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Gall traits and galling insect survival in a multi-enemy context

Uiara Costa Rezende

, João Custódio Fernandes Cardoso

, P. Hanson

& D. C. Oliveira

1. Laboratório de Anatomia, Desenvolvimento Vegetal e Interações, Programa de Pós-Graduação em Ecologia e

Conservação de Recursos Naturais, Universidade Federal de Uberlândia (UFU) Campus Umuarama, Rua Ceará s/n,

Uberlândia, Brasil; uiara.ucr@gmail.com, jcfclg@gmail.com (*Correspondencia).

2. Escuela de Biología, Universidad de Costa Rica, Ciudad Universitaria Rodrigo Facio, San Pedro, San José, Costa

Rica; phanson91@gmail.com

Received 08-VII-2020. Corrected 02-XII-2020. Accepted 08-XII-2020.

ABSTRACT. Introduction: The enemy hypothesis postulates that gall traits protect galling insects against

natural enemies. Galls show a huge range of sizes, colors and ornaments, which vary even intraspecifically.

However, galling insects are targets of various organisms that attack them directly or indirectly. In this con-

text, to consider only one gall trait to investigate gall structure acting against only one guild of enemies can

conceal an understanding of the community-level interactions. Objective: Herein, we take these ideas into

consideration to investigate the conspicuous galls induced by Palaeomystella oligophaga Becker and Adamski

2008 (Lepidoptera) on Macairea radula (Bonpl.) (Melastomataceae) as a model system. We characterize this

system through categorization of the different enemy guilds present in the community. We identified them to the

lowest taxonomic level possible and determined the kind of interaction responsible for galling insects’ deaths.

Considering the enemy hypothesis and the selection of secondary characteristics, we also aimed to determine

which of the multiple gall traits influence the survival success of galling insects in a multi-enemy context.

Methods: We inspected galls and characterized the enemy guilds affecting the galling insect and the mortal-

ity rates produced by each one of them. Next, we tested whether the distinct gall traits measured (parenchyma

thickness, color, projections) promote galling insect survival with respect to each enemy. Results: The mortality

induced by indirect enemies (organisms that interact with gall tissues and can interact secondarily with galling

insect) was 47.3 %, being higher than that caused by parasitoids and predators (31.5 %). Despite the gall’s struc-

tural complexity, live galling insects showed the smallest occurrence (21.2 %). Parenchyma thickness was nega-

tively related to Calliephialtes parasitoids, Gelechiidae cecidophages and predation signals. Conclusions: We

demonstrated that the attacks to gall tissues by the cecidophages represented the highest threat to P. oligophaga

survival, being higher than the mortality caused by direct enemies. That is, the gall traits were not as efficient

as supposed to protect the galling insect from the attack of natural enemies. Nevertheless, we also demonstrated

that parenchyma thickness can be negatively related to some organisms, especially direct enemies. Other traits

hypothesized as defensive (e.g. projections, coloration) may simply play no role.

Key words: gall morphology; indirect interactions; multitrophic; tritrophic; cecidophages; anthocyanin.

Some insects have adapted to control and

redirect the growth, differentiation and physiol-

ogy of host plant organs to their own advantage

and form galls (Mani, 1964; Price, Fernandes,

& Waring, 1987; Stone & Schönrogge, 2003;

Oliveira et al., 2016). This kind of interaction

may be considered the most complex plant-

insect association, with the galling organism

acting as a sophisticated herbivore (Shorthouse,

Wool, & Raman, 2005). Several hypotheses

Costa Rezende, U., Fernandes Cardoso, J.C., Hanson, P., & Oliveira, D.C. (2021). Gall

traits and galling insect survival in a multi-enemy context. Revista de Biología

Tropical, 69(1), 291-301. DOI 10.15517/rbt.v69i1.42826

ISSN Printed: 0034-7744 ISSN digital: 2215-2075

DOI 10.15517/rbt.v69i1.42826

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have been raised to explain the pervasive adap-

tive radiation of galls (Price et al., 1987). One

of these proposes that the galling habit might

evolve as an adaptation related to desiccation

pressure on insect larvae, since the mechanical

structure can provide an ideal microclimatic

habitat (Danks, 2002; Lill, Marquis, Cud-

dington, Byers, & Wilson, 2007). Another

hypothesis suggests that the gall formation may

be related to the absence of foraging behavior,

once within the gall, the galling insect can

obtain nutrients directly from the specialized

tissue, the nutritive one (Mani, 1984; Short-

house, 1986; Bronner, 1992; Rezende, Cardoso,

Kuster, Gonçalves, & Oliveira 2019). Finally,

the enemy hypothesis states that the plant host

tissues surrounding the galling insect protect

it against attack by natural enemies (Price &

Pschorn-Walcher, 1988). In addition to that, the

selective pressure imposed by natural enemies

have been discussed as a main driver to explain

the morphological diversity of galls (Stone &

Schönrogge, 2003; Bailey et al., 2009).

Considering the several traits suggested

as defenses for galling insects, conspicuous

gall coloration seems to be the most intriguing

(Inbar et al., 2010a, Inbar et al., 2010b; White,

2010; Lev-Yadun, 2016). Among the many

ideas proposed for gall color (Bomfim et al.,

2019), the aposematic hypothesis raised by

Inbar et al. (2010a), that galls with conspicuous

colors (as red color) may be aposematic and

protected the galling insect by the presence of

chemical compounds - deserves special atten-

tion and should be tested for validation. The

formation of trichomes and projections is con-

sidered as a plant defense against herbivores

(Yamazaki & Lev-Yadun, 2015; Alahakoon

et al., 2016; López-Carretero, Boege, Díaz-

Castelazo, Domínguez, & Rico-Gray, 2016).

Consequently, it is intuitive to think that this

protection extends to galls that have developed

these traits. In addition, the gall’s position

on the plant and, therefore, in the environ-

ment, may determine different survival rates

(Leite et al., 2017). Likewise, gall size and

parenchyma thickness have already been much

tested as traits acting as barriers, mainly against

parasitoids (Sopow & Quiring, 2001; Van Heze-

wijk & Roland, 2003; Zargaran, Safaralizadeh,

Pourmirza, & Valizadegan, 2011; Figueiredo,

Santos, Fernandes, & Martins, 2014).

Galling insects sustain a variety of natural

enemies that attack them directly as kleptopara-

sites, parasitoids and predators (Abrahamson,

Sattler, McCrea, & Weis, 1989; Van Hezewijk

& Roland, 2003; Bourg & Hanson, 2014; Han-

son & Nishida, 2014; Forbes et al., 2015; Luz

& Mendonça Júnior, 2019). Furthermore, some

organisms interact with galls consuming the

neoformed tissues, such as pathogens, verte-

brates (herbivores) or Cecidophages (insect

larvae that feed on gall tissues), which can

negatively affect the galling insects and even

cause their death as a collateral effect (Zamora

& Gómez, 1993; Sugiura & Yamazaki, 2009;

Cooper & Rieske, 2011; Katilmis & Azmaz,

2015; Luz, Gonçalves, Moreira, & Becker

2015; Mete & Mergen, 2017). Such enemies

can include guilds (i.e., functional groups)

which pose variable direct or indirect risks

to the galling insect. Despite this variety, the

parasitoids are the group predominantly studied

when considering the relevance of gall traits

(Weis & Abrahamson, 1985; Waring & Price,

1989; Bailey et al., 2009; Zargaran et al., 2011)

and the impact of indirect enemies can be

underestimated. This scenario raises questions

that need to be adapted to galling interactions in

the field, and which aim to understand if a vari-

ety of gall traits do in fact function as defenses

against enemies. Understanding the importance

of aposematism or defense positions, and bar-

rier traits (parenchyma thickness, trichomes

and projections) is especially important when

considering enemy guilds that may harm gall-

ing insects though different mechanisms.

Galls induced by Palaeomystella oli-

gophaga (Lepidoptera) on Macairea radula

(Melastomataceae) are conspicuous structures

varying in color, size, length of parenchyma

projections and the height at which they occur

on the plant (Fig. 1). Regardless of these mul-

tiple traits, several types of insects attack the

galling insect, thus representing an excellent

model system. Herein, we characterize this

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multitrophic system through categorization of

the different enemy guilds present. We identi-

fied them to the lowest taxonomic level pos-

sible and determined the kind of interaction

responsible for galling insects’ deaths. Consid-

ering the enemy hypothesis and the selection

of secondary characteristics, we also aimed

to determine which of the multiple gall traits

influence the survival success of galling insects

in a multi-enemy context.

MATERIALS AND METHODS

Study site and system: The study was

carried out at Panga Ecological Station in

Uberlândia municipality, Minas Gerais state,

in an ecotone area between a ‘wet grass-

land’ and a ‘cerrado sensu strictu’ (Cardoso,

Moreno, Bruna, & Vasconcelos 2009). Pal-

aeomystella oligophaga Becker and Adamski

2008 (Lepidoptera: Momphidae) (Fig. 1A) is

a microlepidoptera that, during the larval and

pupal stage, remains inside globoid-shaped

galls (sensu Isaias, Carneiro, Santos, & Olivei-

ra 2014) induced in axillary stem buds of

Macairea radula Bonpl. (Melastomataceae)

shrubs (Becker & Adamski 2008).

Procedures: We obtained the samples at

the end of the rainy season (April), when all

insects (including natural enemies) are found

in the pupal stage, permitting us to infer the

survival rates of the galling insect at the end of

its life cycle. A total of 321 galls were removed

from different plants (N = 321). The collection

of galls was not replicated in other popula-

tions due to the number of samples required

for the analysis, restricting the collections to

one population where a satisfactory number

of galls occurred. We tested the following gall

Fig. 1. Trait variation of Macairea radula galls (bottom; scale bar: 1cm) induced by A. Palaeomystella oligophaga and

associated enemies. The galling insects are indirectly affected by B. a cecidophagous Chloropidae and C. a cecidophagous

Gelechiidae that feed on gall tissues, causing P. oligophaga death. The galling insects are also directly attacked by D.

Calliephialtes sp. parasitoids, E. Bracon sp. parasitoids and an F. unidentified predator, which was recognized by the scar

left on gall parenchyma (arrow) and the dried galling larva inside the larval chamber. Scale bar: 1mm.

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characteristics as a potential defensive role:

the height of each gall on M. radula shrubs,

gall volume, thickness of parenchyma around

the larval chamber, length of projections, and

coloration.

We measured the height of each gall

related to the ground on the host plant before

removal. In the laboratory we opened each gall

for observation and collection of the occupants

using a Leica

500 stereomicroscope coupled

to the U-photo system ICC50HD. Insects were

incubated in plastic microtubules at room tem-

perature until adult emergence and identifica-

tions were carried out to the lowest taxonomic

level possible. Gall height and width were mea-

sured and used to calculate the volume based

on an oblate spheroid. Parenchyma thickness

was calculated using gall height (from its inser-

tion point on the plant to the opposite surface),

discounting the larval chamber height (from

the bottom to the top of the wall) and divid-

ing the value by 2. This calculation provides

an average measurement of both the top and

bottom of the gall parenchyma. Projections

were measured by calculating the average of

three projections present on the surface of the

gall apex (opposite to insertion point on host

plant), since the projections are larger and

more homogeneous in size at the apex. We also

measured the parasitoids body and ovipositor

lengths for a better understanding of the rela-

tionships between the occurrence of each spe-

cies of parasitoids according to the thickness

of the parenchyma. All measurements were

performed using a digital caliper (Digimess

ZAAS-1.0004, 0.01 mm readability).

We used the concentration of anthocyanins

as a proxy for color pattern, since these are the

main pigments responsible for red coloration

in plant organs and they provide a conspicuous

coloration when accumulated in galls (Connor

et al., 2012). For this purpose, we removed

the gall projections, set them horizontally in

a single layer, exposed them (together) to a

handheld USB JAZ spectrophotometer (Ocean

Optics

) and took the mean of three mea-

surements. We used a standard white (Ocean

Optics

) and the absence of light as black for

calibration. We then calculated the Anthocy-

anin Reflectance Index (ARI) based on the

inverse reflectance at 550 nm (anthocyanin

absorption peak) (sensu Gitelson, Merzlyak, &

Chivkunova, 2001). With this procedure, we

obtained a scale of anthocyanin concentration.

Values close to 0 and 1 refer to greener and red-

der galls, respectively.

Statistical analysis: The different organ-

isms present in the gall were grouped into three

guilds: (1) “galling”: galls with the presence of

live P. oligophaga pupae; (2) “direct enemies”:

enemies that fed directly on the galling insect;

and (3) “indirect enemies”: insects that fed

on gall tissues, killing the galling insect indi-

rectly. We performed pairwise group com-

parisons using chi-square goodness of fit tests

with equal expected proportions and obtained

P-values through Monte Carlo simulations (10

000 iterations each). A Bonferroni correction

was applied using the p.adjust function of the

R software stats package.

We applied a multinomial logistic model

using the mlogit R-package version 0.3-0

(Croissant, 2018) to investigate the traits that

influence the presence of different natural

enemies in M. radula galls, and therefore the

killing of P. oligophaga. Thus, the presence of

a live galling insect was taken as a reference

level and the occurrence of each enemy was

considered as alternative outcomes. We consid-

ered the height of the gall on the plant, its color,

length of projections and parenchyma thickness

as predictor variables. Gall volume was not

used because it had a high correlation of 0.89

with parenchyma thickness. We considered

multicolinearity to be no problem among the

remaining explanatory variables (below 0.44 in

all cases). The significance of the model was

assessed by the likelihood ratio (LR) test. Anal-

yses were carried out in the R statistical envi-

ronment version 3.5.0 (R Core Team, 2018).

RESULTS

We found different taxa of insects that

interact directly or indirectly with P. oligophaga

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(Fig. 1A). Most insect enemies used not only

the food resource, but also the shelter provided

by the gall structure, forming pupae within,

and emerging as adults. Although we have

not identified them to the species level, we

are confident that each group considered here

corresponds to just a single morphospecies.

Thus, we found two species of parasitoids,

Caliephialtes sp. (Hymenoptera: Ichneumoni-

dae: Pimplinae) and Bracon sp. (Hymenoptera:

Braconidae: Braconinae). There were also two

morphospecies of cecidophages, which cause

the death of the galling insect, despite they do

not feed directly on these larvae (Sanver &

Hawkins, 2000). One of them, the Chloropidae

(Diptera) (Fig. 1B) occurs only in the larval

chamber, where it feeds on the inner cells until

pupation. The other one is a species of Gelechi-

idae (Lepidoptera) (Fig. 1C) which can forms

tunnels in the galls. The gallings were found

dead while the Gelechiidae larvae were still

feeding on the external gall reached the larval

chamber, therefore were classified here as ceci-

dophages instead of kleptoparasites, considered

as indirect interactors (sensu Luz & Mendonça

Júnior, 2019). One of the parasitoids, Cal-

liephialtes sp. (Fig. 1D), had a larger body

size (Mean ± SD: 9.4 ± 2.5 mm, N = 10) and

ovipositor (7.9 ± 2 mm, N = 10) than the other

species, Bracon sp. (body size: 1.7 ± 0.9 mm,

n = 10; ovipositor: 2.3 ± 1.3 mm, N = 10) (Fig.

1E). Inside some galls (N = 17) P. oligophaga

larvae were found dried, together with a single

scar traversing the whole parenchyma up to the

larval position. These signs were considered as

a predatory action (Fig. 1F) probably caused by

the piercing stylet of an insect.

The rates of enemy occurrence varied

among the groups of organisms. We found that

only 68 galls out of 321 contained live gall-

ing insects (21.2 %) (Fig. 2). The Chloropidae

cecidophages were approximately twice as

abundant as galling insects (N = 131; 40.8 %).

Calliephialtes parasitoids occurred in greater

numbers (N = 61; 19 %) than Bracon (N =

23; 7.2 %). The Gelechiidae cecidophages

occurred in 21 galls (6.5 %) and predation sig-

nals occurred in 17 (5.3 %). When considering

insect guilds, we found that galling insects

showed the lowest rates of occurrence com-

pared with the enemies, differing significant-

ly from both “direct enemies” (enemies that

interact directly with inducer) (χ

= 6.44; P =

0.0127) and “indirect enemies” (enemies that

interact indirectly with inducer)” (χ

= 32.07; P

= 0.0003; Fig. 2). The “indirect enemies” were

the most abundant group of organisms found in

these galls (χ

= 10.28; P = 0.0032).

We found a significant relationship

between the natural enemies of P. oligoph-

aga and the different predictor variables (χ

= 50.03; P = 0.0002). The probability of

Fig. 2. Occurrence rates of the different organism groups

and processes (predation signals) found in galls of

Macairea radula induced by Palaeomystella oligophaga

moths. Enemies are arranged according to their guilds:

“direct attacks” (insects that kill the galling insect by

feeding on its body fluids) and “indirect enemies” (insects

that feed on gall vegetal tissues, causing galling insect

death as a secondary consequence). The letters above the

bars refer to the statistical significance.

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incidence of Bracon parasitoids (Odds Ratio

= 1.014), Gelechiidae cecidophages (OR =

1.012) and predation signals (OR = 1.011)

increased with gall height on the plant (Table

1, Fig. 3A). On average, galls with the presence

of galling insects (mean ± SD height: 86.19 ±

56.26 mm) were positioned 42.6, 29.3 and 28.7

% lower, respectively, then galls with Bracon

parasitoids (122.91 ± 54.18 mm), Gelechiidae

cecidophages (111.48 ± 58.59 mm) and preda-

tion signals (110.94 ± 47.59). On the other

hand, the probability of occurrence of Cal-

liephialtes parasitoids (OR = 0.772), Gelechi-

idae cecidophages (OR = 0.489) and predation

signals (OR = 0.654) decreased as the average

parenchyma thickness was bigger among the

sampled galls (Table 1, Fig. 3B). Galls with

live galling insects (mean ± SD parenchyma

thickness: 6.72 ± 2.07 mm) showed 13.8, 29.5

and 22.6 % thicker parenchyma than those with

Calliephialtes parasitoids (5.79 ± 1.88 mm),

Gelechiidae cecidophages (4.74 ± 1.52 mm)

and predation signals (5.20 ± 2.0 mm). There

were no effects of color or length of projections

(Table 1).

DISCUSSION

Despite the structural complexity of galls

induced on M. radula by P. oligophaga, these

insects were attacked by a diversity of organ-

isms. The occurrence rates of the galling moth

(taken here as galling insect survival rates)

were the lowest, followed by direct enemies

and then indirect enemies. Although the pro-

tective barrier offered by the gall can work at

some level, we suggest that the morphological

characteristics analyzed did not constitute an

Fig. 3. Frequency of different natural enemies’ occurrence according to A. plant height and B. average parenchyma thickness

on Macairea radula galls induced by Palaeomystella oligophaga. Circles indicate data distribution; galls with galling insect

survival are indicated by 0 (black circles) and those with mortality caused by the different natural enemies are indicated by

1 (color circles). Lines represent predicted probability.

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effective defense for the galling insect. The

threat imposed by Chloropidae cecidophages

to P. oligophaga supports the importance of

considering all kinds of enemy guilds interact-

ing with galling insects when testing hypoth-

eses related to galls. These organisms were not

related to any trait studied and posed a greater

threat than those insects feeding directly on the

galling insect.

The parenchyma thickness was the only

negative selective factor in the studied system,

against Calliephialtes parasitoids, Gelechiidae

cecidophages and predatory attacks. Rossi,

Stiling, Strong and Johnson (1992) showed

in experiments that the studied parasitoids

have no preference for a particular gall size,

differing from the data by Weis, Abrahamson

and McCrea (1985) where the chances of

successful oviposition were lower for those

parasitoids, Eurytoma gigantea Walsh (Hyme-

noptera; Eurytomidae), that attack larger galls

due to the time spent on inspection. This

pattern also occurred in other systems where

galling insects had higher survival rates in

larger galls (Sopow & Quiring, 2001; Cooper

& Rieske, 2010; Zargaran et al., 2011), and

thus the parasitoids apparently were more

efficient attacking the smallest galls. On the

other hand, the parasitoids in some systems

showed a preference for the largest galls (Van

Hezewijk & Roland, 2003; Figueiredo et al.,

2014). Here, we showed that gall features can

work in different ways, against different para-

sitoid taxa, in the same gall system. Another

example are the galls induced by Dryocosmus

kuriphilus (Hymenoptera: Cynipidae) in Cas-

tanea spp. (Fagales: Fagaceae) which vary

in size. The larger galls in this system had a

higher presence of Torymus sinensis parasitoids

(Hymenoptera: Torymidae), whereas the small-

er ones had more Ormyrus labotus parasitoids

(Hymenoptera: Ormyridae). This segregation

was explained by the differences in oviposi-

tor length between the two parasitoid species

(Cooper & Rieske, 2010).

Our data suggest that galls with parenchy-

ma thickness greater than the average length

of Calliephialtes ovipositors (comparing the

average size values for both structures) showed

the smallest occurrence of these parasitoids.

Thus, the negative relation may be a result of a

preference for smaller gall sizes or ineffective

oviposition in the larger ones, which may lead

to selection for increased parenchyma thick-

ness against attack by these parasitoids. On the

other hand, the negative relation between Gel-

echiidae cecidophages and parenchyma thick-

ness seems counterintuitive since it potentially

makes available more food and shelter. Preda-

tors probably need to have mouthparts capable

of reaching the larva in the center of the gall,

which may also contribute to selection for

greater thickness.

TABLE 1

Results of multinomial logistic regression demonstrating

the relationships between the predictor variables and the

occurrence of the different natural enemies, taking the

presence of the galling Palaeomystella oligophaga as

reference level. Significant results at the 0.5 level

are expressed in bold

Predictor Natural enemy Error t P

Chloropidae 0.610 0.549 0.583

Calliephialtes sp.

0.719 -0.249 0.803

Color

Bracon sp.

0.908 0.249 0.803

Gelechiidae 1.082 -0.860 0.390

Predation 1.062 -0.461 0.645

Chloropidae 0.003 1.439 0.150

Calliephialtes sp.

0.004 -0.171 0.864

Height

Bracon sp.

0.005 2.861 0.004

Gelechiidae 0.005 2.438 0.015

Predation 0.005 2.000 0.046

Chloropidae 0.090 -1.455 0.146

Calliephialtes sp.

0.110 -2.351 0.019

Parenchyma

Bracon sp.

0.152 -1.115 0.265

Gelechiidae 0.172 -4.146 <0.0001

Predation 0.178 -2.378 0.017

Chloropidae 0.065 -0.445 0.657

Calliephialtes sp.

0.078 -0.358 0.721

Projections

Bracon sp.

0.130 -1.641 0.101

Gelechiidae 0.111 0.594 0.553

Predation 0.143 -0.962 0.336

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Gall location influenced the occurrence of

Bracon parasitoids, Gelechiidae cecidophages

and predators. However, it had no influence on

Chloropidae cecidophages probably because

these organisms are more adapted to using

cues provided by gall metabolism to find

their targets (Unsicker, Kunert, & Gershenzon,

2009; Schaefer & Ruxton, 2011). Data regard-

ing the number of potential sites per height

vs. the number of sites induced may reveal

whether galling insects prefer a particular stra-

tum. However, it appears that P. oligophaga

induces galls on any axillary stem buds avail-

able, which can occur at several heights. In

this respect, a gall induction made at a random

height may determine the probability of expo-

sure to risk of attack by Bracon parasitoids,

Gelechiidae cecidophages and predators. Since

these enemies taken together occupied 19 % of

the opened galls, the choice of induction sites

positioned lower on the vegetation may offer

an advantage to galling insects. The patterns

found here may be related to the natural his-

tory traits of the natural enemies, which may

fly at greater heights or avoid lower strata in

the vegetation.

Finally, despite the wide color variation

of M. radula galls, we did not find any prefer-

ences for green or red ones by enemies. Pos-

sibly, the interacting insects do not recognize

the conspicuous coloration as aposematic, as

the vertebrates’ herbivories studied to test the

galls aposematic hypothesis suggested by Inbar

et al., (2010a). The present data do not support

an aposematic function of gall color (at least

when considering the studied organisms). The

length of projections associated with trichomes

also did not relate to the abundance of any of

the studied enemies. Still, we cannot rule out

the hypothesis that their presence affects attack

by generalist herbivores or parasitoids, since

they may be so effective against these organ-

isms that we simply did not find them. Galls

with a hairy covering may play an important

role in galling-insect defense against some

parasitoids as occurs in Diplolepsis sp. (Cynip-

idae) galls on Rosa sp. (Rosaceae) shrubs

(Askew, Gómez, Hernández, & Aldrey, 2006).

However, in these systems parasitism was also

sensitive to gall size and thickness (László &

Tothmérész, 2013).

In the P. oligophaga - M. radula as sys-

tem we demonstrated how different gall traits

work simultaneously against direct and indirect

enemies of galling insects. Although color and

trichomes were not effective in reducing attack

by the studied organisms, we cannot rule out

the possibility that these traits exist as char-

acteristics that have been molded by selective

pressure from other natural enemies during

evolution. The lack of a relationship between

the traits analyzed and Chloropidae cecido-

phages shows that, despite the apparent defense

offered by gall structure, galling insects can

support large populations of enemies and suf-

fer high mortality (Waring & Price, 1989;

Hawkins, Askew, & Shaw, 1990; László &

Tothmérész, 2013).

Ethical statement: authors declare that

they all agree with this publication and made

significant contributions; that there is no con-

flict of interest of any kind; and that we fol-

lowed all pertinent ethical and legal procedures

and requirements. All financial sources are

fully and clearly stated in the acknowledge-

ments section. A signed document has been

filed in the journal archives.

ACKNOWLEDGMENTS

This study was financed in part by the

Coordenação de Aperfeiçoamento de Pessoal

de Nível Superior - Brasil (CAPES) - Finance

Code 001. The authors are grateful to Fundação

de Amparo à Pesquisa de Minas Gerais (FAPE-

MIG) and Conselho Nacional de Desenvolvi-

mento Científico e Tecnológico (CNPq) for

financial support.

RESUMEN

Características de las agallas, y supervivencia

de insectos que producen agallas, en el contexto de

enemigos múltiples. Introducción: La hipótesis del ene-

migo postula que las características de la agalla protegen al

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agallero contra los enemigos naturales. Las agallas mues-

tran una gran variedad de tamaños, colores y adornos, que

varían incluso de forma intraespecífica. Sin embargo, los

agalleros son objetivos de varios organismos que los atacan

directa o indirectamente. En este contexto, considerar solo

una característica para investigar la estructura de la agalla

actúando contra un solo gremio de enemigos puede ocultar

una comprensión de las interacciones a nivel comunitario.

Objetivos: Para investigar las ideas presentadas usamos las

agallas conspicuas inducidas por Palaeomystella oligopha-

ga Becker y Adamski 2008 (Lepidoptera) en Macairea

radula (Bonpl.) (Meslastomataceae) como sistema modelo.

Describimos este sistema a través de la categorización de

los diferentes gremios enemigos presentes en la comu-

nidad. Los identificamos al nivel taxonómico más bajo

posible y determinamos el tipo de interacción responsa-

ble de la muerte de los agalleros. Teniendo en cuenta la

hipótesis del enemigo y la selección de características

secundarias, también buscamos determinar cuáles de las

múltiples caracteristicas de la agalla influyen en el éxito de

supervivencia de los agalleros en un contexto de enemigos

múltiples. Métodos: Inspeccionamos las agallas y carac-

terizamos los gremios enemigos que afectan al agallero y

las tasas de mortalidad producidas por cada uno de ellos.

Luego, probamos si las distintas caracteristicas de las aga-

llas medidas (grosor del parénquima, color, proyecciones)

promueven la supervivencia de los agalleros con respecto

a cada enemigo. Resultados: La mortalidad indirecta

inducida por los cecidofagos fue del 47.3 %, superior a

la causada por los parasitoides y los depredadores (31.5

%). Apesar de la complejidad estructural de la agalla, los

agalleros vivos mostraron la menor presencia (21.2 %). El

grosor del parénquima se relacionó negativamente con los

parasitoides de Calliephialtes, los cecidófagos de Gelechii-

dae y la depredación. Conclusiones: Demostramos que los

ataques a los tejidos biliares por cecidófagos representaron

la mayor amenaza para la supervivencia de P. oligophaga.

Esto es interesante porque, de acuerdo con la hipótesis del

enemigo, la estructura de las agallas debería proporcionar

protección para los insectos agalleros en lugar de atraer

a los insectos que se alimentan de la agalla misma. Sin

embargo, también demostramos que el grosor del parén-

quima puede estar relacionado negativamente con algunos

organismos, especialmente los enemigos directos. Otras

caracteristicas hipotéticas como defensivas (por ejemplo,

proyecciones, coloración) pueden simplemente no desem-

peñar ningún papel.

Palabras clave: morfología de agallas; interacciones indi-

rectas; multitróficas; tritróficas; cecidófagos; antocianinas.

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