HMSO 23p Forestry Commission Leaflet 58 Forestry Commission ARCHIVE

The Large Pine and Blacl< Pine Beetles T M Scott C J King FORESTRY AUTHmnli¥E{�lijBUiIE WEEVIL AND BLACK PINE NATIONAL OffiCE By T. M. SCOTT, B.Sc. and C. J. KING Forestry Commission LIBRARY INTRODUCTION

This Leaflet revises and replaces Leaflet No.1 felling areas or coupes are not widely separa­ -The Large Pine Weevil and Leaflet No. 4- ted. The Black Pine and other allied closely Heavy infestations of either or both species beetles. may result in the widespread loss of trees for The Large weevil belongs to the genus pine several years after planting if measures against of the which family , them are neglected. forms part of the super-family Rhyncophora of the order Coleoptera (beetles). The Black pine The Large pine weevil and Black pine beetles often be found in the same beetles belong to the genus Hylastes, of the may breeding sub-family Hylesininae, of the family Scolyti­ stump, although the Pine weevil tends to dae, also of the order Coleoptera. Typical invade fresher stumps and may even occasion­ utilise the available material so species are Hylastes ater and H. cunicularius. ally breeding The Large pine weevil, L. fully as to restrict invasion by Hylastes and the Black pine beetles, Hylastes species, species. There is little or no competition, for adult sites. breed in the stumps of and emerge to however, feeding Hylobius abietis feeds on the stem whereas feed as adults on the bark of newly planted young feed from the root collar down conifers. They rank among the most destruc­ Hylastes species to the fine roots. tive forest pests. Infestation by the Pine weevil almost invariably follows fellings. Hylobius abietis and the species of Hylastes This weevil is in fact our only forest pest are clearly different from one another (see against which routine protective measures are cover, Figures 1, 2 and 3, left) except at the taken. Hylastes on the other hand tends to be early larval stage, when however the form of more characteristic of felling programmes the breeding gallery system serves as an aid (particularly of pine and spruce) where annual to identification.

THE LARGE PINE WEEVIL Hylobius abietis

Description wing cases, which completely cover the of the adult weevil The length averages abdomen, are purple-brown in young adults, about 15 mm but it may range from 10 mm to later becoming pitchy-black in colour, with 20 mm. This Pine weevil is one of the largest of longitudinal ridges and furrows bearing oblong the British and is a robust creature, indentations. There are patches of yellow to capable of gripping the ball of a finger with its orange bristles on the elytra and on the sides feet, with considerable power. The elytra or of the thorax and on the underside of the body.

Figure 1. Front cover, left. Adults of the Large pine weevil, Hylobius abietis, feeding on the bark of a young Scots pine. CS 2984

Figure 2. Front cover, right An adult Black pine beetle, Hylastes ater, feeding in the root of a young Corsican pine. CS 18112. 2 These bristles often become lost in older which has p6'J1&ifJilM�u1hiirt�:at the:i'ip:otilu!'" r. specimens. The thorax is slightly broader than antennae are elbowe

Figure 3. Left: Adult of the Large pine weevil, Hylobius abietis, x 5. C920 Right: Adult of Pissodes pini, x 8. C926 Note the difference in the position of the antennae on the snout; those of Hylobius are nearer the tip.

Hylobius abietis may be confused at both Life Cycle adult and larval stages with Pissodes weevils. The eggs are laid singly or in irregular These latter are generally smaller, being only groups in niches excavated in the bark, a half to two-thirds of the size of Hylobius. The generally below ground level, in roots of adults may be most easily distinguished by the stumps, or on the underside of logs, or even position of the antennae on the snout which in large branches lying in contact with the soil. Hylobius are attached near the tip, and in Egg-laying takes place throughout the spring Pissodes near the middle (see Figure 3). The and summer. The larva makes a long rambling larva of Hylobius (Figure 4) has a large wide tunnel increasing in diameter as the larva flattened head whilst that of Pissodes is grows. Feeding takes place in the cambial rounded and much smaller proportioned. region and where the bark is thick the 3 Figure 4. Larva of Large pine weevil, Hylobius abietis, feeding in pine bark. x 3. CS 5707 larva constructs ventilator tunnels up to the delayed until July or August. In unfavourable surface. It packs waste material (frass) densely climates, completion of the life cycle may take behind itself in the tunnel. Just prior to two full years, and outside the United King­ pupation the larva hollows out a pupal dom in northern latitudes, three years is usual. chamber which it thatches tightly with wood fibres. The chamber is made either within the Attack Periods wood or bark or partly in both, depending on Adult pine weevils breed each year but the thickness of the bark. The larva is soft, relatively few survive their second winter. cream-coloured and legless with a light-brown Adult weevils emerging from hibernation in head (Figure 4) and when fully grown measures the spring may be either:- 15-20 mm in The is illustrated in length. pupa (1) Old weevils which have produced Figure 5. broods. The rate of development from egg to (2) Weevils which the previous emergent adult depends largely on prevailing emerged summer or autumn and are for climatic conditions, and to a lesser extent upon ready their first egg laying. the time of year the eggs are laid. Weevils which In warm, dry conditions larvae may be (3) over-wintered in pupal completely developed by late autumn from chambers. eggs laid in the spring. After over-wintering as Weevils in the first two categories will be full-grown larvae, they pupate in the following sexually mature and may begin to lay eggs Mayor June. The young weevils may emerge after a brief feeding period, but adults over­ any time after the end of May, thus at least a wintering in the pupal chambers require a full year is required. The date of emergence is prolonged period of feeding before they can governed by the temperature, so it may be begin to lay. Hibernating weevils emerge when 4 Figure 5. Pupa of Large pine weevil, Hylobius abietis. x 5 CS 9138 it becomes warm enough and in some years summarised in Figure 6, on the central pages. are found above ground in early March. A spring peak of feeding by a large number of weevils is frequently followed by their com­ Damage plete absence from feeding places while they In young plantations serious damage may breed during late May and early June. Mass occur for up to three years after planting. The emergence of new weevils from overwintered adult weevils feed on the bark of young trees, larvae begins in June and reaches a peak in eating out large patches of bark and the under­ July and August. These dates are up to two lying soft tissue. This weakens trees, or kills months later in exposed situations. In either them if they are girdled. Pine weevils will feed case emergence may continue to late October. on any species of conifer or may even attack The attack pattern and breeding cycle are young hardwoods if conifers are not available.

THE BLACK PINE BEETLES Hylastes species

Description is found mainly in spruces. These three species There are six species of Hylastes recorded in are the largest but are morphologically very Britain. The three most important are H. ater similar. H. ater is southern in distribution, Payk. and H. brunneus Er., which are chiefly being replaced in the north by H. brunneus. pests of pines, and H. cunicularius Er., which The three less important are H. opacus Er., 5 Typical cycle of Large Pine Weevil activity in replanted clearfelled conifer forest.

December January

November F.ebruary

October March August May

July June

Key All stages dormant

Light sporadic damage

Heavy damage

Weevil breeding activity

Figure 6. Typical cycle of Large pine weevil, Hylobius abietis, activity on replanted land following clear felling in a conifer forest. Figure 7. Mother gallery and larvae of a Black pine beetle, Hylastes cunicularius, in the bark of a spruce log. CS 18114

which is widely distributed in pines, and excavation near the entrance is characteristic. H. angustatus Hbst. and H. attenuatus Er., Eggs are laid in evenly spaced niches cut on which are both mainly southerly in distribu­ either side of the gallery. On hatching the tion (again mainly in pines) although H. larvae feed first at right angles to the axis of attenuatus also occurs in the north. the mother gallery but later more haphazardly. All species are small cylindrical beetles, The galleries increase in size as the larvae . black or pitchy-brown when mature. H. ater, develop and the wood may be engraved where H. brunneus and H. cunicularius are the largest the bark is thin. The larva is a pale cream of the six, measuring 4-5.5 mm in length; legless grub measuring up to 4 mm when fully H. opacus measures 2.5-3.5 mm; H. attenuatus grown. Pupation takes place in a chamber cut and H. angustatus are the smallest of the group, in the bark or partly in the wood. The larvae being not more than 3 mm long. and mother gallery of Hylastes cunicularius are shown in Figure 7. Life Cycle Spring is the chief breeding season and egg- Pine beetles compete with Pine weevils for laying may be fairly general in March during breeding sites in stumps, logs and branches but mild weather in the south, but takes place can also breed in very much smaller sized during April in the north, at high elevations material. Roots less than 10 mm diameter are or in exposed situations. The rate of develop­ commonly used. All of the British species of ment of the brood varies according to weather Pine beetles have similar breeding habits. conditions and soil temperature which in turn They form simple egg-galleries roughly parallel varies according to the type of soil. Eggs laid to the long axis of the root; a crotch-shaped in the spring may take three months to develop 8 from egg to adult but those laid in the summer eggs laid in the year overwinter as larvae or less may take than two months. Broods of pupae and complete development in the H. cunicularius and H. brunneus produced from following spring or summer.

Figure 8. Young Scots pine damaged both above and below root collar by a Black pine beetle, Hylastes ater. CS 24928 9 New adults often do not leave the bark are forced to emerge and seek the more immediately but feed in the parent stump if succulent tissue of transplants or natural this is still fresh and has not suffered through regeneration. Pine beetles enter the root sys­ heavy infestation by other broods or by Pine tem usually at the root collar, but where dense weevil. Similarly parent beetles may continue vegetation is closely pressed against the tree to feed in the bark of the roots to recuperate entry may be made above ground level. their reproductive organs and may then pro­ In pines the feeding tunnel may be obscured ceed to produce a second brood in the same beneath the thicker bark but the entry hole can material. be identified by spots of red-brown bore-meal. In spruce the feeding galleries are usually Damage exposed and may continue on to the fine roots. Serious damage is caused only by adult Damage occurs throughout summer, being feeding which destroys the cambium and inner most obvious in July or August. In mild bark of young conifers as shown in Figure 8. conditions it continues into late autumn. The The severity of damage depends on how much needles of young plants severely damaged by feeding is done in the stumps and how much pine beetles turn red and later fall off. How­ on nearby conifer transplants. Here soil ever such symptoms are not only caused by moisture seems to be the most important beetles so that suspect cases have to be factor bringing about the quickest deteriora­ confirmed by carefully digging up the plant tion in the suitability of the stump to support and inspecting its roots. If plants are pulled feeding. When it is no longer suitable adults the diagnostic evidence may be left in the soil.

BUILD-UP OF POPULATIONS TO DAMAGING LEVELS

Pine weevils and Black pine beetles occur begin in pines almost immediately whereas in widely throughout coniferous woodland in other species such as larches, Douglas fir and Britain. The populations remain at a low level spruces it may be delayed for up to a year while breeding material is in short supply.When depending on the time of year the trees were this situation is altered by fire, windblow, felled and on the other factors influencing rate heavy thinning or clear felling, a large quantity of drying, namely the climate and soil type. of breeding material becomes available. Generally, small stumps on dry south-facing Mortality due to overcrowding is at a mini­ sites become suitable for breeding sooner than mum and populations can rapidly build up to large stumps on damp peats or on heavy clay an epidemic level. The speed at which this soils, but conversely they remain suitable for build-up occurs varies according to the breeding for a much shorter period than large species of tree stump, the climate and the soil stumps of other species on wet, cold sites as type. Generally, the Pine beetles are more they sooner become too dry. The effect of any discerning about the condition of their soil treatment such as complete ploughing and breeding material than the Large pine weevil ripping which promotes rapid drying of which invades fresher stumps. Pines, particu­ stumps and roots will hasten both occupation larly Scots pine and Corsican pine, when and termination of usability of stumps. The available in mixture with other conifers, are reverse may occur where stumps are left more favoured for breeding sites. Breeding can or less intact but become buried.

CONTROL

Natural Control situation exercise little influence over epidemic The natural predators and parasites which populations which develop in the presence of may operate effectively in the endemic large quantities of breeding material. 10 Artificial Control Trapping methods are not considered Silvicultural Treatment worthwhile nowadays. Delaying replanting for two to four years will effectively allow full exploitation and Insecticidal Control finally exhaustion of breeding material and (a.) Dipping will thus prevent damage, so long of course as Where weevil or beetle attacks are antici­ no new fellings are made nearby in the mean­ pated, plants should be dipped (before plant­ time. The resulting loss in yield and site ing) in 1.6 % Gammacol* in water. Bundles deterioration generally makes this method of plants should be loosened and the tops unacceptable. However, it may be necessary dipped to the root collar only. If Hylastes to delay replanting where successive feIlings beetles are a problem immerse the bundle have allowed the development of enormous completely in 1.6 % GammacoI. Bundles populations of these pests. The effect of should be held under the dip for several silvicultural operations such as complete seconds to allow complete penetration and ploughing, ripping or stump removal are not then the surplus liquid should be allowed to fully understood, but in general they reduce drain back into the dipping tank. Figure 9 the population breeding on the site. They do shows a suitable arrangement for a small not, of course, influence the population of operation. Dipped plants should be heeled-in immigrating weevils. to dry off before packing in polythene bags

Figure 9. Dipping bundles of conifer transplants in drums of insecticide. A simple layout such as this is adequate. Surplus insecticide is recovered at the far end of the draining boards. A 4137. 11 for storage, or before exposing to rainfall. taken to ensure that proper disposal of all 4.5 litres (1 gallon) of Gammacol 80 % concen­ waste or surplus insecticide and soil sludge is trate (making 225 litres (50 gallons) of 1.6 % carried out. Operators mustwear adequatepro­ solution in water) will treat approximately tective clothing including waterproof gloves, 20,000 22.5-37.5 ern (9-15 inch) plants or and they must wash before eating or smoking. 10,000 40-60 ern (16-24 inch) plants when Splashes of concentrate must be washed from used as a total dip*. If only top dipping is used the skin immediately. the numbers of trees may be doubled. It must be stressed that these figures are approximate and that variations will occur depending on (b.) Spraying the type and species of tree dipped and the Where a heavy attack of weevils or beetles size of the operation. is anticipated (or occurs) one or two years after Dipping is best done at the supplying dipping, spray with 0.125 per cent Lindane 20, nursery where greater control can be exercised or an equivalent gamma BHC formulation as over the efficiency of the operation. Gamma­ described below+. Apply to the point ofrun-off, col is harmful to and great care should directing the spray on to the main stem using be exercised to avoid the production of pools a knapsack sprayer. Spraying is much more of spilt insecticide from which animals may expensive than dipping so should not be drink, or the contamination of streams which carried out in place of it. may poison fish and other water life. Where container-grown stock require pro­ Where it cannot be arranged at the nursery, tection, spray either in the nursery or im­ the operation must be strictly supervised to mediately before planting, to run-off, with prevent contaminants accidentally reaching 1.5 % Lindane 20 emulsifiable concentrate or either domestic or field drains. Care must be its equivalent+,

*Gammacol is the trade name for an 80 per cent colloidal suspension of gamma BRC. It is manufactured by Plant Protection., I.C.1. Agricultural Division, Fernhurst, Haslemere, Surrey. It is usually obtainable from agricultural suppliers. It is important not to confuse Gammacol with Gammalin 20 which is unsuitable as a total dip for plants, due to its oil base. tLindane is the international common name for gamma BRC. Gamma BRC formulations normally supplied by agricultural merchants and suitablefor top spraying are:- Gammalin 20 Lindastan EC 20, SDC Pesticides. Strykol BRC, supplied by Boots Chemists. Lindane 20, Pan Britannica Industries, Ltd.

ILLUSTRATIONS All the illustrations herein are drawn from the Forestry Commission collection.

© Crown copyright 1974 Printed in England by Swindon Press, Swindon, Wilts. and published by Her Majesty's Stationery Office

Dct. 505274 K80 8/74

ISBN ° 11 710D74 9