WEEDS, PESTS AND DISEASES No. 59 March 2006 Slug predator identification Key Points · Three species of carabid beetle were commonly found during monitoring of cropping farms in Canterbury. · Lab trials indicate that all three species of carabid beetle will eat slugs with one species being a ferocious predator eating all the slugs. · Many pesticides kill these beneficial beetles even when they eat slugs killed by some slug baits. · Some slug baits are non-toxic to predators. · When adopting an IPM (Integrated Pest Management) approach to pest control, growers have the added bonus of having the pesticide and the beneficials controlling the pest. Introduction Are there predatory species of slugs in NZ? FAR and MAF SFF are funding a three year project to A key part of the IPM project is to identify the natural investigate the potential use of Integrated Pest enemies of slugs in NZ cropping systems. Monitoring and Management (IPM) techniques for slug control. The first laboratory trials over the last year have identified three year of the project involved identifying and monitoring slug main beetle species which prey on at least one life stage of and slug predator populations, and implemention of an pest slugs (Figure 1). IPM strategy being adopted on three cropping farms in Canterbury. These ground beetles are part of a group known as Carabids (Family: Carabidae). They are generalist What is Integrated Pest Management? predators in both juvenile and adult stages. Adults are Intergrated Pest Management (IPM) is a strategy that active foragers and are typically shiny black or metallic in focuses on long-term control of pests (or their damage) colour. through a combination of techniques such as biological control, habitat manipulation, modification of cultural practices, use of resistant varieties and forecasting programmes. Specific pesticides are used only after monitoring indicates they are needed and treatments are applied with the goal of reducing only the target organism (Pest). IPM has been adopted by certain growers and industry due to increasing threat of pest and disease resistance to pesticides. Also there is growing international demand for produce which has been produced with consideration for the environment. One good example in NZ is PipfruitNZ. Use of natural predators Overseas studies have shown that many insect predators A B C play a key role in the control of pests such as slugs and cereal aphids. Figure 1: Three species of carabid beetles from cropping systems that eat slugs However, organophosphates, synthetic pyrethroids or other broad-spectrum insecticides are often employed for A. Megadromus antarcticus – Length: 25-35mm pest control. These not only kill the target pest, but also This large beetle is commonly referred to as the metallic other beneficial insects that could serve as an alternative green ground beetle, due to its shiny metallic green colour. control method. It is a ferocious predator and ate all slug species in all size classes presented to it during the lab trials. The IPM approach involves pest monitoring and, when B. Metaglymma moniliferum – Length: 15-20mm necessary, selective chemicals which are benign to the This black medium sized carabid ate small/juvenille sized environment and beneficial organisms. This allows the slugs only (up to 10mm long). numbers of natural enemies (of pests) to increase over time so that they contribute to long term slug control, in C. Holcaspis angustula – Length: 12-16mm conjunction with the use of more benign chemical This small black carabid ate only freshly hatched slugs. insecticides. PDF created with pdfFactory trial version www.pdffactory.com The following information is from feeding trials in the What are the perceived risks? laboratory. The aim of the lab trial was to determine if Many growers are concerned about adopting IPM because these species of carabids found in arable cropping they feel that yields will be affected because: systems (in Canterbury) are physically capable of 1. the recommended chemicals in IPM may not be as overcoming the slugs defence mechanisms. As preference good at controlling the insect pest as other chemicals experiments have not been conducted, we don’t yet know 2. expectation of high levels of damage before the what proportion of their diet is potentially made up of slugs predator populations build up enough to control the versus other insects and molluscs. What we do know is pest. that these carabids readily accept slugs as prey. However, this is not the case. Growers need to What is the distribution and seasonality of the carabid consider: predators? · The long term solution – are we prepared to apply Three farms had pitfall traps installed to assess the chemicals every year for the rest of our cropping lives? relative abundance and activity of ground beetles. A pitfall · Are current pesticide based controls effective? trap is a container holding a small amount of preservative · The threat of resistance to pesticides. liquid (e.g. diluted antifreeze), which is buried so that the · Markets/policies limiting pesticide use. edge of the container is at ground level. Beetles are · Side effect of pesticides to non target species. trapped when they inadvertently fall into the pitfall. 1. Efficacy of products On the farms surveyed, the metallic green ground beetle Growers using IPM friendly chemicals rely not only on the was found in lowest numbers. The two smaller species pesticide but the natural predators for control, compared to were more abundant. The greatest numbers of beetles just relying on the chemical alone. were recorded on a conventionally tilled farm where pesticides (slug baits & aphicides) had not been used. Lab trials by Crop & Food Research have shown that baits which were less harmful to the beetles (Fig 2) were just as There has been very little research carried out on slug effective at killing slugs (Fig 3). predators in NZ cropping systems. It appears from our observations (and the literature that is available) that the ) 120 % ( species of carabids involved here live for one or more e 100 v years. That means that our observations to date are on i l a existing populations of beetles and any change due to IPM 80 Control s is yet to be seen. Many predators over-winter within field g EDTA u l 60 s Metaldehyde boundaries before moving into the crop during spring. e However, we expect that the cropping system itself can be g 40 Methiocarb a t made more favourable for these carabids and the n e 20 c populations within paddocks will increase. r e P 0 Threats to carabid populations 0 1 2 3 Most pesticides, including slug baits not only kill the target pest, but other beneficial insects that also serve as a Days after baiting control method. Figure 3: Slug survival after consuming three types of slug Lab studies conducted by Crop & Food Research have bait in lab trials shown that carabid beetles can die of secondary poisoning after preying on slugs that have fed on baits (Figure 2) 2. Levels of crop damage Levels of crop damage should be kept to a minimum as ) chemicals can be applied to the crop before the pest % 120 ( population increases. Once established, beetles assist with e v i 100 l pest control throughout the season, keeping pest a s 80 populations at low levels. For example, slug control is e l t EDTA generally targeted only during crop establishment but slugs e e 60 continue to reproduce throughout the season if conditions B e 40 Metaldehyde are suitable. g a t n 20 Methiocarb e c How to monitor beetle populations r e 0 Growers can monitor their own paddocks to see if they P 0 1 2 3 have carabid beetles using the same methods used to Days after baiting monitor slugs. Solid wooden tiles will provide a refuge for them. Carabid beetles can be found under tiles, especially if the tiles are left in the same position for several weeks. Figure 2: Percentage of beetles surviving after consuming slugs which had fed on three types of slug bait Acknowledgements Information for the article was supplied by Dr P Horne (IPM Chemicals used to control aphids for example, can also Technologies) & A Horrocks (Crop & Food Research). remove beetle predators along with other beneficial insects, such as lacewing and ladybird larvae which feed ÓThis publication is copyright to the Foundation for Arable Research and on aphids. may not be reproduced or copied in any form whatsoever without their written permission. This Arable Extra is intended to provide accurate and adequate information relating to the subject matters contained in it. It has Growers adopting an IPM approach will need to consider been prepared and made available to all persons and entities strictly on the all pest treatment options during the lifetime of the crop. basis that FAR, its researchers and authors are fully excluded from any Secondary effects of all pesticide inputs need to be liability for damages arising out of any reliance in part or in full upon considered so that application does not kill the beetles and any of the information for any purpose. No endorsement of named other beneficials that will contribute to pest control. products is intended nor is any criticism of other alternative, but unnamed product. PDF created with pdfFactory trial version www.pdffactory.com.