Abstract
Functional responses at each developmental stage of predators and intraspecific competition associated with direct interactions among them provide insights into developing biological control strategies for pests. The functional responses of Harmonia axyridis (Pallas) at each developmental stage of Melanaphis sacchari (Zehntner) and intraspecific competition among predators were evaluated under laboratory conditions. The results showed that all stages of H. axyridis displayed a type II functional response to M. sacchari. Based on Holling's disc equation, the instantaneous searching rates were highest (a) and handling time was shortest (Th) of fourth instar larvae (a = 0.8818; Th = 3.9 min) and female adults (a = 0.9881; Th = 3.0 min) at larval and adult stages, respectively. The coefficients of mutual interference (m) assessed by the intraspecific competition equation were higher for fourth instar larvae (m = 0.4764) and female adults (m = 0.4183). The present study indicates that fourth instar and female adult were more effective stages of H. axyridis in the context of biological control but suitable predator densities need to be considered before natural enemy release.
Highlights
Melanaphis sacchari (Zehntner) (Hemiptera: Aphididae) is a perennial pest of Sorghum bicolor L
Functional response Our study showed that all developmental stages of H
R2 is the coefficient of determination estimated by fitting the intraspecific competition equation and P is the probability that the intraspecific competition equation will yield significant parameters
Summary
Melanaphis sacchari (Zehntner) (Hemiptera: Aphididae) is a perennial pest of Sorghum bicolor L. Melanaphis sacchari originates from Java, Indonesia (Zehntner, 1897). Melanaphis sacchari is initially reported on sorghum when their largely damaging populations invaded in Beaumont, Texas (Villanueva et al, 2014). Over the past several years, M. sacchari has caused measurable economic effects due to the damaged plant growth correlated with the sticky “honeydew” covering the plant. Control of M. sacchari is difficult as pesticides cannot penetrate the greater canopy of sorghum. Melanaphis sacchari cannot destroy sorghum in a short term period, but the large populations growing out of control lead to the chlorosis correlated with damage of plant tissues because of the rapid aphid reproduction (Colares et al, 2015). If the M. sacchari colony has the characteristic of thermal tolerance, it could contribute significantly to its pest status under hot summer conditions
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