Author：Wang Chia-Yu, Project Assistant, Taiwan Agricultural Research Institute
Yao Mei-Chi, Associate Research Fellow, Taiwan Agricultural Research Institute

Recent high temperatures and humid conditions have made farm work increasingly challenging for growers. In particular, the hot weather shortens the life cycles of small insect pests such as whiteflies and aphids, which accelerates their development and leads to rapid population growth. Organic and eco-friendly farmers often ask us if there’s an effective way to control the waves of pests attacking their fields. In addition to using registration-exempt plant protection materials for pest control, we highly recommend the release of natural enemies—beneficial insects that proactively seek out and eliminate pests in the field. Yes, where there are pests, there are also beneficial insects. They are two sides of the same coin. Nature is truly fascinating!

In this article, we’ll explore a few examples of using insects to combat insects. When we encounter bugs in the field, the instinctive response is often: "Kill them!" But this reaction can unintentionally eliminate our helpful allies. It’s easy to confuse pests with beneficial insects, isn’t it? Today, let’s get to know some of the tiny helpers that work to maintain ecological balance. Get your notes ready—it’s time to meet them!

Trusted Allies in the Field: Beneficial Insects for Safer, Sustainable Farming

In the narrow definition of biological control, natural enemies (beneficial insects) are classified into two main types: parasitoids and predators. The Smart Pest and Disease Management and Decision Support System has recently added several new predatory natural enemies to its database, including: Six-spotted Zigzag Ladybird (Menochilus sexmaculatus), Lemnia saucia, Mealybug Destroyer (Cryptolaemus montrouzieri), Megalocaria dilatata, Illeis koebelei, Tomato bug (Nesidiocoris tenuis), Brown Lacewings (Micromus timidus), and Phytoseiid mite (Neoseiulus barkeri). Additionally, previously listed species like the Green Lacewing (Mallada basalis) and Predatory stink bug (Eocanthecona furcellata) (see Table 1) are also commonly used in field applications. Predatory natural enemies feed on pests throughout both their larval and adult stages. They are typically of quick and more direct effect, making them especially suitable for controlling pest species that appear in clusters, such as scale insects, aphids, spider mites, and thrips. On the other hand, parasitoid natural enemies (mainly parasitic wasps) lay their eggs inside or on host pests. The larvae then develop by consuming the host, ultimately killing it. New parasitoid species recently added to the system include Gifu braconid wasp (Aphidius gifuensis) and Minute polyphagous wasp (Trichogramma spp.), as well as existing entries such as Eretmocerus Orientalis, Anastatus wasp (Anastatus japonicus), Dirhinus giffardii, Closterocerus okazakii, Chrysocharis pentheus, Opius caricivorae, and Tamarixia radiata (see Table 2).

▼ Table 1. Common Types of Predatory Natural Enemies (* indicates commercially available species domestically)

◆ Common Predatory Natural Enemies
Insect Names	Physical Features	Target Pests
Six-spotted Zigzag Ladybird (Menochilus sexmaculatus) *		Scale insects, aphids
Lemnia saucia		Scale insects, aphids
Mealybug Destroyer (Cryptolaemus montrouzieri) *		Scale insects, aphids
Megalocaria dilatata		bamboo horned aphid (Astegopteryx bambusifoliae)
Illeis koebelei		Powdery mildew spores
Tomato bug (Nesidiocoris tenuis)*		Whiteflies, leaf miners, lepidopteran larvae, aphids, spider mites
Predatory stink bug (Eocanthecona furcellata) *		Lepidopteran larvae
Green Lacewing (Mallada basalis) *		Aphids, whiteflies, thrips, scale insects, leafhoppers, psyllids, spider mites, citrus leaf miners (Phyllocnistis citrella), and early instar larvae and eggs of various Lepidoptera and Coleoptera insects
Phytoseiid mite (Neoseiulus barkeri) *	(Please refer to the Smart Pest and Disease Management and Decision Support System)	Various mites, thrips nymphs, whitefly eggs

▼ Table 2. Common Types of Parasitic Natural Enemies (* indicates commercially available species domestically)

◆ Parasitic Natural Enemies
Insect Names	Physical Features	Target Pests
Minute polyphagous wasp (Trichogramma spp.)		Lepidoptera, Diptera, Hymenoptera, Neuroptera, Hemiptera, etc.
Eretmocerus Orientalis	(Please refer to the Smart Pest and Disease Management and Decision Support System)	Whiteflies
Anastatus wasp (Anastatus japonicus) *	(Please refer to the Smart Pest and Disease Management and Decision Support System)	Litch stink bug
Dirhinus giffardii	(Please refer to the Smart Pest and Disease Management and Decision Support System)	Tephritidae

In this section, we take a closer look at parasitoid natural enemies, as we’ve found that compared with predators, many people are less familiar with parasitoid wasps. These insects are indeed quite different from other wasps we commonly encounter. Parasitoid wasps rely on host insects (such as pests) during their larval stage for development. They lay their eggs either inside or on the surface of a host, which can be in the form of eggs, larvae (or nymphs), pupae, or even adult insects. Once hatched, the wasp larvae feed on the internal tissues of the host, eventually killing it and emerging as a new generation of parasitoid wasps. This natural parasitism plays a vital role in regulating pest populations and has a positive impact on both ecosystems and agricultural productivity. One key advantage of parasitoid wasps is their host specificity. They target only certain pests and pose no threat to other beneficial insects or non-target species. For example, the pupal parasitoid Dirhinus giffardii is highly effective against fruit fly pests. Once released into the field, there is no need to distinguish between different species of melon or fruit flies—the wasp targets them all. About the size of an ant, this tiny parasitoid lays its eggs inside fruit fly pupae. The developing wasp larva consumes the pupa from within, ultimately destroying the pest while producing a new generation of helpful wasps (see Figure 1).