In a laboratory study two coccinellid species, Coleomegilla maculata (DeGeer) and Harmonia axyridis Pallas, completed preimaginal development on lacewing eggs, Chrysoperla carnea Stephens or pea aphids, Acyrthosiphon pisum (Harris) in similar times. Preimaginal survival on C. carnea eggs was similar to survival on A. pisum for all stages of C. maculata and H. axyridis. Coccinellid adults that developed on C. carnea eggs were smaller than adults reared on A. pisum. Coccinella septempunctata L. did not complete preimaginal development on C. carnea eggs. Chrysoperla carnea preimaginal developmental time was approximately 20 days when fed either C. maculata eggs or A. pisum. Chrysoperla carnea fed C. maculata eggs developed into smaller adults, compared to adults reared as larvae on A. pisum, Ostrinia nubilalis (Hübner) eggs, or A. pisum alternated daily with O. nubilalis eggs. C. carnea did not complete preimaginal development on H. axyridis eggs. Cannibalism occurred more frequently between C. carnea third instars than between C. maculata fourth instars. When a C. carnea third instar was paired with a C. maculata fourth instar, more C. maculata were preyed upon by C. carnea, regardless of the herbivorous prey density. In the field these two predator species may negatively affect each other and reduce their suppression of pest densities.

Life-history characteristics of four populations of Coccillella septempullctata L. were quantified and compared at 26°C and 18:6 (L:D) h on a diet of pea aphids, Acyrthosipholl pisum (Harris). Populations were from two locations in the United States (Iowa and Delaware) and two locations in Eurasia (France and Ukraine/Moldavia/Crimea). Large intrapopulation variation was observed in preoviposition, interoviposition, and number of days on which eggs were laid. This variation was a result of 10-35% of females entering diapause, whereas most females initiated oviposition within 12 d of eclosion and continued egg laying with interoviposition periods of <6 d. No significant differences among the four populations were detected in preoviposition, interoviposition, or number of days on which eggs were laid. In addition, preimaginal development time, sex ratio, and life table parameters, including intrinsic rates of increase and fecundity, did not differ significantly among the four populations. On the basis of the parameters measured, we conclude that these four populations of C. septempullctata have not undergone local adaptation that would define these populations on the basis of geographical origin.

Five treatments were used to exclude naturally occurring predators and parasitoids, based on body size and flight ability, to assess their effect on Ostrinia nubilalis (Hübner) populations on corn plaits. Two initial O. nubilalis egg densities (one egg mass and three egg masses per plant) were assigned to each treatment. Egg predation was higher in uncaged treatments than in caged treatments. Flying insect predators, primarily Coleomegilla maculata DeGeer (Coleoptera: Coccinellidae), reduced egg densities by 50%. Thirty-five to 84% of O. nubilalis larvae were infected with Nosema pyrausta (Paillot) (Microspora: Nosematidae). The incidence of Beauveria bassiana (Balsamo) Vuillemin (Deuteromycotina: Hyphomycetes), ranged from 0 to 21%, whereas larval parasitism, mainly by Macrocentrus cingulum Reinhard (Hymenoptera: Braconidae) ranged from 0 to 31%. In contrast to previous studies, this 3-yr field study documents that egg predation and larval infections of O. nubilalis were significant and consistent biotic mortality factors.

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A linear relationship was observed between ovarian developmental rate in Coccinella septempunctata L. and five constant temperatures (14-30°C). The estimated lower temperature threshold for follicle development was 13°C. Development of follicles to maturity (egg chorionation) required 833 degree-hours (°H > 13°C). A five-stage rating system to describe ovarian development in C. septempunctata was based on the length of the terminal follicle, number and shape of developing follicles in each ovariole, and presence of yellow color in the terminal oocyte. In 60-70% of females at each temperature, follicle development in relation to female age (time) followed a sigmoidal pattern. This sigmoidal curve had three phases, a previtellogenic or lag phase, a vitellogenic development phase characterized by rapid increase in follicle length, and a postvitellogenic or chorionization phase characterized by a constant follicle length. An equation to predict either the proportion of gravid females on the basis of degree-hour accumulations, or the degree-hour accumulations on the basis of proportion of gravid females, was developed.

For insects such as aphidophagous lady beetles, whose preferred food varies naturally in space and time, variation in adult body size is most likely a reflection of food acquired and allocated to growth by the final instar. We conducted a laboratory study to evaluate the nature of body size variation in Coleomegilla maculata (DeGeer), Harmonia axyridis (Pallas), and Hippodamia convergens Guerin‐Meneville (all Coleoptera: Coccinellidae) by assessing how fourth instars respond developmentally to food deprivation. We also determined which growth functions best describe larval growth trajectories and evaluated whether these fourth instars regulate their growth based on initial body size. Access to food for a minimum of 1 day during the fourth stadium appeared to be a requirement for pupation in all three species. Putative critical weight for pupation falls within 10–14 mg for C. maculata, 13–16 mg for H. convergens, and 19–22 mg for H. axyridis, and development period after attaining the critical weight is not affected by food deprivation. The mixed‐effect logistic function that accounted for individual and gender differences provided the best description of growth in the fourth instars of the three species. The reduced major axis regression revealed that growth in these lady beetles was convergent‐regulated. The logistic growth trajectory, existence of critical weight, and determinate developmental response to food deprivation are traits that seem to suggest that fitness increase is attained by maximizing body size rather than survival in these beetles.

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