Page 1 of 6

Marketing and Regulatory Programs – Agricultural Marketing Service – Specialty Crops Program – Specialty Crops Inspection Division

Inspection Aid No. 115

Identification of Defects in Raisins July 2016

Insect Identification

The most common insects found during microanalysis are: pomace or fruit fly 

(Drosophila), dried fruit beetle (Carpophilus hemipterus), raisin moth (Cadra figuliella) 

Indian meal moth (Plodia interpunctella), and sawtooth grain beetle (Orzaephilus 

surinamensis). Also encountered may be springtails (Order: Collembola), psocids or 

bark lice (Order: Corrodentia), leaf-hoppers and sharpshooters (Order: Homoptera), 

and mites (Class: Acaria). Parasitic wasps (Order: Hymenoptera) and thrips (Order: 

Thysanoptera) occur rarely, as do aphids (Order: Homoptera, Family Aphididae).

Of the above insects, drosophila flies, moths, beetles, and wasps exhibit complete 

metamorphosis. This means that the egg hatches into a larva (plural larvae) which 

eventually enters the pupa or resting stage, from which the adult emerges. The other 

insects listed (and the mites, which are not insects) hatch from eggs and develop into 

nymphs which more or less resemble the adults. The nymphs increase in size and 

development and shed their skins until they are adults. This is known as incomplete 

metamorphosis, as the insect does not go through the four states (egg, larva, pupa, and 

adult) of complete metamorphosis.

The adult insects usually have three main body regions: head, thorax, and abdomen. 

The head bears the eyes, antennae, and mouth parts. Typically, insects have three 

main pairs of legs and two pairs of wings, all carried on the thorax. The thorax may be 

divided into three segments with a pair of legs on each. When present, the wings are 

attached to the middle (mesothorax) and last (metathorax) segments. The abdomen of 

an adult insect usually does not have appendages and resembles a segmented sack.

A. Drosophila

Drosophila flies are known by several common names, including pomace, fruit 

and vinegar flies. They are common in and around fermenting fruit and are pests 

of raisin plants.

An egg is laid on fermenting fruit. It hatches in 24 hours, producing a slender 

white maggot (larva) which feeds on yeasts in the fermenting fruit. After four 

days, the maggots form pupae from which the adults emerge after another four 

days. A generation is completed in only nine days.

The eggs are minute and oblong, with two appendages as long as the egg.

Drosophila larvae are whitish, and measure up to 7 mm (1⁄4 inch) long. They are 

identified by their typical maggot appearance and the presence of mouth hooks -

dark H-shaped structures seen beneath the skin at the anterior end of the larva.
Page 2 of 6

Marketing and Regulatory Programs – Agricultural Marketing Service – Specialty Crops Program – Specialty Crops Inspection Division

The pupae are somewhat shorter and bigger around than the full grown larvae,

and have two characteristic horn-like respiratory tubes. The color is yellow to 

brown and often the red eyes of the developing adult may be seen within the 

pupa.

The adult is a yellowish fly about 3 mm long, and is easily identified by its red 

eyes.

B. Raisin and Indian-meal Moths

The raisin moth and Indian-meal moth are treated as similar for the purposes of 

microanalysis of raisins. Both moths infest dried fruit and can greatly damage 

the raisins. The eggs are oval to nearly spherical, and may be yellowish (raisin 

moth), or pearly white and look like a golf ball (Indian-meal moth).

Larvae of the moths appear as typical caterpillars. They may be brown, white, 

yellow, pink, or lavender in color, with a head. Since the pupae are seen only 

occasionally, it is sufficient to be able to identify the typical hard, brown pupa 

case of a moth. Adults may be observed flying about the lab and are rarely 

found in the samples. They are about 3/8 inch long, and the wings are folded 

around the body when at rest. The wings of the Indian-meal moth are dark 

brown and cream-colored; those of the raisin moth are drab gray.

C. Dried Fruit Beetles

The dried fruit beetle, a sap beetle, is widely distributed throughout the world and 

attacks ripe and overripe vegetation, especially fruits. In California, the dried fruit 

beetle breeds in stone fruits, figs, melons, citrus and grapes, then migrates from 

crop to crop as the fruits ripen. Its population increases through the season, and 

it is especially attracted to grapes with bunch rot.

Adults are dark brown with lighter brown or amber spots on their wing covers. 

They are about 3 mm (1/8 inch) long, oval-shaped and robust.

The wing covers are short, leaving the tip of the abdomen exposed. The 

antennae are knobbed at the tips. Legs and antennae are reddish or amber.

The newly hatched larva is yellowish and translucent, but soon becomes creamy 

white with brownish ends. It has a pair of pointed tubercles on the end of the 

abdomen. Fully grown, it is sparsely haired and about 6 mm (1⁄4 inch) long. The 

pupa is pale yellow until nearly mature; then it darkens and is somewhat spiny. 

No cocoon is formed.

Inspection Aid No. 115

July 2016
Page 3 of 6

Marketing and Regulatory Programs – Agricultural Marketing Service – Specialty Crops Program – Specialty Crops Inspection Division

D. Saw-toothed Grain Beetles

The sawtoothed grain beetle is a very common pest that feeds on practically any 

stored dried food. Fairly dry foods are preferred. Both larvae and adults attack 

the commodities. The sawtoothed grain beetle infests all cereals (rice, wheat, 

maize, barley, and pastas such as macaroni), bread, flour, nuts, copra, starch, 

drugs, tobacco and dried fruit. Raisins are a favorite. In raisins stored for a year 

or more, this insect can become a real problem. It crawls rapidly, even on 

vertical surfaces, but it has not been observed to fly. Newly hatched larvae can 

enter extremely narrow crevices in search of food.

The eggs are laid individually in small clusters in the crevices of the skin of 

raisins. The eggs are white, shiny and elongated-oval in shape. They measure 

less than .25 mm (1/20 inch) in length. Except for the color, they resemble dried 

fruit beetle eggs. The larva is pale yellow with a dark band on each segment and 

a yellowish-brown head. It has six legs and its body is covered with numerous 

long hairs. The abdomen tapers to a blunt tip and lacks the four posterior 

tubercles of the dried fruit beetle.

Both the pupae and the adults show the characteristic "saw teeth" on the thorax. 

The adult is a slender brown beetle, about 3 mm long.

E. Sap Beetles

Different species of sap beetles are found in raisins and other fruit: the pineapple 

sap beetle, the Freeman sap beetle, the confused sap beetle and the yellowbrown sap beetle.

The yellow-brown sap beetle may be prevalent in raisin products and lay 

hundreds of eggs which hatch in 2-5 days. The eggs are whitish in color, oval 

and slightly curved. It takes 5-11 days before the larva mature and develop into 

pupae. The larva of the beetle has nearly parallel rows of prominent dorsal 

tubercles on each segment, and the color is whitish-brown. The adult is a 

uniform yellow-brown color and is oval, flattened and long (2-21⁄2 mm) in shape. 

The complete life cycle is 21 days.

F. Springtails

Springtails are very small insects, many of which have a forked furcular or 

"spring" folded beneath the abdominal segment. These insects are 

characterized by a fused abdomen of not more than six segments and antennae 

with four to eight joints. The young are usually white or colorless and they 

assume a bluish-gray appearance when reaching maturity. Before failing any lot 

account Springtails, consult your supervisor.

Inspection Aid No. 115

July 2016
Page 4 of 6

Marketing and Regulatory Programs – Agricultural Marketing Service – Specialty Crops Program – Specialty Crops Inspection Division

G. Leafhoppers and Sharpshooters

Both leafhoppers and sharpshooters belong to the same order of insects and are 

very similar in appearance. Adult grape leafhoppers are small slender insects 3 

mm or less in length. They are usually pale yellow with reddish and dark brown 

markings. Coloration and markings vary with each species. The outstanding 

characteristics of this group of insects is the triangular head and slender, tapering 

body.

H. Mites

Mites are not insects but are closely related to ticks, which they resemble. They 

are exceedingly small and clear-bodied. The coloration varies greatly according 

to species. They can be distinguished from insects by the presence of eight legs.

I. Parasitic Wasps

Parasitic wasps probably occur in raisin samples because of their relationship 

with the insects upon which they prey. Only adults will be found in the raisin 

samples. They are very tiny and most of them are dark brown to black. They 

have the characteristic "wasp waist" between the abdominal and thoracic 

sections.

J. Thrips

Thrips occur only occasionally in raisins, and most of these will be nymphs. 

Nymphs are lighter in color than the adults and lack the characteristic fringed

wings and red eyes.

K. Psocids

Psocids are an easily identified insect, usually pale grey or yellow in color. They 

are approximately 1 mm long with the head making up a third of the length. The 

antennae is segmented. The insect has a short thorax and large oval-shaped 

abdomen. The abdomen is segmented and the digestive track may sometimes 

be seen in it.

Inspection Aid No. 115

July 2016
Page 5 of 6

Marketing and Regulatory Programs – Agricultural Marketing Service – Specialty Crops Program – Specialty Crops Inspection Division

Other Defects 

Other defects refer to insect parts and other contaminants such as feather barbules and 

barbs and striated hairs.

A. Insect Heads

"Insect Heads" do not include empty head capsules which are left behind when 

the skin is shed. Insect heads include those coming from insects that were 

obviously living but killed by processing or treatment for microanalysis. Such 

heads will appear to contain "flesh." Score these in the "Insect Head" section of 

the worksheet.

B. Insect Fragments

Some of the most common fragments found in raisin samples are: empty egg 

cases, empty pupae cases, pieces of eggs, insect legs, wings, antennae and 

segments of skin. Moth scales may also be found. These are extremely small, 

flat objects of a long, triangular shape.

"Insect Fragments" also includes broken-off portions of insects.

However, if one of the following is found it is not scored as a fragment, but

as a whole insect: 

 two thirds of an insect, 

 head and thorax of an insect, 

 more than one-third of a larva or pupa which includes the head, or 

 more than one-half of an adult insect which includes the head. Care 

should be taken not to score an "Insect Head" and then a whole insect of 

which the head was a portion.

C. Insect Eggs

Only full egg cases are counted as eggs. Broken or empty insect egg cases are 

classified as "Insect Fragments." Drosophila eggs are only counted under the 

"Dros. Eggs" heading. All others are recorded as "Other Eggs."

D. Mouth Hooks

"Mouth Hooks" refers to the H-shaped mouth parts of the Drosophila larvae or 

pupae, separated from the insect body. Although it is tallied in a separate 

category, it is totaled with other fragments. Thus there is no total for mouth 

hooks alone.

Inspection Aid No. 115

July 2016
Page 6 of 6

Marketing and Regulatory Programs – Agricultural Marketing Service – Specialty Crops Program – Specialty Crops Inspection Division

E. Feather Barbules and Barbs

"Feather barbules" and "feather barbs" refer to portions of bird feathers. Barbs 

are branches from the shaft of a feather and bear many barbules. A barbule has 

several nodes which appear as swellings, much like bamboo. Nodes may 

appear as blank portions in the colorations.

F. Striated Hairs

Hairs from cats, rodents, and other animals may be striated. "Striated Hairs" are 

hairs with striations of narrow bands around them. Under the microscope, the 

hair between striations may be clear and almost invisible so that often only the 

striations can be seen. This gives the striated hair an appearance of "cross-ties 

of a railroad track." The analyst must learn to distinguish between feather 

barbules with nodes and hair with striations.

Inspection Aid No. 115

July 2016