REARING OF FIELD COLLECTED LARVAE OF THE MAHOGANY SHOOT BORER, Hypsipyla robusta (MOORE) ON AN ARTIFICIAL DIET A PRELIMINARY STUDY

Hypsipyla robusta (Morre) (Lepidoptera: Pyralidae) is an important pest of mahogany,Swietenia macrophylla (King) in Sri Lanka and world over. Larval attack at an earlystage of growth, leads to branching which reduces the quality and value of timber,significantly. Work is in progress to study the effect of shade on the growth anddevelopment of mahogany and attack by the shoot borer. This paper presents aspects ofdevelopment of shoot borer larvae reared on an artificial diet, as well as field informationrelated to damage and parasitism. Larvae collected from two field sites at fortnightintervals were reared in the laboratory on an artificial diet at 27-32° C. Development offield collected larvae were followed until the emergence of adults, during which duration ofthe developmental stages, adult sex ratio, parasitism level and mortality were recorded.Measurement of head capsule widths of larvae collected and their location on the shoot,was also made. A total of 774 larvae were collected and reared during the study, out ofwhich 120 Hypsipyla adults emerged giving a male: female sex ratio of 1:8. Nearly 40%of the field collected larvae were parasitized by Cotesia app. (Hymenoptera: Braconidae).Head capsule measurements indicated five larval instars that were found to infest differentparts of the growing shoot. Duration of development of larvae differed depending onwhether they were parasitized or not. Several problems encountered during rearing arediscussed

EFFECT OF SHADE ON LlMONOID AND NITROGEN COMPOSITION IN SHOOTS OF Swietenia macrophlla.(KING)

The main factor limiting cultivation of mahogany, Swletenia macrophylla King(Meliaceae), in plantations is damage by shoot borers (Hypsloyla spp.). Shade hasbeen repeatedly cited as reducing shoot borer attack but the responsiblemechanisms have not been determined by experimentation. Shade may altereither secondary compounds such as limonoids or nitrogen concentrations or bothin the plants making them unsuitable for insect survival and development.Previous studies have not examined whether shade influences Iimonoid andnitrogen content of S.marcrophylla and thereby alter shoot-borer attack.Therefore, these studies were designed to identify the variation in incidence ofshoot borer attack under three levels of shade treatments in the field conditionsand the variation in plant chemistry of Ssmarcrophylla shoots grown under threedifferent artificial shade treatments. The hypotheses tested were under high lightavailability (i) incidence of shoot borer attack increases (ii) the concentration oflimonoids present in the shoots of S. macrophylla decreases ind(iii) total nitrogencontent of shoots increases.This study was done from 1997-99 in Sri Lanka and UK. Attack by the shootborer was assessed 54 weeks after planting. The Limonoid content wasinvestigated by Thin Layer Chromatography (TLC) and the total nitrogen byKjeldhl method using freeze-dried ppowdered shoots. The incidence of shootborer attack was significantly higher under low shaade (dJ.=2, F=8.6, p=O.0003).The intensity of the green-blue fluerescence under UV seen in the TLC plates wasgreater using the extracts from the high shade treatment compared to that from thelow shade treatment. The total nitgrogent content was satistically lower in thehigh shade (1.l14± 0.22%, n=33) compared to that in full light (1.36± 0.22%;n=31). These results suggest that light environment may have a significant effecton the concentrations of limonoids and nitrogen in S.macrophylla which in turninfluences the shoot borer attack.The study forms part of a larger project on 'Silvicultural prescription formahogany plantation establishment; Research grant funded by DFlD, UK isgreatfullyacknowledged.