The structure of the sclerous parts of representative Rhynchota is analyzed and compared with those of Psocoptera and Thysanoptera. Known data on embryology and musculature are also considered in deriving homologies of the structures. The term "suture" is redefined. Standardized terms for the sclerous parts of the head capsules of Rhynchota are recommended and compared with those of previous authors. A phylogenetic synthesis is presented, demonstrating the evolution of the homopterous head capsule through intermediate stages represented in the modern fauna by Psocoptera, Thysanoptera, and Hemiptera–Gymnocerata. Evidence is presented that Coleorrhyncha are related to Hemiptera rather than to Homoptera, that the Gymnocerata and Cryptocerata are natural groups within the Hemiptera and that Cicadomorpha, Aphidomorpha, and Fulgoromorpha are natural groups within the Homoptera.

Frazer and Gilbert (1976) described the predation of pea aphids, Acyrthosiphon pisum (Harris), by adult coccinellids. They developed a formula to predict the predation rate as a function of temperature, predator density, and prey age-distribution and density. Gutierrez et al. (1979) extended the formula to describe several predators sharing the same prey. The following papers develop the study to cover the complete predator-prey relationship, including the dynamics of both predators and prey.

Changes in the numbers of adults of Coccinella californica Mannerheim and C. trifasciata Mulsant in small plots of alfalfa and oats were monitored over the summers of 1974 and 1975 by mark–recapture methods. Aphid population dynamics in the plots were studied concurrently. In the second summer, movements of the beetles were also monitored by means of individual marking and sticky net traps. Approximately 1000 beetles of each species were marked in the first summer; in the second, roughly 5000 and 3000 respectively. The capture–recapture method was tested with a caged population, and was found to be feasible for estimation of the coccinellid numbers. Catch per unit effort, using visual sampling that was not dependent on marking, provided an acceptable index of numbers which could give population estimates when calibrated against mark–recapture estimates.

The number of beetles trapped on the sticky nets was primarily a function of numbers in the plots and temperature, with the two species having different relationships between temperature and flight. But for C. californica, the numbers trapped were also a function of aphid density in the plots; the data suggested that for C. trifasciata the same is probably true, but the range of densities of pea aphids was too narrow to show it. In both seasons, C. trifasciata was predominant in the alfalfa and C. californica in the oats. Plot to plot movements by overwintered beetles reflected the same apparent preference. Changes in the numbers of coccinellids in the experimental plots, and their reproductive success, are discussed in the light of these findings.

The relationship between feeding rate and egg production of Coccinella trifasciata Mulsant and C. californica Mannerheim feeding on pea aphids, was investigated in the laboratory at 15.0°, 18.5°, 21.5°, and 25.5°C. Both species increase their feeding rate with increasing temperature above 13.6°C, with C. californica, the larger species, increasing its food consumption faster. C. californica also has the higher maintenance requirement but when food consumption is expressed relative to the beetles’ body weight, there is no difference between the species in either attribute. Coccinella californica converts excess food to eggs more efficiently than C. trifasciata.

No significant influence of temperature on either the conversion rate or the maintenance requirement could be detected. The adverse effects of a very low feeding rate, whether due to restricted food supply or low temperature, influenced the beetles’ response to subsequent treatments.

The behavior of larval stages of the green lace wing, Chrysopa carnea Stephens, and of the ladybird beetle Hippodamia convergens G.-M. were studied in the laboratory. With increasing hunger level, only first instar H. convergens larvae spent more time searching in the upper part of alfalfa stems, where both prey aphids, Acyrthosiphon pisum (Harris) and Acyrthosiphon kondoi (Shinji), are found. All larval instars tested except first instar C. carnea visited more stems per unit time with increasing hunger level. The weight gain, the developmental time, and the mortality of all larvae were adversely influenced at low food levels, but differently for each predator size and species. C. carnea larvae had higher rates of fat body utilization and weight gain than coccinellid larvae.

Previous work described the effects of predation of pea aphids by adult coccinellids. That work has been extended to cover the entire reproductive cycle of the coccinellids. The relationship between amount of aphids eaten, and numbers of coccinellid eggs produced, was determined in the laboratory and used to predict numbers of eggs produced in the field. The survival rate of the eggs to adults, as a function of aphid density, was estimated in large field cages and in small enclosures. These relationships were incorporated into a population model for both predators and prey. The model has been validated against field data. It suggests that predator reproduction is optimized when conditions are very good. The significance for optimal foraging theory and biological control is discussed.

Hunger and abundance of adult Coccinella californica (Mannerheirn) preying on pea aphids, Acyrthosiphon pisum (Harris), on alfalfa, Medicago sativa L., were assessed in the field. There was no consistent relationship between abundance or hunger and aphid density. The field beetles encountered in sampling were 4 times hungrier at each observed aphid density than expected from a simulation model of the predation that is driven by hunger. Laboratory studies revealed a circadian rhythm of beetle activity that was modified by hunger. An index of predatory potential (number of beetles times average hunger) was found to be a better indicator of impact of the beetles than absolute numbers of all coccinellids or hunger separately. It is suggested that the beetles encountered in simply walking through a field produce the most useful index of numbers of hungry beetles. This census must be done daily however because of the high vagility of adult coccinellids.

A series of field experiments using large field cages were used to evaluate the role of aphidophagous predators on the population dynamics of the pea aphid, Acyrthosiphon pisum (Harris), on alfalfa, Medicago sativa L. The pea aphid numbers increased rapidly in the cages to as much as 5 times the density in the adjacent fields. The difference between densities in the cage and field decreased as the season progressed. No significant differences in fecundity of the aphids were found either in clip cages in the field and cages, or in the laboratory using field-collected aphids that were allowed to larviposit for 24 h. We used an earlier simulation model of the aphid to show that if fecundity alone were responsible it would have to be 3 times the maximum rate we have ever observed. The return of the aphid density to the field value when one cage was removed and the aggregation of predators show the importance of predator movements in limiting prey numbers.

We studied first and fourth instar larvae of Coccinella trifasciata L., C. Californica Mannerheim, C. undecimpunctata L., and Cycloneda polita Casey searching for Acyrthosiphon pisum (Harris) on alfalfa seedlings and for A. dirhodum (Walker) on oat seedlings, in the laboratory. Styles of search varied considerably, but each species of larva could capture aphids on each species of plant. Observed differences in relative abundance of the four species of adult coccinellid in alfalfa and oat fields are not related to the success of their larvae in finding aphids.

Consider a predator which, when hungry, has a discovery rate (= search rate × probability of finding prey) of a prey per unit time. When satiated, its demand rate for prey is 1/T, where T is the time-interval between successive prey captures when the predator is surrounded by excess of prey. Both a and T may vary with temperature, etc. Let s(N) be the expression for prey survival rate, during an infinitesimal time-period dt, as a function of prey density N.