Capacity for Flight and Egg Production in Lochmaea Suturalis (Col., Chrysomelidae)
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CAPACITY FOR FLIGHT AND EGG PRODUCTION IN LOCHMAEA SUTURALIS (COL., CHRYSOMELIDAE) by P. G. VANSCHAICK ZILLESEN and A. M. H. BRUNSTING (Universityof Utrecht, Departmentof ZoologicalEcology and Taxonomy,Plompetorengracht 9, 3512 CA Utrecht, The Netherlands) SUMMARY Adults of the heather beetle (Lochmaeasuturalis) show well-developed flight muscles during a large part of their lifetime. They fly in large numbers in spring and in autumn on days with favourable climatic conditions. Beetles starved for 12 days showed greater flight activity than well-fed beetles. After migration in spring, females histolyse their flight muscles and oviposit. This process is influenced by the availability of food. Females fed with small quantities of food produced no eggs and maintained their flight muscles. Males maintained well-developed flight muscles throughout their life irrespective of feeding conditions. The importance of these phenomena is dis- cussed ; it is concluded that the phenomena are all part of an adequate survival strategy. INTRODUCTION Lochmaea suturalis is a phytophagous chrysomelid beetle occurring in NW Europe. The species is univoltine. The beetle and its larvae are both monophagous and feed on heather (Calluna aulgaris). Severe plagues of this beetle have occurred destroying large parts of the heather stands (BLANKWAARDT, 1968). Under such conditions migration to new habitats is essential for the survival of the species. The beetles fly in spring on days with favourable climatic condi- tions. Oviposition takes place after migration and the adults subse- quently die. Larvae appear from May to August. The first adults of the following generation are usually observed in August. Adults also migrate by walking to the edges of the affected areas where suitable food is still available. In this way a "front" is formed where densities may be very high. From this front the beetles migrate by flight the following spring (BRUNSTING, 1982). The beetles hibernate in the soil. A more detailed description of the biology of L. suturalis has been given by CAMERON (1944) and SCHRIER (1981). Migration and reproduction alternate in many insects. Both flight and reproduction make demands on the insects' energy resources. Between these activities there is an unstable equilibrium; it has been called the oogenesis-flight-syndrome OOHNSON, 1969). Insect hor- mones play an important role in the concept of the oogenesis-flight- 267 syndrome and the titre of these hormones is influenced by en- vironmental conditions such as photoperiod, temperature, quantity and quality of food available (RANKIN, 1978). Flight activity is usually tested under artificial circumstances, the insect being fixed to a pin or tethered to a mill (SOLLBRECK, 1974). Flight depends not only on the presence of well-developed flight machinery but also on the insect's motivation. The motivation is strongly dependent on the conditions during the flight test. Data on flight activity under constant laboratory conditions cannot completely explain the timing of flight under natural circumstances. A more direct picture of the dynamics of the flight activities of in- sects can be obtained by studying the condition of the flight muscles and the flight activity both in the field and in the laboratory; data on reproduction should be gathered too. These data should indicate how and to what extent the oogenesis-flight-syndrome is influenced by en- vironmental conditions. This is the approach used in this paper. Data are given concerning the influence of food quantity on flight activity and on egg production of L. suturalis. MATERIAL AND METHODS Field Research This study was carried out at two locations in The Netherlands. In 1979 observations were made at "Oud Reemsterveld" (ca 600 ha), a heathland which is located in the "Hoge Veluwe" national park, 8 km NW of Arnhem. Since in 1980 the heather had died in the major part of this location, investigations were continued on the "Hoorneboegse heide" (ca 60 ha), a heathland located about 1 km South of Hilver- sum. Samples were collected by insectnets or by sorting sods of heather by hand. Egg Productionand Fight Muscles The influence of the availability of food on egg production and flight muscle condition was studied under controlled conditions. A total of 100 males and 100 females was sampled on 1 April 1981 on the Hoorneboegse heide. The animals were kept in plastic petri-dishes (o 85 mm; h 15 mm). Each petri-dish contained 5 males and 5 females. The petri-dishes were incubated at 16°C during a photoperiod of 16 h light and 8 h darkness. The light intensity was about 1000 lux. The bottom of the petri-dishes was covered with moist filter paper in order to achieve a high humidity. The beetles were divided into two groups. The first group was fed three times a week with fresh twigs of heather and consequently food was available continuously. For the beetles of the second group a situation of limited food supply was created. These beetles were fed only once a week with fresh twigs of heather, which were removed after 31/, days. The egg production was determined three times a week. The development of the flight muscles was studied each week by dissecting 10-15 males and females from each group. .