CHAPTER 9: ALIEN INVERTEBRATE CONTROL PROGRAM Summary This chapter describes the status and outcome of actions carried out under the direction of the Oahu Army Natural Resource Program (OANRP) Alien Invertebrate Control & Research Specialist which, this year, included the successful renewal of a Special Local Needs (SLN) permit for the use of Sluggo in natural areas. Modifications to the permit are discussed here and were implemented following its expiration and renewal in October 31, 2015. We increased our slug control efforts to include eight vulnerable plant populations thereby expanding the Sluggo application area by 65%. Details on which species are protected and their locations are outlined in section 9.1. This year we completed research aiding in the development of a rat bait with slug-repellent properties. We found that the addition of 5% citric acid to the rat bait repelled slugs while remaining attractive to rodents. The complete study appears in section 9.2. We continue to survey for and assist in the control of two incipient invertebrate pests which have not yet naturalized: the Coconut Rhinoceros Beetle (Oryctes rhinoceros) and the Little Fire Ant (Wasmannia auropunctata), as well inspecting high risk areas for invasive ants (Hymenoptera, Formicidae). None have been detected in 2015-2016 in areas surveyed (Schofield Barracks and surrounding environs). The status of those efforts are reported in section 9.3 and 9.4. 9.1 SUMMARY OF SLUG CONTROL ACTIONS JULY 1, 2015-JUNE 30, 2016 Background: Slugs can cause dramatic declines in the survival of rare native Hawaiian plants (Joe & Daehler 2008). Control of slugs using the organic molluscicide Sluggo® (trademark omitted from the rest of this document) (Neudorff, Germany) was shown to encourage seedling germination and recruitment of certain rare plant species (Kawelo et al. 2012) in particular those within the Campanulaceae. In 2010 Sluggo was approved for forest use by the Hawaii Department of Agriculture (HDOA) under a Special Local Needs (SLN) permit. We solicited, and received, letters of support from agencies which use this product for rare plant conservation. We included these, as well as our research since 2010 (http://manoa.hawaii.edu/hpicesu/dpw_slug.htm) pertaining to slug control and compiled it into a single application packet for Sluggo SLN renewal (the permit expired October, 31 2015). Some modifications to the prior label were requested by the Department of Land and Natural Resources (DLNR) because of concerns about non-target impacts to native snails. The previous label stated: “Do not apply in areas where it may come into contact with known populations of endemic Hawaiian snail species from the following rare families or subfamilies: Amastridae, Achatinellinae and Endodontidae. Bait must not be applied within 20 m of any tree known to harbor endangered Hawaiian tree snails (Achatinella spp.).” It now instructs: “Do not apply within 20 m of known populations of endemic Hawaiian snail species from the following rare families or subfamilies: Amastridae, Achatinellinae and Endodontidae.” Achatinella, though not mentioned by name in the new label, remains protected as it is included in the subfamily Achatinellinae. The approved label appears in Figure 1 with the new wording highlighted. It may be accessed online via the HDOA webpage (http://hawaii.gov/hdoa/labels/sln/1004_2020.pdf). Notice that the tradename has been changed from FirstChoice to LeafLife Sluggo. The subregistratant (Loveland), the manufacturer (Neudorff) and the formulation remains the same, as well as the EPA registration number. HDOA confirmed that the SLN is valid for both Sluggo products. 2016 Makua and Oahu Implementation Plan Status Report 241 Chapter 9 Alien Invertebrate Control Program Figure 1: Renewed Sluggo SLN permit. It is valid through October 27, 2020. Changes from the previous label are highlighted. This SLN has made large scale slug suppression possible around rare plants in the wild. In response, OANRP has expanded its slug control program every year since the SLN approval in 2010. Though this remained the case in 2015-2016, we discontinued slug control at two reintroduced plant populations: Cyanea superba subsp. superba (population reference code PAH-A; hereafter referred to as C. superba) in the Pahole Natural Area Reserve (NAR) and Phyllostegia mollis (population reference code EKA-D) in the Ekahanui Forest Reserve. In the case of P. mollis, by May 2016, only one plant remained and did not justify continued effort (Table 1, row one shows a decrease in slug control). While a number of C. superba persist in Pahole, we are shifting our efforts towards Palikea where the ratio of seedling recruitment per mature pant is much higher (see C. superba 5 Year Plan in this document). We controlled slugs to order to protect 8 species in 9 Management Units (MUs) across an area equal to 7 acres, a 65% increase (in area) from the previous year (4.2 acres) (Fig. 2). Rare plant species which received Sluggo treatments at a rate of 1 lb. Sluggo per 184 m2 per month (half the maximum label rate) appear in Table 1. New or expanded areas receiving slug control this year are shown in bold. Two populations are remote and only receive Sluggo once every 6 to 8 weeks (marked with *). 2016 Makua and Oahu Implementation Plan Status Report 242 Chapter 9 Alien Invertebrate Control Program Table 1: List of rare plant species treated monthly with Sluggo. Bold lettering indicates changes from the prior year. An asterisk (*) indicates remote populations which receive Sluggo at a reduced rate. MU Plant species treated (Population Reference Treatment area Sluggo required Code) (m2) per treatment (lbs.) Ekahanui Cyanea grimesiana subsp. obatae (EKA-C) , 2,950 (-1,282) 16 (-7) Delissea waianaeensis (EKA-D), Schiedea kaalae (EKA-D) Kahanahaiki Cyanea superba (MMR-E & MMR-H), S. 1,650 9 nuttallii (MMR-E), S. obovata (MMR-C & MMR-G) Kaluaa and Delissea waianaeensis (KAL-C), S. kaalae 3,500 (+ 1,900) 20 (+ 11) Waieli (KAL-B) Makaha Cyanea longiflora (MAK-B), C. grimesiana 2,450 (+ 450) 13 (+ 3) subsp. obatae (MAK-B), S. obovata (MAK-A), S. nuttallii (MAK-A) Opaeula Cyrtandra dentata (OPA-F*) 1,000* 5.5* Lower Pahole Schiedea nuttallii (PAH-D & PAH-E), C. 8,496 (+ 5,496) 46 (+ 30) grimesiana subsp. obatae (PAH-D), S. kaalae (PAH-C), Euphorbia herbstii (PAH-G & PAH-R, PAH-F & PAH-S), C. longiflora (PAH-A & PAH-I) Palikea Cyanea grimesiana subsp. obatae (PAK-A & 4,625 (+ 2,405) 25 (+13) PAK-B), C. superba (no pop code), Phyllostegia hirsuta (PAK-A) Upper Schiedea kaalae (KAP-A) 1,100 (+ 394) 6 (+ 2) Kapuna West Cyanea longiflora (LEH-B), S. obovata (LEH- 2,461 (+ 1,265) 13.5 (+7.5) Makaleha A, LEH-C & LEH-B*) 2016 Makua and Oahu Implementation Plan Status Report 243 Chapter 9 Alien Invertebrate Control Program Figure 2: Locations of rare plant species within Managament Units (MUs) undergoing slug control in the Waianae Mountains. A single slug control site in the Koolau Mountains (Opaeula Lower) is not shown. 9.2 DEVELOPMENT OF A RAT BAIT WITH SLUG-REPELLENT PROPERTIES Introduction: Slugs are generalist feeders that are attracted to the peanut butter baits used in rat traps (both A24 automatic and Victor snaps). Bait consumption by slugs is an impediment to successful rat control in a number of ways. Slugs can consume all of the bait or make it less attractive to rats (via slime) and large slugs can trigger the snap traps. Our goal was to determine whether citric acid added to a peanut butter bait at a 5% concentration would repel slugs while remaining attractive to rats. For the purposes of these experiments, we used food grade 100% granular citric acid. We conducted three studies in pursuit of these goals. Study 1 involved a two-choice food experiment wherein captive slugs were offered the peanut butter bait with and without citric acid to investigate food preference. Here we refer to the former (5% citric acid) bait as the ‘test’ bait and the latter as the ‘control’ bait. Study 2 involved a single-choice feeding experiment wherein captive slugs were provided only the test bait for two weeks to reveal whether they would consume it if faced with starvation. In both Study 1 & 2 we used GoodNatures Rat Lure. This is the lure regularily used in the A24 traps. Study 3 was a field trial wherein we investigated whether Victor snap traps set with test and control baits caught similar 2016 Makua and Oahu Implementation Plan Status Report 244 Chapter 9 Alien Invertebrate Control Program numbers of rats after a two week period. For the final study we used Skippy brand peanut butter for the bait as this is the standard bait we use for our Victor snap traps. Study 1: Slug food preference experiment. Methods: Fifty slugs were collected from the Waianae Mountains in Oahu during the month of March 2016 (Table 2). These were kept moist and fed lettuce, carrots and Beneful brand dog food until the start of the trial on April 19th. Slugs were not starved prior to this experiment. The trial ended two weeks later on May 3rd. During this period slugs were kept in individual plastic containers and offered 2 g of the test and 2 g of the control bait, dyed with red and green food coloring respectively. Small slugs (<3 g in weight) were housed in 3 ounce cups 7 cm in diameter while larger ones (>3 g) were placed in 8 ounce cups 11 cm in diameter (Fig. 3). Every 48 hours, each slug and their baits were weighed, cages cleaned of feces, and observations made on the condition of the bait such as whether any evidence of feeding occurred (radula marks) or whether mold was present.