Larvae of eight sea spiders from three families (Ammotheidae, Pycnogonidae and Phoxichilidiidae) are described for the first time. The external morphology of the first larval stage of each species is presented in detail using scanning electron microscopy photographs in order to determine the mode of postembryonic development. Three types of larval development are apparent in the species examined. The species Achelia gracilipes, Eurycyde spinosa, Pycnogonum rickettsi and Pycnogonum stearnsi (families Ammotheidae and Pycnogonidae) have larval morphologies indicative of an ‘ectoparasitic’ development. Morphological characteristics of Achelia simplissima and Achelia chelata (family Ammotheidae) larvae suggest an ‘endoparasitic’ development, while larvae of the species Anoplodactylus viridintestinalis (family Phoxichilidiidae) have traits implying an ‘encysting’ postembryonic mode of development. Larvae of the species Nymphopsis spinosissima have unusual morphological characteristics that may be indicative of a new developmental mode.

Postembryonic development and adult emergence of Tribolium castaneum (Herbst) were adversely affected in varying degrees when its larval stage was reared on wheat flour treated separately (at concentrations of 0.001–1.0%) with one of the following commercially available extracts: roots of both sweet flag, Acorus calamus Linn. and Java devil pep per, Rauwolfia serpentina Benth ex Kurz, fruit cortex of soap nut, Sapindus trifoliatus Linn. and gum of Indian Myrrh Commiphora mukul Jacq. A marked decline in the reproductive potential, in terms of female fecundity and egg hatchability was observed when the extracts were applied topically or administered orally through diet.