HODGE, KEESING, WRATTEN: INDUCED DEFENCES IN KAWAKAWA 91

SHORT COMMUNICATION

Induced defences in kawakawa (Macropiper excelsum): do caterpillars avoid previous leaf damage?

S. Hodge, M. Barron1 and S. D. Wratten* Ecology and Entomology Group, PO Box 84, Lincoln University, Lincoln, New Zealand 1Present address: AgResearch, PO Box 60, Lincoln, New Zealand *Corresponding author (E-mail: [email protected])

______Abstract: This study examined whether two species of lepidopteran larvae ( scriptaria and Epiphyas postvittana) were deterred from feeding on the leaves of kawakawa (Macropiper excelsum) after the leaves had been damaged in three different ways: by larval feeding, using a hole punch or a metal rasp. A hierarchy of choice experiments was performed in the laboratory, examining the feeding ‘preference’ of these between undamaged or previously damaged tissue within the same leaf, between different leaves and between different plants. On no occasion did larvae of either species show a significant preference for undamaged or damaged leaves. It is concluded that, on present evidence, kawakawa does not have a system of induced chemical defences which deters the feeding of these two insects. ______Keywords: Kawakawa; Macropiper excelsum; Cleora scriptaria; Epiphyas postvittana; induced defences; herbivory.

Introduction Hodgeet al. (1998), however, found that kawakawa leaves subjected to herbivory or artificial damage were Kawakawa (Macropiper excelsum (Forst. f.) Miq.; not rendered less acceptable to C. scriptaria larvae. In Piperaceae) possesses a range of anti- compounds. their experiments, larvae were not presented with any Leaf material is toxic to the larvae of Musca domestica feeding choice and the conclusion was that damage did L. (Diptera: Muscidae) and deters feeding in some not reduce the palatability of the leaves. No information other insects (Russell and Lane, 1993). A number of was obtained on whether the larvae would have fed on bioactive compounds have been identified in kawakawa undamaged leaves given the freedom to do so. leaves, including juvadecene, myristicine and novel The aim of this investigation was to assess the lignans related to the juvenile hormone mimic sesomolin potency of any wound-induced defences in kawakawa (Russell and Fenemore, 1973; Nishida et al., 1983; by performing a series of choice experiments. To Brooker et al., 1987). examine the generality of the response, the larvae of In spite of this range of insect anti-feedant two lepidopteran species were examined; these were chemicals, kawakawa leaves often exhibit a ‘bullet- the primary insect herbivore on kawakawa, C. hole’ pattern, caused by the feeding of the larvae of scriptaria, and the polyphagous lightbrown apple , Cleora scriptaria (Walker) (: Geometridae) Epiphyas postvittana (Walk.) (Lepidoptera: (Beever, 1987). This pattern of feeding is characteristic Tortricidae). of systems of plant defence where damage induces the production of anti-feedant compounds (see Edwards et al., 1985). The deterrent compounds increase in Methods concentration as the herbivore continues to feed and the is eventually impelled to move away. This C. scriptaria larvae (II / III instar) were obtained by process produces a pattern of relatively regularly- beating kawakawa branches in Okuti Valley, Banks spaced, discrete areas of feeding damage, and the Peninsula, New Zealand. These larvae were kept in pattern seen on kawakawa may be an example of this. plastic boxes (24 x 17 x 8 cm) in a controlled

New Zealand Journal of Ecology (2000) 24(1): 91-95 ©New Zealand Ecological Society 92 NEW ZEALAND JOURNAL OF ECOLOGY, VOL. 24, NO. 1, 2000

environment room (20 ±1 oC) with a 16:8 hour light:dark The experiment was repeated using E. postvittana cycle and maintained on a diet of kawakawa leaves. larvae but using only the treatments employing the hole E. postvittana larvae and their rearing diet were obtained punch and rasp to create leaf damage. from HortResearch, Mount Albert Research Centre, Auckland. Damage avoidance between detached leaves Kawakawa seedlings (20 to 50 cm in height) were In the previous experiment, there was a possibility that obtained from the Department of Conservation nursery, damaging one side of the leaf may have induced Motukarara, Canterbury, and from Trees for Canterbury, defensive compounds to occur over the whole leaf, so Christchurch. The plants were maintained in an outside the larvae were not actually presented with a feeding shade house, in polythene planter bags (PB 18; 18 cm choice. This second experiment was carried out to x 18 cm x 32 cm) using a general bark/sand/compost assess whether larvae ‘preferred’ tissue from an potting mix. undamaged leaf compared with that from a separate, previously damaged leaf. Leaves on five undamaged Damaging the leaves kawakawa plants were damaged by each of the three damage techniques outlined above. Five leaves were As the induced defences of some plants respond allocated to each damage treatment on each plant. differently to damage caused by insect feeding compared Twenty-four hours after the leaf damage had been to artificial damage (Karban and Myers, 1989), carried out the leaves were removed as described kawakawa leaves were damaged in three different above. The leaves were then separated into two halves ways. The first method used a metal punch to create by cutting longitudinally through the midrib and one holes (4 mm diameter) in the leaves. This removed half was placed on moist filter paper in a Petri dish. A discrete areas of leaf tissue, mimicking the pattern of matching half, obtained from undamaged leaves on natural damage. The second method involved crushing control plants, was then placed alongside each of the the leaf against a steel rasp, which created an array of damaged leaf halves. A single C. scriptaria larva was punctures (c. 12 punctures per cm2) in the leaf without then placed in the centre of each dish. The position of removing leaf tissue. The third method used II / III the larva (damaged or undamaged leaf half) was instar C. scriptaria larvae contained in muslin bags tied recorded 1 hour and 24 hours after introduction to the around a leaf and allowing them to feed. This latter dish. treatment assessed whether herbivory or general damage The experiment was repeated using E. postvittana led to the induction of chemical defences. Twenty- larvae but using only the treatments employing the hole four hours were allowed after damage (or, for the punch and rasp to create leaf damage. C. scriptaria damage, 24 hours after the larvae were introduced to the leaf) for the development of any Damage avoidance within a plant responses to wounding (see Nelson et al., 1983). In the previous experiment, there was a possibility that removing the leaves from the plant and bisecting them Damage avoidance in detached leaves may have induced the production of any chemical defences, so masking the effects of experimental leaf These experiments examined whether larvae preferred damage. To counter that problem, an experiment was intact areas of a leaf, compared with those parts which carried out which retained the damaged and undamaged had suffered some previous damage. Leaves on five leaves on the plant. Twenty-five kawakawa seedlings undamaged kawakawa plants were damaged on one (approximately 20 cm high with 8 to 10 leaves) had side of the midrib. Five leaves on each plant were alternate leaves damaged using a hole punch. The allocated to each of the three damage treatments seedlings were placed into individual nylon mesh cages described above. Twenty-four hours after leaf damage, (1m x 1m x 1m), maintained at room temperature o the leaves were removed from the plant by cutting (c. 20 C) and illuminated using two halogen bulbs the base of the petiole with a scalpel. The leaves (Phillips TLD 58W). One C. scriptaria larva was were placed individually on a moistened filter paper placed on the upper leaf 24 hours after the plants were inside plastic Petri dishes (9 cm diameter). A single damaged. The position of the larva was recorded C. scriptaria larva was then placed in the centre of each (damaged or undamaged leaves) 1, 3, 6 and 24 hours leaf. The position of the larva (damaged or undamaged after introduction to the plant, excluding any ambiguous side of the leaf) was recorded 1 hour and 24 hours later. larval positions. Any ambiguous larval positions, such as straddling the Damage avoidance between plants middle of the leaf or on the lid of the Petri dish, were not included in the data (similarly in the experiments In the previous experiment, there was a possibility that described below). damaging some leaves on a plant caused an induction HODGE, KEESING, WRATTEN: INDUCED DEFENCES IN KAWAKAWA 93

of defences in all leaves. To counter that problem, in Results this experiment the damaged and undamaged leaf treatments were confined to separate plants. Kawakawa The results of the all the choice tests are summarized in seedlings were matched into pairs according to height. Table 1. On no occasion was there a significant One plant had each of its leaves damaged by using a preference for the undamaged (or the damaged) leaf hole punch, with 4-6 holes per leaf depending on the tissue by C. scriptaria or LBAM larvae (2 with Yates’ size of the leaf. The other seedling was retained as a no- correction applied to account for 1 d.f.). Using a 2 test damage control. The pairs of seedlings were placed with Yates’ correction for a single degree of freedom beside each other in a 1m x 1m x 1m nylon mesh cage, can be conservative, especially when the number of maintained as above. Twenty-four hours later, a single replicates is small. This can lead to a Type II statistical C. scriptaria larva was placed on top of one of the error, where the null hypothesis is erroneously accepted seedlings; half the larvae were placed initially on the due to the low power of the test (Zar, 1984). However, damaged plant and half on the controls. The plants the distribution of the larvae between the control and were close enough so that their leaves overlapped, damaged leaves was generally fairly even, and when providing the larva with easy opportunities to cross considering the distribution of all the larvae at 1 hour between plants. The position of the larvae was then and at 24 hours there was no significant difference recorded (damaged or undamaged plants) 1, 3, 6 and 24 found from a predicted median of 50% of larvae on the hours after introduction to the plants. Twenty-one control leaves (Wilcoxon test; N=11; P> 0.4 for both 1 replicates were used. hr and 24 hrs).

Table 1. Distribution of C. scriptaria and E. postvittana larvae between damaged and undamaged kawakawa leaves, expressed as total numbers of individuals. ______Comparison Species of Damage made larvae tested technique Time Control Damaged 2 P ______Within a leaf C. scriptaria Hole punch 1 hr 10 11 0 1.00 24 hrs 7 14 1.71 >0.10 File 1 hr 990 1.00 24 hrs 10 10 0 1.00 Cleora 1 hr 13 10 0.17 >0.50 24 hrs 13 11 0.04 >0.80 Between split leaves Hole punch 1 hr 10 13 0.17 >0.50 24 hrs 13 17 0.30 >0.50 File 1 hr 9 7 0.06 >0.75 24 hrs 15 11 0.35 >0.50 Cleora 1 hr 8 15 1.56 >0.20 24 hrs 11 10 0 1.00 Within a plant Hole punch 1 hr 11 10 0 1.00 3 hrs 14 8 1.14 >0.20 6 hrs 18 9 2.37 >0.10 24 hrs 15 10 0.64 >0.30 Between plants Hole punch 1 hr 12 9 0.19 >0.50 3 hrs 12 9 0.19 >0.50 6 hrs 11 10 0 1.00 24 hrs 10 11 0 1.00 Within a leaf E. postvittana Hole punch 1 hr 5 10 1.07 >0.25 24 hrs 4 11 2.40 >0.10 File 1 hr 4 12 3.06 >0.05 24 hrs 10 6 0.56 >0.30 Between split leaves Hole punch 1 hr 4 11 2.40 >0.10 24 hrs 9 10 0.00 1.00 File 1 hr 12 6 1.39 >0.20 24 hrs 13 6 1.89 >0.10 ______94 NEW ZEALAND JOURNAL OF ECOLOGY, VOL. 24, NO. 1, 2000

Discussion though see Mauricio and Bowers, 1990). These hypotheses concerning the mechanism behind the There have been a number of critiques of experiments feeding pattern of C. scriptaria larvae require further examining induced defences, on the grounds that no investigation. account is taken of possible induction between leaves, or between stems (e.g., Fowler and Lawton, 1985; Neuvonen and Haukioja, 1985). Damaging one leaf Acknowledgements may induce the production of defensive compounds in another, undamaged leaf, so that there are no real We thank Merv Spurway for maintaining kawakawa plants, Anne Barrington for providing LBAM larvae, experimental ‘controls’ (see Wratten et al., 1984). This and Kim at Trees for Canterbury and Jorge Santos at has been accounted for in the present study by using a Motukarara Nursery for providing the plants. Thanks hierarchy of experimental systems; these examined a to Chris Frampton for statistical advice. larva’s response to damage within a leaf, between leaves and between plants. The feeding position of C. scriptaria larvae was not affected by previous damage to kawakawa leaves. References Although these larvae are nocturnal in the field, in the Beever, R.E. 1987. The holes in the leaves of kawakawa laboratory they fed throughout the day and were almost (Macropiper excelsum). Auckland Botanical always found close to the most recent feeding damage. Society Newsletter 42: 9-11. It is probable, therefore, that feeding position of the Brooker, S.G.; Cambie, R.C.; Cooper, R.C. 1987. New larvae - rather than just ‘resting’ position - was measured. Zealand medicinal plants. Heinemann Publishers, The larvae showed no avoidance of damaged leaves Auckland, N.Z. and have previously been shown to feed at a similar rate Chapin, F.S. III; Bryant, J.P.; Fox, J.F. 1985. Lack of on damaged leaves as they do on undamaged leaves induced chemical defence in juvenile Alaska (Hodge et al., 1998). woody plant in response to stimulated browsing. Kawakawa is the primary host of C. scriptaria and Oecologia 67: 457-459. it can be speculated that this herbivore has evolved Edwards, P.J.; Wratten, S.D.; Cox, H. 1985. Wound some tolerance of the constitutive defences of the plant induced changes in the acceptability of tomato to (Levin, 1976). Because of the close association between larvae of Spodoptera littoralis: a laboratory assay. the two species, it is also plausible that C. scriptaria has Ecological Entomology 10: 155-158. evolved a tolerance of any induced compounds that Fowler, S.V.; Lawton J.H. 1985. Rapidly induced kawakawa produces. However, the polyphagous larvae defenses and talking trees: The Devil’s advocate of the LBAM also showed no avoidance of damaged position. American Naturalist 126: 181-195. leaves, supporting the hypothesis that kawakawa does Heinrich, B. 1979. Foraging strategies of caterpillars; not have any major system of induced defences. leaf damage and possible predator avoidance Although induced defences are widespread they are by strategies. Oecologia 42: 325-337. no means a general rule (Chapin et al., 1985; Fowler Hodge, S.; Keesing, V.; Wratten, S.D.; Lovei, G.; and Lawton, 1985) and it appears that kawakawa lacks Palmer, J.; Cilgi, T. 1998. Herbivore damage and such a system, possibly relying on its suite of constitutive leaf loss in the New Zealand pepper tree. New chemical defences to deter most phytophagous insects. Zealand Journal of Ecology 22: 173-180. From these results, it seems likely that the Karban, R.; Myers, J.H. 1989. Induced plant responses characteristic patchy feeding pattern of C. scriptaria is to herbivory. Annual Review of Ecology and not produced by a larval response to induced defences. Systematics 20: 331-348. Observations in the laboratory suggest the larvae feed Levin, D.A. 1976. The chemical defenses of plants to for short periods and then rest, often by lying along a pathogens and herbivores. Annual Review of petiole or dangling by a silken thread. It can be Ecology and Systematics 7: 121-159. speculated that feeding may be interrupted to allow Mauricio, R.; Bowers, M.D. 1990. Do caterpillars the larvae to digest the host-plant tissue (Reynolds, disperse their damage?: larval foraging behaviour 1990) or to detoxify (or sequester) toxins (Slansky, of two specialist herbivores, Eupydras phaeton 1992). Alternatively, the feeding pattern may (Nymphalidae) and Pieris rapae (Pieridae). result from behaviour evolved to facilitate predator Ecological Entomology 15: 153-161 avoidance (Heinrich, 1979). C. scriptaria larvae are Neuvonen, S.; Haukioja, E. 1985. How to study induced cryptically coloured and exhibit many of the plant resistance? Oecologia 66: 456-457. associated ‘anti-predator’ behaviours (e.g., forage on Nelson, C.E.; Walker-Simmons, M.; Makus, D.; underside of leaves, feed at night, etc.; Heinrich, 1979; Zuroske, G.; Graham, J.; Ryan, C.A. 1983. HODGE, KEESING, WRATTEN: INDUCED DEFENCES IN KAWAKAWA 95

Regulation of synthesis and accumulation of Russell, G.B.; Lane, G.A. 1993. Insect antifeedants - a proteinase inhibitors in leaves of wounded tomato New Zealand perspective. Proceedings of the 46th plants. In: Hedin, P.A. (Editor), Plant Resistance New Zealand Plant Protection Conference: 179- to Insects, pp. 103-122. American Chemical 186. Society, Washington DC, U.S.A. Slansky, F. 1992. Allelochemical-nutrient interactions Nishida, R.; Bowers, W.S.; Evans, P.H. 1983. A juvenile in herbivore nutritional ecology. In: Rosenthal, G. hormone mimic from Macropiper excelsum. A.; Berenbaum, M. R. (Editors), Herbivores; their Archive of Insect Biochemistry and Physiology 1: interactions with secondary plant metabolites, 17-19. Volume 2, pp. 135-174. Academic Press, New Reynolds, S.E. 1990. Feeding in caterpillars; maximising York, U.S.A. or optimising food acquisition? In: Mellinger, J. Wratten, S.D.; Edwards, P.J.; Dunn, I. 1984. Wound- (Editor),Animal nutrition and transport processes. induced changes in the palatability of Betula 1. Nutrition in wild and domestic , pp. 10- pubescens and B. pendula. Oecologia 61: 372- 118. Karger, Basel, Switzerland. 375. Russell, G.B.; Fenemore, P.G. 1973. New lignins from Zar, J.H. 1984 Biostatistical Analysis. Prentice-Hall, leaves of Macropiper excelsum. Phytochemistry New Jersey, U.S.A. 12: 1799-1803.