Solenopsis Mealybugs are small, sucking insects, related to aphids. These pests are known to affect a wide range of cultivated plants and weeds; occasionally, however, populations increase and damaging infestation or ‘hotspots’ can occur.

Several Mealybug species are recorded from field crops with no, or minor effects on the crop. Solenopsis Mealybug has recently been recorded as a serious pest of cotton, and is found in most cotton-growing regions of the world.

Identification: The female Mealybug is wingless with a 3-4mm long oval shaped body which is covered with white hydrophobic (water repellent) mealy wax. There are dark bare spots on the thorax and abdomen, which appear as dark longitudinal lines.

The adult male is about 1mm long, with a grey body and a single pair of transparent wings. Two filaments of white wax project from the end of its abdomen. The adult male has no feeding mouthparts and causes no damage.

May be confused with: There are a number of native species of Mealybug that may be encountered in cotton landscapes. Solenopsis Mealybug can be visually distinguished from some species because of a difference in colour. For example, the Hibiscus Mealybug is pinkish and the Long-tail Mealybug has a distinct projection from the tail end. However, there are many species that cannot be distinguished in the field from Solenopsis Mealybug, even with the help of a hand lens. Formal identification of Mealybugs is done by examination of characters on the ‘skin’ of slide mounted, prepared specimens.

Lifecycle:  Mealybugs have a high reproductive rate, with adult females capable of producing hundreds of eggs. Egg development takes 3–9 days and the nymphal stage can last 22–25 days. Development from egg to adult takes an average of 26 days. Adult Mealybugs can live for about three months. Research has found that the crawler stage can live for up to 6 days, and the 3rd instar stage for up to 50 days without food or water.  During winter Mealybugs can be found up to 5cm below the soil on the tap root of host plants. 

Methods of spreading:  Mealybugs have limited mobility but are readily spread from infested plants and weeds by wind, water (they float), birds and animals (including ants), and on equipment, vehicles and clothing. They will also crawl to neighbouring plants.

Damage: Adults and nymphs suck the sap from plant tissue. This can occur at all stages of crop development. Infestations cause crinkled and twisted leaves, reduced flower and boll development, smaller bolls, and distorted and stunted plants with a bushy appearance. Boll opening may also be affected, resulting in significant yield losses. Heavy, prolonged infestations can lead to plant death. In the field, Mealybug damage often appears in patches, especially in areas where plants are suffering stress.

Heavy infestations excrete honeydew, which can contaminate lint and promote the development of black sooty mould on leaves, which can inhibit plant photosynthesis and growth. Ants feed on the honeydew and spread the Mealybugs. Ants also clean the colonies and protect the Mealybugs from predatory insects (such as ladybird beetles).

Control: There are no insecticides registered for the control of Mealybugs in cotton. However there are a number of management options that can reduce infestations and the overall impact of this pest.

• Weeds and volunteer cotton in and around fields should be removed during the winter to prevent carryover and breeding of Mealybugs from one season to the next. Mealybugs multiply on different hosts and may initially breed on weeds before migrating to cotton crops.
• Do not throw uprooted weeds into water channels.
• The removal of affected cotton plants at the early stage of infestation may reduce Mealybug numbers in the rest of the crop.
• Practice good farm hygiene and clean all equipment that has been in affected fields. 
• Be aware that physical contact with infested plants may result in mealybugs adhering to clothing and implements and be spread through and between fields.
• Choose the insecticides that are used in control of other insect pests carefully to help conserve natural enemies of Mealybugs.

Natural enemies: In Australia, ladybeetles and lacewings have been identified as key predators of Mealybug. In particular the Mealybug specialist ladybeetle, Cryptolaemus montrouzieri whose larvae look like an oversize Mealybug. There is still a lot we don’t know about the ecology of Solenopsis Mealybug and it’s natural enemies in Australia.

The oval shaped mealybug adult is covered in a white wax. 4mm Photo: C. Mares

 
Remove affected plants early to reduce Mealybug numbers in the rest of the crop.  Photo: S. Mass

 
Mealybugs can cause crinkled and twisted leaves, reduced flower and boll development, smaller bolls, and distorted and stunted plants with a bushy appearance. Photo: S. Addison

 
The Long-tail Mealybug has a distinct projection from the tail end. 3-4mm Photo: Bugs for Bugs

The Mealybug ladybeetle larvae look like oversized Mealybugs. 9-10mm Photo: R. Whyte