Hymenopteran Pests

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A number of Hymenoptera, mainly sawflies (Symphyta), are pests in agriculture and forestry, largely due to their phytophagous and gall forming life styles. Other pests are recruited from the families Tenthredinidae, Cephidae, Siricidae, Anthophoridae and a few others. The Siricidae are a small family of wasps that is not (yet) represented in PNG. The family originates from Europe and contains some major pest species of Pinus, like Sirex noctilio, whose larvae feed inside Pinus radiata. Sirex was accidentally introduced into Australia and could be theoretically established in P. radiata plantations in PNG, if appropriate quarantine procedures are neglected.

However, compared to other parts of the world, fortunately not many of the phytophagous and destructive Symphyta occur in PNG. A very small number of forest insect pests occurring in Papua New Guinea are wasps and bees. The larval and adult Hymenoptera that are relevant in this context mainly have chewing mouthparts. Apart from phytophagous pests, a large number of wasps and ants are a nuisance for humans inflicting painful or sometimes even fatal stings or, as in the case of ants, infesting buildings and stored products. However most Hymenoptera species are of invaluable benefit to mankind and nature in general. The domesticated bees produce honey and wax. Predacious and parasitic wasps play an important role in the natural and biological control of insect pests. Trichogramma (Trichogrammatidae) for instance is commercially reared and sold as a specific biocontrol agent against particular agricultural pests. Lastly, many plants depend on the impact of pollinators like bees and wasps, culminating in the specific mutualistic relationship between pollinating fig wasps (Agaonidea) and their corresponding hosts, the figs (Moraceae).

Hymenoptera are one of the most diverse orders of insects and organisms in general. 7.7% of the world’s described species of animals, plants and microorganisms are Hymenoptera. Estimates, based on studies of the tropical rain forest on Borneo, indicate that the number of Hymenoptera species could be almost 20% of all species of organisms and about one third of the insect species. The Hymenoptera are the third largest insect order following the Coleoptera and Lepidoptera, but according to the estimates, the Hymenoptera could easily outnumber the Lepidoptera. There is a lot of taxonomic work left to be done, especially for myrmecologists, to describe all the new species. The most diverse hymenopteran family are the ants (Formicidae). The almost 100 hymenopteran families are divided into the two suborders Symphyta (sawflies) and Apocrita (wasps, bees and ants).

Important are gall-forming wasps, particularly of the family Torymidae. Oviposition by Megastigmus spp. females induces leaf, shoot and fruit galls on Eucalyptus, a condition that is usually of minor significance but might reduce the growth increment of the host. Interestingly, Megastigmus wasps are known to be inquilines of galls and can often be found together with Fergusonina spp. (Fergusoninidae) sharing the same gall. Therefore it is difficult to decide which of the two insects is the gall culprit.

Megastigmus sp.

The long-tongued bee Megachile frontalis (Fabricius) (Megachilidae) can defoliate all ages of its host Eucalyptus deglupta, causing a minor loss of increment.

Megachile sp.
(reproduced from CSIRO, 1991²)

The carpenter bee Xylocopa aruana (Anthophoridae), a close relative of Megachile, is a common but minor pest of untreated softwoods and can be found along the Papuan coast. Neither the adults nor the larvae feed on wood, but the adult bees bore holes in timber to establish their nests. Since only timber that is in a poor condition is infested, control measures are not necessary. Once the poor piece of timber is replaced, carpenter bee damage usually no longer occurs.

Xylocopa aruana

(reproduced from Gray, B. and Wylie, F.R., 1974)

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Michael F. Schneider, 1999