Most previous data suggesting maternal inheritance of mtDNA have come from single-generation mating experiments, and most of the analytical techniques utilized would not have detected paternal mtDNA molecules in progeny at levels less than about 5%. Long-term mating experiments, in which a fertile female lineage derived from hybridization of two species with distinguishable mtDNAs is backcrossed recurrently to the male parental species, provide an ideal opportunity to assess possible low-level paternal leakage. We have analyzed the 45-and 91-generation backcross progeny of such matings between two species of lepidopteran insects [Heliothis (Noctuidae)], using autoradiographic techniques that can detect rare mtDNA molecules in <1 part per 500. The analysis failed to detect any paternal mtDNA and sets an upper limit of paternal leakage at about 1 molecule per 25,000 per generation in this system. In higher eukaryotes, the majority of mtDNA is known to be transmitted to progeny through egg cytoplasm (1-9). However, sperm also carry small numbers of mtDNA molecules, and the possibility of a low-level paternal contribution of mtDNA to progeny (paternal leakage) has seldom been addressed.This study was motivated by the recent findings of extensive mtDNA sequence variation and divergence in higher eukaryotes and by the evolutionary interpretations placed upon these findings (5, 10-16). For example, because mitochondria are generally thought to be maternally inherited, variation in mtDNA has been used to estimate matriarchal phylogenies within and among species (10,12) and to determine the female parental species of parthenogenetic hybrids (13). Such interpretations could be compromised if sperm commonly contribute small numbers of mtDNA molecules to zygotes. The possible consequences of paternal leakage have been modeled mathematically (17,18), and results demonstrate that even small amounts of paternal input can be significant, acting as a "gene-flow bridge" between otherwise isolated female lineages and importantly influencing the evolutionary dynamics of mtDNA variation. The purpose of this report is to empirically reexamine the possibility of low-level paternal leakage of mtDNA. MATERIALS AND METHODSMale Heliothis virescens (F.), the tobacco budworm, hybridized with females of a related species, H. subflexa .Guenee, produce fertile female and sterile male progeny (19,20). Male sterility is perpetuated through recurrent backcrossing to H. virescens males and forms the basis of a control strategy for this major agricultural pest (21-23). Two independent malesterile strains were used in our experiments: BC-91 had been continuously backcrossed for 91 generations and BC-45, for 45 generations. Both strains are maintained in Stoneville, MS, and colonies derived from them were reared for several generations in one of our laboratories prior to this study. The number of females mated in each generation has usually exceeded 100 and, in the case of BC-45, has been as high as several thousand.Mitochondria from 70-110 ...

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The genetics of host selection, in terms of oviposition behavior, was investigated in two species of monophagous gall-forming flies. The existence of a single major allele difference in the genetic basis of host selection was established by a series of hybrid crosses between these flies. The complimentary role of conditioning was also investigated. The apparently simple genetic change required to produce a change in host selection suggests a mechanism of sympatric speciation applicable to these insects.

Colonies of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) were established from field‐collected pupae and reared for 12 generations (G) using 3 different methods; given special care (C). eased from special care into mass rearing (E), and forced directly into mass rearing (F). The respective average numbers of viable pupae per ♀ increased from 1.5, 1.7, and 2.0 at G1 to 6.3, 6.6, and 8.5 at G12. The number of viable eggs per fertile ♀, though varying greatly depending on generation, never had an increasing or decreasing trend. Thus, since the fertility of individual ♀ ♀ remained relatively constant, improved yields were primarily due to an increase in the proportion of reproducing females. Furthermore, switching the E colony to the F regimen after G5 was as detrimental as initial colonization. RÉSUMÉ Stratégies de colonisation et d'entretien deCeratitis capitata Des souches de Ceratitis capitata ont été formées à partir de pupes récoltées dans la nature et élevées pendant 12 générations (G) suivant 3 méthodes différentes: avec soins particuliers (C) soins particuliers pendant 5 générations puis tranfert sur régime et substrat artificiel en élevage de masse (E), élevage de masse continu sur régime et substrat artificiel (F). Les nombres moyens de pupes viables par femelle ont augmenté respectivement de 1.5, 1.7, et 2.0 and G1 à 6.3. 6.6 et 8.5 en G12. Les nombres d'oeufs viables par femelle féconde ont varié beaucoup suivant les générations sans aucune tendence marquée. Ainsi, puisque la fécondité par femelle est restée relativement constante, l'augmentation de la production est parvenue avant tout de l'augmentation de la proportion de femelles fécondes. Par ailleurs, le transfert de la souche E en régime F après G5 a eu des effets aussi négatifs que la colonisation initiale.

A model was developed which corrects and extends an earlier one proposed for the control of the tobacco budworm, Heliothis virescens (F.), through hybrid male sterility. Population suppression is effected through the release into natural populations of the backcross progeny of a hybrid between H. virescens and a related species. Thereafter, the system perpetuates itself in nature through continual backcrossing of the fertile backcross females to native H. virescens males. When the proportion of backcross hybrid females in the total population is large enough to draw off the insemination potential of the native males, the native females fail to replace themselves. The present model demonstrated that the ratio of released backcross hybrids to natural H. virescens remains constant in a closed population. Furthermore it was shown that the release ratio necessary to achieve extinction of a closed population is related to the number of females that a male can inseminate and to the population growth rate. Release ratios required to slow natural population growth and to lessen the impact damage of releases on crop plants were also examined. Effects of selection against the backcross females on the predictions of the model were explored.