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Differential Host Handling Behavior between Feeding
and Oviposition in the Parasitic Wasp
Haplogonatopus hernandezae
Floria M.K. Uy
1,2
&Ana Mercedes Espinoza
3,4
Received: 30 November 2017 /Revised: 2 October 2018 /Accepted: 5 October 2018
#Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
Lifetime fitness is directly influenced by the decision to use resources for either current
or future reproduction. Thus, females should weigh the costs and benefits of each
reproductive opportunity and allocate resources accordingly. Here, we explore
decision-making and the time spent handling hosts of different instars in the parasitoid
Haplogonatopus hernandezae, which uses a single planthopper host to either oviposit
(i.e., current reproduction) or feed (i.e., future reproduction). Our results indicate that
manipulation time in attacks that led to either oviposition and feeding increased with
host instar and size. Consequently, attacks were less successful on older host instars
than younger ones. Similarly, attack and handling time during oviposition was greater
when manipulating fifth instar nymphs compared to younger ones, but oviposition time
was similar. Surprisingly, host grasping by the chelate forelegs differed between
oviposition and feeding events, and the specific chelate foreleg morphology of
H. hernandezae facilitates the specific grasp of the clypeus and gena of the host. We
also link this previously undescribed host grasping and differential handling behavior in
this species to the final decision to oviposit or feed. Given the differences in handling
time and effort among different host instars, we found that older hosts were more often
chosen for consumption than younger hosts, and younger hosts were chosen more often
for oviposition. Our study suggests that the tradeoff between current and future benefits
is influenced by the investment in handling hosts of different instars, and the assess-
ment of host suitability for successful offspring survival.
Keywords Decision-making .Dryinidae .Haplogonatopus hernandezae .host-feeding .
host-handling .oviposition .parasitoid .Tagosodes orizicolus
Journal of Insect Behavior
https://doi.org/10.1007/s10905-018-9699-4
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10905-018-
9699-4) contains supplementary material, which is available to authorized users.
*Floria M.K. Uy
f.uy@miami.edu
Extended author information available on the last page of the article
Introduction
Fitness strongly depends on the decision to invest either in current or future reproduc-
tion. This tradeoff is known as the cost of reproduction, which assumes that females
make decisions to maximize reproductive success over their lifetime (Desouhant et al.
2005; Williams 1966). To maximize their reproductive success, females must weigh the
costs and benefits of current reproduction opportunities against finding food to secure
future reproduction (Rosenheim 1999; Sæther et al. 1993). Studies in many taxa,
including moose, sticklebacks, sea birds, rodents, and burying beetles, suggest that
these decisions to invest in current and future reproduction is influenced by female age,
environmental constraints and resource availability (Ericsson et al. 2001;Poizatetal.
1999; Sæther et al. 1993; Scott and Traniello 1990;Weiletal.2006). For example, if
current reproduction is costly, females may choose to reproduce at a later time
(Creighton et al. 2009). In addition, the decision to invest in current or future repro-
duction may be influenced not only by quantity and quality of available resources, but
also by the energetic investment required to acquire these resources (Creighton et al.
2009; Heimpel and Rosenheim 1995; Yurewicz and Wilbur 2004). Therefore, under-
standing the tradeoff between current and future reproduction is essential for elucidat-
ing the evolution of adaptive decision making, and reproductive investment.
Balancing the tradeoffs between current and future reproduction is especially im-
portant in organisms where current and future reproduction depend on a single resource
(Desouhant et al. 2005; Rivero and West 2005). For example, carnivorous plants face a
direct tradeoff between utilizing arthropods as prey or instead for pollination services,
known as the pollinator-prey conflict (Jürgens et al. 2012; Youngsteadt et al. 2018;
Zamora 1999). Similarly, one-piece nesting termites live inside wood that serves as
both their nesting site and nourishment, rarely leaving to exploit new shelter (Korb and
Hartfelder 2008). Because the colony dies after exhausting its food source, colony
members must allocate enough resources for colony maintenance but leave enough for
brood provision (Korb and Hartfelder 2008). Finally, in parasitoids that exhibit host-
feeding, hosts represent the single resource for either feeding or offspring development
(Godfray 1994). This decision to either feed or oviposit, in turn, is influenced by
intrinsic factors such as egg load and nutritional status of the parasitoid, and extrinsic
factors such as the abundance, age, size, quality and the developmental stage of the
specific host (Barzman and Daane 2001; Jervis et al. 1996; Jervis and Kidd 1986;King
1998;Kitamura1988;Nishimura1997). For example, old parasitoids with access to
low quality hosts lay fewer eggs and feed more frequently than well-fed females
(Lebreton et al. 2009). Some species of parasitoids may avoid early instars if the host
is too small for survival of offspring (Jervis et al. 2008). They may also avoid late host
instars as it may be harder to penetrate through their cuticle (Gross 1993), and/or hosts
previously parasitized by conspecifics (Yamada and Kitashiro 2002). Previous research
also shows that after this initial assessment, hosts of low quality (Lebreton et al. 2009),
or those that are difficult to access due to defense mechanisms (Gross 1993), may be
less preferred for oviposition and instead are used for feeding (Lebreton et al. 2009).
Given the high diversity of host-parasitoid systems, we focus on synovigenic
parasitoids because they provide an excellent a model system for exploring decision-
making. These parasitoids can mature eggs throughout their adult stage (Jervis et al.
2008). Consequently, when encountering a host, the tradeoff between current and future
Journal of Insect Behavior
reproduction may be strongly influenced by various intrinsic and extrinsic factors
(Rivero and West 2005). For example, in the synovigenic parasitoid Itoplectis
naranyae, females are capable of maturing eggs without feeding on hosts (Ueno and
Ueno 2007). However, females that previously fed on hosts had higher fecundity than
those who did not feed (Ueno and Ueno 2007). Thus, the condition of the parasitoid
should influence their decision to feed or oviposit. In addition, host quality has been
shown to effect a parasitoids decision to either invest in immediate reproduction or to
choose to survive and increase future reproduction (Rivero and West 2005;Siekmann
et al. 2001; Sirot and Bernstein 1996). Finally, hosts are often not passive, and
successful oviposition or feeding attempts by parasitoids may be reduced by defensive
behaviors such as vigorous squirming and jerking movements, kicking and jumping
(Gross 1993;Slansky1986; Stadler et al. 1994; Villagra et al. 2002). Thus, handling
time, which comprises the interval between the first contact with the host and the
completion of the oviposition or host feeding event (Gross 1993), may vary depending
on the specific chosen host. For example, smaller hosts may require less handling time
and represent less injury risk for the parasitoid, because behavioral defenses are
frequently more effective in older host developmental stages (Gross 1993). However,
a small host may not offer enough nourishment and time for the offspring larvae to
develop (Mora-Kepfer and Espinoza 2009). In contrast, a larger host may represent a
higher energetic cost in handling, but also have a higher probability of successful
development of the offspring. However, in some cases, larger hosts can overcome the
attack by subsequently encapsulating the parasitoid eggs or larvae (Blumberg 1997), or
may be too advanced in their life cycle to provide enough time for the parasitoid to
develop (Vinson and Iwantsch 1980). The parasitoid must therefore balance the tradeoff
between investment in host-handling and the appropriate host instar towards current or
future fitness. Although the final outcome of either oviposition or host feeding in
synovigenic and koinobiont parasitoids, and the defenses of its hosts have been
documented (Harvey and Strand 2002; Jervis et al. 2001), little is known about
decision-making and host-handling strategies depending specifically on the develop-
mental stage of the host.
In this study, we use the parasitoid wasp Haplogonatopus hernandezae (Dryinidae:
Hymenoptera) to study host decision for either oviposition or feeding. A unique
characteristic in the Dryinidae, and present in this species, is the presence of chelate
forelegs (Guglielmino 2002;Olmi1995; Tribull 2015), which they use to grasp and
handle the host. The female wasp uses her chelae and mandibles to seize the host and
consequently sting the ventral side of the thorax to paralyze the host (Hernandez and
Belloti 1984; Mora-Kepfer and Espinoza 2009; Yamada and Imai 2000). Previous
studies within Dryinidae suggest that the relationship between capturing the host and
the host’s reaction to the attack may be a driving force in the evolution of this family of
parasitoids (Guglielmino 2002;Olmi1994). The particular morphology of the chelae in
each species also serves as a key characteristic for the identification of adult females
(Olmi 1994; Tribull 2015). However, the functional significance of chelate foreleg
variation found even among closely related species is still poorly understood (Olmi
1984). Of particular interest, the potential relationship between chelae morphology and
the specific attacked host has not been studied.
Haplogonatopus hernandezae is a solitary and specialist endoparasitoid of the
nymphs of the planthopper Tagosodes orizicolus in Colombia and Costa Rica
Journal of Insect Behavior
(Hernandez and Belloti 1984; Mora-Kepfer and Espinoza 2009;Olmi1984;Olmiand
Virla 2014). This species is strongly synovigenic, which is characteristic of apterous
Dryinidae, and can therefore mature eggs throughout their reproductive life as an adult
(Jervis et al. 2008). Females of H. hernandezae are also koinobiont parasitoids that
temporarily paralyze their hosts, and have a high ovigeny index, small egg size, and
high fecundity (Jervis et al. 2001,2008; Jervis and Kidd 1986). Our study population
reproduces exclusively by parthenogenesis, avoiding constraints associated with mat-
ing (Mora-Kepfer and Espinoza 2009). When finding a potential host, the female may
presumably assess host quality (Mora-Kepfer and Espinoza 2009), and consequently
choose to either feed or oviposit on this host (Hernandez and Belloti 1984). Females
paralyze the host and proceed to probe its abdomen with their ovipositor, similarly to
Haplogonatopus atratus, which has been described as an infanticide strategy to detect
any eggs previously deposited by another female (Yamada and Kitashiro 2002). Our
previous work in H. hernandezae did not find an effect of experience, as the proportion
of hosts that were parasitized, predated upon or not attacked was similar in experienced
and unexperienced females (Mora-Kepfer and Espinoza 2009). In addition, the pro-
portion of male and female hosts being parasitized remained similar in females of
different ages (Mora-Kepfer and Espinoza 2009). However, the effects of host instar in
decision-making has not been previously explored in this parasitoid species. We predict
that because planthopper nymphs actively try to escape, older nymphs may represent a
higher handling investment than earlier instars. We also predict that host-handling will
be different for feeding versus oviposition, because manipulation will influence the
survival of both the host and parasitoid offspring.
Thus, given the knowledge of the reproductive physiology of Dryinidae and our
previous results for parasitism and predation in H. hernandezae, the aims of this study
were threefold. First, we investigated the effect of inspecting the host to either oviposit
or feed, and the decision to invest in feeding or ovipositing depending on host instar as
a proxy for quality. Second, we described differential host-handling behavior between
these two strategies and predict that the time spent in handling different host instars.
Finally, because planthopper nymphs actively try to escape from the attack, we
explored how the chelate forelegs are used in the initial grasp and subsequent handling
in both feeding and oviposition attacks for different host instars.
Materials and Methods
Insect Collection and Rearing
We collected individuals of H. hernandezae and its host, the planthopper Tagosodes
orizicolus, throughout the province of Guanacaste in the Pacific North of Costa Rica,
during 2001 and 2002. All the insects were collected exclusively in inundated rice
fields. We isolated nymphs and adults planthoppers that showed visible signs of
parasitism, such as a dark cyst on their thorax or abdomen. We reared them individually
in small cages designed for Dryinidae (Chandra 1980)toobtainparasitoidlarvaethat
emerged from the host and pupated on the rice leaves. In addition, we established
experimental populations of planthoppers that were reared in cages with rice plants
placed on a flat tray filled with water to exclude ants, in an insectary under controlled
Journal of Insect Behavior
humidity (70–80%) and temperature (25–30 °C). We selected parasitoid females of two
to four days of age, as our previous study in this species found that the proportion of
parasitized and predated hosts does not vary during these first days of a parasitoid’slife
(Mora-Kepfer and Espinoza 2009). During the first day that a female emerged as an
adult, it was kept individually (Chandra 1980), and provided with ten third instar
nymphs of T. orizicolus to assure it was not starving before the trial period. We
specifically chose to feed wasps on their day of emergence as adults because starved
parasitoids face a higher risk of sudden mortality (Harvey et al. 2001). Moreover,
starved synovigenic parasitoids may choose not to oviposit and instead exclusively feed
on hosts, or have low fecundity (Ueno and Ueno 2007). While establishing our
parasitoid population in insectary conditions, we observed higher mortality in females
that were not fed the first day compared to the ones that did feed from hosts, which
could have compromised our experimental design for H. hernandezae (Uy, FMK
unpublished data).
Behavioral Assays
To observe behavior, we placed each female in an 8.5 cm × 1.8 cm deep clear Petri dish
with rice leaves and ten host nymphs of the same instar. We did not use instars 1–2in
the behavioral assays, because previous studies show that this species usually only
feeds on nymphs of instars 1 and 2, as they are too small for oviposition and offspring
survival (Hernandez and Belloti 1984; Mora-Kepfer and Espinoza 2009). Thus, we
specifically selected instars 3 and 4 because they are frequently chosen for either
oviposition or predation by Haplogonatopus species (Hernandez and Belloti 1984;
Yamada and Kawamura 1999). Instar 5 was used to check whether manipulation
became more difficult because of the host size. The nymphal instars were selected by
using the morphological criteria described by Mora et al. (2001).
We ran the experiment following our previously established protocol for this species
(Mora-Kepfer and Espinoza 2009), for a total of seven days from 8 am to 12 pm,
following the natural highest availability of hosts in the natural environment of
inundated rice fields in Costa Rica. The experimental protocol is as follows: each
day, a female parasitoid was introduced in a Petri dish for four hours with ten nymphs
of one instar. After this observation period, the female was then housed individually
until the next day. On the following day, she was transferred at 8 am to another
container with ten new nymphs of a different instars for a new observation period.
This procedure was repeated for seven consecutive days (Mora-Kepfer and Espinoza
2009). We rotated the order in which the nymphs of instars 3, 4 and 5 were presented to
the parasitoid, to control for any experience bias. For each attack, we recorded handling
behavior and the final outcome of either oviposition or predation behavior using a
Sanyo Color CCD Camera Model VCC-3912 coupled to the ocular of a dissecting
microscope. We recorded each interaction between the female wasp and the nymphs,
and then transferred each attacked nymph to an individual container. Therefore, each
female parasitoid encountered the opportunity to host-feed or oviposit each individual
planthopper only during one observation period. The outcome of each attacked host
was classified as successful (the female was able to paralyze the nymph and subse-
quently fed on it or oviposited) or unsuccessful (the parasitoid grasped but was not able
to dominate and paralyze the host). To compare the paralyzation time of nymphs in
Journal of Insect Behavior
different instars and their manipulation in successful oviposition and feeding attacks,
we established behavior categories for both the host and the parasitoid. Total and mean
durations (seconds ± SE) of the total handling time and each of the behavior categories
of the parasitoids were calculated. We recorded the duration and frequency of each of
these behavior categories with the program JWatcher (Blumstein et al. 2000). We also
determined a size ratio between the host and the parasitoid in each attack by measuring
the head width of the dryinid (Yamada and Miyamoto 1998) and the total body length
of the host nymph in the video images. We utilized our established method in this
species to determine host instar and size as an indication of host quality (Mora-Kepfer
and Espinoza 2009).
Lastly, we froze several specimens during the specific moment of either oviposition
or feeding attacks using liquid nitrogen. These frozen specimens were placed in a −
20 °C freezer, then transferred still frozen to the −20 °C absolute ethanol. After being
fixed for more than one week, they were brought to room temperature, and then later
dehydrated and sputter coated with gold. Finally, we took photographs of these
specimens in attack mode to test for differences in host-handling between oviposition
and feeding events with a Scanning Electron Microscope.
Parasitoid Handling Behavior
We described and divided the handling time of the parasitoid into two steps: 1)
paralyzation as the period of seizing the host until stinging the host and paralyzing it,
and 2) manipulation as the period of further handling until the achievement of
ovipositing or host-feeding. During the second step of manipulation that led to ovipo-
sition attacks, we observed the following behaviors: a) probing, as when the parasitoid
moved her sting several times along membranes between the abdominal segments of
the nymph to inspect if a host was previously parasitized (Yamada and Kitashiro 2002),
until she pressed against a point in the intersegmental membranes, b) drilling, as the
period from pressing against this specific point to exposing her valvifers, c) oviposition,
as the time between exposing the valvifers, retracting her sting into the third valvulae,
pushing out her valvifers to the greatest extent possible and inserting the egg (Yamada
and Imai 2000; Yamada and Kawamura 1999). In contrast, during the second step of
manipulation that led to host feeding, we observed two consecutive behaviors: a) where
the female grasped the host and directed her mandibles to press against the host body
and b) feeding time, when the wasp fed from the nymph masticating with her
mandibles into the thorax or abdomen tissue of the nymph.
We divided use of the chelae into two categories. The first category of “set”
occurred when a female attacked and then used its chelae synchronously to set the
paralyzed host on the rice leaf so the planthopper nymph had its legs on the
substrate, and would not fall off the rice leaf before recovering from the attack.
After placing the nymph back on the substrate, the wasp released its grasp simulta-
neously with both chelae, the nymph recovered and walked off. The second category
of “dropped”occurred when a female released the host after feeding, in asynchro-
nous motion of its chelae and without placing the nymph’s legs back on the rice leaf.
When dropped, the paralyzed host often fell lopsidedly or with its dorsal side
towards the substrate, often falling off the rice leaf. We also recorded the host body
parts that the wasp grabbed with its chelae.
Journal of Insect Behavior
Host Behavior
We divided host behavior into three categories: 1) resistance, as the period in which the
nymph offered resistance such as kicking, jumping and jerking after being caught by
the parasitoid, 2) paralyzed, as the period in which the nymph showed no movement
after being stung, and 3) recovery, as the period from which the female wasp left the
nymph after oviposition until the host was able to move again and walk. In contrast to
oviposition, feeding events resulted in the host failing to recover and instead dying
from the wound inflicted by the parasitoid.
Statistical Analyses
We performed a Spearman correlation to determine if there was a relation between the
host instar and its size. To analyze whether the proportion of oviposition, feeding and
unsuccessful attacks varied according to nymph developmental stage, we used a Chi-
square test and its standardized residuals. To compare the duration of each behavior
category of the nymphs according to their developmental stages and avoid
pseudoreplication constraints, we performed Repeated Measures ANOVAS. We used
this same test to explore differences in the handling time of the parasitoid and the time
of occurrence of each category of oviposition and host feeding behavior among the
different nymphal stages of the host.
Differences between the final manipulation strategies of the hosts after the predation
and oviposition events were analyzed by using a Chi-square test. To determine if the
number stinging events varied according to the nymphal instars, we employed a
Repeated Measures ANOVA. We analyzed the use of the chelae to grasp the host in
oviposition and predating events by using a Chi-square test. Finally, we also explored
differences in the grasping with the chelae among nymphal instars using a Chi-square
test.
Results
Host and Parasitoid Behavior during Attacks
Out of a total of 199 attacks, 58.3% were successful oviposition events, 21.6% were
successful predation events, and 20.1% were unsuccessful, either because the
planthoppers escaped from the grasp of the wasp (14%) or the planthopper was seized
but then rejected (6.1%). We found a positive relation between the host age and size
(R=0.06, T(n-2)=10.28,N=165, P= 0.001). The percentage of unsuccessful attacks
due to the nymphs escaping was higher for fifth instar nymphs compared to fourth
instars and third instars (χ2=13.31, df=4, P=0.010, N=161,Fig. 1). The handling
time prior to oviposition was also higher as the nymphal instar increased (H = 20.60,
P = 0.00, Fig. 2). In contrast, the handling time prior to feeding did not change in
relation to the host stage (H = 0.94, P= 0.62, Fig. 2).
The time that nymphs resisted an attack varied depending on whether the parasitoid
fed or instead oviposited on a host. Resistance time was longer in older nymphs for
attacks that led to oviposition (H = 23.44, P<0.001,Fig.S1A). However, the resistance
Journal of Insect Behavior
time did not differ for different host instars for attacks that ended in feeding (H = 0.32,
P= 0.85, Fig. S1A). The same tendency was found for the paralyzation time: older
hosts took longer to be paralyzed in attacks that led to oviposition (H = 20.40, P <
0.001, Fig. S2B). The time to paralyze the hosts did not differ among the nymphal
instars in attacks that led to feeding (H = 0.24, P=0.88,Fig.S2B). Finally, the recovery
time was shorter for 5th instar nymphs following oviposition (H = 12.06, P=0.02,
Fig. S2C).
The time to catch and paralyze a host was influenced by host age and the decision to
either feed or oviposit. The time to paralyze a host was greater with older host instars in
attacks that led to oviposition (H= 8.95, P= 0.01), but this trend was absent in attacks
that led to feeding (H = 0.14, P= 0.93). Handling time was also higher for 5th instar
hosts in those attacks that ended in oviposition (H = 20.97, P < 0.001), but not in those
that led to feeding (H = 20.98, P=0.421).
Fig. 1 Effect of host instar on success in oviposition and feeding attacks by females of Haplogonatopus
hernandezae. Events in which the hosts escaped the grasp of the parasitoid were categorized as unsuccessful
attacks
Fig. 2 Time of occurrence (seconds) of each behavior category of the parasitoid to either feed or oviposit in
hosts of different instars. LSD Posthoct Test. Significant differences among attacks towards host instars are
indicated with different letters (P<0.05)
Journal of Insect Behavior
For trials that ended in oviposition, the handling time of hosts after paralysis was
also longer in 5th instar hosts compared to 3rd and 4th instar hosts, both for the probing
period and anchorage time to lay an egg (Table S1). However, once anchoring had
occurred, the time required for oviposition did not vary among host instars (Table S1).
Handling time prior to feeding was not different among the host stages, nor did the
duration of feeding itself (Table S2).
For trials where the planthopper hosts were later parasitized, the number of 4th and
5th instar nymphs that were stung twice by the parasitoid was significantly greater than
for younger hosts (G = 30.47, df = 2, P=0.00, N= 101). In feeding attacks, the most
frequent behavior in all host stages was stinging continuously while the dryinid fed on
the nymphs (G = 7.17, df = 2, P=0.127,N=41).
Host Manipulation after Feeding and Oviposition Events
Close-up video images revealed that the final manipulation of each host after being
attacked differed between trials that let to oviposition or feeding. If the female decided
to feed on a nymph, she paralyzed the host and fed on the dorsal side of the thorax or
abdomen by masticating with her mandibles. With a few exceptions in fifth instar
nymphs, we observed that the wound caused the death of the host, confirming the
observations of our previous study (Mora-Kepfer and Espinoza 2009). The most
frequent behavior of the parasitoid after feeding was to quickly drop the paralyzed
nymph (Fig. 3a.), which fell with its lateral or dorsal side on the substrate or rice leaf. In
some cases, the parasitoid stepped on the nymph it had just fed on as it started to forage
after the attack (N = 10), or released the grip on the nymph and started foraging while
still dragging the nymph with the other chela for a few seconds (N= 8). In contrast,
after the female finished ovipositing on a host, she slowly set the paralyzed host with its
ventral side oriented towards the substrate (χ2=69.13, df=2, P=0.00, Fig. 3a). The
wasp released the nymph simultaneously with both chelae, and after the nymph
recovered from the attack, it walked or jumped when it became active again.
The video images also indicated that the wasp’s chelate forelegs are used for
grasping specific body parts of the host and that this gripping differs in oviposition
and feeding attacks. The female grasped the nymph either by its clypeus (holding the
clypeus of the nymph with one chela and legs or abdomen with the other chela) or other
body structures (holding the host with both chelae the side of the thorax or abdomen or
legs, rather than the clypeus). The clypeus was grasped most frequently in all nymphal
stages after paralysis and until the dryinid either dropped or gently set it on the
substrate, (χ2=28.97, df=1, P< 0.001, Fig. 3a). We also found that the clypeus of
the host is used for grasping with the chelae in attacks that led to oviposition. The
clypeus was gripped significantly more frequently than other host body structures after
the host was paralyzed (χ2= 49.58, df = 1, P < 0.001, Figs. 3band4). However, in
attacks that led to feeding, the wasp did not grasp specific body structures of the host.
Discussion
Our findings provide novel evidence for differences in host-handling behavior between
oviposition and feeding attacks, which provide evidence for the role of host instar in the
Journal of Insect Behavior
choice of investing in current reproduction, or instead feed from a host presumably to
secure resources for future reproduction. In H. hernandezae, females chose hosts for
either oviposition or feeding based on host size, which is similar to other parasitoids
(Gross 1993; Wang and Messing 2004). Although we did not measure host quality
directly, our results are consistent with the hypothesis that size may be correlated to the
nutrient content of the host (Vinson and Iwantsch 1980) and/or the ability of hosts to
evade parasitism and predation (Gerling et al. 1990). That is, our data indicate that even
though a dryinid is capable of handling and attacking nymphs of all instars, manipu-
lation time increased with host age and size. Consequently, the number of successful
attacks that ended in oviposition or feeding were strongly influenced by the nymphal
instar. In addition, older hosts were chosen for consumption more frequently than
younger hosts, while younger hosts were parasitized more often than older hosts. This
result is consistent with other studies suggesting that hosts that are of lower quality and
Fig. 3 aFinal manipulation of each host after either an oviposition or a predation event. bDifferential chela
grasp of host body structures by the female parasitoid during feeding and oviposition attacks
Journal of Insect Behavior
less suitable for oviposition and/or are more difficult to handle are used for feeding,
which ultimately provides the necessary energy for future reproductive efforts when
finding more suitable hosts (Lebreton et al. 2009).
Host Defense and Handling Time
As in studies of other parasitoids, we observed that older host nymphs defended
themselves more vigorously by shaking and kicking when held by a wasp causing
the resistance time to increase (Bokononganta et al. 1995; Rivero 2000). Hence, the
time invested in handling an older, larger host increases in oviposition attacks. Previous
work suggests that oviposition cost (including searching and handling the host) is
related to the time and/or energy expenditure to oviposit an egg (Stephens and Krebs
1986). If laying eggs in different host stages results in different oviposition costs, a
tradeoff exists between offspring rearing conditions and difficulty of oviposition and
host suitability for the offspring (Nishimura 1997).
Handling time prior to oviposition increased with host instar for several reasons.
First, resistance time is significantly greater in older nymphs. That is, a parasitoid may
be able to successfully approach a small host to oviposit, while being less exposed to
the range of the defensive leg kicking, but, in larger hosts, a closer approach may be
needed. This forces the parasitoid to move within the “leg distance”of the host (Gerling
et al. 1990), making it more difficult to sting the host to paralyze it. Our observations
show that older nymphs actively kick the ventral side of the wasp body as it stings the
thorax to paralyze the nymph. Further, body shaking and jumping were more efficient
in older hosts as a strategy to escape than in younger hosts.
Second, after capture, fifth instar nymphs required more investment to be paralyzed
for longer periods compared to younger instars. Searching for a site on the host body to
parasitize also took longer in this instar. Previous studies show that a female of
Haplogonatopus atratus examines the membranes between the host abdominal terga
with her ovipositor before ovipositing to detect if the host has been previously
parasitized (Yamada and Kitashiro 2002; Yamada and Ikawa 2005; Yamada and
Fig. 4 Open chela (ch) of the parasitoid grasping the host face: clypeus (cp) and gena (g). The parasitoid
grasped the host face and anchored its chelated forelegs, and consequently begun to paralyze the host to
initiate oviposition. Scale = 400 μm
Journal of Insect Behavior
Kawamura 1999; Yamada and Sugaura 2003). If a female dryinid located an egg from a
previous oviposition event of another female, the egg was stung to kill this offspring.
This pattern suggests that longer handling and inspecting time with a larger and older
host serves to make sure it has not been previously parasitized (Ito and Yamada 2007;
Ito and Yamada 2006). Thus, older hosts were frequently stung twice, prior to finding a
spot to oviposit. The resistance time for these hosts was longer and more than one
period of paralyzation was necessary to perform a successful oviposition in them
majority of the 5th instar planthopper hosts.
Finally, after paralyzation, anchoring time (during which drilling took place) was
also longer for older nymphs, suggesting a greater difficulty in penetrating the host
cuticle. This pattern suggests that the ovipositor sheaths possibly serve as an anchor
during the initial phases of the process (Vilhelmsen 2003). This results coincides
with observations for other parasitoids, in which a strong correlation was found
between the cuticle thickness of the host and oviposition success (van Lenteren et al.
1998). As such, last instar nymphs become more costly in energy and time-
consumingtohandle.
Overall, our results suggest that increased handling time for older hosts may favor
parasitoids in using them for feeding. Alternatively, because the hosts may develop into
adults soon, parasitoids may favor younger hosts to assure that the parasitoid offspring
will have enough time to develop and leave the host to pupate. That is, choosing the
appropriate host instar is essential for the survival of the developing parasitoid larva due
to differences in growth rates and time limitations (Roitberg and Bernhard 2008). A
female adult of T. orizicolus lives on average 31 days and males live less at an average
of 14.6 days (Gomez Sousa and Kamara 1980), and H. hernandezae larva can take up
to 27 days to develop inside the host (Mora-Kepfer and Espinoza 2009). In a previous
study, we found that H. hernandezae chooses female nymph hosts for oviposition and
males hosts are fed upon, suggesting ovipositing in female nymphs will allow enough
time for the parasitoid larva to develop and result in successful current fitness (Mora-
Kepfer and Espinoza 2009).
Host-Handling Behavior
Host-handling behavior likewise varies between oviposition and feeding attacks, spe-
cifically in the grasping of the host by the chelae and the final manipulation after the
attack. The clypeus was the body structure of the host most frequently used for grasping
in oviposition attacks. The particular chela morphology, having an enlarged claw with
subapical tooth and six lamellae, and segment 5 of the front tarsus having two rows of
nearly eight lamellae (Olmi 1984), facilitates efficient grasping of the host. This
suggests the unexpected observation that the function of the particular chela morphol-
ogy is to specifically grasp the clypeus and gena of T. orizicolus.
When a wasp decided to feed on a nymph, stinging, which was used both to grasp
and paralyze was continuous, caused damage to the host body. The clypeus and other
body parts were used frequently for grasping since the feeding did not need to be in a
specific site. Instead, the parasitoid fed from anywhere on the thorax or the abdomen.
The host was subsequently killed by destructive feeding and dropped. As predation
events are single encounters, the host age or the manipulation that a nymph receives has
no further consequences on the future reproduction of the parasitoid.
Journal of Insect Behavior
In contrast, when a female decides to lay an egg, she must manipulate the host
carefully to assure that her progeny will be able to survive and develop successfully.
Our observations showed that in oviposition attacks the wasp grasped the host precisely
by the clypeus and either the tip of the abdomen in young nymphs or a leg in older
instars. After the dryinid oviposited, she set the nymph carefully with its ventral side
towards the rice leaf by releasing the grip of the chelate forelegs simultaneously, which
allowed the host to recover from being paralyzed and hold on to the rice leaf. Rice
fields in Costa Rica are frequently flooded; therefore, this behavior might save the
parasitized host from falling into the water while still paralyzed to assure the successful
recovery of this nymph, and the survival of the parasitoid egg that will develop inside
the host.
Conclusions
Our study shows an effect of host instar on the decision to either oviposit or feed. The
subsequent handling behavior also differed between these two choices as hosts used for
oviposition were handled more carefully after oviposition, suggesting that the host
carrying the parasitoid’s egg will have a higher probability of recovering and surviving
after being paralyzed in a flooded rice field. In contrast, hosts that were used for feeding
were handled carelessly and did not recover from the attack. Although our results do
not directly test future fitness, they provide novel evidence for costs and benefits of
manipulation of hosts of different instars, and choice of current fitness versus feeding
according to nymphal instar, as a proxy of host quality. Thus, the decision to feed or
oviposit may be influenced by the assessment of available host instars, the investment
in handling a host of a specific developmental instar, and the tradeoff between current
and future reproductive fitness by the parasitoid. Our findings raise new questions
about the mechanisms that influence decision-making and differential behavior in
parasitoids. Future studies that include manipulations of the physiological state of the
parasitoid and host density to explore its effect on offspring survival, would provide
key insights into the mechanisms underlying the tradeoff between current and future
reproduction.
Acknowledgements We thank C. Barboza and R. Mora-Castro for their assistance in maintaining the
planthopper and parasitoid colonies in the insectary of the Centro de Biología Celular y Molecular
(CIBCM) of the University of Costa Rica. P. Hanson, W. Eberhard, A. Uy and W. Searcy, and members of
the Uy and Searcy labs provided insightful comments on this manuscript. We are grateful to M. Vargas for
Scanning Electron Microscope images. The filming equipment was provided by the Animal Behavior
Laboratory at the Department of Biology, University of Costa Rica.
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Affiliations
Floria M.K. Uy
1,2
&Ana Mercedes Espinoza
3,4
1
Escuela de Biología, Universidad de Costa Rica, San Pedro, Costa Rica
2
Department of Biology, University of Miami, Coral Gables, FL 33124, USA
3
Centro de Investigaciones en Biología Celular y Molecular, Universidad de Costa Rica, San Pedro, Costa
Rica
4
Escuela de Agronomía, Facultad de Ciencias Agroalimentarias, Universidad de Costa Rica, San Pedro,
Costa Rica
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