Introduction

In 1999 a conspicuous longhorn beetle (Coleoptera: Cerambycidae), was collected from pistachio trees, Pistacia vera Linnaeus and Pistacia atlantica subsp. mutica (Fischer & C.A. Meyer) at Sirjan (South Iran) for the first time. The beetle (Figs 7, 8, 10) proved to be undescribed and was named as Calchaenesthes pistacivora by Dr C. Holzschuh (Holzschuh 2003). According to Hashemi-Rad (2005) the pistachio longhorn beetle caused very severe damage to weakened pistachio trees. During April, 2007 the second author managed to rear a parasitoid from the longhorn beetle, which may play a role in the biological control of the pest. It proved to be a new species of the genus Megalommum Szépligeti near jacobsoni (Hymenoptera: Braconidae: Braconinae). The new species, Megalommum pistacivorae, is described below. It is the first record of a cerambycid host for the genus, and is the first record of the genus Megalommum from Iran.

Material and methods

The material was partially reared from the larvae of the pistachio longhorn beetle boring in pistachio trees and partially collected at light in the wild pistachio growing areas of Sirjan (South Iran). The material is deposited in the Netherlands Centre for Biodiversity Naturalis at Leiden (RMNH).

For the recognition of the subfamily Braconinae, see van Achterberg (1990, 1993, 1997), for a key to the genera of Braconinae, see Quicke (1987), and for the terminology used in this paper, see van Achterberg (1988).

No taxonomic history is presented in this paper; for information, we refer to the Taxapad interactive catalogue (Yu et al. 2007 and later updates).

Key to the genera Aphrastobracon Ashmead and Megalommum Szépligeti

Notes. Curreia Ashmead, [Oct.] 1900 (Figs 26–37) and Endovipio Turner, 1922 (Figs 52–64) are new junior synonyms. Endovipio was synonymized with Curreia by Falco and Quicke (1997) and Curreia is here synonymized with Megalommum (syn. n.). The differences between the genera Megalommum Szépligeti s.s. (species from Australasia), Endovipio Turner (Afrotropical) and Curreia Ashmead (remainder of Palaeotropical area and South Palaearctic) are gradual and, therefore, they are considered congeneric here. The only small difference that seems to be valid is the development of the dorso-lateral carinae of the first tergite posteriorly; absent in Megalommum s.s. and present (but often only weakly developed) in Curreia and Endovipio. The shape of the ovipositor valves is variable in both groups as is the relative length of veins 1-CU1 and 1-M of the fore wing.

Key to West Palaearctic and Oriental species of the genus Megalommum Szépligeti Taxonomy Biology

The development of the cerambycid host Calchaenesthes pistacivora Holzschuh lasts two years; the first winter it survives as a larva and during the second autumn it usually develops into an adult (Hashemi-Rad 2005). The adult beetle stays inside the feeding canal (Fig. 10) for about five months, from mid October to late March. In early April, the adult beetles appear on the pistachio trees and usually feed on the fresh pistachio leaves (Fig. 7); the resulting damage is considered to be minimal. The beetles lay their eggs on twigs, branches or stems of weakened pistachio trees, preferably on the pruned sites where the tiny larvae promptly penetrate into the twigs or branches. Changes in the environmental conditions of pistachio growing areas in the collection site are thought to be drought, an increase of salinity in irrigation water, which in turn is caused by a decrease of water resources and mismanagement by pistachio producers. These appear to be the major reasons for the establishment and development of this pest on cultivated pistachio trees (Hashemi-Rad 2005). It is predicted that the contaminated areas will expand as more pistachio trees lose vigor. Our survey in wild pistachio growing areas of Sirjan clearly showed that Calchaenesthes pistacivora had already been living in the wild pistachio trees for a long time, because the beetle canals are clearly visible on both dead and living trunks of very old trees of Pistacia khinjuk Stocks (Figs 4, 5) and Pistacia atlantica mutica. It is assumed that the beetle has been a minor phytophagous pest on wild pistachio trees for hundreds of years, however, populations increased due to weakening of these trees. The wild pistachio species have been suffering from the effects of erosion caused by human activities, particularly overgrazing and harvesting for use as firewood or charcoal as well as from severe drought periods for several years. In addition, the cultivated pistachio regions at Sirjan are not far from areas with wild pistachio trees. Therefore, emigration of Calchaenesthes pistacivora to pistachio orchards is likely. At present the pistachio growers experience many serious problems caused by pests and diseases (Mehrnejad 2001) and the longhorn beetle is one of those that can cause considerable tree damage and reduction of yields.

The cocoons of the parasitoid were collected inside the tunnels of the beetle (Fig. 6). The cocoons are 12–15 mm long, brownish and consist of thin paper-like silk. The beetle usually pupates inside the tunnel about 2–3 cm from the emergence hole, where the cocoons of Megalommum pistacivorae are also found. Field studies showed that the parasitoid enters the tunnel of the beetle through the hole made by the last instar beetle larva before pupation. The parasitoid attacks the last instar beetle larva in September and October and the parasitoid larva is solitary. Members of Braconinae are all thought to be ectoparasitoids. Surprisingly, the second author did not see any parasitoid larva or egg when he collected a fully developed beetle larva from the feeding tunnel. The beetle larva (still in the tunnel) was transferred to the laboratory where it was kept under controlled conditions. After a week a naked pupa of the wasp (that did not construct the usual cocoon) was present and the pupa developed into an adult Megalommum pistacivorae. Further investigations are necessary to rule out the possibility that a minute wasp larva was present on the non-exposed side of the beetle larva.

Megalommum pistacivorae overwinters in the prepupal stage and it has an obligatory diapause to pass the winter. The parasitoid cocoons containing the prepupa were kept under controlled conditions (27.5°C, 16L:8D photoperiod and 55±5 RH), but they did not pupate until early March. In the field, pupation takes place from mid to late March and the adults of Megalommum pistacivorae appear in the orchards from early April onwards. The rate of parasitism was estimated to be about 23% (n = 110) in experimental orchards. Alternative hosts for this parasitoid remain undetermined, also it is not clear if the adult wasps attack another host after emergence in early April or they pass the hot summer period and attack the larvae of Calchaenesthes pistacivora the following September.

In the same tunnels several other insects were found; the most common was a bee belonging to the genus Hylaeus. It uses the tunnels as shelter for its brood cells. Several small cells of bees are usually found at the same site where Megalommum pistacivorae makes its cocoons (Fig. 15). From late September till late October the female bee makes 3–5 small cells (4 mm length and 3 mm diameter each) in each tunnel, and fills them with a yellowish jelly mixed with pollen. In each cell an egg or a young larva was found (Fig. 12). The female bees cover the emergence hole (tunnel cup) with a very thin and delicate grayish waxy layer (Fig. 14). The cover protects the offspring of the bee as well as that of the wasp, Megalommum pistacivorae, against predation or parasitism during the overwintering period. The bee larvae overwinter in these cells at the prepupal stage and pupate from late March on. The tunnels are also used as a nest site (Fig. 13) by a Crabronid wasp.