natural-products-in-plant-pest-management

Allelochemicals in Pest Management 135As mentioned above, there are many types of plant–insect interactions;however, the interaction between plants as a source of food and phytophagousinsects as their pests is one of the most interesting and important onesfor practical applications in agriculture. In this case, it is a relationship between‘food’ on one hand and ‘consumer’ on the other; the plants were forced todevelop numerous defensive mechanisms to prevent uncontrolled destructivepest attacks. The most important defensive plant mechanisms include thesynthesis of biologically active compounds, the so-called secondary metabolites.First, such substances may provide direct insecticide effects, causingmortality of phytophagous insects, and/or second, they may exert indirectinsecticide effects, only influencing insect behaviour in some manner. Knowledgeof such relationships leads not only to useful information necessary forcultivating plants with resistance, but also to the direct utilization of extractsin cultural plant protection using the so-called botanical insecticides.Although the first group of compounds, i.e. those with direct insecticidalactivity, has been used by humans as extracts for millennia, both in fightingphytophagous pests as well as against parasites or storage pests, the othergroup of compounds, generally called allelochemicals, has become thesubject of more profound interest only in recent decades (Pavela, 2007a).The term allelochemicals (from Greek allelon: ‘one another’) is used todescribe the chemicals involved in interspecific interactions. It is defined asa chemical significant to organisms of a species different from its source.Allelochemicals are divided into four subgroups, depending on whether theemitter, the receiver, or both benefit in the interaction.●●●●An allomone (from Greek allos – ‘another’; horman – ‘to stimulate’) isdefined as a chemical substance, produced or acquired by an organism,which evokes in the receiver a reaction adaptively favourable to theemitter, e.g. a plant emits allomones to deter herbivores.A kairomone (from Greek kairos – ‘opportunistic’) is defined as achemical substance, produced or acquired by an organism, which evokesin the receiver a reaction adaptively favourable to the receiver but not tothe emitter, e.g. secondary plant compounds help herbivores in findingplants to feed on.A synomone (from Greek syn – ‘with or jointly’) is defined as a chemicalsubstance, produced or acquired by an organism, which evokes in thereceiver a reaction adaptively favourable to both the emitter and thereceiver. This group of allelochemicals includes floral scents and nectarsthat attract insects and other pollinators and substances that play animportant role in symbiotic relationships.An apneumone (from Greek a-pneum – ‘breathless or lifeless’) is definedas a substance, emitted by a non-living material, which evokes a reactionadaptively favourable to the receiving organism, but detrimental toanother organism that may be found in or on the non-living material.For example, parasites or predators are attracted to non-living substancesin which they may find another organism, their host or prey, byapneumones released from the non-living substance.