Effectiveness of a mass release of the mealybug predator Cryptolaemus montrousieri in a Queensland apple orchard.

Abstract

The tuber mealybug, Pseudococcus viburni, has a worldwide distribution, being found in South Africa, United States of America, South America, New Zealand, Europe, Bangladesh, China and Australia. Tuber mealybug is found on all parts of the plant and is considered to be the most important of the underground mealybug pests in Australia. Tuber mealybug became an important pest of apples and pears at Stanthorpe, Queensland in 1993. The longtail mealybug Pseudococcus longispinus, previously a pest only in southern states, is now present in many Queensland apple orchards. Mealybug infestations on pome fruit result in the development of black sooty mould which grows on the sticky honey dew at the stem and calyx ends of the fruit. Such fruit is unmarketable as fresh fruit. Infested fruit is rejected for export to overseas countries as export standards require nil live insects. Control of tuber mealybug and longtail mealybug in pome fruit relies mainly on insecticides with generally unsatisfactory results. The wasp parasitoid, Pseudaphycus maculipennis was introduced into Queensland orchards and follow up work needs to be done to confirm the status of this biological control species. Cryptolaemus montrouzieri (Cryptolaemus) also can be effective in biological control of mealybugs in apple orchards and is commercially available. The differences between the two pest species of mealybug are difficult to establish morphologically and it would highly advantageous to develop a PCR assay to aid in accurate identification. A PCR assay was developed and show great promise in accurately identifying the two mealybug pest species. Correct identification is important in selecting effective control measures for each species.

Mass releases of Cryptolaemus reduced mealybug populations but not sufficiently to satisfy the expectations of the fresh produce market. Further field research investigating the use of adult beetles instead of larvae, different timings of releases and more use of control blocks is likely to demonstrate better mealybug control using Cryptolaemus. The PCR analysis was highly promising and further work is required to prove the rigour of an accurate assay.