UNITED STATES 

 DEPARTMENT OF AGRICULTURE 



MISCELLANOUS PUBLICATION NO. 626 



Washington, D. C. 



Issued January 1948 



HANDBOOK ON INSECT ENEMIES OF 

 FLOWERS AND SHRUBS 



By C. A. Weigel, senior entomologist, Division of Truck Crop and Garden Insect 

 Investigations, and L. G. Baumhofer, 1 associate entomologist, Division of 

 Forest Insect Investigations, Bureau of Entomology and Plant Quarantine, Agri- 

 cultural Research Administration. 



HOW INSECTS DEVELOP AND 

 FEED 



To combat insect pests successfully 

 the gardener should know something 

 about the manner in which they develop 

 and feed. Insects normally hatch from 

 eggs laid by the adult females. The 

 adults are usually individuals with fully 

 developed wings, although a few species 

 of insects never have wings. Insects 

 pass through several stages during their 

 development. Plant lice, plant bugs, 

 leafhoppers, thrips, and grasshoppers 

 hatch from the egg in a form known as a 

 nymph. The nymph resembles the 

 full-grown insect, except that it lacks 

 wings and is smaller. It sheds its skin 

 periodically as it gradually increases in 

 size. Moths, beetles, and flies, on the 

 other hand, hatch from the egg as a 

 wormlike form, or larva. The larva of 

 a moth or butterfly is commonly called 

 a caterpillar, the larva of a beetle is 

 called a grub, and the larva of a fly is 

 known as a maggot. After the larva 

 has grown to full size, it changes to an 

 inactive form, which is known as a pupa. 

 From this pupa the adult insect emerges. 

 The length of life varies greatly with 

 different species of insects. Some devel- 

 op from egg to adult in a few weeks, 

 many require a full year, and a few take 

 2 or 3 years to reach maturity. 



Insects are provided with either chew- 

 ing or sucking mouth parts (fig. 1). 

 The chewing insects bite off and swallow 

 portions of the plant tissue. They may 



devour the leaves or flowers, bore into 

 the stems, or feed on the roots. Sucking 

 insects have beaklike mouth parts, 

 which are used for piercing the plant 

 tissue and sucking the plant juices for 

 food. This difference in the manner of 

 feeding is important when control work 

 is considered, since certain insecticides 

 used to poison chewing insects will have 

 no effect on sucking insects. 



Figure 1. — A, Insect with chewing 

 mouth parts; B, insect with sucking 

 mouth parts. 



Not all the insects encountered in the 

 flower garden are injurious. A number 

 of species help us by destroying injurious 

 pests. These beneficial insects are 

 generally divided into two groups — the 

 predators and the true parasites. The 

 predators pre} 7 upon and devour other 

 insects. Examples of these are the 

 praying mantis, ladybird beetles, certain 

 ground beetles, assassin bugs, and the 

 larvae of syrphid flies and lacewing 

 flies. The iarvae of parasitic insects 

 live on, or within, the eggs or bodies of 

 other insects, which they destroy. The 



1 Mr. Baumhofer died June 13, 1942: after his death R. A. St. George, Division 

 of Forest Insect Investigations, assisted in revising the manuscript. 



