Notes on the Oviposition Preferences of Uresiphita Maorialis (Felder & Rogenhofer) (Lepidoptera: Crambidae) on Three Sophora Species in Laboratory Conditions
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38 Enrique Mundaca Notes on the oviposition preferences of Uresiphita maorialis (Felder & Rogenhofer) (Lepidoptera: Crambidae) on three Sophora species in laboratory conditions Enrique A. Mundaca Universidad Católica del Maule, Facultad de Ciencias Agrarias y Forestales, Escuela de Agronomía, Casilla 7-D, Curicó, Chile. Email: [email protected] Running title: Oviposition preferences of the kowhai moth Abstract Between 2008 and 2009, and as part of my PhD studies, I carried out a number of short experiments to observe oviposition preferences of the kowhai moth, U. maorialis, on three species of Sophora plants of common occurrence in Wellington urban gardens. The results of such experiments indicate that U. maorialis females prefer Sophora microphylla and S. tetraptera as oviposition substrates when simultaneously confronted with the three choices. Sophora prostrata does not seem to be an oviposition substrate for the female moths. Regardless of the plant species, the adaxial surface of the leaflet was the preferred area to oviposit egg clusters. These results provide preliminary insights that may help to understand the presence of high loads of larvae on individuals of S. tetraptera and S. microphylla normally seen in urban gardens in the Wellington city area. Key words: Wellington urban gardens, kowhai moth, egg clusters. Introduction In New Zealand, U. maorialis is considered to be an ornamental pest, particularly of Sophora (kowhai) plants (Mulvay 1978; Leen 1997). The taxon was formerly treated as a subspecies of U. polygonalis (now U. gilvata), but is currently listed as an endemic New Zealand species (Nuss et al. 2003-2013). In the Wellington city area, especially urban gardens and parks, larvae of U. maorialis can The Weta 46:38-43 39 often be seen defoliating Sophora plants. Although larvae can be observed in most Sophora plants, the species S. tetraptera and S. microphylla seem to show particularly high densities of larvae in their foliage. In an attempt to identify the existence of a specific preference of the kowhai moth for any particular species of Sophora, I selected three species of Sophora plants with a variable range of leaflet morphology, namely, S. tetraptera, S. microphylla and S. prostrata, and exposed them to female moths to test for the existence of oviposition preferences for a particular Sophora species. Methods Three substrates were exposed simultaneously to a gravid female of U. maorialis, in 40×40×40cm experimental cages containing three 10 (± 3)cm twigs, one of each Sophora species. To minimise the potential interference provoked by the larva’s previous feeding experience, the adult moths were obtained from second and third instar larvae collected from the field from S. molloyi plants, and reared in the laboratory in multi-purpose insect diet tubes (Singh 1983) until they reached adulthood. The experiment was carried out by introducing a pair of moths into 3 cages (one pair of recently emerged male and female moths in each cage). The experiment lasted three days, after which dead moths were removed from the cages. Plant twigs were also removed from the cages and examined for the presence of eggs using a stereomicroscope. Simultaneously a control treatment cage, containing S. molloyi non-foliated twigs, was implemented by introducing a pair of recently emerged adult moths (male and female). The purpose of the control cage was to observe the oviposition behaviour of the female moth in the absence of an appropriate oviposition substrate. Moths were fed with a liquid mix of honey–sugar–water located inside each cage during the experiment. Cages were kept in temperature-controlled environments at 22 ± 2°C, with a L16:D8 photoperiod. I recorded the total number of eggs, clusters and the adaxial/abaxial location of the eggs on each host plant. I tested data for normality and variance distribution using Shapiro-Wilk and homoscedasticity tests. 40 Enrique Mundaca Oviposition preferences (number of eggs per treatment), adaxial/abaxial location of the eggs and the interaction between the two factors were analysed through a GLM (Generalised Linear Model) for over dispersed count data with a quasi-Poisson distribution. A Tukey Honest Significance Difference (HSD) post hoc test was used to check for differences among treatments (Sophora species). Results I found differences among the total number of eggs oviposited on the three Sophora species (GLM; degrees of freedom (d.f.) = 2; t = 8.65; P < 0.01) (Figure 1). Figure 1. Mean of number of eggs recorded on each Sophora species in the experimental cages (± SD) (n = 11). Different letters above error bars indicate significant differences between each treatment; same letters indicate no difference between treatments (Tukey HSD pos hoc test, P < 0.01). Sophora tetraptera and S. microphylla were the most preferred plants as oviposition substrates, although I found no differences between these species (P = 0.25). I did not detect oviposition on twigs of S. prostrata or in the control cages. Uresiphita maorialis females laid their eggs in clusters, ranging from a single egg to thirteen eggs on both surfaces of the leaflets. Leaflet surface The Weta 46:38-43 41 showed differences between the number of eggs laid on each leaflet side (GLM; d.f. = 2; f = 8.30; P < 0.01) (Figure 2). Adaxial surface was the preferred side chosen by females to oviposit. Interaction between the host plant species and the leaflet surface was not identified (GLM; d.f. = 2; f = 0.64; P = 0.53), indicating that the selection of plant species and leaflet side were independent of each other. Female moths in control cages died without laying their eggs after a few days of enclosure, suggesting that female moths would rather keep their eggs inside their body than oviposit them on an unsuitable surface. Figure 2. Proportion of eggs recorded on the adaxial/abaxial position of the leaflet for each plant species in the experimental cages (n = 11). Egg clusters typically contained between 2 and 13 eggs. Discussion Uresiphita maorialis is known to oviposit and feed on species of Sophora and other quinolizidine-rich Fabaceae plants (Spiller & Wise 1982; Leen 1997). Oviposition preferences of U. maorialis for particular plant species had not been formally tested before. Although restricted to only three Sophora species, my experiment 42 Enrique Mundaca showed that females mostly oviposit on the adaxial surface rather than the abaxial surface of the leaflet. This result contradicts, to a certain extent, previous reports made by Mulvay (1978) and Leen (1995), who indicated that in Sophora plants the abaxial surface of the leaflets was the preferred area to lay eggs by the female moths. My results, on the other hand, are consistent with my own field observations in the Wellington city area, where I observed most eggs on the adaxial, rather than the abaxial, surface of the leaflets. The test for Sophora species host specificity revealed preferences for S. tetraptera and S. microphylla as oviposition substrates over S. prostrata. Each plant species tested in this experiment possessed a very distinctive leaflet morphology, with S. tetraptera having the longest and widest leaflets and, compared to S. prostrata, having the smallest and more sclerotized leaflets of the three species. It is known that some features of the leaf surface, e.g. trichome density, can influence the female egg-laying preferences as documented for noctuids (Navasero & Ramaswamy 1991). Although my experiments did not control for the physical (e.g. trichome density) or chemical (e.g. quinolizidine concentration) features of the leaflets, these could have influenced the results of this experiment. Such factors should be considered as the next step towards exploring the mechanisms involved in the egg laying preferences observed in this experiment. Acknowledgements I would like to thank Dr. Phil Lester and Dr. Stephen Hartley from Victoria University for supporting my PhD thesis project. Thanks also the Comisión Nacional de Investigación Cientifica y Technológica (CONICYT) – Victoria University Scholarship that allowed me to do my PhD in New Zealand . Finally, I would like to thank Dr. Wan Fatma Zuharah for providing me with the experimental cages, Dr. Alejandro Perez–Matus for assisting me with the data analysis and my wife Dr. Mariana Lazzaro-Salazar for her support and for proof reading this manuscript. The Weta 46:38-43 43 References Leen R. 1995. Biology of Uresiphita reversalis (Guenee) and comparison with U. polygonalis maorialis (Felder) (Crambidae). Journal of the Lepidopterists' Society 49: 163-170. Leen R. 1997. Larval hosts of Uresiphita Hubner (Crambidae). Journal of the Lepidopterists' Society 51: 139-148. Mulvay RT. 1978. Biology of the kowhai moth, Uresiphita polygonalis maorialis. Unpublished. MSc Thesis,. University of Auckland, Auckland, New Zealand. Navasero RC, Ramaswamy SB. 1991. Morphology of leaf surface trichomes and its influence on egglaying by Heliothis virescens. Crop Science 31: 342-353. Nuss M, Landry B, Vegliante F, Tränkner A, Mally R, Hayden J, Segerer A, Li H, Schouten R, Solis MA, Trofimova T, De Prins J, Speidel W 2003–2013. Global Information System on Pyraloidea. - www.pyraloidea.org Singh P. 1983. A general purpose laboratory diet mixture for rearing insects. Insect Science and its Application 4: 357-362. Spiller DM, Wise KAJ. 1982. A catalogue (1860-1960) of New Zealand insects and their host plants. New Zealand Department of Scientific and Industrial Research Bulletin 231, Wellington. 260 p. .