Biological Control 150 (2020) 104346 Contents lists available at ScienceDirect Biological Control journal homepage: www.elsevier.com/locate/ybcon The additive effect of a stem galling moth and a competitive plant on T parthenium weed under CO2 enrichment ⁎ Asad Shabbira,b, , K. Dhileepanc, M.P. Zaluckid, Steve W. Adkinsb a The University of Sydney, School of Life and Environmental Sciences, Camden 2570, Australia b School of Agriculture & Food Sciences, The University of Queensland, Gatton 4343, Australia c Biosecurity Queensland, Department of Agriculture and Fisheries, Ecosciences Precinct, Boggo Road, Dutton Park 4102, Australia d School of Biological Sciences, The University of Queensland, St Lucia 4072, Australia GRAPHICAL ABSTRACT ARTICLE INFO ABSTRACT Keywords: Parthenium weed (Parthenium hysterophorus) is a highly invasive plant that has invaded many parts of world Plant competition including Australia. The present study reports on the effects of rising [CO2] on the performance of one of its Biological weed control biological control agents, stem-galling moth (Epiblema strenuana) when combined with a competitive plant, Epiblema strenuana buffel grass (Cenchrus cilliaris). The study was carried out under controlled environment facilities during Parthenium hysterophorus −1 2010–11. P. hysterophorus when grown under elevated [CO2] of 550 µmol mol , produced a greater biomass Climate change − (27%), attained greater stature (31%), produced more branches (45%) and seeds plant 1 (20%), than those −1 grown at ambient [CO2] of 380 µmol mol .Buffel grass reduced the biomass and seed production of P. hys- terophorus plants by 33% and 22% under ambient [CO2] and by 19% and 17% under elevated [CO2], respec- tively. The combined effect of buffel grass and E. strenuana reduced dry biomass and seed production by 42% and 72% under ambient [CO2] and 29% and 37% elevated [CO2], respectively. Although the suppressive effect was different between ambient and elevated [CO2], the effect is likely to be retained. Stem gall formation by E. strenuana significantly enhanced the lateral branch production in plants grown under both [CO2]. Epiblema strenuana did not reduce the seed production of P. hysterophorus under the elevated [CO2] nevertheless, our earlier study had confirmed that many of the seeds produced under such conditions are not filled. This study has highlighted that the additive suppressive effect of E. strenuana and buffel grass on P. hysterophorus growth would be retained under future atmospheric CO2 enrichment. ⁎ Corresponding author at: The University of Sydney, School of Life and Environmental Sciences, Camden, NSW 2570, Australia. E-mail address: [email protected] (A. Shabbir). https://doi.org/10.1016/j.biocontrol.2020.104346 Received 16 June 2019; Received in revised form 9 June 2020; Accepted 11 June 2020 Available online 17 June 2020 1049-9644/ Crown Copyright © 2020 Published by Elsevier Inc. All rights reserved. A. Shabbir, et al. Biological Control 150 (2020) 104346 1. Introduction competition), one P. hysterophorus seedling with two buffel grass seedlings (high competition), and one buffel grass seedling alone Parthenium weed, Parthenium hysterophorus L. (Asteraceae) is a (control) with four replicates per treatment. Eight pots were set up for highly problematic invasive weed of natural and agricultural ecosys- each treatment and the controls. All plants were watered daily with a tems across many countries (Adkins and Shabbir, 2014; Shabbir et al., hand-held sprinkler. 2019a). A native of Mexico and southern United States of America, P. hysterophorus has now invaded c. 50 countries in Asia, Africa and 2.2. Epiblema strenuana Oceania (Shabbir et al., 2019a). In its introduced range, this plant has become a serious weed of crop and pasture lands, forests and national Galls of E. strenuana were harvested randomly from ragweed parks (Adkins and Shabbir, 2014). The negative effects of P. hyster- (Ambrosia artimissifolia L.) or P. hysterophorus plants growing in a pas- ophorus are not limited to environment and agriculture, it is reported to ture near Kilcoy, south east Queensland in November 2010. Upon be a significant allergen in both humans and domestic animals (Ahmed harvest, the stem galls were packed (six per bag) into ziplock plastic et al., 1988; McFadyen, 1995). bags and brought back to the plant processing laboratory at the In Australia, biological control is the underlying approach used to University of Queensland. When the P. hysterophorus plants growing manage P. hysterophorus supplemented by other strategies (Dhileepan alone or in combination with buffel grass were 6 weeks old, two 2nd and McFadyen, 2012). Epiblema strenuana Walker, a stem-galling moth, instar larvae were carefully removed by hand from the galls and was introduced into Australia from Mexico as a biological control agent transferred to the middle of the leaf rosette of the P. hysterophorus of P. hysterophorus in 1982 (McClay, 1987; McFadyen, 1992). It is now plants, using a fine paint brush. Observations of transferred larvae widespread and effective as a biological control agent. (Dhileepan and showed that all entered the growing tips of the rosette within 24 h. McFadyen, 2012). Epiblema strenuana is active throughout the growing season and can complete its life cycle within 4–6 weeks, with an 2.3. Experimental approach and facilities average of 6 to 7 generations per season in central and north Queens- land (McFadyen, 1987). Galling by E. strenuana can significantly sup- The effect of E. strenuana, in the presence or absence of buffel grass press the vegetative and reproductive growth of P. heterophorias, with (C. ciliaris) upon the vegetative and reproductive capacity of P. hyster- the impact being more pronounced if the plants are young when in- ophorus growing under an ambient or elevated [CO2] was assessed. Half itially attacked (Dhileepan, 2001), or if competitive pasture plants, such of the pots (32), were distributed onto the surface of three steel benches as buffel grass (Cenchrus cilliaris L.) are sown within P. hysterophorus in a completely randomized fashion (1.0 × 1.0 × 1.5 m; l × w × h) infestations (Navie et al., 1998). and placed inside a CER with an ambient CO2 concentration − Sowing competitive pasture plants in P. hysterophorus invaded pas- (380 µmol mol 1) and the other half distributed in the manner onto tures had shown potential to suppress the growth of P. hysterophorus three benches in an identical CER where the [CO2] concentration had −1 under field conditions (Shabbir et al., 2020), and when tested under been elevated (550 ± 10 µmol mol ). The ambient [CO2]of −1 simulated grazing (Khan et al., 2019). Further, this strategy worked 380 µmol mol represent the atmospheric [CO2] of 2010–11 while −1 additively with biological control agents to suppress the weed growth elevated [CO2] 550 µmol mol is predicted [CO2] for 2050 and seed production (Navie et al., 1998; Shabbir et al., 2013, 2015, (Anonymous, 2012). The CO2 levels were set and maintained by an ADC 2018, 2020). For instance, two competitive plants, Astrebla squarrosa CO2 monitor (ANRI Instruments and controls, Victoria) attached to a G C.E. Hubb. and Clitoria ternatea L. additively act with E. strenuana to size CO2 cylinder containing food grade gas (for details see Shabbir suppress seed production of P. hysterophorus by up to 73 and 81%, re- et al., 2014). The temperature inside both CERs was set to 30 ± 2/ spectively under ambient [CO2](Shabbir et al., 2020). 18 ± 2 °C (day/night) each with a thermoperiod of 12 h day and 12 h Rising [CO2] levels may affect the growth of plants, and perfor- night (7:00 pm to 7:00 am) and a RH of 65 ± 5%. The day light in- − − mance of their biological control agents (Johns and Hughes 2002; tensity inside each of the CERs was c. 400 µmol m 2 s 1 at the level of Stiling and Cornelissen, 2007; Robinson et al., 2012). Our earlier study the plant canopy. The climatic parameters set inside the CERs provided demonstrated that E. strenuana, can significantly suppress P. hyster- favourable growing conditions for P. hysterophorus (Navie et al., 1996). ophorus biomass and seed fill under elevated [CO2](Shabbir et al., The environmental conditions in each CER room were controlled 2019b). However, it is unknown how E. strenuana might interact with a through a centrally located and hanging sensor, monitoring tempera- competitive plant under a changing climate, involving [CO2] enrich- ture and relative humidity, attached to a computer. In addition, the ment. light, RH and temperature levels were also manually measured fort- The aim of this study was to investigate if there could be any in- nightly to double check the maintenance of uniformity of the conditions teraction between the biological control agent, E. strenuana and a inside each CER. The location of each pot upon the benches was ran- competitive plant, C. cilliaris, in suppressing P. hysterophorus growth domly rearranged every 14 days to minimize location effects. The de- and reproduction under elevated [CO2]. veloping plants were watered daily with tap water and using a hand- held sprinkler. 2. Materials and methods 2.4. Data collection 2.1. Plant husbandry The experiment was harvested 120 days (Nov 2010–March 2011) Seeds of P. hysterophorus and buffel grass were obtained from the after its start. Upon harvest, the height (from soil level to the tip of the University of Queensland seed bank and were sown into four seedling tallest leaf) and basal stem diameter (taken at soil level with a set of trays (35 × 30 × 6 cm; l × w × h) containing a commercial potting Vernier callipers) of each of the P. hysterophorus plants. The numbers of mix moistened to field capacity with tap water. The trays were placed in flowers and branches produced by each plant were counted, then the a controlled environment room (CER) set at a temperature regime of plants were cut at soil level and all of the aerial parts were placed in- 30/18 ± 2 °C (day/night), with 60% relative humidity (RH).