Control Methods and Planning

Evaluating Tools and Methods using the Integrated Pest Management Approach

Integrated Pest Management

Integrated Pest Management, or IPM, is a process that relies on knowledge of the pest’s behavior and population dynamics to design the most effective combination of methods for managing the pest. These can include cultural, mechanical, chemical, and/or biological control tools. A fundamental principle of IPM is to select those methods, or combination of methods, that are feasible, efficacious, and yet most protective of non-target resources, including wildlife, the public, and the environment. The IPM framework requires establishing action thresholds, monitoring, and ongoing evaluation of the effectiveness and the risks of the control methods selected. The target pest activity must be monitored within the treatment area and, following principles of adaptive management, the methods may be adjusted or changed to respond to pest behavior, pest population levels, and non-target impacts.

However, the basic information on rodent and mongoose behavior and population dynamics in non-urban and non-agricultural areas, and the analysis of the best available control methods has not yet been researched, vetted, and documented as a common resources.  The Draft PEIS process will attempt to accomplish this.

Evaluation of methods

A number of specific methods will be evaluated for possible use within this IPM framework. These include: (1) mechanical traps and multi-kill devices; (2) the use of the rodenticides diphacinone, chlorophacinone, and brodifacoum; (3) the ways that rodenticides could be applied (in bait stations, tree canopy baiting, broadcasting rodent bait pellets by hand, or from aircraft over large and/or remote areas).  These methods will be evaluated for viability, efficacy, potential non-target impacts, cost, and other factors on a range of possible scenarios (size of control area, environmental factors, complexity of habitat, etc.).  Providing all the known information in one document can aid in the planning for rodent and mongoose control projects.

Mechanical options:

Live Traps: Cage traps of a variety of designs allow an animal to enter through an open door which closes when the animal steps on a plate or pulls at a bait. Food baits, scent lures, or visual lures are used to attract the animal into the trap. The animal may be euthanized or released unharmed. Examples of traps used in Hawaii include Hagaruma, Tomahawk, and Havahart.

Kill Traps: A food bait is placed on a triggering mechanism that releases a spring-loaded bar designed to break the animal’s neck. The animal is pinned down by the bar. Traps may be placed inside bait stations, Coreflute tunnels, or wooden boxes to exclude birds and other nontarget animals. Examples of traps used in Hawaii include Victors, KaMates, and DOC 250s.

Multi-kill Devices: These devices are defined under FIFRA Sec 2h as an instrument intended for trapping or destroying a pest, and includes a type of device manufactured in New Zealand that is being used for rat and mongoose control in Hawaii (Goodnature®). The animal sticks its head inside a vertically placed plastic tube, touches a trigger in front of a scent lure inside the top of the tube, and compressed carbon dioxide gas from a canister fires a piston into the side of its head. Unlike traps, the animal drops out of the device onto the ground, and the device can be triggered by new animals for as long as gas remains in the canister, up to 21 to 24 times, according to the manufacturer.

Rodenticide options:

Brodifacoum, chlorophacinone, and diphacinone are anticoagulants. Anticoagulants act by inhibiting the clotting of blood and also damage the small blood vessels. Symptoms include bleeding nose and gums, extensive bruises, anemia, fatigue, and difficulty breathing. Symptoms are delayed until clotting factors circulating in the blood are used up and no new factors are made in the liver to replace them. This can take from several days to more than a week. Whether or not an individual survives depends on the amount of anticoagulant consumed and the duration of time they are exposed. Also, an animal suffering from anticoagulant poisoning may be more vulnerable to predators because of weakness and abnormal behavior, and also to dying from other causes such as starvation, hypothermia, and otherwise minor injuries. Susceptibility to anticoagulants varies among individuals and among species.

There are two categories of anticoagulants. First-generation anticoagulants were developed in the 1950s, and include diphacinone, chlorophacinone, and warfarin (also called Coumadin). Diphacinone and warfarin have been used extensively as human pharmaceuticals to prevent and treat blood clots. Because they are excreted more rapidly by the body, the first-generation anticoagulants must be consumed over a number of days before enough accumulates to cause an effect. This significantly lowers the risk of poisoning to nontarget species, because a single exposure is usually not enough to cause symptoms. First generation anticoagulants persist in animal tissues for days to a maximum of a few weeks. Diphacinone and chlorophacinone are the most commonly used rodenticides to protect crops worldwide, and are also available to the public for use in and around buildings.

The second-generation anticoagulants were developed in the 1970s and 1980s. There are four compounds: brodifacoum, bromadiolone, difenacoum, and difethialone. They bind more tightly in the liver and are excreted more slowly, so they can persist in tissue for months. They are toxic in lower doses and in shorter exposures (from a single feeding to a day or two of feeding) than are the first-generation anticoagulants. They are not used in agriculture and are restricted to use in bait stations in and around buildings. However, despite being limited to uses around buildings, they are the most commonly found rodenticides in wildlife worldwide and in Hawaii. The EPA in 2008 limited the public’s ability to purchase the second-generation anticoagulants, and in 2014 the state of California banned their sale to and use by the general public because of the widespread exposure of the second-generation anticoagulants to many species of wildlife.

Baits of all of these rodenticides contain extremely low concentrations of the active ingredient: 0.0025% (25 parts per million) for brodifacoum, and 0.005% (50 parts per million) for diphacinone and chlorophacinone. The other proportion of the baits consists of grain, dye to color the bait, flavorizers, and nontoxic fillers, all of which are contained in formulas proprietary to the manufacturers.

All uses of rodenticides are regulated by the U.S. Environmental Protection Agency and the State of Hawaii Department of Agriculture, Pesticides Branch.

Rodenticide Application Methods:

Bait Stations: Bait is placed into a sturdy plastic box with several holes allowing the target animal to enter and feed on the bait. Bait stations are required to exclude nontarget animals from accessing bait, and prevent bait from being removed from the stations by rodents.

Canopy baiting (also referred to as bola baiting): Bait is placed in plastic or cloth bags and then placed into the canopy of trees or shrubs using poles or sling shots.

Hand Broadcast: Bait pellets are flung by hand or by using a hand-operated mechanical spreader by applicators walking along parallel transects. The pellet density (number of pellets on the ground per unit area) must be at the application rate specified on the product label.

Aerial broadcast:  Bait pellets are dispersed from an agricultural spreader bucket suspended from a helicopter at an application rate specified on the product label.   When the pilot remotely triggers open a gate at the bottom of the conical hopper, the pellets flow out through an aperture onto a motor-powered spinner which flings them over 360 degrees in swaths many meters wide as the helicopter flies in parallel paths over the application area. A GPS (Global Positioning System) in the helicopter records the flight paths, which are downloaded when the helicopter lands into a GIS (Geographic Information System) program to produce maps of where the bait was applied and at what density. Pellet density on the ground (application rate) and swath width are determined by a number of factors, including width of the aperture, flight speed, height of the helicopter, wind speed, and terrain. Prior to the treatment, the application rate must be calibrated by the pilot using placebo pellets or the rodenticide pellets, in an area where the pellet density can be measured on the ground. Pellet density should also be measured in subsamples of the treated area, but if the area is too remote or too dangerous to access, then the calibration rate can be used to estimate the application rate.