Scouting for silverleaf whitefly (it's like an episode of CSI)

Given that this particular insect is very small and pretty fast, one of the easier options is to look for evidence of its offspring left behind on the cotton leaf.

It just so happens that SLW lay very small eggs that are pear shaped and usually visible (0.2mm). The eggs hatch within 6-10 days into a crawler or 1st instar nymph. This nymph moves to a good feeding site, inserts its feeding mouthparts into the leaf and will not move until it pupates then emerges as an adult. This is when the crime scene investigation (CSI) skills can come into play. 

REOs collected leaf samples from a number of fields and took them back to the ‘lab' (our offices) to see if we could work out what was happening out in our fields. Some of the leaves were heavily infested with SLW nymphs and it is the job of the ‘investigator’ to work out how many of these nymphs are destined to turn into SLW adults.

Sounds easy right? Well turns out there is a bit to it. Some leaves are a simple crime scene. Others are a mass murder or mass breading site. Some are both….

Taking a hand lens into the field (at least x10 magnification) is a simple way to have a look at what is going on , however there are  also other tools that can help you to delve into what is happening at plant and field level with SLW populations.

SLW Scouting Equipment
Range of equipment available depending on your needs

1. Hand lens

2. Smart phone lens

3. Microscope Camera

4. Microscope

 

Having access to microscopes means that the crime scene can be fully investigated, and we can look closely at the SLW population to figure out what is going on. One of the best parts of this project was using some great technology and being able to get direct input from Dr Jamie Hopkinson. We could capture the images then place them in a share folder and Jamie would comment on what was happening. We were also able to label pictures with what we thought was going on and he would see if we were right. Any number of things could be happening such as a viable nymph close to emergence (the red eye nymph), a parasitised nymph (where one of the parasitoid wasps species Encarsia and Eretmocerus have laid their eggs) , an emerged nymph, or one that has been eaten by a predator. We also used a range of aids (like this), to assist in assessment of SLW nymphs.

Here are some of the snap shots of the pictures taken during the season and the identification advice and guidance we received from Jamie that allowed us to contribute to this project and include samples from our regions.

Dead nymph, dried out inside

 

Early parasitised can see C shaped larva inside. 

Emerged whitefly case

SLW about to emerge, wingbuds obvious. 

Can't tell, likely emerged SLW where 'flaps' have collapsed back shut. 

Parasitised, mycetome (yellow structure) displaced to side and bottom.

The REOs involved in this project were amazed to see the high levels of predation by the beneficial insects in the fields.  We have also been able to see some of the larger predators in action – even catching them 'in the act'. In this case a green lacewing larvae is feeding on a SLW nymph.

There were certainly some tricky ones but once you get your eye in, the crime scene evidence on a leaf is a very telling story. This evidence can help solve the mystery for future spray decisions. We look forward to growers and consultants bringing in crime scenes and with us, being detectives!