UC Riverside

Aphytis melinus DeBach is a parasitoid wasp that is used for biological control of California red scale, Aonidiella aurantii (Maskell), in California and other areas of the world. The quality of A. melinus reared in five California insectaries was determined by measuring the sex ratio, size, and percentage of individuals still alive on certain sampling days. All five of the insectaries displayed reduced A. melinus quality and fitness parameters during certain times of the year. Wolbachia, an endosymbiotic bacterium, was also found to cause cytoplasmic incompatibility in A. melinus and associated fitness costs were seen in infected individuals based on longevity and fecundity measurements.

Classical biological control has been utilized for decades to help manage pests, but little research has been done on how these introductions alter genetic variation in natural enemies. We developed 10 microsatellites for assessing the genetic variation of and between different populations of A. melinus. The original material used to propagate A. melinus for mass release came from four relatively small collections in Pakistan and India and we sought to determine how much genetic diversity remains in this potentially inbred original colony, in comparison with that found in other captive colonies, California field populations, and in populations from the native range of A. melinus. Not surprisingly, the field samples from Pakistan had the highest average number of alleles per locus and captive colonies the lowest. A number of unique alleles were also found in both Pakistan and California.

Lastly, a well-known issue in the field of biological control is the lack of accurate identification of pests and natural enemies. We collected Aphytis lingnanensis Compere in the University of California, Riverside's campus biological control grove, a species that was previously thought to have been competitively excluded from the inland areas of southern California by Aphytis melinus. We also used 28S-D2 and COI sequences to examine the genetic variation and relatedness of Aphytis individuals in native, field-released and captive populations as well as in crossing experiments between the captive populations of A. melinus.