Adults In July Research Articles

Contagious egg‐distribution on host pods and avoidance of pods received eggs in a wild bruchid Kytorhinus sharpianus

SummaryThe present study investigated the way a wild bruchid, Kytorhinus sharpianus, distributes its eggs on host pods. First, we counted the number of eggs per pod on the host plant (Sophola flavescens) in the field. The egg‐distributions by the overwintered‐generation adults in July and by the second‐generation adults in mid October did not deviate from Poisson distribution because of small numbers of eggs laid. However, the egg‐distribution in late August when many first‐generation adults emerged was significantly contagious.The deposition of eggs was determined for three types of pods: (A) clean pods, (B) pods with eggs, and (C) those which eggs had been laid on but were removed from later. The numbers of eggs laid newly on three types of pods were significantly different; A>C>B, suggesting that an oviposition marker pheromone (O.M.P.) caused females to avoid pods on which eggs were deposited. Egg‐shells reinforced that response.Monte Carlo simulations for the egg‐distribution on pods predicted that even if females avoid pods with heavy egg‐load through O.M.P., the egg‐distribution becomes contagious when there is a large heterogeneity in quality of the pods.

POLYDORA COMMENSALIS ANDREWS—LARVAL DEVELOPMENT AND OBSERVATIONS ON ADULTS

1. Polydora commensalis larvae were found in the plankton from July to November, 1963, and fertilized eggs were found in the tubes of adults in July and August.2. Fertilized eggs develop into 5-segment larvae within 5 to 7 days, at which stage they are liberated to the plankton.3. Ciliation, setation, pigmentation and other taxonomically important features are described for larvae from the trochophore to 29-segment stage. Planktonic larvae of all stages possess a dorsal median row of black ramified chromatophores. Advanced larvae may exceed 2 mm. in length. The pigmentation and large size attained are the most outstanding characteristics of P. commensalis larvae.4. Due to the similarity between larvae of P. commensalis and P. hermaphroditica, a comparison of the two is given.5. The length of larval life of P. commensalis is estimated to be between one and one and a half months.6. Data on distribution, habitat and reproduction are reported. It is suggested that this annelid is more widely distributed than reported, and that fertilization is accomplished by copulation.