Banishing glasshouse mealybug

Snug as a bug, but are there ways to oust that unwanted guest?

By Jen Banfield-Zanin, entomologist at Stockbridge Technology Centre

Safely tucked away on the stems and, often, hard-to-reach places of a plant, one may spot a seemingly fluffy tuft of white. Upon closer inspection, a number of oval-shaped, soft-bodied lodgers may be revealed, often in greater numbers than might be expected for the area covered and certainly overstaying their welcome.

Glasshouse mealybug, Pseudococcus viburni, is a longstanding, chronic pest in many horticultural crops. Along with other mealybug species, direct feeding damage affects plant yield and vigour, and excreted honeydew causes visual fouling on the surface of produce.

Control on a commercial scale is often challenging. The white, waxy filaments that cover the bodies of mealybugs are hydrophobic and offer some protection from treatments applied for remedial control. Their cryptic nature, and habit of securing themselves in concealed, hard-to-reach places offer additional protection, particularly where contact and good coverage are important to achieve good efficacy.

Mealybugs also have high reproductive rates, and so populations are able to bounce back after treatment.

In order to identify any potential new avenues and confirm current practice, work has been undertaken to put together a literature review, looking at existing options and evaluating novel discoveries or actives with management potential.

Control options

In addition to robust hygiene and cleaning down protocols, monitoring remains extremely important in order to identify potential problems well in advance and inform treatment strategies, though this is time and labour-intensive.

There have, however, been recent advances – in 2005 the sex pheromone for glasshouse mealybug was identified and synthesised. Production is still relatively expensive, but studies show that pheromone-baited traps could be cost-effective as a monitoring tool. Research overseas has also been developing optimised trap deployment strategies and lure strength. Hopefully, this will encourage commercial development of lures that may be useful for application in UK industry.

In terms of control, a number of relatively novel chemistries and, in particular, botanically derived biopesticides also show promise as control options as components within an integrated management strategy, with efficacies that are improved with careful adjuvant selection, though application challenges are still likely to affect mortality observed under glasshouse conditions.

The final review, coming soon, summarises evidence of a broad range of control options, from conventional chemistries through biopesticides, biologicals and physical, hopefully helping to inform any future trials of particularly promising management options.