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Female Oncopeltus fasciatus in long-day photoperiods lay eggs 15-20 days after their adult molt. Individual bugs transferred to short-day photoperiods extend age at first reproduction to about 80 days, but populations maintained in that same short-day condition show rapid decrease in extent of reproductive delay. Results from breeding experiments suggest that this decrease cannot be avoided, and those from parent-offspring comparisons for extent of reproductive delay in newly encountered short-day conditions indicate heritability of about 0.70. We suggest that the high level of additive genetic variance influencing female sensitivity to photoperiod functions as a "genetic rheostat" and results in eggs of the fall field population being optimally distributed geographically in the face of varying association between photoperiod and temperature. Genetic variance for the response is probably maintained by seasonally reversing selection pressures and by substantial genetic interchange among populations of this...

Using two geographically adjacent, temperate-zone populations of the milkweed bug Oncopeltus fasciatus, we employed a split-family experimental design to estimate genotype-environment interaction (g-e) and across-environment genetic correlations for two female life history characters, age at first reproduction and fecundity over the first 5 days of reproduction. For each of a number of families, some sisters were reared in a short-day environment (LD 11:13, 23$^\circ$C) and others in a long-day environment (LD 14:10, 23$^\circ$C); the environments were chosen to simulate the temporal environmental heterogeneity experienced by lineages of temperate-zone bugs. Bugs normally exhibit a plastic response to such heterogeneity by delaying the onset of reproduction in short days relative to that in long days, the delay providing time for migration to occur. In one population, there is significant variation caused by g-e for the age at first reproduction, indicating the existence of genetic variance for plasticity...

Agonistic and feeding behavior and morphological structure were studied in five stomatopod crustaceans with raptorial appendages adapted for spearing prey. Agonistic behavior was less frequent and less vigorous than in species adapted for smashing. Of the spearers, the most aggressive species, Cloridopsis scorpio, possessed a heavier raptorial apparatus and constructed the most complex burrow. Harpiosquilla harpax preyed on fish and had the longest raptorial appendages and largest eyes. The remaining species (three Oratosquilla spp. and C. scorpio) possessed similar raptorial appendages but sorted out by water depth, body size, eye size, and length of antennules. The latter two measurements suggest that differences in the structure and function of sensory systems may be important considerations in the analysis of foraging strategies and resource partitioning.

Density, photoperiod, and temperature exert profound effects on the life history and population growth of Oncopeltus. High temperature, long photoperiod, and low density result in earlier onset of reproduction, negatively skewed egg curves, and hence greater rates of population increase. Values or r (intrinsic rate of natural increase) vary from .0861 on a 16-hr day at 27⚬C with density of 10 pairs per container to .0369 on a 12-hr day at 23⚬C and 20 pairs. When r is low, length of life increases in partial compensation for suppressed reproduction. Photoperiod and density exert their influence only after adult eclosion, while temperature acts directly at all stages of life history to regulate the rate of development. The population responses of the phenotype to the environmental parameters studied are positive adaptations for a migrant insect such as Oncopeltus. It enters an essentially empty universe in the spring, when day length is increasing and temperatures are rising. The fact that all these factors...

1. Mating, feeding, and oviposition cycles were observed in the large milkweed bug, Oncopeltus fasciatus, under four regimens of varying temperatures and 24-hour photoperiods.2. Mating and feeding activity reached maximum at the end of the light phase while oviposition occurred 8 hours after light on.3. When placed in continuous light or dark, cyclic activity of all three behaviors persisted for at least one cycle and in the case of oviposition for five cycles. In general, the period of the first one or two cycles for all three activities, in both continuous light and dark, was approximately 21 hours; subsequent cycles, if present, had periods of 24 hours or longer.4. Photoperiod was found to affect the maximum mating and feeding activity which occurred during the day. Long photoperiods promoted higher levels of mating and feeding than did short photoperiods.5. The time from eclosion to first mating was photoperiod- as well as temperature-dependent; longer photoperiods and higher temperatures shortened th...

1. Courtship and copulation are brief in G. bredini. Either sex can indicate courtship by approaching; after antennular palpation the male then grasps the female by the carapace and copulation takes place.2. Receptive females can be distinguished morphologically by darkened internal organs visible through the telson and behaviorally by their acceptance of a male's approach. Unreceptive females attack males immediately.3. Males share cavities with females during the few days prior to spawning. Following egg-laying females defend cavities against males. The eggs are kept in the cavity and frequently manipulated; the newly hatched larvae remain in the cavity with the female until they reach Stage IV.4. The form and duration of reproductive and maternal behavior in G. bredini are apparently a consequence of cavity living.

1. Giant water bugs swim when suspended free of the substrate. This situation contrasts with that of terrestrial insects which fly when freely suspended. Swimming can be stopped by returning contact to the bugs.2. Suspended bugs respond to wind with a general increase in rate and duration of swimming, followed by a decrease in both.3. When bugs are in water, swimming is stimulated by a hair bed located on the trochanter at the coxo-trochanteral joint. These hair beds seem to be stimulated by cuticular folds which cover them when the legs hang down, but roll back and heave them uncovered when the legs float, resulting in swimming.4. Flight or wing opening occurred with 8 of 44 suspended bugs. A hair bed on the head functions in both the maintenance and initiation of flight in response to wind.5. The bugs possess an elaborate pre-flight behavior which is apparently necessary to unlock a ball and socket mechanism attaching the wings to the pterothorax. This pre-flight behavior inhibits swimming and causes th...