Insects And Humans

The r pests are characterized by their potentially high rates of population increase 745

(resulting from the high fecundity and short generation time), well-developed powers of dispersal (migration) and ability to locate new food sources, and rather general food preferences. These features enable r pests to colonize temporarily suitable habitats, in which there is typically little interspecific competition for the resources available. Because r pests may occur in such large but unpredictable numbers and rapidly change their location, predators (of which there may be many) have relatively little effect on their population. Further, although like other organisms r pests are subject to disease, the latter is slow to take effect, by which time significant damage may have been done. Finally, because of their high reproductive potential, r pests are able to tolerate mass mortality and rapidly regenerate their original density. Hence, biological control, which is a relatively slow but long-term method, is of little use against r pests. For such pests specific insecticides, which can be stored for application at short notice, continue to be the most important tool in their control. Included in the r-pest group are the "classic" pests: locusts, aphids, mosquitoes, and house flies (Table 24.3).

K pests, on the other hand, have lower fecundity and longer generation time, poor ability to disperse, relatively specialized food preferences, and are found in habitats that remain stable over long periods of time. Under natural conditions, insects with the features of K strategists seldom become pests. If, however, probably as a result of human activity, their niche is expanded (e.g., their food plant becomes an important crop), or if they can occupy a new niche (e.g., feeding on domestic cattle rather than wild ungulates) they may become a pest. Once established, such pests are often difficult to eradicate over the short term, for example, through the use of insecticides. Insecticides are frequently not feasible tools because the K pests attack the fruit rather than the foliage of crop plants, or because the cost is prohibitive in view of the low density of the pest population. (In some instances, however, where even at low population density a pest may cause considerable damage, for example, codling moth on apple, insecticidal control may be profitable.) Nor is biological control an appropriate method because K pests have few natural enemies, a feature probably related to their low density under natural conditions. For K pests, the best methods of control are those that disturb their habitat, for example, the breeding of resistant strains of plant(s) or animal(s) attacked by the pests, and cultural practices. Examples of K pests are given in Table 24.3.

The majority of pests are classified as intermediate pests in the Conway scheme because they exhibit a mixture of the features of r and K pests. For some of these, with a relatively high reproductive potential, insecticidal control may be necessary under certain conditions, and conversely, for pests approaching the K end of the spectrum, cultural control sometimes may be adequate. However, the most important feature of intermediate pests is the relatively large number of natural enemies that they have. These enemies, under normal circumstances, are important regulators of the pest population. In addition, intermediate pests are frequently foliage- or root-damaging pests, for example, spruce budworm and some scale insects, and, therefore, the economic injury threshold is reasonably high; that is, a fair amount of damage can be tolerated without economic loss. Hence, for these pests, biological control would appear to be the single most appropriate method of control, which can be supplemented as necessary with insecticidal and other methods. The latter is, in other words, an integrated control program.

With these general considerations in mind, it is now appropriate to consider in more detail the methods available for pest control.

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

Get My Free Ebook


Post a comment