The shootborer <u>Hypsipyla</u><u>grandella</u> (Zeller) (Lep., Pyralidae) is the main obstacle to the artificial regeneration of valuable meliaceous tree species such as mahogany ( <u>Swietenia</u> spp.) and Spanish cedar ( <u>Cedrela</u> spp.) in Latin America. On the other hand, the natural regeneration of these species is endangered due to depletion of the naturally existing resources and burning in colonization projects.<p/>This dissertation concerns the development of several fields of research, which when incorporated in a programme of integrated control may contribute to a solution of the <u>Hypsipyla</u> problem.<p/>Chapter 1 contains a general introduction on this insect pest and its host plants in Costa Rica. In addition, a review is provided of the economic importance of the pest in tropical forestry and of the previous and contemporary investigations on the possibilities of its control.<p/>The research carried out in the framework of the Inter-American Working Group on <u>Hypsipyla</u> at the tropical Research and Training Centre of the Inter-American Institute of Agricultural Sciences at Turrialba, Costa Rica, is dealt with in Chapter 2.<p/>These investigations refer to the natural resistance of Meliaceae, host selection, development of an artificial rearing technique for <u>H</u> . <u>grandella</u> and to a survey of parasites in Costa Rica which might be employed in a biological control of the shootborer.<p/>The main results are:<p/>a. Two exotic Meliaceae, African mahogany ( <u>Khaya</u><u>ivorensis</u> ) and the Australian cedar ( <u>Toona</u><u>ciliata</u><u>var</u><u>australis</u> ) were introduced and were found to be immune against attacks of the shootborer. Biological and chemical screening for the basis of resistance of the Australian cedar led to the location of two toxic components in the aqueous fraction of young leaves and shoots of this tree species. The toxicity of <u>Toona</u> can be translocated to <u>Cedrela</u><u>odorata</u> grafted on the Australian cedar.<p/>b. Experiments on the host selection of <u>H</u> . <u>grandella</u> point at the existence of a host selection mechanism in which the female adult orients itself towards the host by means of olfaction. Fourth instar larvae of the borer prefer native hosts to exotic species as food sources.<p/>c. An artificial rearing technique was developed for <u>H</u> . <u>grandella</u> . A diet (Vanderzant) used for rearing <u>Heliothis</u><u>zea</u> appeared to be a suitable medium for mass rearing <u>Hypsipyla</u> . Although initially mating of adults could only be obtained in outdoor cages in Costa Rica, subsequent rearing in Wageningen, under completely artificial conditions, proved to be perfectly feasible. Larval and pupal periods of <u>H</u> . <u>grandella</u> reared on artificial and natural diets were determined, and compared. Female adults are generally larger than males and live longer. Artificially reared females still restrict oviposition to meliaceous host plants.<p/>d. A survey of biological control agents of -the shootborer resulted in the following new records of <u>H</u> . <u>grandella</u> parasites in Costa Rica: <u>Trichogramma</u> f <u>asciatum</u> , <u>T</u> . <u>pretiosum</u> , <u>T</u> . near <u>pretiosum</u> , <u>T</u> . <u>semifumatum</u> , <u>Hypomicrogaster</u><u>hypsipylae</u> sp. n., <u>Brachymeria</u><u>conica</u> and <u>Bracon</u><u>chontalensis</u> ; an <u>Agathis</u> sp. has to be identified yet. In addition the nematode <u>Hexamermis</u><u>albicans</u> was found to parasitize larvae of the shootborer in <u>Swietenia</u><u>macrophylla</u> and <u>Cedrela</u> spp. The egg parasite <u>Trichogramma</u><u>semifumatum</u> could be reared easily on eggs of <u>H</u> . <u>grandella</u> .
There are no comments yet. You can post the first one!
Post a comment
Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.