Impact and differential effect of certain biomortality factors on the eggs and newly‐hatched larvae of the Pink Borer, Sesamia cretica Led. (Lep., Noctuidae) on two sugarcane varieties

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Abstract
A study was initiated during spring 1977 sugarcane‐growing season to evaluate the potential impact of certain biocontrol mortality agents on the eggs and early instar larvae of the pink borer Sesamia cretica Lederer naturally infesting a susceptible (GT 54‐9) and a relatively resistant (NCO 310) sugarcane varieties.The following major results have been reported: 1. egg parasitism by the scelionid, Telenomus sp. was the key mortality factor during the egg stage. It was also found that percent parasitism (ca. 74 %) did not differ significantly between the varieties. Egg predation by predaceous arthropods played a minor role in egg mortality (less than 2 %), 2. significant higher natural loss and fewer number of early instar larvae were reported on NCO 310 than on GT 54‐9, 3. dispersal loss of early instar larvae did not play a significant role in larval mortality and 4. the apparent differential susceptibility of the 2 varieties to borer damage was primarily detected during the early period of larval establishment.It was also found that adult moths showed no “ovipositional preference” between varieties (no. and size of egg mass did not differ). This was also true for percent egg hatchability. It was generally concluded that parasitism during the egg stage and predation during the early larval stage (especially by true spiders) were the 2 most important key mortality factors of this pest.Zusammenfassung: Über die Wirkung von Mortalitätsfaktoren bei den Eiern und Eilarven von Sesamia cretica Led. (Lep., Noctuidae) auf zwei verschiedenen ZuckerrohrsortenBei populationsanalytischen Untersuchungen der Eier und Eilarven von S. cretica an einer schädlingsempfindlichen und einer relativ unempfindlichen Zuckerrohrsorte wurden folgende Ergebnisse erzielt: Hauptmortalitätsfaktor war der Eiparasit Telenomus sp. (Scelionidae) dessen Parasitierungsquote mit ca. 74 % an beiden Zuckerrohrarten gleich war. Arthropoden als Eiräuber spielten mit ca. 2 % Mortalität eine nur geringe Rolle. Dagegen war die Eilarvensterblichkeit an der empfindlichen Sorte signifikant höher als an der relativ unempfindlichen. Ausbreitungsverluste hatten bei den Larven keine Bedeutung. Die weiblichen Falter zeigten hinsichtlich der Eiablage keine Präferenz zwischen den beiden Pflanzensorten. Auch die Schlüpfperiode der Eier war gleich. Die zwei wichtigsten Regulationsfaktoren bei diesem Schädling sind einmal die Eiparasitierung und zum anderen die Vernichtung der Jungraupen durch Prädatoren, vor allem Spinnen.