Agriculture and fishing are the primary source of almost all our food, as well as of many other products, so remain vital activities even though their share in the economy is small and in continuous decline. Partly for this reason public policy in these areas is almost entirely integrated at European level in the Common Agricultural Policy (CAP) and Common Fisheries Policy (CFP). Forestry policies are also heavily affected by EU-level decision-making. As agriculture dominates in terms of direct contribution to GDP and numbers of people engaged in it, as well as accounting for the largest amount of public support expenditure, it is agriculture that will receive the greatest attention here.

Agriculture, Forestry and Fisheries

Advances in cowpea research , Advances in cowpea research , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Advances in cowpea research

Oviposition behavior in phytophagous insects and entomophagous parasitoids is often modified by the presence of conspecific brood (eggs and larvae). Often, females avoid laying eggs on or in hosts bearing brood, a behavior that acts to reduce the level of competition suffered by their offspring. Avoidance of occupied hosts is typically mediated by cues and/or signals associated with brood. In this article, we review the role of Marking Pheromones (MPs) as signals of brood presence in both phytophagous and entomophagous insects. We place information about the function and evolution of MPs in the context of recent theory in the field of animal communication. We highlight the dynamics of host-marking systems and discuss how effects of MPs vary according to factors such as female experience and egg load. We also examine variation in the form and function of MP communication across a variety of insect taxa. While studies of MP communication in phytophagous insects have focused on the underlying behavioral mechanisms and chemistry of MP communication, studies in entomophagous insects have focused on the functional aspects of MPs and their role in ‘decision-making’ in insects. We argue that an approach that incorporates the important contributions of both of these somewhat independent, but complementary areas of research will lead to a more complete understanding of MPs in insects. Finally, we suggest that MP systems are model systems for the study of animal signaling and its evolution.

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Host marking behavior in phytophagous insects and parasitoids

 

1
The eggs of the cowpea seed bettle Callosobruchus maculatus (Fab) are attached to cowpeas On hatching, the larvae penetrate the testa and remain in the seed until development is complete and adult eclosion has occurred The adults do not need to feed and were not allowed to do so

2
Strains from Brazil and Nigeria can produce more than twelve adults from a seed bearing numerous eggs, whereas a strain from the Yemen Republic rarely produced more than three

3
In all three strains the mean weight of the adults produced from a single cowpea declined with increasing initial larval density in the seed

4
Egg production by females is positively correlated with their weight at the time of mating, shortly after emergence

5
Lifetime egg production by females of the Brazilian and Nigerian strains was lower if they came from cowpeas with higher initial larval densities No such relationship could be demonstrated in the Yemen strain

6
The fecundity of one generation of these beetles, at least in some geographical strains, is significantly affected by the number of larvae entering the hosts in which the adults of that generation have developed

Relationships between larval density, adult size and egg production in the cowpea seed beetle, Callosobruchus maculatus

Environmental manipulations have consistently demonstrated a cost of reproduction in the capital-breeding seed beetle, Callosobruchus maculatus, as females deprived of seeds or mates lay fewer eggs and thereby increase their longevity. Yet fecundity and longevity tend to be positively correlated within populations, perhaps as a consequence of individual differences in resource acquisition. We conducted a split-brood experiment that combined a manipulation of seed availability (seeds present or absent) with a quantitative-genetic analysis of fecundity and lifespan in each environment. Each trait was significantly heritable in each environment. Seed availability not only altered mean fecundity and longevity between environments, but also modified how the traits were correlated within environments. The signs of both the phenotypic and genetic correlations switched from positive when seeds were present to negative when seeds were absent. This reversal persisted even after the effect of body mass (a potential indicator of resource acquisition) was statistically controlled. Cross-environment genetic correlations were positive but significantly less than one for each trait. We suggest that the reversal of the fecundity–longevity relationship depends on a shift in the relative importance of resource-acquisition and resource-allocation loci between environments. In particular, a cost of reproduction may be apparent at the individual level only when seeds are scarce or absent because differences in reproductive effort become large enough to overwhelm differences in resource acquisition. Despite their common dependence on resources acquired during larval stages, fecundity and lifespan in C. maculatus do not appear to be tightly coupled in a physiological or genetic sense.

Kenneth M. Dick

Papers

Relationships between larval density, adult size and egg production in the cowpea seed beetle, Callosobruchus maculatus

Egg production and development of three strains of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

Variation in the response of Callosobruchus maculatus (F.) to a resistant veriety of cowpea

Changes in the response of Callosobruchus maculatus (Coleoptera: Bruchidae) to a resistant variety of cowpea

Food consumption by larvae of three strains of Callosobruchus maculatus (Coleoptera: Bruchidae)