Identification of the Philippine outbreak populations of the coconut scale insects using molecular markers with morphological confirmation

Issue Date

10-2014

Abstract

The alarming outbreak of the coconut scale insects (CSI) in the country prompted scientists to reexamine and validate the identity of this insect pest species with the use of molecular markers. Although morphological characters suggested that the outbreak species is Aspidiotus destructor, overlaps on the range of values and measurements of characters used to differentiate Aspidiotus species, such as the number of perivulvar pores and length of pygidium, were observed among the CSI samples. Thus, three barcoding genes, namely, the elongation factor 1 a (elf1a), the D2 and D3 regions of the ribosomal 28S (28S), and cytochrome C oxidase 1 (CO1), were amplified and analyzed. Comparison of the nucleotide (nt) sequences of elf1a and 28S with those nt sequences in the GenBank revealed only 90% to 92% and 95% to 97% identify with A. cyptomeriae, respectively, indicating that these samples were different from A. destructor. Surprisingly, there were CSI samples from Tanauan, Batangas and Tiaong and Dolores, Quezon [Philippines] that were positively identified as A. destructor (98% to 100% nucleotide identify). The presence of A. rigidus in the outbreak populations were confirmed using DNA samples extracted from CSI collected in Indonesia. Nucleotide identities of 99% to 100% nucleotides were observed between the 28S gene of A. rigidus from Indonesia and that of the local CSI samples. In addition, CO1 gene revealed the presence of another scale insect species, As. excisus, in the non-outbreak CSI population in Davao. In conclusion, molecular markers confirmed the following: 1) the validity of resurrecting As. rigidus from the synonym with As. destructor and its status as a good species; 2) the presence of both A. rigidus and A. destructor in the outbreak areas of Luzon and 3) the presence of A. excisus and in Davao area. Results implicate that 1) the biological control agents being reared in various facilities for control of CSI areas must be reevaluated as to their effectiveness against the mixed populations of CSI; 2) existing species complexes of scale insects and other pests should be subjected to molecular studies to detect sibling species; and 3) there is a need to explore other morphological characters that may help distinguish A. rigidus from A. destructor.

Source or Periodical Title

The Philippine Entomologist

ISSN

0048-3753

Volume

28

Issue

2

Page

209

Document Type

Article

Frequency

semi-annually

Language

English

En – AGROVOC descriptors

ASPIDIOTUS; COCOS NUCIFERA; PEST INSECTS; PESTS OF PLANTS; SPECIES; DNA; NUCLEOTIDE SEQUENCE; GENETIC MARKERS; PHILIPPINES

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