Factors Affecting Parasitization of Spodoptera exigua (Lepidoptera: Noctuidae) and Sex Ratio of the Parasitoid Cotesia marginiventris (Hymenoptera: Braconidae)

2001 ◽  
Vol 36 (2) ◽  
pp. 188-198 ◽  
Author(s):  
P. Glynn Tillman
Keyword(s):  
Sex Ratio ◽  
Adult Female ◽  
Spodoptera Exigua ◽  
Beet Armyworm ◽  
Cotesia Marginiventris ◽  
Biological Factors ◽  
Female Progeny ◽  
Factors Affecting ◽  
Lepidoptera Noctuidae

Biological factors hypothesized to affect parasitization by Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae), an endoparasitoid of larvae of the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), as well as its sex ratio, were examined in the laboratory. Highest parasitization occurred when (1) adult female parasitoids were closely associated with hosts, (2) adult female parasitoids were 1 day old, (3) a host:female parasitoid ratio of between 10:1 and 30:1 was maintained, (4) second-instar beet armyworms were used as hosts, and (5) adult female parasitoids were exposed to hosts for 24 h. Percentage of female progeny was higher when females were closely associated with second instars.

Superparasitism Occasionally Predisposes Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae) to Develop Gregariously in Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae)1

2002 ◽  
Vol 37 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Eric Wellington Riddick
Keyword(s):  
Sex Ratio ◽  
Spodoptera Exigua ◽  
Host Density ◽  
Adult Emergence ◽  
Cotesia Marginiventris ◽  
First Instar ◽  
Emergence Rate ◽  
Lepidoptera Noctuidae ◽  
Density Treatment

Experiments were designed to estimate the incidence of superparasitism of Spodoptera exigua (Hübner) and gregarious development of Cotesia marginiventris (Cresson). Dissections of host larvae revealed that superparasitism was common at all host densities (5, 10, or 20 larvae per 0.05 liter arena). At least two parasitoid eggs were present per host on day 1 after parasitoid oviposition; eggs were scarcely found on day 2 and never found on days 3, 4 or 5. More than one parasitoid first instar was present per host on day 2 at all densities, although more were found in hosts of the 5 density rather than the 20 density treatment. Second instars were present in hosts on days 3, 4 and 5, and at least one was present per host on day 5. Third instars (the final instar stage) were not present inside hosts by day 5. Rearing of host larvae demonstrated that gregarious development was rare, since less than 6% of parasitized hosts yielded two third instars that spun cocoons. Neither host density nor exposure time (24 h, 48 h) had an effect on the occurrence of gregarious development. The adult emergence rate was 64% and the sex ratio was male-biased for parasitoids that developed gregariously. The adult emergence rate was 73% and the sex ratio was unbiased for those that developed solitarily. This research suggests that superparasitism of hosts by C. marginiventris can occasionally predispose parasitoid larvae to develop gregariously. Frequent superparasitism of hosts may be detrimental to the long-term propagation of C. marginiventris.

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