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Field and laboratory techniques for assessing infestations of the nettle caterpillar, Latoia viridissima Holland (Lepidoptera: Limacodidae)

Published online by Cambridge University Press:  19 September 2011

I. B. Igbinosa
I. B. Igbinosa
Affiliation:
Zoology Department, University of Nigeria, Nsukka
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Abstract

Techniques for assessing infestation trends of Latoia viridissima are presented in this report. A plot of the head capsule widths of larvae indicated six larval instars with instars one and two being more abundant. It also illustrated the composition of larval instars in the population and hence would serve as a standard against which future samples of the species could be compared. Larval survivorship data indicated heavy mortality (>60%) during instars one and two. Major mortality factors were an aggregate of natural enemies, particularly predators (causing 40–50% of the death during the age interval), parasitoids and pathogens responsible for 60–80% mortality throughout the entire larval life. The residual cocoon populations were further reduced by about 20–30% by parasitoids (Brachymeria sp., Chrysis spina, Cocygodes coccyx, Palexorista sp and Systropus pelopoeus) and a pathogenic fungus. Data from cocoon samples showed that the sexes of the moth could be separated on the basis of cocoon size. Cocoon weights were therefore, a better criterion than cocoon diameter values for separating the sexes; since overlap between the sexes was less than 5 % for cocoon weight as against 20% In the case of cocoon diameters. The separation point tended to lie between cocoons weighing 350–399 mg. Fecundity of the females was highly correlated with female weights (r = 0.901) and wing length (r = 0.89), The calculated fecundity of 143 eggs/female (using wing length) was not statistically different (P ≤ 0.05) from the observed value of 149 eggs/female. The significance of the findings as regards forecast of outbreaks and assessment of outbreak situations are discussed.

Résumé

Les techniques de l'évaluation de la tendence de l'invasion de Latoia viridissima sont présenté dans ce rapport. Un graphique des lageurs de la capsule des tétes des larves indique six stades larvaires, dont 1 et 2 étaient les plus abundant. Il a aussi iltustré la composition des stades larvaires dans la population, et peut done servir comme standard auquel des échantillons futurs peuvent être comparer. Les données de la survie de la larve indiquent une grand mortalité (>60%) pendant les stade 1 et 2. Les facteurs majeurs causant la mort étaient un agrégé des ennemis naturels—particulièrement les prédateurs (causant 40–50% des morts pendant l'âge interne), parasitoides et pathogènes responsable pour 60–80% de mortalité durant toute la vie larvaire. La population résiduel du cocon était encore réduit par 20–30% par parasitoides, Brachymeria sp., Chrysis spina, Cocygodes coccyx sp. et Systropus pelopoeus et un champignon pathogénique. Les données l'échantillons du cocon montrent que les sexes des papllions des nuits pouvent ètre séparer par lageurs du cocon.

Les poids des cocons étaient alors un critérium mailleur que les valeurs du diamètre des cocons pour séparer les sexes; car le recouvrement entre les sexes était moins de 5 % pour les poids du cocon, contre 20% dans le cas des diamètre du cocon.

Le point de séparation tend d'être situer entre les cocons qui pesent 350–399 mg. La fécondité de la femelle était bien lie aux poids femelle (r = 0.901) et longeur de l'aile (r = 0.89). La fécondité calculée des 143 oeufs/femelle (employant la longeur de l'aile) n'était pas différent dans la statistique (P ≤ 0.05) de la valeur observée des 149 oeufs/femelle. L'importance des découvertes en ce qui concerne la prévision des manifestations et l'évaluation des situations des manifestations sont discuté.

Keywords

TechniquesLatoia viridissimaabundancesurvivorship fecunditysegregationsex ratioforecastoutbreaksnatural enemies
Type
Research Articles
Information
International Journal of Tropical Insect Science , Volume 13 , Issue 3 , June 1992 , pp. 389 - 398
Copyright
Copyright © ICIPE 1992

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