The Natural Enemies of Bagworms on Oil Palms in Sabah, East Malaysia
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Pacific Insects 14 (1): 57-71 20 March 1972 THE NATURAL ENEMIES OF BAGWORMS ON OIL PALMS IN SABAH, EAST MALAYSIA By T. Sankaran1 and R. A. Syed2 Abstract: Three species of bagworms, Mahasena corbetti Tams, Metisa plana Wlk. and Cremastopsyche pendula Joannis, are major pests of oil palms in Sabah. Parasites recorded from these and other Psychids during 1969 and 1970 were: Apanteles sp., Aulo- saphes sp., Echthromorpha agrestoria Swed., Xanthopimpla sp., Sympiesis sp., Pediobius sp., Eozenillia equatorialis Towns., Palexorista solennis (Wlk.) and Sarcophaga sp. from M. corbetti; Apanteles metesae Nixon, Eupelmus catoxanthae Ferr. and Eozenillia psy- chidarum Bar. from M. plana ; Aulosaphes psychidivorus Muesebeck and A. metesae from C. pendula; Xanthopimpla pedator Fabr., E. equatorialis and Brachymeria sp. from Clania tertia Tempi.; Sericopimpla flavobalteata Cam. from Cryptothelea cardiophaga Westw.; and Parasierola sp., Brachymeria sp. and Pediobius lividiscutum (Gahan) from? Pteroma sp. C. tertia and C. cardiophaga were also attacked by A. psychidivorus. Paraphylax rufipes Cam. was a common secondary parasite of bagworms. Brachymeria sp., B. dee- sensis Cam. and B. lugubris Wlk. were reared from E. equatorialis ; E. catoxanthae, P. lividiscutum and Brachymeria sp. from A. metesae; and Brachymeria sp. from E. psy- chidarum. Apanteles angaleti Muesebeck and Anastatoidea brachartonae Gahan emerged in cages with M. corbetti. A. psychidivorus, P. lividiscutum and E. sp. ? equatorialis were reared from M. corbetti bags formed of leaves from an unknown host plant. A Fislistina sp. was obtained from Eumeta sp. on cocoa. Two predators, Callimerus bellus Gorh. asso ciated with M. corbetti, and Sycanus sp. with C. pendula, were very scarce. Pathogens isolated from dead bagworms were Paecilomyces fumoso-roseus (Wize) Brown and Smith, from larvae of M. plana, C. pendula, C. tertia and C. cardiophaga, and a possible nonoccluded virus and an Aspergillus sp. from those of M. corbetti. Although several species of bagworms (Lep., Psychidae) occur on oil palms (Elaeis guineensis Jacq.) in Sabah, East Malaysia, only three of them, Mahasena corbetti Tams, Metisa plana Walker and Cremastopsyche pendula Joannis are, at the present time, of major economic importance as pests (Sankaran, 1970), In W. Malaysia M. corbetti has long been known to be a pest of coconut palms, while the other 2 species have caused severe outbreaks on oil palms. Native parasites play an important role in checking these bagworms but experience in W. Malaysia has shown that the use of broad-spectrum, residual, contact insecticides has hampered the beneficial work of these parasites, leading to fresh pest outbreaks (Wood, 1968). Our knowledge of the parasites of these bagworms was more or less confined to Indonesia and W. Malaysia. With the in troduction and rapid extension of oil palm cultivation in E. Malaysia bagworms have become serious since 1966. Their indigenous parasites and other natural enemies were investigated in Sabah by the authors during 1969 and 1970 with a view to the introduc- 1. Indian Station, Commonwealth Institute of Biological Control, Bangalore, India. 2. Sabah Sub-station, Commonwealth Institute of Biological Control, Tuaran, Sabah (Malaysia). 58 Pacific Insects Vol. 14, no. 1 tion of additional species from other areas as suggested by Simmonds (1967). A search for promising bagworm parasites has been taken up by the C.I.B.C. W. Indian Station in Trinidad. This paper deals with the natural enemies of oil palm bagworms recorded in Sabah during 1969 and 1970. The same or other species of bagworms were collected on vari ous other economic plants in order to rear out parasites, if any, to ascertain the host- range and host-plant associations of the species concerned. PARASITES AND PREDATORS OF OIL PALM BAGWORMS No egg-parasite of any species of bagworm has so far been obtained in Sabah. It seems unlikely that these would occur because the eggs remain well protected within the mother's hardened pupal skin, which itself is enclosed in a bag. Several species of larval and pupal parasites obtained are listed under their hosts. Mahasena corbetti Tams Several species of larval parasites were reared from this bagworm but with most levels of parasitism were low. A Tachinid larval parasite, Eozenillia equatorialis Town send, and an Ichneumonid, Echthromorpha agrestoria Swed., which emerged from the pupal cases, were by far the most important species recorded but appeared to be in capable of building up their populations to bring about any substantial reduction of the pest in an outbreak. HYMENOPTERA Braconidae Apanteles sp.: Cocoons of this solitary parasite were found in 4 of 45 small larval bags collected at Sg. Manila near Sandakan in September 1969. In January 1970 a single parasite emerged from one bag in a lot of 469 young larvae collected at Mostyn Estate. There has been no previous record of any Apanteles sp. parasitising M. corbetti. Aulosaphes sp.: Twelve cocoons of an Aulosaphes sp. were obtained from a larval bag in a lot of 47 specimens collected at Giram Estate in June 1969. Many of these cocoons were empty or had imperfectly developed adults. In November a single adult emerged from a bag and a group of 6 cocoons was found in another bag collected at the same estate. This species is different from Aulosaphes psychidivorus Muesebeck, which is a common parasite of several genera of Psychids in Sabah. Ichneumonidae Echthromorpha agrestoria Sw Qd.: In December 1969 this large Ichneumonid was reared for the first time from female pupal cases of M. corbetti collected at Mostyn Estate. In one field ll specimens in a collection of 95 were found parasitised. The parasite adults emerged from the hardened pupal skins of the hosts. In unparasitised individuals such pupal skins contain female moths. Therefore, it seems that parasitism actually occurs in the late larval or pupal stage but the parasite completes its development only after the host reaches the imaginal stage but is still enclosed in the pupal skin. The hardened pupal skin of the host is lined internally by a thin, parchment-like membrane. Xanthopimpla sp.: A single specimen was reared from a female pupal case of M. 1972 Sankaran and Syed : The natural enemies of bag worms on oil palms 59 corbetti in a lot of 71 bags collected at Giram Estate in August 1969. A pupa of the same parasite was found in another specimen which was dissected in the field. This is also a new record of an Ichneumonid from M. corbetti. Eulophidae Pediobius sp.: A single specimen was obtained from a larval bag among 404 speci mens of various stages of M. corbetti collected at Mostyn Estate in April 1969. The Commonwealth Institute of Entomology, London, has retained the specimen, comment ing that this is a peculiar species, not represented in the British Museum collection. Sympiesis sp.: Eighteen parasites emerged from three larval bags of M. corbetti collected at Giram Estate in November 1969. On opening the bags, empty pupal skins of the parasite were found in them. Species of Sympiesis are generally parasitic on coleopterous, dipterous and lepidopterous leafminers. The only other record of a Sympiesis sp. parasitising a Psychid (Cryptothelea crameri West.) is from Ceylon (Thomp son, 1954). DIPTERA Tachinidae Eozenillia equatorialis Townsend: This was the only important dipterous parasite of M. corbetti in Sabah. It was frequently reared from fully grown larvae collected in all the plantations visited in eastern Sabah but was scarce in the Beaufort area on the west coast. Rarely two or three parasites but generally only one emerged per host. In two instances, final stage larvae of this Tachinid passed through a pupal period of 9 and ll days, respectively. In the laboratory, adult parasites fed on dilute honey lived for a maximum of 5 days. Puparia have been found in larval bags collected almost throughout the year. However, parasitism never increased along with the host's popula tion when outbreaks occurred at Mostyn Estate. This Tachinid appears to exercise some measure of control of Mahasena only when the bagworm population remains at low levels on oil palms and other alternative host plants. At the time of an outbreak at Mostyn Estate in November and December 1969 parasitism was hardly 1-2 %. In the same estate, E. equatorialis and another Tachinid, Palexorista solennis (Walker), to gether accounted for only 12.6 % parasitism in a collection of 400 bags in April 1969 although the bagworm population here had increased earlier during an outbreak. In the Lormalong Scheme, 200 bags were collected in the same month, out of which only 7 had parasite puparia. In April 1970 up to 55 percent parasitism of Mahasena corbetti on Albizzia sp. was recorded in areas around Kota Kinabalu, and at Pamol Estate 80 % of the bagworms in a small sample was found parasitised by E. equatorialis in September. In both areas the bagworm population was low. Some specimens of E. equatorialis in the insect collection of the Agricultural Research Center, Tuaran, were earlier determined as Ex orista psychidarum Bar. Several specimens reared from M. corbetti by the authors and submitted to the Commonwealth Institute of Entomology, London, were identified as Eozenillia equatorialis Towns. E. equatorialis and E. psychidarum are very closely allied but distinct species and have been confused in the past. The true E. psychidarum, of which the holotype is in the British Museum, has the eyes completely bare, and E. equatorialis has the eyes densely haired. There are also differences in the male genitalia (R. W. Crosskey, pers. com.). 60 Pacific Insects Vol. 14, no. 1 Exorista (=Zenillia) quadrimaculata Bar. is a parasite of Cryptothelea variegata Sn. in India and Malaya (Thompson, 1945), M. corbetti in Malaya and Thailand (Thompson, 1946a; Meksongsee, 1963) and unidentified Psychids in Ceylon, India, Malaya and Sumatra (Thompson, 1946b).