Fertilizers Cont

Cuticular hydrocarbons are part of the lipid layer of the insect cuticle that protects from desiccation (Lockey, 1988) and are thus present in basically every social insect (see Chapter 6). Insects have the sensory apparatus to detect these profiles. So it is not surprising that they utilize variations in hydrocarbon profiles between individuals within and between species to detect various properties in other individuals, such as species identity, gender, colony membership (Howard and Blomquist, 1982, 2005 and various chapters in Part II of this book). In this chapter I will review the evidence indicating that hydrocarbon profiles are also used in colonies of ants, bees, and wasps for the regulation of reproduction. I will especially focus on patterns of variation in hydrocarbon profiles on the cuticle and the eggs in relation to fertility differences, which has not been done in such detail in previous reviews (Heinze, 2004 Monnin, 2006 Hefetz, 2007 Le Conte and Hefetz, 2008 Peeters and Liebig, 2009). 

We also need to understand how social insects are capable of extracting different kinds of information from the cuticular profile (Peeters and Liebig, 2009). Besides information about fertility, many other types of information are encoded. The interference in nestmate recognition based on cuticular hydrocarbons with information about fertility is particularly interesting. Different thresholds for recognition of different information may be involved (Le Conte and Hefetz, 2008). Further challenges to the understanding of profile discrimination are obvious when we consider task-specific cues (see Chapter 12). 

The multifaceted function of cuticular hydrocarbons necessitates further theoretical as well as empirical clarification. For example, their use as both fertility signals and nest-mate recognition pheromones may seem contradictory, since the first function requires within-nest idiosyncrasy, i.e., for discriminating fertile from sterile individuals, while the second function requires within-colony odor uniformity. The response threshold hypothesis (Le Conte and Hefetz, 2008) attempts to resolve this apparent conflict in function, as well as to provide a suitable framework for future experiments to test specific parts of the hypothesis. 

Cont ental authors. H. Davy, although he gives more emphasis to the mineral contents of soil, thought the peculiar extractive matter formed in the decomposition of vegetables appears to constitute a prime cause of the fertility of soil. Karl Sprengel (see p. 310) rejected the humus theory in books of 1837 and i 839, but it was defended by Thaer (see p. 252). ... 

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