Part 2: Targeting Aphids, Thrips, Scales, and Whiteflies
- Eric Collier
- 1 day ago
- 5 min read
For organically managed farms, knowing exactly which beneficial insects target your most stubborn pests is crucial technical assistance. Let us look at the specific biocontrols used to manage four major threats in Hawaiian agriculture.
Managing Aphids
Aphids can multiply rapidly, as one single female can develop an entire colony. Aphids present a significant challenge to Hawaiian agriculture and native ecosystems, acting as both destructive plant sap-feeders and vectors for plant viruses. Due to Hawaiʻi’s tropical climate, these pests can thrive year-round, bypassing the traditional overwintering egg stage found in temperate zones. Instead, populations in Hawaiʻi reproduce primarily through parthenogenesis (virgin birth), where adult females give birth to live, clone-like nymphs without mating (Messing & Wright, 2006). This allows for rapid generation cycles and explosive population growth. When host plants become overcrowded or the nutritional quality declines, aphids produce winged forms (alates) that disperse via wind currents to colonize new crops.
To combat these infestations without heavy chemical intervention, organic agroecosystems rely heavily on established natural enemies. In Hawaiʻi, the primary biological control agents include predatory ladybeetles (such as Coelophora inaequalis) and specialized parasitoid wasps like Aphidius colemani. These tiny wasps lay eggs directly inside the aphid, causing the pest to swell and harden into a tan, hollow shell known as a "mummy". Protecting these natural enemies through the preservation of flowering insectary plants is a cornerstone of sustainable, local pest management.
Parasitic Wasps: These tiny wasps lay their eggs inside the aphid. The larva consumes the pest from the inside out, leaving behind a hard, brown shell known as an "aphid mummy."
Ladybugs and Lacewings: The larvae of these common insects resemble tiny alligators and possess voracious appetites, consuming hundreds of aphids during their development.
Syrphid Maggots: The larvae of hoverflies are excellent aphid predators, actively hunting them down on plant stems and leaves.
Controlling Thrips
Thrips cause severe damage to high-value crops like onions, orchids, and papayas. These tiny, fringe-winged insects damage plants by puncturing tissue and sucking out cellular contents, which leaves behind a characteristic silvery scarring. Thrips act as vectors for plant pathogens, such as the Tomato Spotted Wilt Virus (TSWV), which threatens local food security.
In Hawaiʻi’s warm climate, the thrips life cycle progresses rapidly from egg to adult in as little as two weeks. Females deposit eggs directly into plant tissue. After hatching, the insects pass through two active, feeding larval stages before dropping to the soil or lower leaf litter to enter non-feeding prepupal and pupal stages. This soil-dwelling phase makes them particularly difficult to manage with foliar contact sprays.
To suppress populations organically, growers rely on a complex of natural enemies. Key biological control agents present in Hawaiʻi include predatory mites (Amblyseius spp.), minute pirate bugs (Orius spp.), and parasitic wasps like Ceranisus menes, which attack thrips larvae (Mau & Martin, 2007). Maintaining healthy soil organic matter and planting diverse floral borders help sustain these beneficial predators.
Minute Pirate Bugs: These tiny predators aggressively hunt thrips, stabbing them with a sharp beak to consume them.
Microbial Insecticides: Fungi like Paecilomyces fumosoroseus naturally occur in the soil and infect thrips. Under highly humid conditions, the fungal spores attach to the insect, penetrating its cuticle and killing it.
Stopping Scales
Severely impacting local citrus, coffee, and ornamental crops. Scales damage plants by piercing tissue to drain sap, which reduces plant vigor and leads to yellowing leaves. Furthermore, scales excrete a sticky, sugary substance called honeydew, which promotes the growth of black sooty mold and blocks photosynthesis (Wright, 2007).
The life cycle of scale insects varies between armored (Diaspididae) and soft (Coccidae) varieties, but generally begins as an egg protected beneath the mother's body. Upon hatching, the mobile first-instar nymphs, known as "crawlers," disperse to find a permanent feeding site. Once settled, they insert their mouthparts, lose their legs, and secrete a protective waxy or armored covering, remaining sedentary for the rest of their lives (Vargas et al., 2013).
In organic agroecosystems, keeping scale populations below damaging thresholds relies heavily on biological control. Important natural enemies in Hawaiʻi include predatory ladybeetles, such as Telsimia nitida, and tiny parasitic wasps like Encarsia species (Wright, 2007). These parasitoids pierce the scale’s protective armor to lay eggs inside, killing the pest from within.
Rhyzobius Lady Beetles: This specific lady beetle has been highly effective in Hawaii, particularly against the cycad scale. They voraciously attack the scales on new growth.
Parasitic Wasps: Specific wasps have also adapted to target scale populations, keeping them balanced and preventing major outbreaks.
Eradicating Whiteflies
Whiteflies are notorious for spreading plant viruses and leaving behind sticky honeydew. Whiteflies are major agricultural pests in Hawaiʻi, inflicting damage on high-value crops like sweet potatoes, tomatoes, and taro. They damage plants by inserting their needle-like mouthparts to suck out vital sap, which wilts leaves and stunts growth. Like scales, whiteflies excrete copious amounts of sticky honeydew. This honeydew serves as a substrate for black sooty mold, which severely reduces the plant’s photosynthetic capacity and lowers the market value of produce.
The whitefly life cycle transitions from egg to adult in approximately three to four weeks under warm conditions. Females deposit tiny, oval eggs on the undersides of leaves. Once hatched, the mobile first-instar nymphs—called "crawlers"—move a short distance before settling down to feed. During the subsequent nymphal stages, they become completely sedentary, taking on a flattened, scale-like appearance until they emerge as winged adults.
In organic systems, suppressing whiteflies requires protecting their natural enemies. In Hawaiʻi, effective biological control agents include predatory lacewings, ladybeetles, and highly specialized parasitic wasps, such as Encarsia formosa and Eretmocerus species, which attack whitefly nymphs.
Encarsia and Nephaspis: These natural enemies were imported from Trinidad and brought the spiraling whitefly under excellent control across Hawaii.
Idioporus affinis: As mentioned earlier, this parasitic wasp is the primary control agent for the giant whitefly.
College of Tropical Agriculture and Human Resources (CTAHR). (2003). IPM for Home Gardens—Insect ID and Control. University of Hawaiʻi at Mānoa. https://www.ctahr.hawaii.edu/oc/freepubs/pdf/IP-13.pdf
Messing, R. H., & Wright, M. G. (2006). Biological control of aphid pests in Hawaii. Proceedings of the Hawaiian Entomological Society, 38, 1–13. http://hdl.handle.net/10125/112
Hata, T. Y., & Hara, A. H. (1992). Evaluation of systemic insecticides on thrips in anthuriums. University of Hawaiʻi at Mānoa, College of Tropical Agriculture and Human Resources. https://www.ctahr.hawaii.edu/oc/freepubs/pdf/RES-134.pdf
Mau, R. F., & Martin, J. L. (2007). Western Flower Thrips Frankliniella occidentalis (Pergande). Crop Knowledge Master, University of Hawaiʻi Extension Entomologist. http://www.extento.hawaii.edu/kbase/crop/type/f_occide.htm
Vargas, R. I., Souder, S. K., Morse, J. G., & Grafton-Cardwell, E. E. (2013). Response of armored scale (Hemiptera: Diaspididae) and soft scale (Hemiptera: Coccidae) to biological control treatments in Hawaii. Proceedings of the Hawaiian Entomological Society, 45, 23–32. http://hdl.handle.net/10125/33456
Wright, M. G. (2007). Scale insects and their natural enemies in Hawaii agricultural systems. University of Hawaiʻi at Mānoa, College of Tropical Agriculture and Human Resources. https://www.ctahr.hawaii.edu/oc/freepubs/pdf/IP-27.pdf
Hamasaki, R. T., Valenzuela, H. R., & Shimabuku, R. S. (2011). Silverleaf Whitefly Management in Hawaii Agricultural Systems. University of Hawaiʻi at Mānoa, College of Tropical Agriculture and Human Resources. https://www.ctahr.hawaii.edu/oc/freepubs/pdf/IP-32.pdf
Mizuyama, K., Wright, M. G., & Kaufman, L. V. (2021). Biological control of Bemisia tabaci (Hemiptera: Aleyrodidae) in Hawaiian vegetable crops by introduced and native natural enemies. Proceedings of the Hawaiian Entomological Society, 53, 15–24. http://hdl.handle.net/10125/75883
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