Using natural enemies (predators, parasites, parasitoids) to reduce pest populations is defined as biological control. There are three main types:

1. Classical: introducing a natural enemy of exotic origin to permanently control a pest that is also from the same region.

A successful example of classical biological control in Hawaii is the control achieved of the spiraling whitefly (Aleurodicus dispersus), which attacks numerous tree crops and plumeria and transmits plant diseases. Entomologists traveled to the home range of this pest and released three species of predatory beetles and two parasitoid wasps to control the spiraling whitefly. Now, when there are outbreaks of this pest, it is because the natural enemies have been eliminated from those areas. Thus, this insect is not a pest so long as the introduced predators and parasitoids are also present.

2. Augmentative: the mass rearing and release of natural enemies already present in a region.

A local example is that of the melon fly (Bactrocera cucurbitae), a pest of ivy gourd and other cucurbit crops. Two parasitoids naturalized in Hawai'i were mass reared and released on the North Shore of Oahu to control the melon fly, with some field success at pest suppression.

3. Conservation (CBC): enahncing the habitat of natural enemies.

This can be achieved by incorporating insectary plants into the landscape to attract prey and serve as alternative food sources (nectar and pollen) for predators, and providing cover for predators like spiders and ground beetles by mulching and leaving brush piles. Insectary strips are also shown to help with pollination services in Hawaiian cucurbits. 

All of these biocontrol methods are conducive to healthy pollinator communities as they promote the reduced need for pesticides, agricultural diversity, and enhance floral resources, all of which otherwise contribute to pollinator declines.

Adjusting farm management styles to make the crop environment less suitable for pests is called cultural control. There are four methods that can be incoroprated into control strategies:

1. Reducing and disrupting pest habitat around crops. Sanitation practices, such as removing crop residues that may host pests, is one way to remove pest habitat in a field, though this would limits plant materials available as green manure, particularly in no-till systems. Removing non-crop pest habitat, such as non-crop host plants, also removes habitat reservoirs, though this may also mean removing habitat for natural enemies and pollinators. Tilling is another way to disrupt pest habitat, though this also breaks up soil aggregates and could contribute to weed issues.

2. Diverting pests away from crops. Trap cropping is when you plant the same or a similar preferred host species away from your crop field in order to draw pests out of the harvestable area. Once they have been "trapped" in this additional habitat, they can be targeted with pesticides or left to compete with each other. Strip harvesting is another means of diluting pest pressures at harvest. Instead of harvesting an entire field at once, which could mobilize all pests to an adjacent field, harvest smaller patches at a time.

3. Adjusting planting schedules to interfere with pest life cycles. Crop rotations are a very effective way at interrupting the life cycles of pests, whether they are insects or microbial. Dissimilar crops may be located near each other to reduce the visual and chemical cues the pests may be drawn to. Weather permitting, crop planting times can be adjusted such that the crop is in the ground after the pest has peaked, or are planted early and harvested early before pest populations have a chance to reach critical thresholds.

4. Reducing overall yield losses. Plants have an immune system that is activated when they experience pest or disease pressure. However, like people, if they do not have any immunity to those stressors, then they can be overwhelmed. Genetically resistant or tolerant crop varieties is one way to reduce other inputs and reduce the buildup of disease. Keeping plants healthy through fertilization, irrigation, and weed control will promote the overall vigor and immunity. Harvesting a little early to avoid losses to marketability is another option.

Choosing the best cultural practices for your farming operation, for the pests actually present in your field, is important. Some methods may not always be appropriate. It is important to weigh the costs and benefits of different practices to identify those that will be best for your IPM framework, as some may be contradictory or ineffective for a particular crop.

The UH Seed Lab sells seeds of various crops that have been bred for disease and insect resistance, and are adapted to our subtropical climate. 

Physical control involves the use of structures or barriers that block the pests from being able to access the crop. In Hawai'i, the most widely used form on farms is screenhouses. Unlike greenhouses, these protected structures are made of 17-mesh screens, which allows for better air circulation. They successfully exclude larger insect pests such as melon fly, lepidopterans, and pickleworm, and reduce the numbers of smaller insects like aphids and whiteflies. Smaller versions, or floating row covers, can be applied in home gardens. Click HERE to learn more about screenhouse construction and the benefits of these structures in Hawaiian zucchini production.

Unfortunately, for the same reason they keep harmful insects out, screenhouses also exclude beneficial insects, particularly honey bees. Faculty at CTAHR are hoping to find ways to modify screenhouses to overcome this obstacle, for example by introducing dual-entrance honey bee hives so only a small tube needs to be inserted into the screenhouse and honey bees can enter during crop anthesis. 

Tanglefoot® is a product that may be used in orchards to prevent crawling insects from reaching tree canopies. It is particularly effective against ants, which may climb in to trees to tend other pests, like aphids. Since aphids feed on plant fluids their excrement is effectively sugar water. Ants will defend the pests from natural enemies and harvest this "honey dew." Thus, their presence can interfere with biological control. Excluding them from orchards adds another layer of protection to an IPM framework.

While it may be time consuming and not always practical for larger operations, do not overlook good-old-fashioned hand picking and squishing as an effective way of removing larger pests, such as lepidopteran larvae! Think of it as a satisfying way to unwind after a long day at work.

When pests do not respond to other control methods, or populations increase too rapidly, choose appropriate pesticides for chemical control. These can be either organic or conventional pesticides. Organic pesticides are derived from natural sources, while conventional pesticides are created in a lab. However, lab created chemicals may otherwise be the exact same as the chemical derived from natural sources and thus it is important to keep in mind that organic pesticides are not automatically "safer" than conventional products. A broad spectrum insecticide will not distinguish between harmful and beneficial insect groups, for example, regardless of whether it is organic or not. 

Regardless of which type you choose, it is important to first identify the pest problem, choose a pesticide that is certified for controlling that particular pest, and follow the label instructions to minimize damage to the target plant and the environment. The label will provide critical information on:

• Product dilutions
• Application timing to reduce nontarget effects
• Whether the chemical is safe for use on edible plants
• How improper applications may damage plants
• Application intervals

Again, do not assume that because a product is certified organic it is completely environmentally safe. And just because a product is conventional, does not necessarily mean it cannot be used judiciously and safely when precautionary steps are taken.

When chemical control measures are necessary, steps can be taken to minimize risks to pollinators and other beneficial insects, such as:

• Spraying when pollinators are not active (early morning or in the evening)
• Spraying outside of bloom times, if possible
• Choosing targeted pesticides as opposed to broad spectrum when possible
• Only spraying areas with pests, as opposed to an entire field, and avoid spraying refuges
• Relocate honey bee colonies before wide-scale sprays
• Cautiously consider systemic insecticides

The EPA developed a warning label alerting applicators to the dangers posed to pollinators by particular pesticides - pay attention to Directions for Use on the label and heed all restrictions and instructions to protect bees and other beneficial insects.