“I  Have  Whiteflys!!!”

whitefly-featured-imageFrom one morning to the next you mossy over to your pet bushes and bend down to smell one of your favorites. Like a bad dream, you see a white flex fleeting the vicinity of your incoming nostril breath. An old wound in your soul opens as you realize, “there back!”. Immediately you run to the microbe biological medicine cabinet in the garden house’s refrigerator. There you frantically search for the right bacteria, or was it fungus. A cold sweet breaks out on your forehead as you fumble for your list and notes. It reads:

  • Bacillus subtilis
  • Streptomyces griseoviridi
  • Pseudomonas fluorescens
  • Rhizobium
  • Cladosporium herbarum
  • Bacillus thurigiensis var israelensis
  • Lecanicillium spp

Biological Control

whitefly-dead-fungus

Dead whitefly and fungus

Biological control is a very effective method. There are two microbial fungus that will place the persistent adult whitefly on on his knees. They are Isaria fumosorosea and two Lecanicillium spp, L. lecanii and L. muscarium. There is also a fungus named Paecilomyces lilacinus that can destroy the young in the nymphal stage. A mix of the four I use as a preventative if I have had a prior attack. For a preventative, give your plants a light spraying every month and you should be good. Once infested, make a strong concentration of the fungus spores and give the plants a thick spraying. Spray in the morning when the flies are just getting up. It’s still cool at that time and they will more or less stay put as you apply the fungal predators. You are spraying fungal spores, so it will take a few days for them to pop and grow hyphae. Spray every 3 or four days until the fly population decreases and you notice a light white fungus on some leaves. This will be between 10 and 15 days.

Image of the life cycle of the pest white fly

click to enlarge

Six WhiteFly Stages:

  1. egg
  2. 1st nymphal stage (crawls)
  3. 2nd nymphal stage (stationary)
  4. 3rd nymphal stage
  5. pupal
  6. adult

 About Whiteflys

Whiteflies are closely related to aphids, mealybugs and scale, all of which feed by sucking sap from plants. Whiteflies can be found on the undersides of leaves and are active during the daytime when the temperature is warm. Whiteflies damage plants by sucking out plant juices. Large amounts of sap are removed by the developing nymphs, seriously weakening them. Leaves often turn yellow, appear dry and drop prematurely. If that doesn’t sound bad enough, whiteflies suck out more plant juice than they can digest. They excrete the excess sweet, sticky substance referred to as honeydew. The honeydew covers leaf surfaces and acts as a growth medium for a black, sooty mold. If left to live, the adult whitefly’s lifespan is roughly 40 days depending on  temperature, plant, and fly species.

Egg Stages

Whiteflies deposit eggs on the underside of plants leaves. Adult females usually lay between 200 and 400 eggs. Though individually the eggs are almost non-detectable to the naked eye. But upon close inspection you can see the small whites of their ova. The whitefly many times lays her eggs in circle groupings, because the female will often keep her mouth feeding on the plant to feed while rotating in a circle. Normally the eggs are surrounded by their characteristic white, powdery film, making them easier to see. Unfertilized eggs will become male, fertilized eggs will become female. After the eggs hatch, begins the 3 nymph stages called instars.

Nymphal Instar Stages

The nymphal stage of a whitefly.

1st instar nymphal crawlers.

The 1st instar stage is the crawling stage, wondering about the plant. Soon, he will insert his mouthparts into the plant and begin to feed. After his 1st molt, the crawler loses his legs and antennae. He attaches himself onto the undersides of a leaf with several wax like rods coming from his body. This gives him the appearance of small white oval scale. The nymph does not move during the subsequent instar stages to follow. During this time the nymphs remain fixed to the plant and feed for about four weeks. Between stages they molt. During molting, the flies shed silver skins, which are left on the leaves. During the instar phases, the whitefly maintains an opaque white appearance. At the feeding site the nymphs use parts of their mouth to stab into the plant and consume the plant’s juices.

Pupal Stage

The stage following the nymph stages is the pupal stage where the eyes become a deep red color, body color is yellow and the body structure thickening in size. During this stage the nymph will grown more plump to about 1 to 2mm in length. The pupal nymph begins to resemble the adult. Though the last instar stage is commonly referred to as the pupal stage, it is not a true pupa. It does not molt into a complete non-feeding, resting stage.

Adult Stage

Whitefly Emerging from it's Pupa stage.

Adult Emerging from it’s Pupa stage.

The adult emerges from a pupal case in a little over a week. The powdery, waxy, white film that covers the whitefly is produced and secreted through abdominal glands following emergence. They may mate within hours of emergence and may lay eggs one to eight days after mating.

Whitefly Stage Timeline:

  • First instar: 4-6 days depending on species and temperature
  • Second instar: 7-10 days depending on species and temperature
  • Third instar: 7-10 days depending on species and temperature
  • Pupal: 10-11 days depending on species and temperature
  • Adult  lifespan: 5-30 days depending on species and temperature

Mechanical Control

The use of traps can be very helpful in controlling light infestations of whiteflies.  Hang the trap vertically just above the plants. The adults are attracted to the yellow color and become trapped on the sticky substance. One trap for every two large plants is recommended. Clean the traps periodically to remove insects and other debris, and apply fresh adhesive to the yellow surface.

Another mechanical technique that can help control whiteflies is to vacuum them with a small, hand-held vacuum cleaner. Put the vacuum bag containing the insects inside a large plastic bag and freeze for 24 hours to kill the insects. Vacuuming adults is most helpful and effective when an infestation is just starting and when the adults have not laid many eggs.