Relative Fitness of Near Isogenic Lines for Melanic and Typical Forms of the Oriental Armyworm, Mythimna separata (Walker)

Abstract

Melanism in the oriental armyworm Mythimna separata (Walker) is characterized by a black color in adults instead of the normal body color of off-white. Because inheritance of melanism in this moth follows Mendel's law, with the melanic allele (t) recessive to the normal allele (T) at a single autosomal locus, a backcrossing procedure was used to develop near isogenic lines (NILs) for melanic (NILs-tt) and typical forms (NILs-TT) of this moth. Melanic males (tt) and typical females (TT) were crossed in the laboratory, their progeny (F(1)) were interbred, and F(2) melanic males were backcrossed to typical female offspring of the parallel line. This cycle was repeated five times to create NILs for melanic and typical forms of this moth. The effects of the melanic allele on relative fitness were evaluated in terms of developmental and reproductive characteristics. Life tables of the NILs were constructed to determine net reproductive rate (R(0)). Results indicated that NILs-tt possessed apparent developmental and reproductive advantages, including shorter immature development time, higher larval and pupal survival, a shorter adult preoviposition period, and more eggs laid per female compared with the NILs-TT.

Overexpression of Tyrosine hydroxylase and Dopa decarboxylase associated with pupal melanization in Spodoptera exigua

“…For example, melanization is expressed locally in the two dipterans Drosophila polymorpha 4 and Drosophila immigrans 6, but globally in almost all the documented lepidopterans239101112131415161718. In terms of temporal expression pattern, melanic phenotype may express in larva91011, pupa14, adult231619, larva and adult ( Bombyx mori mln mutant strain20), larva and pupa ( B. mori sooty mutant strain21), or pupa and adult ( Helicoverpa armigera 15) stages. Further, melanism in these diverse taxa may confer one or more adaptive advantages22 that are associated with a fitness cost (e.g.…”

“…in Manduca sexta 11 and H. armigera 15) or a fitness gain (e.g. in Mythimna separate 16, Spodoptera littoralis 13 and D. immigrans 6) in life-history traits. Such variable expression profiles and adaptive impacts of melanization imply a great diversity of genetic/molecular mechanisms controlling melanism.…”

Biocontrol of the oriental armyworm, Mythimna separata, by the tachinid fly Exorista civilis is synergized by Cry1Ab protoxin

“…Adults were transferred in pairs to 850-mL jars provided with wax paper for oviposition, and eggs were collected daily. Jars were covered with gauze to facilitate ventilation and adults were provided with 5% honey solution (v/v) replaced daily3152.…”

“…Emergence rate was calculated as the number of successfully emerged adults divided by total number of pupae. Pre-oviposition period and lifetime fecundity were determined following the methods employed in previous studies3152.…”

The peppered moth and industrial melanism: evolution of a natural selection case study

“…Their synthesis is involved not only in melanin production but also immune defence and sclerotin production, so that competitive trade-offs are possible (Windig, 1999;Stoehr, 2006). Pre-adult fitness differences between melanic and non-melanic morphs are reported for the noctuid species Mythimna separata (Jiang et al, 2007). In some moths and other insects, individuals with darker cuticles tend also to have stronger immune defence (True, 2003;Mikkola and Rantala, 2010) and immune defence and wing melanization can interact (Freitak et al, 2005).…”