Pacific Pests, Pathogens and Weeds - Online edition

Pacific Pests, Pathogens & Weeds

Maximising biocontrol (outdoor vegetables) (472)


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Important biocontrol agents (BCAs)

In this fact sheet we list the important biological control agents (BCAs); how to attract and conserve them, the risks from using different pesticides, and show how to maximise BCAs within an integrated pest management (IPM) framework.

Predatory insects: ladybird beetles; hoverflies (or syrphid flies); lacewings. Note, they:

  • Reproduce in crops or in weeds nearby.
  • Often eat many kinds of insects, whether pests or BCAs (i.e., they are polyphagous).
  • Are continuously available from planting to harvest.
  • Lay their eggs near pest prey.
  • Differ according to the life stage that attacks pests. For some it is the adult, but for others it is the larva (or maggot), or both, i.e.:
    • Ladybird beetles (Photos 1&2): the adults and larvae eat other insects (see Fact Sheet no. 083).
    • Hoverflies (Photo 3): only the larvae (maggots) eat other insects; adults feed on nectar and pollen (see Fact Sheet no. 084).
    • Rove beetles (Photo 4): adults and larvae eat other insects.
    • Lacewings: green lacewings - only the larvae eat other insects, and the adults feed on nectar, pollen and honeydew; brown lacewings - adults and larvae eat other insects (as well as spider mites) (see Fact Sheets nos. 270 & 406).

Parasitic wasps (Photos 5-11, Diagram). Note, they:

  • Usually they attack one or a few species of pests.
  • Reproduce by female wasps laying eggs in or on bodies of host insects - eggs, larvae, pupae or adults. The eggs hatch and wasp larvae consume the host insect eventually killing it and forming pupae. Some species produce one pupa from a host, others produce many.
  • Require nectar-producing plants; adult wasps need sugar resources to develop their eggs.
  • Lay eggs inside larvae, pupae or adults of pests, depending on the species. They kill their prey and are called parasitoids. Some attack many different pests, e.g., Aphidius species prey on aphids, others are specialists with a very narrow host range, e.g., Cotesia vestalis preys on diamondback moth caterpillars. (See Fact Sheets nos. 287 & 285).

Spiders. Note, they:

  • Are not insects; they have eight legs (Photos 12&13)
  • Eat many types of insects (polyphagous), pests and other biocontrol agents.
Management of Biocontrol Agents

  • Conserve BCAs by avoiding broad-spectrum pesticides - synthetic pyrethroids, organophosphates and carbamates.
  • There is no need to attract many of the important BCAs. Note the following:
    • Many BCAs move into crops very soon after crop germination, or when transplants are moved to the field.
    • Spiders and lacewing adults can be located in the middle of newly transplanted crops within 1-2 days.
    • Many BCAs use signals from plants that help them detect when crops are infested with their prey; for example:
      • Hoverfly and lacewing females can detect prey and will lay a small batch of eggs next to them.
      • Female parasitoid wasps can detect volatiles from damaged plants to attract them to chewing pests, such as caterpillars.
  • If there is need to attract BCAs, do the following:
    • Grow flowering plants near crops, providing food sources (pollen and nectar) for hoverfly adults, parasitoid wasps, and pollinating insects. Note, it is probably best to limit this to brassica crops to avoid growing flowering plants that harbour thrips, polyphagous aphids and those aphids that spread viruses.
    • Plant grasses near vegetable crops to attract BCAs such as ladybird beetles and lacewings; they will be attracted initially by the grass aphids and other insects, and later spread to the vegetable crops. Note, grass insects are not likely to infest vegetable crops.

Pesticides compatible with BCAs

  • Pesticides belong to several different chemical groups and so their impact on BCAs differs. Those that contain active ingredients that are toxic to a wide range of pests and non-target pests should be avoided, the so-called broad-spectrum insecticides.
  • Impacts on bees must be considered for any product. Remember bees and parasitic wasps are in the same order, the Hymenoptera, so their reaction to any pesticide is likely to be similar.
  • Also, consider the behaviour of BCAs. Many are on the foliage when sprays are applied, and also come into contact with residues after spraying as they move about the foliage.

A summary of the risks that pesticides present to parasitic wasps, bees and predators is given below (Table 1).

Table 1. Active ingredients of insecticides and miticides, their mode of action (MoA) group numbers, risks to non-target natural enemies (parasitic wasps, bees and predators). [Risks of toxicities are averages of reported effects and should only be used as a guide. Toxicity of a specific insecticide depends on several factors, including formulation, application rate, environmental conditions, and life stage and species of the parasitoid or predator. The information for parasitoids is mainly on risks to parasitic wasps, but likely similar to that for bees, as both are beneficial insects in the Hymenoptera, the wasp family.]

 

Active ingredient

Mode of Action*

RISKS to parasitoids and bees

RISKS to Predators

Comments and Exceptions

Biopesticides and natural products

Bacillus thuringiensis
var. kurstaki

11

Very low

Very low

 

Bacillus thuringiensis
var. aizawai

11

Very low

Very low

Reports of some risk to honey bees in laboratory feeding experiments

Beauveria bassiana

UNB3

Low

Low

Potentially pathogenic to bees. Some negative impacts on predators

Helicoverpa NPV

virus

Very low

Very low

 

Soap

NA

Low

Low

 

Mineral oils

NA

Low

Low

Some toxicity to bees observed in field studies

Vegetable oils

NA

Low

Low

 

azadirachtin/Neem oil

UN2

Low

Low

Toxic to bees if ingested. Indirect effects on early instars of some natural enemies

oxymatrine

UN 

Low

Very low

 

sulphur

NA

Low

Low

Some risk to egg parasitoids

spinosad

5

Moderate

Low

Direct spray is toxic to bees, but dry residues should not affect foraging bees. High risk to egg parasitoids

rotenone

21B

High

Low

Moderate risk to bees

pyrethrin/pyrethrum

3

High to moderate

Moderate

Very toxic to all beneficials on contact short term, but not persistent

Other IRAC* Mode of Action (MoA) groups

pirimicarb

1

Low

Low

Some risk to bees, egg parasitoids and hoverfly

Other carbamates, carbaryl, methomyl, etc.

1

High

High

Not suitable for use

Organophosphates

1

High

High

Not suitable for use

fipronil

2

High

Moderate to low

Dangerous to bees. High risk to egg parasitoids

Synthetic pyrethroids

3

Very high

Very high

Not suitable for use

imidacloprid, thiamethoxam, clothianidin (as seed treatment or soil drenches)

4A

Low to moderate

Variable

Toxic to predatory sucking bugs. Some indirect effects on predators feeding on intoxicated sucking bugs

acetamiprid, thiacloprid

4A

Moderate

Moderate

This ‘cyano’ group of neonicotinoids exhibit lower toxicity to bees than the ‘nitro’ group

imidacloprid, thiamethoxam, clothianidin, dinotefuran (as foliar sprays)

4A

High to moderate

Moderate to high

This ‘nitro’ group of neonicitinoids are high risk to bees and egg parasitoids. Toxic to bees exposed to direct treatment or residues. Toxic to predatory sucking bugs and chewing beetles

spinetoram

5

High

Variable

Direct spray is toxic to bees, but dry residues should not affect foraging bees

emamectin benzoate

6

Moderate

Low to moderate

Some risk to bees and predatory sucking bugs

abamectin

6

High

Moderate to high

Prolonged impact on bees, predatory mites, some parasitoids and predators

pyriproxyfen

7

Low to moderate

Low to moderate

Indirect impact on larvae and pupae of bees and parasitoids. Some toxicity with direct contact with predatory sucking bugs and predatory beetles

pymetrozine

9

Low

Low

Some impact to bees observed in the field. Minor impact on parasitoids and ladybird beetles

diafenthiuron

12

High

Moderate

High risk to bees

chlorfenapyr

13

Moderate

Low

High risk to egg parasitoids. Foraging behaviour affected in bees

novaluron, lufenuron, diflubenzuron

15

Low

Low to moderate

Some toxicity to bees. Indirect effects on larval stages of some general predators

buprofezin

16

Low

Low

Risks to larvae of ladybird beetles. Indirect effects on early instars of some natural enemies

fenpyroximate

21A

Very low

Very low

High risk to predatory mites

indoxacarb, metaflumizone

22

Moderate

Low

Some risk to bees and predatory beetles

spiromesifen, spirotetramat

23

Low

Low

 

chlorantraniliprole, flubendiamide

28

Low

Low

 

cyantraniliprole

28

Low

Very low

High risk to bees if applied during flight, but dried residues have minimum impacts

^metaldehyde

NA

Low

Low

High risk to ground predators that consume metaldehyde-intoxicated snails and slugs

^iron phosphate

NA

Low

Low

 
*IRAC (Insecticide Resistance Action Committee, www.irac-online.org)
^for control of snails and slugs.

Main sources for Table 1
Gardner-Gee R, Puketapu A, MacDonald F, Walker G, Connolly P (May 2013) Effect of selected oils and insecticides on beneficial insect species: 2013/14 results. A report prepared for: Potatoes New Zealand Ref: SFF11-058: Developing IPM tools for psyllid management in potato. Plant & Food Research Milestone No. 58208. Contract No. 30308. Job code: P/336016/12. PFR SPTS No. 10059.
Holden P (2020) New Zealand NOVACHEM Agrichemical Manual 2020/2021.
May E, Wilson J, Isaacs R (2015) Minimizing Pesticide Risk to Bees in Fruit Crops. Extension Bulletin E3245, May 2015, Michigan University.
Ndakidemi B, Mtei K, Ndakidemi P (2016) Impacts of Synthetic and Botanical Pesticides on Beneficial Insects. Agricultural Sciences 7:364-372.
Walsh B ( 2005) Impact of insecticides on natural enemies found in brassica vegetables. Poster, National Diamondback moth project team, Horticulture Australia Ltd.
www.irac-online.org
University of California Statewide Integrated Pest Management Program [accessed February 2021] http://ipm.ucanr.edu/GENERAL/pesticides.html.

IPM decision pathways

IPM consists of a number of linked actions which are most effective when coordinated by a Decision Pathway. The key components are as follows:

1. Scout crops:

  • Careful, continuous observations in crops to:
    • Identify BCAs and pests present.
    • Carry out twice weekly surveys in tropical countries.
    • Assess increase/decrease in pest numbers and/or crop damage.

2. Identify infestations and record findings:

  • After every scouting, summarise and record results:
    • Identify changes in infestations over time:
      • Record fresh damage.
      • Record crop growth stage.
      • Record over all health of the crop.

3. Assess RISKS:

  • Stage of crop growth:
    • Seedlings - at high risk from virus vectors.
    • Leafy growth stage - relatively low risk from most pests.
    • Flowering stage - relatively high risk from flower thrips.
  • Stage of pest life cycle:
    • Eggs and pupal stages - low risk (they cause no damage).
    • Small caterpillars - relatively low but increasing risk.
    • Large caterpillars - relatively higher risk.
    • Increasing numbers of high risk pests - increased risk.
  • Wellness, weeds and weather:
    • Healthy plants with good nutrition and appropriate irrigation - low risk.
    • Weeds within a crop or nearby - increases risk.
    • Virus-infected plants adjacent to crop - high risk.
    • Cool weather - decreases risk from insect and mite pests (they develop and reproduce slowly).
    • Hot weather - increases risk from insect and mite pests (they develop and reproduce rapidly).
  • Market:
    • A market that rejects or downgrades produce with minor pest damage - higher risk.

4. Make decision to Spray or Not-to-Spray (based on scouting results and risk assessment).

5. Choose pesticide (if decision is to Spray).

  • Choose effective active ingredient to control target pest or pests:
  • Low hazard to humans and animals.
  • Low hazard to BCAs.

6. Assess history of local pesticide use:

  • Rotate between different MoA groups if needed.
  • Rotate between different MoA groups after 3-4 applications or 2-3 weeks of same pesticide.

7. Apply pesticide safely and effectively:

  • Read the pesticide label.
  • Check pesticide sprayer is operating correctly; check nozzle type.

8. Continue to scout crop:

  • Assess:
    • Infestations.
    • Change of risks.
    • Efficacy of spray application.

AUTHORS Graham Walker & Grahame Jackson
Information from Gardner-Gee et al. (2014) Effect of selected oils and insecticides on beneficial insect species: 2013/14 results. Report for Potatoes NZ. Plant & Food Research; and May et al. (2015) Minimizing Pesticide Risk to Bees in Fruit Crops. Extension Bulletin E3245, May 2015, Michigan University; and  Ndakidemi B, et al. (2016) Impacts of Synthetic and Botanical Pesticides on Beneficial Insects. Agricultural Sciences: 7, 364-372; and Walsh B (2005) Impact of insecticides on natural enemies found in brassica vegetables. Poster, National Diamondback moth project team, Horticulture Australia Ltd.; and from University of California Statewide Integrated Pest Management Program. (http://ipm.ucanr.edu/GENERAL/pesticides.html). Diagram Science Learning Hub. Pokapū Akoranga Pūtaiao, University of Waikato.

Produced with support from the Australian Centre for International Agricultural Research under project HORT/2016/185: Responding to emerging pest and disease threats to horticulture in the Pacific islands, implemented by the University of Queensland and the Secretariat of the Pacific Community.

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