The insect growth regulator NC-184, a juvenile hormone mimic, prevents moulting to the adult stage in the desert locust, Schistocerca gregaria (Forskål) (Orthoptera: Acrididae). Male nymphs treated in the penultimate or final nymphal instar with NC-184 exhibit precocious mating behaviour in the final instar. We examined whether this chemical affects the development of the internal reproductive organs of crowded nymphs. In treated males, both accessory glands and seminal vesicles were underdeveloped, and no sperm was found in the seminal vesicle, whereas these organs in control individuals had greatly increased in size 10 days after treatment, when all the insects had moulted to adults. Testis size in treated males was similar to that in controls, regardless of their smaller body size due to the inhibition of moulting. Oogenesis and development of spermatheca in females treated with NC-184 continued to some degree, but no eggs matured, unlike what occurred in the control. In conclusion, treatment of S. gregaria nymphs with NC-184 resulted in changes in the reproductive organs in both sexes.
The number of larval moults, larval head capsule width and pupal weight were investigated in both direct-developing and diapausing individuals of a South-West European population of Coenonympha pamphilus. The frequency distributions of head widths of successive larval instars overlapped, partly due to variation in the number of larval moults. The larvae that entered diapause went through five instars, instead of the four reported from this species. The evidence indicates that the five instar developmental pathway represents a plastic response rather than an example of compensatory growth. This alternative growth pattern was expressed in response to short photoperiods in parallel with, or as a consequence of, larval diapause. On average, the larvae with five instars had larger heads than their normal siblings. This resulted in comparatively heavier male pupae, while the opposite trend occurred in females. It is concluded that the variation in the number of larval instars is a plastic response to diapause when temperatures remain mild and that it might have an adaptive value in areas with mild winter climates. The sexually dimorphic expression in the larval growth patterns, in terms of pupal weight, may well imply different patterns of allocation of larval resources to adult structures, although sex-dependent differences in investment into purely larval structures cannot be discounted.
Several culture media as well as some factors that may affect the in vitro development of the nematode Anisakis simplex Rudolphi, 1809 have been studied. After testing six media and four temperatures, the conditions for the in vitro culture selected were as follows: RPML1640 + 20% (v/v) heat-inactived fetal bovine serum or Meyer’s М3 (without agar) media, at 37"C, under 5% C02 in air atmosphere, and renewal of the medium twice a week. The average survival rates of the larvae were significantly increased when the pH of the culture medium was increased (from 4.0 to 7.2) or decreased (from 7.2 to 4,0) after L, to L4 moulting. The length of the larvae at the onset of culture affected the survival and moulting of themselves, but these were culture medium-dependent. On the other hand, we have observed that several L, and L, were attached, by means of a brown unknown substance apparently secreted by themselves, to the bottom of the substratum. Frequently, when a larva was spontaneously detached, a “cap” of the brown substance blocked, apparently, its mouth. The possible absorption of nutrients through the L, larvae cuticle of A. simplex is discussed.