Beneficial insects in an IPM system

Summary

  • There does appear to be potential for biological control of green bean pests, such as heliothis, loopers, aphids and mites, due to the wide range of beneficial insects found within this crop.
  • The large diversity of predators and parasitoids that can help make up part of the crop environment could play a significant part in pest management.
  • Beneficial insects will not eliminate the need for insecticides but will reduce the reliance upon them.

Introduction

In a natural ecosystem, enemies of insect pests may be other insects, predatory mites and spiders. They are given the collective term 'beneficials'. There are two groups of beneficials: predators and parasitoids. A range of predators and parasitoids attack a wide range of insect pests in many cropping situations. It is safe to assume that the same beneficials may also be attacking the wide range of insect pests that damage green beans.

Knowledge of these naturally occurring beneficial insects is essential when developing an integrated pest management (IPM) program for green beans. Using harsh broad spectrum insecticides, such as synthetic pyrethroids, can seriously reduce the number of beneficial insects that would otherwise be helping manage a range of insect pests.

Predators

Table 1 shows some of the generalist predators that may be found in a green bean crop. Such diversity could have a large impact on the number of insect pests likely to be attacking green beans. Predators eat a wide range of pests such as aphids, mites and other insects that are mostly slower moving or at vulnerable stages, such as eggs and pupa.

Predators:

  • are organisms that feed directly on their prey
  • include such insects as lacewings, ladybird beetles, predatory shield bugs, pirate bugs, hoverflies, predatory mites and spiders
  • are known to attack insects such as aphids, thrips, moth eggs, and small, medium and large caterpillars
  • will supplement their diet with nectar, pollen and fungi as adults
  • are easily killed by broad-spectrum insecticides and some narrow-spectrum insecticides
  • can survive and thrive in crops if biological sprays are used
  • may be reared commercially.

From the list of predators in Table 2, only the hoverfly is considered to be pest specific. Hoverfly larvae look like slugs, are generally pale green and feed on aphids. The hoverfly adults can be found hovering around weed flowers and the crop. Figure 1 shows a predatory shield bug feeding on a caterpillar.

Parasitoids:

  • are generally tiny wasps but may also be parasitic flies
  • lay their eggs within or on the host pest at a critical life stage, completing their entire development with that host by consuming it
  • are recognised as important pest management tools
  • attack specific host stages, as indicated in Table 2
  • need to supplement their diet with nectar as adults, so some flowering weeds may be important for their continued presence
  • are easily killed by broad-spectrum insecticides and some narrow-spectrum insecticides
  • can survive and thrive in crops if biological sprays are used
  • can be reared commercially
  • are monitored by collecting and rearing the relevant pest stages to see whether parasitoids emerge.

Tables 1 and 2 show the relationships between key predators/parasitoids and major insect pests found in green bean crops.

Table 1. Relationships between key predators and major insect pests found in green bean crops.
Pests Predators
Spiders Lacewings Ladybird beetles Other predatory
beetles
Predatory shield
bug
Other predatory
bugs
Hover flies
Heliothis eggs x x x x   x  
Heliothis larvae x x x x x x  
Other caterpillar
pest eggs
x x x x   x  
Other caterpillar
pest larvae
x x x x x x  
Aphids x x x x   x x
Thrips x   x x   x  
Silverleaf whitefly
nymphs
x x x x    
Green vegetable
bug adults
x       
Green vegetable
bug eggs
x       
Mites x x x    x  
Table 2. Relationships between key parasitoids and major insect pests found in green bean crops
Pests Parasitoids
Trichogramma/
Telenomus
Aphid
parasitoids
Trissolcus
basalis
Trichopoda
giamocelii
Tachinid flies Microplitus Other larval
parasitoids
Eretmocerus
Heliothis eggs x        
Heliothis larvae      x x x  
Other caterpillar pest eggs x        
Other caterpillar pest larvae      x x x  
Aphids   x       
Thrips         
Silverleaf whitefly nymphs         x
Green vegetable bug adults     x     
Green vegetable bug eggs    x      
Mites         

Source (Tables 1 and 2): Brassica grower's handbook (see Other resources)

Enhancing beneficial insects

The number of beneficial insects in a crop can be enhanced by observing the following points:

  • monitor crops to help reduce unnecessary insecticide usage
  • use pesticides only when necessary (includes insecticides, miticides and fungicides)
  • use an appropriate pesticide to control the pest and limit its direct impact on beneficial insects (e.g. Bt sprays)
  • provide alternative food sources for the adult parasitoids and predators (e.g. weeds are a good source of nectar and pollen)
  • make inundative releases of beneficial insects
  • tolerate some level of insect pest activity in your crop to allow the beneficial insects to survive and multiply.

All of the above should be considered as part of an IPM system either in a crop or on the farm.

Other resources

  • Cantrell, BK, Donaldson, JF, Galloway, ID, Grimshaw, JF & Houston, KJ 1983, Survey of beneficial arthropods in potato crops in south-east Queensland, Queensland Journal of Agricultural and Animal Sciences, vol. 40, no. 2, pp. 109-119.
  • Department of Primary Industries 1996, Managing insects and mites in horticultural crops, Department of Primary Industries, Brisbane.
  • Heisswolf, S, Davis, B, Carey, D, Henderson, C, Walsh, B & Bagshaw, J 2004, Growing guide: brassica grower's handbook, Department of Primary Industries and Fisheries, Brisbane.
  • Llewellyn, R 2000, Sweet corn insect pests and their natural enemies: an IPM field guide, HRDC.
  • McDougall, S, Napier, T, Valenzisi, J, Watson, A, Duff, J, Geitz, G & Franklin, T 2002, Integrated pest management in lettuce: information guide, NSW Agriculture, Orange, NSW.
  • Mound, LA & Gillespie, P 1997, Identification guide to thrips associated with crops in Australia, NSW Agriculture, Orange, NSW.
  • Pyke, BA & Brown, EH 1996, The cotton pest and beneficial guide, GOPRINT, Woolloongabba, Queensland.
  • Scholz, B 1998, Integrating natural enemies into heliothis management, in Insect pest management in sweet corn, Workshop 1, 19-20 May 1998 at the Gatton Research Station, Queensland.
  • Wood, P, Ferguson, J, Brown, E, Cahill, M, English, M, Brennan, L & Elder R 2000, Crop insects: the ute guide northern grain belt edition, Department of Primary Industries, Queensland.

Further information

Last updated 25 October 2013