The cigarette beetle Lasioderm a serricorne (F.) (Coleoptera: Anobii- dae): a serious herbarium pest

The herbarium pest Lasioderme serricorne (F.) is described and illustrated, and aspects of its life cycle and eradication


INTRODUCTION
One serious curation problem in herbaria is the protec tion of specimens from damage by insects. In the past, various animal pests have occurred in the National Her barium, Pretoria (PRE): cigarette beetles, cockroaches, rats and fish moths. O f these, Lasioderm e serricorne (F.), the cigarette beetle or tobacco beetle, has caused the most severe damage to herbarium specimens. Re cently, infested material received from a collector and damage done to specimens in the cupboards again drew attention to this beetle.

The insect
L asioderm e serricorne (Fabricius) was first described in France in 1792 from specimens collected in America, but the oldest record of occurrence of the tobacco beetle comes from Egypt, remains of the insect having been found in the tomb of Tutankhamen. These beetles are therefore probably indigenous to Egypt, and they have scarcely altered morphologically in the 3 500 years that have elapsed (Reed & Vinzant 1942). The insect has gained a wide distribution through commerce and is nowadays found throughout the tropical and subtropical parts o f the world.
The adult beetle ( Figure 1) is small ( 2 ,0 -3 ,7 mm), reddish brown, and its head is retracted under the front part of the body. Distinguishing characteristics include the smooth elytra and serrate antennae (Croat 1978). The similar drugstore beetle, Stegobium paniceum (L .), which is also extremely common and also occurs on a wide range of products, possesses distinctly grooved ely tra and clubbed antennae. Cigarette beetles are slow fly ers and can easily be spotted when flying.
L. serricorne females oviposit directly onto dried ma terial. The eggs are pearly white and elongated and hatch in 6-8 days. The larvae, ± 3 mm long, are C-shaped, greyish white and thinly covered with fine brown hairs ( Figure 2). When growth is completed, the larva trans-forms into an inactive pupa and emerges a fully devel oped beetle in about 7 days in summer and 1 4 -1 8 days in the cooler weather of spring and autumn (Reed & Vinzant 1942).
The complete life cycle of L. serricorne spans about 4 5 -7 0 days, and 3 -6 generations occur per year, de pending on the availability of food, as well as tempera ture and humidity (Edwards et al. 1980). Huge popula tions of L. serricorne can build up very quickly-a pro tected breeding pair produced 2 000 offspring in four months (Howe 1957)-and infestations and damage can reach alarming proportions before adults are spotted. L. serricorne can breed on a wide variety of commodities including herbarium specimens, insecticides containing pyrethrum, animal matter such as dried insects and dried fish, leather, cloth, paper and books (Lever 1945, Mossop 1950, Howe 1957. Symbiotic yeasts, which occur intracellularly in mycetomes at the junction of the foreand mid-gut, supply B-group vitamins in significant amounts and make it possible for L. serricorne to subsist on foods very low in vitamins of that group (Pant & Fraenkel 1950). The yeasts also supply their hosts with sterols, a necessary constituent of their diet. In the ab sence of any other food the newly hatched larva may eat the egg shell. They are negatively phototropic and will enter very small holes in search of food (Howe 1957), and evidence at PRE also suggests that they can find their way into tightly closed cabinets. Experiments have shown that the tobacco beetle can exist at temperatures between 2 °C and 36 °C (Powell 1931); however, the beetle will tolerate a much wider range in temperature, and all stages of the life cycle may survive temperatures below 2 °C. According to Powell (1931), the greatest numbers of tobacco beetles complete their life cycles at humidities of about 75 per cent; humidities above 90 per cent are unfavourable because of the attack by fungal and bacterial diseases. It is likely that only the eggs and young larvae are vulnerable to low humidity and that the later stages may survive several months at low humidity (Howe 1957).

Damage
Both the adult and larval stages of the life cycle are capable of feeding (Lefkovitch 1963). The most severe damage is done to the flowers of herbarium specimens, although leaves and stems are also eaten ( Figure 3). Seeds inside fruits of exposed material are usually se verely attacked. Plant parts are turned into a mixture of dust and faeces (Figure 4).
Two basic approaches are usually taken to control pests in herbaria, namely 1, the sterile entry approach, i.e. building closure coupled with humidity control, tem perature control and sterile entry techniques; and 2, fu migation, i.e. the use of short or long duration fumigants or poisons in direct association with the herbarium speci mens (Croat 1978). At present in PRE all incoming ma terial is treated in the service room by freezing (deep freeze temperature averages -6 °C) for two days or by heating in a microwave oven for six minutes (100 mm pile) to kill any insects present. The herbarium and asso ciated rooms are fumigated once a year and paradichlorobenzene has been put into herbarium cabinets regularly to act as a repellent. However, because of a recent out break of cigarette beetle, present insect pest control measures at PRE are undergoing critical examination, and new control measures are to be tested. Recent out breaks o f the beetle were isolated and the contaminated specimens either microwaved or frozen. Some of the contaminated cupboards were fumigated using Vapona* strips (dichlorvos), while others were sprayed with Baygon knockdown* spray. This is a 'dry' spray that can be sprayed directly onto mounted specimens without mark ing or damaging them, the active ingredients being dichlorvos, a pyrethroid (tetramethin) and a synergist (piperonylbutoxide). These measures have proved successful in controlling the infestations. An initial treat ment with commercially available fumigating tablets proved unsuccessful.

CONCLUSION
Herbarium specimens and their associated mounting boards, species covers, genus covers and wooden cabi nets are all susceptible to attack by insect pests. Infesta tions that go unnoticed or untreated can cause extensive, irreversible damage. Collections that have taken time, effort and money to compile can be completely de stroyed. No herbarium can afford to let this happen, * Mention o f a trade name does not imply its approval to the exclusion o f other products. especially when historically valuable collections and type specimens are involved. The control and eradication of a pest like L. serricorne in herbaria is therefore of utmost importance to curators.