Watt. — Leaf-mining Insects of New Zealand. ■ 439 



Art. XXXVII. — The Leaf-mining Insects of New Zealand. 

 By Morris N. Watt, F.E.S. 



{Read before, the Wanganui Philosophical Society, 3rd December, 1919 ; received by Editor, 

 31st December, 1919 ; issued separately, 16th July, 1920.] 



■ " Plate XXX. 



INTRODUCTION. 



Perhaps no other class of insects is so fascinating to study as the leaf- 

 miners. Inconspicuous and retiring in their habits, these tiny atoms easily 

 escape notice ; this and their microscopic size have kept these insects among 

 the least known in any country. But actually their study is comparatively 

 easy. Their life-cycle is so short, especially the active or larval part of it, 

 that there is little worry about procuring fresh food. Infected leaves can 

 be kept fresh sufficiently long if placed in a damp atmosphere and the air 

 not allowed to stagnate. I have found glass Petrie dishes invaluable 

 for this purpose ; a piece of damp blotting-paper in the bottom of the 

 dish keeps the interior sufficiently moist, and if the lids be lifted fairly 

 frequently, so as to change the air, a plentiful crop of moulds is prevented. 

 Leaves can be kept sufficiently fresh in this way for several weeks — quite 

 long enough to allow the larvae to pupate. In other cases branchlets bearing 

 the infected leaves may be kept in water in vases ; and where the larval 

 stage is long, or the observer wishes to watch the insects tmder natural 

 conditions, the entire food-plant, if not too large, may be carefully trans- 

 planted. Occasionally it has been necessary to transfer a larva from a 

 withered leaf to a fresh one, a small artificial gallery being first constructed 

 under the cuticle of the fresh leaf and the larva coaxed into it. In the case 

 of one minute weevil-larva eight such transfers had to be made during 

 the three months of larval life. Some larvae do not confine themselves to 

 one leaf, and destroy several or many in their lifetime. The ^embers of 

 another class of larvae are pseudo-miners ; they act the part of miners 

 for a part only of their larval existence. It is not sufficient to observe these 

 insects in a state of captivity ; it is essential to observe them in the field. 

 Rearing them is the only way in which the collector can obtain perfect 

 specimens (otherwise unprocurable) in plenty for his collection. There 

 are no slack months in the j-ear for the investigator of leaf-mining insects ; 

 they are almost as plentiful in winter as in spring, and undoubtedly winter 

 is the time to look for new species. 



Of the seventy species that I have at present under observation the 

 . great majority are either new or only recently described. There are 

 indications that New Zealand possesses a large number of leaf-mining 

 insects. I have never yet failed to come home from an expedition with 

 several species new to me. It has therefore become necessary to divide 

 the paper into a number of parts, and for the sake of order and complete- 

 ness each part will deal separately with a single genus or group in so 

 far as they are kno\\Ti. Odd species will be published in separate parts. 

 The parts at present in hand are : The genus BedeUia ; the Nepticulids ; 

 several species belonging to the ginus Glyphteryx ; the Elachistidae ; the 

 genus Gelecia (all belonging to the Lepidoptera) ; new species of the genus 

 Phijtomyza (leaf -mining Diptera) ; the leaf -mining weevils. There is also 

 in preparation a monograph on the New Zealand gall-producing insects. 



