective narrow _range petroleum oil sprays can be used
to help redu ce scal_e numbers.This leaflet gives some
background that will help growers evaluate the effective-
ness or natural enemies of California reel scale through
knowledge or the scale life cycle, the stages of scale that
are attacked by parasites and predators, and the signs of
parasitism.
California Red Scale-
General Phenology
FEEDING AND DORMANT
LIFE STAGES
California red scale start out as mobile crawlers* (fig.
2). Crawlers remain mobile only long enough to find a
suitable location on a !ear, fruit, or branch to seule on
and begin reeding. From this stage onward , all lire stages
are immobile except for the adult males (fig. 3).
*Words in bold are imp ortant termin ology needed for identification
of scale and parasite stages.
UN IVERSIT Y OF CA LIFO RN IA DIVISION O F AGR ICU LTU RE AND NAT URAL RESO UR C ES
Publication #21529
Photos by L Forster and M. Badgley • Graphics by G. Conville
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FIRST AND SECOND INST A RS
After the crawle rs sett le, they begin to reed and secre te a
material that cove rs the sca le body and becomes the
white cap stage (fig. 5). As the scales continue to develop,
the top or the cove r forms a distinct circu lar ridge for the
nipple stage. The cove r will even tuall y Oow on to the
plant and beco me whi tish-gray. Th e craw ler, white cap
and nipple stages are al l first ins tar sca le. The first instar
is the only stage when the cove r has no oran ge pigme n-
tat ion (fig. 6) . The orange pigment ation in the cover of
later scale stages results rrom the molting process . Once
Figure 6. Firs t ins tar sca le
first inslars stop reed ing, the reedin g Lube is detached
and the sca le is sea led off inside the cover. This is called
the firs t molt and is s lightly convex in shape when
inverted (fig. 7) . The sca les remain as first molts for
approx imately 4 days. Event ually, the sca les insert a new
reeding tube into the subst rate as they transform into
seco nd instars (fig. 8). All second insta rs have an
orange molt ring roug hly the diameter of the first molt.
This orange molt ring is the cast skin of the first molt,
which beco mes incorpo rated into the cove r. By noting
and cou nting the numb er of pigmented rings in the sca le
cove r you can determi ne the age and stage of sca le. The
gray porti on of the cove r (the skin) surroundin g the
moll ring is a new secret ion of wax and protein pro-
duced by the insect during the second instar. This gray
skirt varies in size depending on the age of the second
insta r (fig. 8).
MALES
As second instar sca les cont inu e to develop, second
instar males and second instar females develop distinctly
different shapes. Th e males elonga te and develop eyes ,
whereas the females remain circular and do not develop
eyes (fig. 9). Male scale comple te three distinct imma-
tu re stages: the secon d instar male , the prepupa l male
and the pupal male. Seco nd ins tar males are distin-
Figure 5. First ins tar scale; wh ite cap s tage
Figure 7.
Firs t molt scale (No te
convex und erside. Body
& cove r are sea led
togeth er)
Figur e 8. Second ins tar scale (No te body size and gray skirt
of th e cove r increase with age , bu t th e ora nge molt rin g stays
th e sa me s ize)
Figure 9.
Second insta r female
(top ) and male scale
(bottom ) with
inverted cove rs
3
guished by the brown pig-
mentation of the posterior
end or pygidium (fig. 10)
which is V-shapecl . After
approximately 5 days, sec-
ond instar males begin to
pupate. This is called the
prepup al male . This stage
is characterized by a slight
squaring-off of the distal
end and loss of the brown
pigmentation (fig. 10).
The slight nub at the distal
end indicates the early
development of the geni-
talia. ln about a clay and a
half, the prepupa l males
transform into male
pupae , which have a dis-
tinctly pointed genitalia
(fig. 10). Adu lt males
emerge about 3 clays after
pupation (fig. 11 ).
FEMALES
Figure 10 . Immature male
sca le stages
While second instar males develop into prepupae and
pupae, second instar females mature into seco nd molts
(fig. 12) As with the first molt, the body and cover are
sealed together and cannot be separated. Again, live
healthy second molts, when inverted, are slightly con-
vex. Dead scales have a similar shape and color, howev-
er they are not convex. After molting, which takes
approximately 6 clays, the females reinsert their rostrum
to resume feeding. This is the third instar stage (fig. 13).
Third instars vary greatly in overall cover and body size.
However, the first and second orange molt rings of the
cover remain relatively constant in size (fig. 13). Lobes
develop on each side of the pygiclium during the third
instar stage, giving the body a more circular shape than
the second instars. The pygidium of the third instar
females protrudes out to the edge of the skin. It is during
this stage that mating occurs (fig. 14). Third instars con-
tinue to grow, but do not develop into mature females
unless mated. Therefore, the length of the developmental
period for the third instar females depends on when they
mate. After insemination, the pygidium retracts past the
lobes of the body so that mating by other males is impos-
sible (fig. 2). At this stage, the body of the mature
female is sealed inside the scale cover and the female
eventually ceases feeding. At this point, the females look
similar to the molt stages and will produce crawlers
(fig. 2) in approximately 12 days.
4
Figure 11. Adult male scale (No te long feathery
antennae, close -set eyes , and dark bar across
the back)
Figur e 12 . Inverted female second molts (Note bod y and
cover are seale d toge ther)
inverted scale covers
1stmoltring ~ J
2nd molt ring / l
gray skirt
\
scale bodies pygidium
Figure 13. Th ird ins ta r female sca le ( ote body size and gray
skirt of th e cover increase wit h age, but the orange molt ring
stays th e sa me size)
Figure 14. Male scale inseminating a thir d ins tar female
Natural Enemi es of
California Red Scale
Numerous natural ene mies are associated wi th
Ca liforni a red scale and each citru s region will have a
different comb ination. Thi s is because eac h beneficial
insect or mite has different temp eratur e and humidity
limitati ons, as we ll as insec t host stage req uirements.
Recogn ition of the local natura l enemy compl ex is esse n-
tial to any effect ive I PM pro gram. The nat ural enemy
com plex in southern California generally co ns ists of the
three co mmon wasps: Aphytis melinus, Comperie/la bifas-
ciata, and Encarsia perniciosi (fig. 15, 25 & 29, respec-
tively). In centra l Ca lifornia, Aphytis me/inus an d
Comperiella bifasciala are the main co mpon ents o f the
natural enemy co mpl ex . In inter io r southern Ca liforn ia,
Encarsia perniciosi was d isplaced by the intr oductio n of
Aphytis in 1956 . In add ition to th ese natur al enem ies,
there are man y genera list predators such as beetles and
lacewi ngs .
PRIMARY CONT RO L AGENT:
Hymenoptera Aphy tis melinus De Bach
Aphylis melinus DeBach is the pri mary natura l enemy
associated with Ca lifo rnia red sca le (fig. 15) This exter-
nal wasp or ectoparcisitoid inse rts its ov ipos ito r through
th e sca le cover and deposits its egg(s) on the top (dorsal)
o r bouom (ven tral) side of the sca le insect body. Prior
to laying an egg, Aphytis paralyzes th e scale by insert ing
the ovipos itor into th e body and inject ing veno m.
The paralysis is permanent, and even if eggs are not
depos ited the sca le will even tu ally die from th e venom .
The food available to developi ng Aphytis offsprin g is
de termin ed by th e size of the sca le body when it was
paralyzed.
life stages
Egg stage. Aphytis eggs are teardrop -shaped and translu-
cent (fig. 16) . Healthy eggs are deposite d on the ven tral
or dor sa l side of the sca le body. Often , eggs are depos it-
ed in creases, espec ially around the pygidium. Eggs may
beco me damaged or naue ned if su itable sca le stages are
not found, since compet ition for desirable sca le stages
often results in more than one Aphytis parasitizing a sin-
gle host (superparasitism) fla uened eggs are usua lly
found on the vent ral side of th e sca le cover, on the p lant ,
and on the insect body. Un like healthy eggs, 0attened
eggs are very difficult to see using a hand lens in the
field A condi tion often associated with su perparasitism
and easily seen with a hand lens is sca le mutilation (fig .
17). When Aphytis inse rts its oviposito r in to the scale
Figure 15. Aph y lis fema le penetratin g gray skirt of the cover
to deposit egg on a th ird instar scale body
Figure 16 . Aphylis egg on third instar scale body (sca le cove r
removed)
Figure 17. Aphy lis mutilati on marks on third instar scale
bodies caused by the ovipos itor
body, dark rusty b rown mo ul ed spo ts often app ear on
the scale. These are the wound response marks of the
scale insect. Mutilated scale seldom host healthy Aphy tis
eggs or larvae. Recognizing supe rparasit ism and mutil a-
5
tion is an imporlanl Looi for assessing Aphylis activity.
Larval stage. After 2 days* Aphylis eggs hatch into larvae
(fig 18) Individuals in this stage vary the most in size.
To recognize this stage, look for an elongate sac with
body segments. As the larvae feed, gut material becomes
visible through the opaque segmented body. The gut
material changes in color from golden yellow to brown as
the larvae mature.
Prepupal stage. In about 5 days, larvae develop into
prepupa e (fig. 19) This stage is similar to the larval
stage (opaque with segments) except it lacks the col-
oration in the gut. Larvae excrete the gut material from
the body as meconial pellets as they transform into the
prepupal stage (fig. 19). These pellets are easily seen at
low magnification (5X to 15X), and they remain under
the empty scale cover even after the adul t Aphylis
emerges.
Pupal stage. After about one day the Aphytis prepupae
complete pupation. Initially, pupae have no eye color but
over 4- 5 days eventually develop eye pigmentation pro-
gressing through a sequence of colors The eye pigment
first turn s pink , then transforms to red, then reddish
brown and finally green (fig. 20) . The adult Aphytis
(fig. 15) emerge about one day after the eyes turn green.
Host feeding. Adult female Aphylis will feed on honeydew,
but will also host-feed for nutri tion to produce more
eggs. When host-feeding, Aphytis probes the scale body
as it does before oviposition, but even more extensively.
Then it feeds on the body fluids that ooze from the
wounds. The signs of host-feeding are difficult to see
using a hand lens in the field. The bod ies of host-fed
scales are usually collapsed, leaving only the outer skin of
the scale body. Host-feeding occurs when Aphytis depletes
its eggs because of oviposition or absorp tion. Thus,
Aphytis feeds on small scale while searching for suitable
hosts upon which to lay eggs. Host feeding kills a sub-
stantial percentage of California reel scale beyond those
killed through parasitism. Occasionally, there may be
some signs similar to mut ilation, as discussed above
(fig. 17).
Aphylis and scale remains. As larvae, Aphytis feed by
inserting their mouth parts into the scale body and
siphoning out the body fluids. Therefore, the remains
of the scale insect after being consu med are the emaci-
ated, collapsed walls of the body (fig. 21) The remains
• All day development periods round ed off to the neares t day and
based on co nstant temp era ture & re lative humi dity of 26.7° C and
60% R.H.
6
figure 18. Aphy tis larvae ( L) on third instar scale bodies
(Note variation in s ize anti number of larvae on each sca le)
Figur e 19. Aphy tis prepupa excre ting meco nial pellets
Figu re 20. Ap hy tis pupae: from left to r ight , clear, pink , red ,
reddi sh-br own , and gre en eye color (Note meco nial pellets )
Figure 21. Scale and Ap hy lis rema ins : dr ied scale bod y and
cover with exit hole (top ), scattere d meconia l pellets, and
pupa l case of Aphy tis (bottom )
of the Aphy tis after emergence are pieces of shiny
brown pupal case and meconial pellets scattered under
the scale cover (fig 21).
Hos t preference
Not all scale stages are consistently available or of equal
quality. Aphytis can only parasitize certain scale stages
and of those, it prefers large scale (chart l ). A female
Aphytis must make three basic choices.
Host stage. Aphy tis prefer scale in the instar stage over
those that are molting. The scale body during the instar
stage is soft and easily penetrated by the ovipositor
(fig. 22). The scale cover is free of the body in this stage;
thus Aphylis can lay eggs on both the top and bottom
surfaces of the scale body. During the molt and mature
female stages, the outside of the body hardens and fuses
to the cover, making oviposition difficult. These hard-
ened stages present only the ventral surface of the body
on which to lay eggs. More importantly, the ventral sur-
face dur ing these stages is very tough, making it difficult
for immature larvae to feed. Most immature Aphy lis die
if they have to develop on molting scale.
Host size. Aphy lis prefer to oviposit on third instar scale
because of their large size. By paralyzing the scale
before ovipositing on it, Aphytis choose the amount of
food that will be available to the offspring as it develops.
The larger the scale, the larger is the resulting Aphy lis
offspring, or the more offspring that can be produced
per scale (fig. 23). Mostly female off-
spring are produced on third instar
scale.
Host accessibility. The only portion of
the scale cover that the Aphylis ovipos-
itor can penetrate is the gray skin area
surrounding the orange molt circle
(fig. 24). The longer a scale has been
feeding, the larger the gray skin area
of the cover becomes. Therefore,
Aphy tis may pref er a large second
instar scale with a large skirt, over a
young third instar with a small skirt.
Scale access may be more important
than overall scale body size in the host
selection process.
Figure 24. Host access ibili ty. Large skirt
s ize provides easy access for Ap/1y ris
oviposition
large ~
skirt
Figure 22. Female scale from left to righ t: second molt , thi rd
insta r with cover removed , and matur e female (pygidium
retracted) .
scale body
Figure 23 . Large hos t s ize provides food for seve ral Aphy tis
larvae (L)
I
large skirt
, 2ndlnstar
•- male
2nd instar
female
' 3rd lnaUit
female
7
SECONDARY CONTROL AGEN T:
Hymenopt era Comperiella bifasciata Howard
The endoparas itoid Comperie/la bifasciata Howard
(fig. 25) is common mainly in arid regions of California,
such as in the Central Valley and inland southern
California. Compe1iel/a are found in coastal areas in low
numbers. Comperiel/a coexist with A. melinus in all of
Cali forn ia'.5 citrus regions. The preferred scale stage for
both parasitoids is the third instar female scale (chart
1). Comperiel/a has an advantage over Aphylis because iL
does not paralyze the host , so it can parasitize almost all
stages of scale, even the mature female. Comperie/la
deposits eggs inside the body of the scale. After a period
of inactivity the larvae develop inside the maturi ng scale
body, which eventually dies.
Life stages
Because Comperiel/a eggs and larvae are inside the scale
body, it is not possible to see eggs and young larvae with
a hand lens in the field. As larvae approach pupation , a
greenish gray gut material within the larvae is visible
with a hand lens through the scale body (fig. 26). If
more than one larva is present in a scale, one of the lar-
vae will eventually consume the othe rs. Once the larva
pupates, mecon ial pellets (similar LO Aphylis) inside the
mummified scale body are visible with a simple hand
lens (fig. 2 7). The meconia often form dark parallel lines
or a crescent. This is because as the prepupa excretes
meconia, it wedges between the sides of the pupa and
the walls of the mummified scale body. It is important to
remember that the meconia of Comperiel/a are always
inside the mummified scale body and not scattered
freely as with Aphytis. This characteristic along with
mummification of the scale body is the most definitive
way to dist inguish Comperiella parasitism from Aphytis
parasitism. The final immature stage of Compehella is
the pupa . Pupae are opaque just after pupation , but
eventually they turn black (fig. 27a, b). This turn s the
overall color of the scale dark and is easily seen without
magnification. Once the adul t emerges, the remains
are the mummified scale body with the meconia inside
and an exit hole through the scale cover (fig. 28) These
scales usually stay attached to the fruit or leaf unless the
fruit cont inues lo grow. Fruit growth loosens the glued-
on scale, which causes the mummified scale LO slough
off the fruit.
8
Figure 2 7. Comperiella pre pu-
pae (le fi) and pupae (right)
(a) ins ide female sca le and
(b) ins ide male sca le (Note
meco nium is pushed to the
edges of the scale body)
Figur e 25 . Comperiella
adult s: an adult female (top)
penetrating cove r to deposit
egg insid e sca le bod y and an
ad ult male (ins et at left)
Figure 26. Comperiella larvae (L) i.nside third instar scale bodies
(Note puffed out scale body. Note reddish-brown scale rost rum
attaclun ent (RA) compared to Comperiella larval gut material)
Host Preference
Compericlla prefer third instar and mated female scale
for oviposition (chart 1). Offspr ing develop more rapid-
ly in these stages. Aphytis also prefer third instars, and
immature Comperiella sharing the
