ENTOMOPHAGA 35 (2), 1990, 195-202

O V I P O S I T I O N P A T T E R N BY COTESIA A Y E R Z A I [HYM. : BRACONIDAE]

O N ASCIA M O N U S T E [LEP. : PIERIDAE] U N D E R L A B O R A T O R Y C O N D I T I O N S

N. GOEBI (I), M. C. A. CUNHA (2), R. ZUCCHI (2) & H. G. FOWLER (1)

(~) Departamento de Ecologia, Instituto de Biocirncias, Universidade Estadual Paulista (UNESP), 13500 Rio Claro,

Sao Paulo, Brasil (2) Departamento de Biologia, Faculdade de Filosofia, Ci~ncias

e Letras de Ribeirao Preto (USP), 14100 Ribeirao Preto, Sao Paulo, Brasil

Various aspects of the parasitism of caterpillars of Ascia monuste orseis by Cotesia averzai, were studied in laboratory choice tests. Individual ~ were found to be extremely variable in ovipositional duration, as well as in the number of eggs oviposited. To simulate parasitoid dispersal, or low host density, we isolated 25 for 60 min following initial exposure and compared our tests with ~ which had not been isolated. No differences in (1) the number of eggs oviposited per host instar ; (2) the conditional probability of host encounter ; (3) host acceptance ; and (4) the conditional probability of instar specific parasitism were found between these groups. Held ~?$ did, however, reject hosts after ovipositor insertions in a higher proportion.

KEY-WORDS : Cotesia, Ascia, parasitoid, Brazil, cabbage, behavior, parasitism.

In the Neotropics, species o f the braconid genus Cotesia are parasitoids of the cabbage butterflies, Ascia monuste orseis (Godart) (Lima, 1948 ; Lordello & Rodrigues, 1953 ; Link,

st th 1977). Recently, Gobbi & Cunha (1983) experimentally confirmed that the 1 to 4 instars of A. monuste were suitable hosts for a gregarious parasitoid, Cotesia ayerzai (Br&hes), based upon the criterion of parasitoid development. However, these results were derived from experiments in which C. ayerzai ~ were presented a single caterpillar for parasitism. As the incidence of field parasitism of A. monuste by C. ayerzai is quite variable (Lordelio & Rodrigues, 1953 ; Link, 1977), additional knowledge of the host selection behavior of C. ayerzai becomes evident. Do the same patterns of host suitability from no choice experiments apply to conditions in which parasitiaids must actively search and choose among available hosts ?

In order to answer this question, we performed a series of choice experiments, and at the same time we simulated an interruption of parasitoid search to also evaluate the effects of adverse weather or dispersal. Our interruption experiments were also based upon some practical considerations. Does handling parasitoids in the laboratory affect host selection or ovipositional behavior ? As behavior has been shown to be an important factor in the evaluation of biological control agents (Cook & Hubbard, 1977 ; Hendrikse & Zuechi,

196 N. GOBBI, M. C. A. CUNHA, R. ZUCCHI & H. G. FOWLER

1979 ; Waage, 1983), we included the study of some basic behaviors in our data acquisition procedures. Our data are of some importance in the evaluation of dield rates of parasitism (Van Driesehe, 1983), as well as for the production of this parasitoid under laboratory conditions.

MATERIALS AND METHODS

Caterpillars of A. monuste were obtained from both laboratory and field collected egg masses. C. ayerzai were laboratory reared on caterpillars from field collected stock. Caterpillars were reared in wooden boxes, 19 x 20 x 5 cm, and fed leaves of cabbage, Brassica oleraceae L. Adult parasitoids were maintained in glass vials, 6.0 cm (diameter) x 10.5 cm (high), and given a sugar solution presented in cotton. For all experiments reported here, female parasites used for studies varied from 2 to 5 days after adult emergence.

To evaluate ovipositional behavior as well as the number of eggs per oviposition, we presented unexperienced female parasitoids to 2 nd instar caterpillars. Females were remo- ved from the caterpillars after only one bout of oviposition, timed by a digital chronometer.

Host instar preference was studied following the suggestion of Van Lenteren & Bakker (1975), who demonstrated that inexperienced ~ have a lower level of host discrimination than is found in experienced ~ . To mimimize this effect, we subjected each tested female of C. ayerzai to a 5 min ovipositional contact with caterpillars. At the end of this period, each female (n = 17) was immediately transferred to a 6.6 cm diameter Petri plate. During the proximate 60 min, 10 unparasitized caterpillars, consisting of 2 of each of the 5 larval instars of A. monuste which had been individually marked previously, were placed on a fresh cabbage leaf and presented to the parasitoid within the Petri plate.

Another series of experiments was performed in a similar manner to evaluate the effect of interruption of search behavior. After a 5 min contact period with 2 nd instar host caterpillars, individual ~ (n = 12) were held for 60 min in glass vials before being presented with 2 individuals of each host larval instar, as previously described.

During each of the 29 replicate choice tests, which were run individually, notes on the general behavior of the parasitoid, host acceptance and rejection, and stinging behavior were recorded. Because of distinct behavioral differences, we distinguished 2 types of stinging activity. Long stings, which corresponded to ovipositional activity, lasted various seconds, while quick stings Consisted of rapid insertions of the ovipositor within a 5 second time interval.

All caterpillars, after having been parasitized, were maintained an additional 2 days on cabbage leaves. Caterpillars were then frozen at - 18 *C, and posteriorly dissected for counts of parasitoid eggs under a dissecting microscope.

All statistical tests were performed using the appropriate parametric (Sokal & Rohlf, 1981) or non-parametric tests (Siegel, 1956). In particular, the Kolmogrov-Smirnov test was used for distribution comparisons.

RESULTS

On the 221 second instar caterpillars ofA. monuste exposed to one ovipositional bout by C. ayerzai, a considerable variation in both the duration of the ovipositional bout and the number of eggs laid per female per bout was found (fig. I). The mean number of eggs oviposited per caterpillar was 18 ___ 7.1, with ranges from 3 to 35, over a mean duration of 8.8 + 3.06 s (fig. 1). Based upon the number of eggs per ovipositional bout, optimal ovipositional duration was 11 s (fig. 1).

O V I P O S I T I O N P A T T E R N O F COTESIA A Y E R Z A I 197

=. , t l . r _ ~ ' ~ I.d,.. /=/~ ~, ~ .--

o ~1 "

> 1 I o

n ~0 +- , ' / . ' " " - T

o ~ -- ~--I~'/S/' "%~t o .

CUMULATIVE SECONDS OF OVIPOSITION

Fig. I. The relationship between the duration of an ovipositional bout and the egg output of C. ayerzai o n

2 ''d instars of its host, .4. mmmste.

In choice tests, the conditional probability of host encounter by searching C. ayerzai ~ was found to increase with later host instars (fig. 2). No significant differences, using the G statistic, were found between qTq7 held for 60 min after initial host exposure, and those not held, for encounter rates on the same host instar (fig. 2). However, significantly more 3 ra

th st nd th and 5 instar hosts were found in comparison with I", 2 and 4 instars (fig. 2). A simple allometric null hypothesis, starting with an initial value observed for I st instar caterpillars and subsequently progressing by Dyar's constant, reasonably fit the observed patterns (fig. 2). However, 4 th instar larvae deviated significantly from the expected pattern when compared with the G statistic (fig. 2).

No significant differences were found between the 2 treatment groups of C. ayerzai in the st nd number of eggs oviposited per host instar (fig. 3). Nevertheless, 1" and 2 instars had a

higher ovipositional load than found in other instars (fig. 3). Due to the large variation in individual ovipositional intensity by female C. ayerzai, however, no significant differences were found among host instars in terms of egg loads, although a trend of declining ovipositional intensity with increasing later host instars was detected (fig. 3).

No significant differences were found between ~7 held or not held in terms of their acceptance of host caterpillar instars (fig. 4) and probability of host instar parasitism (fig. 5). In our behavioral observations, we found also no significant differences in the number of short and long ovipositional insertions, but we did find differences in the number of ovipositional insertions leading to rejection between treatment groups (table 1). In these observations, there were significant differences between our female parasitoid groups for the I st t O 3 rd host larval instars, with previously exposed and held qT~ demonstrating significantly more insertions associated with rejection for the 1st to 2 "a host

198 N. GOBBI, M. C, A. CUNHA, R. ZUCCHI & H. G. FOWLER

>" 1"0 r [ ] NOT HELD FEMALES

t 2 3 4 5 CATERPILLAR INSTAR

Fig. 2, The conditional probability of host encounters in choice tests using equal numbers of instars of the host caterpillar by searching ~ of C. ayerzai. Parasitoids were either held for 60 rain after initial exposure, or not held and released directly in our choice tests. Also shown is the expected encounter probability based upon a simple allometric growth equation for the host larval instars.

Z I o_ t - u) o n

m =E

Z 2O

c~

: " tC < t~ =f

NOT HELD FEMALF.,f

HELD FEMALES

t 2 3 4 5

CATERPILLAR INSTAR

Fig. 3. The number of eggs deposited by C. ayerzai $~ on different host instars in choice tests. Parasitoid treatment groups are given in fig. 2.

OVIPOSITION PATTERN OF COTESIA A YERZAI 199

t.0

~ G 8

o.

0.6

.<

t 2 3 �9 4 5

CATERPILLAR INSTAR

1

Fig. 4. The conditional probability of host acceptance after encounter by Cotesia ayer:ai q~9 on different larval instars of the host, Ascia monuste. Parasitoid treatment groups are as given in fig. 2.

l - in

o.2

o '11 2 3 4 5

CATERPILLAR JNSTAR

Fig. 5. The conditional probability of successful parasitism (oviposition) of each host caterpillar instar by Cotesia ayerzai. Probabilities were derived from information presented in figs. 2 and 4. Parasitoid treatment groups are given in fig. 2.

instars, and significantly less for the 3 rd. These behaviors, however, did not influence the overall evaluation of parasitoid activity (figs. 4 and 5).

DISCUSSION

Upon placing C. ayerzai females in containers With cabbage leaves and A. monuste caterpillars, the parasitoids initially explored intensively. This exploratory activity consis- ted in antennating the cabbage leaves until a host caterpillar was found. Upon detection of a host, the ovipositor was immediately inserted into the host, often without a continual antennal contact o f the host. Frequently, the parasitoid would insert the ovipositor into a cabbage leaf, or deposit eggs on the container wall. A similiar behavior has been reported by Sato (1976) for Cotesia ( = Apantales)glomeratus L. Furthermore, the parasitoid female apparently located caterpillar hosts in a proportional function of host size (fig. 2), even

200 N. GOBBI. M. C. A. CUNHA, R. ZUCCHI & H. G. FOWLER

TABLE I Comparisons between ~ held for 60 rain after initial exposure to hosts and ~- not held in terms of

ovipositor insertions and host rejection

Number of ovipositor insertions per host instar Condition/outcome Total

ISt 2ha 3rd 4th 5 th

Not held ~$/ rejected 3 2 8 4 19 46 accepted 18 22 25 12 6 83

Held ~ / rejected 22 13 3 5 11 54 accepted 22 10 11 8 12 63

G. statistic 8.394 13.605 13.439 0.606 4.114 2.804

The 95 % probability levels associated with the G statistic, based upon the X2 statistic with 1 degree of freedom is 7.879 or greater.

though the earlier instars have fewer defenses than later instar caterpillars. Defense by caterpillars consisted principally of expelling a viscous liquid through the mouth, which, when in contact with the parasitoid, caused fouling and motor deficiencies of the parasitoid. It should be emphasized that the rejection of 5 th larval instars of the host by C. ayerzai (table I), reflect this effect. However, parasitoid females were often able to free themselves of this liquid, and subsequently resumed ovipositional activity, following a thorough cleaning behavior. A similar behavior has been previously reported for C. glomeratus (Huffaker & Messenger, 1976), which is also able to attack and parasitize various larval instars of the cabbage butterfly, Pieris brassicae L., and can repeatedly attack the same larva. As in C. ayer-ai. C. glomeratus has a greater difficulty in parasitizing larger instars, due principally to the defensive behavior of the host, leading to an avoidance on the part of the parasitoid (Huffaker & Messenger, 1976). Moreover, Hendrikse & Zueehi (1979) have shown that Opius pallipes Wesmael is unable to parasitize as successfully larger instars of its host, Liromyza bryoniae Kalt, because older instars are more mobile and have thicker external membranes.

Our ovipositional results (fig. 1) are similar to those reported by Sato (1976) with C. glomeratus, who found an output of 7.7 to 13.3 and 24.3 to 25.4 eggs per host caterpillar on Pieris melete Men6tri6s and Pieris rapae crucivora Boisdval, respectively. However, our data demonstrate a significant individual variability in both ovipositional duration and egg output, which has also been reported in field studies of other parasitoids (Waage, 1983). The proportion of ovipositor insertions which resulted in host rejection were significantly different for parasitoids held for 60 min after initial exposure, and those not held (table 1). However, in spite of this behavioral difference, host encounter rate, host acceptance, ovipositional intensity, and oviposition (figs. 2-5) did not differ between held and not held $~. Therefore, the significance of this behavioral difference remains unclear, although operationally it does not lead to parameter modification. However, the interruption of ovipositional activity, as should occur in low host density or during parasitoid dispersal, was not found to alter host encounter rates or parasitism rates. This suggests that C. ayerzai should be a behaviorally flexible parasitoid for use in A. monuste control programs.

OVIPOSITION PATTERN OF COTESIA A YERZAI 201

Our results shed addit ional light on the results o f Gobbi & Cunha (1983), who found that parasitized 5 th instar caterpillars o f A. monuste failed to yield viable adult parasitoids, and that a higher percent o f viable aduldt parasitoids was associated with earlier larval instars. Thus, this system may be an ideal candidate for opt imizat ion analysis in which higher encounter rates o f later instars, a l though at lower densities, are offset by reduced parasitoid product ion. Such an approach could yield explanations o f the apparent fluctuations in the reported data o f the few field studies o f parasitism rates o f A. monuste (Link, 1977; Lordello & Rodrigues, 1952).

ACKNOWLEDGMENTS

Funding for our studies was provided by the CNPq (Brazil) and the FFCL-Ribeirao Preto provided laboratory and support facilities during our studies. UNESP-Rio Claro provided conti- nuing support for our research. We thank Luis De Saatis for the identification of C. ayerzai, and Nozor Pinto for inking the figures.

RESUME

Exemplc d'oviposition en conditions de laboratoire de Cotesia ayerzai [Hym. : Braconidae] sur Ascia monuste [Lep. : PierMae]

Divers aspects du parasitisme par Cotesia ayerzai des chenilles d'Ascia monuste orseis ont 6t6 6tudids au laboratoire par des essais de choix. La dur6e de ponte, comme le nombre d'oeufs d6pos6s, sont extr6mement variables d'une femelle fi I'autre. Pour simuler la dispersion du parasitoide ou une faiblc densit6 d'h6tes, nous isolons les femelles durant une heure aprds l'exposition initiale et comparons nos essais avcc les femelles qui n'ont pas 6t6 isol6es. I1 n'y a aucune diff6rence entre ces groupcs : (I) dans le nombre d'~eufs d6pos6s par stade h6te - - (2) dans la probabilit6 de rencontre de l'h6te - - (3) dans I'acceptation de I'h6te et (4) dans la probabilit6 d'un parasitisme sp6cifique d'un stade. Cependant les femelles emprisonn6es ne rejetaient pas les h6tes apr6s des insertions de la tari6re dans une plus grande proportion.

MOTS CL~S : Cotesia, Ascia, parasito'ide, Br6sil, chou, comportement, parasitisme.

Received : 7 March 1988 ; Accepted : 21 December 1988.

REFERENCES

Cook, R. M. & Hubbard, S. F. - - 1977. Adaptive searching strategies in insect parasites. - - J. AnOn. EcoL, 46, I 15-125.

Gobbi, N. & Cunha, M. C. O. de A. - - 1983. Observaqoes preliminares referentes ao relacionamento entre a lagarta de Ascia monuste orseis [Lepidoptera, Pieridae] e seu parasita Apanteles ayerzai [Hymenoptera, BraconMae]. - - Naturalia (Sao Paulo), 8, 193-196.

Hendrikse, A. & Zucebi, R. - - 1979. The importance of observing parasite behaviour for the development of biological control of tomato leafminer [Liromyza bryoniae Kalt.]. - - Med. Fac. Landbouww Ryksuniv. Gent., 44, 107-116.

Huffaker, C. B. & Messenger, P. S. - - 1976. Theory and practice of biological control. - - Academic Press. New York.

Lima, A. da C. - - 1948. Entom6fagos sul americanos de insetos (parasitas e predadores) nocivos ;i agricultura. - - Bol. Soc. Bras. Agron., il, 1-82.

202 N. GOBBI, M. C. A. CUNHA, R. ZUCCHI & H. G. FOWLER

Link, D. - - 1977. Observaqoes sobre algumas lagartas que danificam a couve, em Curitiba, PR. Dusenia, 10, 201-204.

Lordello, L. G. E. & Rodrigues, R. R. - - 1952. Estudos sobre Ascia monuste orseis (Godart, 1818) [Lepidoptera, Pieridae]. ~ An. Esc. Sup. Agr. Piracicaba, 9, 181-184.

Sato, Y. - - 1976. Experimental studies on parasitism by Apanteles glomeratus [Hymenoptera, Braconidae]. I. Parasitization to different species of the genus Pieris. ~ Appl. Entornol. Zool., 11, 165-177.

Siegel, S. - - 1956. Non-parametric statistics for the behavioral sciences. - - McGraw Hill. New York. Sokal, R. R. & Rohlf, F. J. - - 1981. Biometry. 2 na Ed. - - W. H. Freeman and Co. New York. Van Driesehe, R. G. - - 1983. Meaning of 'percent parasitism' in studies of insect parasitoids.

Environ. Entomol., 12, 1611-1622. Van Lenteren, J. C. & Bakker, K . - 1975. Discrimination between parasitized and unparasitized

hosts in the parasitic wasp, Pseudeucolia bochei : a matter of learning. - - Nature, 254, 417-419. Waage, J. K. - - 1983. Aggregation in field parasitoid populations : foraging time allocation by a

population of Diadegma [Hymenoptera : Ichneumonidae]. - - Ecol. Entomol., 8, 447-453.