BIOLOGI, GEJALA SERANGAN, DAN PENGENDALIAN HAMA BUBUK JAGUNG Sitophilus zeamais MOTSCHULSKY (COLEOPTERA: CURCULIONIDAE)

<p>Salah satu kendala dalam penyimpanan jagung adalah serangan hama<br />gudang. Salah satu hama gudang jagung adalah <em>Sitophilus zeamais</em><br />Motschulsky (Coleoptera: Curculionidae). Hama ini ditemukan di<br />daerah panas maupun lembap. Hama ini bersifat polifag, dapat<br />merusak serealia seperti beras/gabah, jagung, gandum, dan sorgum,<br />namun dilaporkan sebagai hama penting pada jagung. Kehilangan<br />hasil jagung di wilayah tropis akibat <em>S. zeamais</em> berkisar antara 30-<br />100%. Biji jagung yang disimpan selama 6 bulan menunjukkan<br />kerusakan 85% dan bobot biji menyusut 17%. Telur hama tersebut<br />diletakkan di dalam biji dan dalam beberapa hari akan menetas<br />menjadi larva. Larva menyelesaikan siklus hidupnya di dalam biji.<br />Telur berwarna putih bening, berbentuk lonjong, lunak dan licin,<br />berukuran 0,7 mm x 0,3 mm. Larva berwarna putih kekuningan,<br />tidak bertungkai, kepala berwarna cokelat, terdiri atas empat instar,<br />panjang 1,5–4 mm. Periode larva berlangsung 25 hari. Imago <em>S.</em><br /><em>zeamais</em> berukuran 3-4,5 mm. Hama <em>S. zeamais</em> dapat dikendalikan<br />dengan cara: 1) menyimpan jagung dalam wadah maupun gudang<br />secara higienis, 2) menanam varietas tahan, 3) menggunakan<br />musuh alami yaitu parasit, predator, dan patogen, seperti parasitoid<br /><em>Lariophagus distinguendus</em> dan <em>Anisopteromalus calandrae</em>, serta<br />patogen <em>Beauveria bassiana</em>, 4) memanfaatkan insektisida nabati<br />yang memiliki toksisitas tinggi terhadap <em>S. zeamais</em>, yaitu <em>Ageratum</em><br /><em>connyzoides</em> (bandotan), <em>Andropogon nardus</em> (serai), <em>Allium sativum</em><br />(bawang merah), <em>Nicotiana tabacum</em> (tembakau), <em>Zingiber officinale</em><br />(jahe), dan <em>Azadirachta indica</em> (mimba), serta 5) menyemprotkan<br />insektisida sintetis metil pirimifos.</p>

Does early learning drive ecological divergence during speciation processes in parasitoid wasps?

Central to the concept of ecological speciation is the evolution of ecotypes, i.e. groups of individuals occupying different ecological niches. However, the mechanisms behind the first step of separation, the switch of individuals into new niches, are unclear. One long-standing hypothesis, which was proposed for insects but never tested, is that early learning causes new ecological preferences, leading to a switch into a new niche within one generation. Here, we show that a host switch occurred within a parasitoid wasp, which is associated with the ability for early learning and the splitting into separate lineages during speciation. Lariophagus distinguendus consists of two genetically distinct lineages, most likely representing different species. One attacks drugstore beetle larvae ( Stegobium paniceum (L.)), which were probably the ancestral host of both lineages. The drugstore beetle lineage has an innate host preference that cannot be altered by experience. In contrast, the second lineage is found on Sitophilus weevils as hosts and changes its preference by early learning. We conclude that a host switch has occurred in the ancestor of the second lineage, which must have been enabled by early learning. Because early learning is widespread in insects, it might have facilitated ecological divergence and associated speciation in this hyperdiverse group.

Composition of cuticular lipids in the pteromalid wasp Lariophagus distinguendus is host dependent

The insect cuticle is covered by a thin layer of hydrocarbons not only preventing desiccation but also playing an important role in the sexual communication of several species. In the pteromalid wasp Lariophagus distinguendus, a parasitoid of grain infesting beetles, female cuticular hydrocarbons (CHCs) elicit male courtship behaviour. We analyzed the CHC profiles of male and female L. distinguendus wasps reared on different beetle hosts by coupled gas chromatography- mass spectrometry (GC-MS). Statistical analysis of the data revealed significant differences between strains reared on different hosts, while spatially isolated strains reared on the same host produced similar profiles. CHC profiles of parasitoids reared on Stegobium paniceum were statistically distinguishable from those of wasps reared on all other hosts. A host shift from Sitophilus granarius to S. paniceum resulted in distinguishable CHC profiles of L. distinguendus females after only one generation. Considering the role of CHCs as contact sex pheromones, our data suggest that host shifts in parasitic wasps might lead to reproductive isolation of host races due to the modification of the cuticular semiochemistry.