Whitefly

Life cycle of whitefly

Whiteflies have six distinct developmental stages: the egg, first, second, third and fourth larval instars, and an adult insect.

The eggs are elliptical and often deposited in circles. The young larvae, which on hatching already have well-developed legs and antennae, are known as, ‘crawlers’. After hatching they are actively engaged for several hours in seeking a suitable place on the leaf where they can feed. Once they have found such a spot, they remain there throughout the period of larval development. In the second and third larval stages, both the legs and the antennae are reduced to one or two segments and are no longer visible. In the fourth larval stage, the insect finally becomes flatter, then subsequently fatter, and the cuticle hardens.

The growth of hairs on the insect depends on the leaf: the longer the hairs on the leaf, the longer the hairs on the insect. In other words, the larva adapts itself to the structure of the leaf on which it lives. On very hairy leaves, the larva can sometimes become deformed if the growth is obstructed by the stiff hairs. As soon as the red eyes of the adult whitefly are visible in the fourth larval instar, the stage is referred to as a ‘pupa’. The different species of whitefly can be most easily distinguished from each other at the pupal stage.

The adult emerges from the hardened cuticle of the pupa through a characteristically shaped opening; the pupa splits on the upper surface along pre-existing seams, to create a T-shaped opening. Newly emerged whiteflies have two pairs of transparent wings; later these two pairs of wings and the body are covered with a white, waxy powder that gives the insect its characteristic appearance. Adult whiteflies are mostly found on the underside of young leaves where they lay their eggs. If the plant is shaken, the adults fly up, and then return to the undersides of leaves.

How to prevent whitefly

To prevent whitefly infestations in crops, there are several measures you can take:

Implement good crop management practices

Maintain plant health by providing proper irrigation, nutrition, and adequate spacing between plants. Healthy plants are less susceptible to whitefly infestations.

Practice strict hygiene

Keep the growing area clean and free from debris, weeds, and plant residues that can serve as reservoirs for whiteflies. Regularly remove and dispose of any infested plant material.

Monitor regularly

Regularly inspect your crops for signs of whiteflies, including adult insects, nymphs, or their characteristic sticky honeydew. To aid in monitoring, strategically position sticky traps throughout the crop to capture adult whiteflies and provide insight into population levels. Early detection allows for prompt action and prevents the infestation from spreading.

Use physical barriers in greenhouses

Install insect-proof screens on openings such as vents and doors to prevent whiteflies from entering the crop area. This helps create a physical barrier and reduces the chances of infestation.

Introduce biological control agents

Utilize natural enemies of whiteflies such as parasitic wasps, predatory mites, predatory bugs, or entomopathogenic fungi. These beneficial organisms can help control whitefly populations by feeding on them or their eggs.

Rotate crops and plant diversity – outdoor crops

Avoid continuous cropping of susceptible plant species. Rotate crops to disrupt whitefly life cycles and reduce the buildup of infestations. Additionally, planting a diverse range of crops can create an environment less favorable for whiteflies.

Biological control of whitefly

There are several natural enemies that can be used for the biological control of whitefly, including parasitic wasps, bugs and predatory mites. These beneficial insects and mites feed or parasitize on whitefly at different stages of their life cycle, reducing populations and preventing further damage to crops.

Parasitic wasps

The parasitic wasps Encarsia formosa (En-Strip) and Eretmocerus eremicus (Ercal) are commonly used for controlling whitefly populations in greenhouse crops. The female wasps lay eggs inside the whitefly nymphs, where the developing wasp larva consumes the host from the inside out, ultimately killing the whitefly.

Predatory mites

Similarly, predatory mites such as Amblyseius swirskii (Swirski-Mite, Swirski-Mite LD, Swirski-Mite Plus, Swirski Ulti-Mite), Amblydromalus limonicus (Limonica) and Amblyseius andersoni (Anso-Mite, Anso-Mite Plus) are also effective natural enemies of whitefly. These predatory mites feed on whitefly eggs and nymphs, and can significantly reduce the populations of whitefly in a short period of time. These predatory mites cannot be used in tomato as they get stuck in the sticky stuff the glandular hairs of the tomato produce.

Predatory bugs

In tomato the predatory bug Macrolophus pygmaeus (Mirical) is frequently used for the control of whitefly.

Entomopathogenic fungi

Entomopathogenic fungi, such as Lecanicillium muscarium (Mycotal) are also effective for biological control of whitefly. These fungi infect and kill whitefly by penetrating their cuticle and growing inside the insect, eventually causing death.