DOI: 10.5061/dryad.fttdz0953
title: Can parasitized diamondback moth larvae avoid ant attacks?

description: Although koinobiont parasitoids exploit their hosts without killing them,
 consuming the body tissues of hosts that avoid predation via high motility
 should increase the risk of the parasitoids being preyed upon along with
 their hosts. Cotesia vestalis (Haliday) (Hymenoptera: Braconidae)
 is a koinobiont parasitoid of the diamondback moth Plutella xylostella
 (L.) (DBM). Although DBM larvae exhibit predation avoidance behaviors
 based on their high locomotor ability, we hypothesized that DBM larvae
 parasitized by C. vestalis might not be able to maintain this ability and,
 hence, are exposed to higher predation pressure than unparasitized larvae.
 We compared locomotor and predation avoidance abilities of parasitized and
 unparasitized DBM larvae. Compared to unparasitized DBM larvae,
 parasitized DBM larvae had lower wriggling ability to mechanical stimuli
 and were more likely to be preyed upon by the black wood
 ant Formica japonica (Motschoulsky) (Hymenoptera: Formicidae) in
 situations where they had to avoid predation by wriggling. In contrast,
 hanging ability did not differ between parasitized and unparasitized DBM
 larvae, nor in predation avoidance ability in situations where they had to
 avoid F. japonica predation by hanging. The results demonstrate
 that parasitism by C. vestalis reduces the wriggling ability of
 DBM larvae, which consequently exposes the parasitoid to higher intraguild
 predation risk under some conditions. This finding also suggests that the
 conventional research methods used to reveal the mortality factors of DBM
 larvae may have underestimated parasitism, because they did not take into
 account parasitized DBM larvae missing due to predation. It seemed that
 host species with vigorous defensive behaviors are likely to have such
 behaviors impaired when parasitized, while whether parasitized hosts are
 actually more vulnerable to predation depends on the specific defensive
 strategies used by the hosts.
description: <strong>Wriggling ability</strong>
 Wriggling ability in response to physical stimuli was compared
 between parasitized and unparasitized DBM larvae. It was practically
 impossible to confirm directly whether the living DBM larvae were
 parasitized by <em>C. vestalis</em>. Therefore, DBM larvae
 that had been exposed to <em>C. vestalis</em> were used as
 provisionally parasitized larvae and were reared individually after the
 experiment to confirm parasitism, i.e., the emergence of the parasitoid.
 The parasitoid emerged within 5 days, and <em>C. vestalis</em>
 larvae emerge 9 days after oviposition at 25°C (Yu et al. 2008), so the
 time elapsed after oviposition of the parasitoid must have been 4 ~ 9
 days. DBM larvae from the study population that had never been exposed to
 <em>C. vestalis</em> were used as ‘unparasitized’
 specimens. We placed each parasitized or unparasitized
 fourth instar DBM larva on a piece of graph paper, and stimulated its head
 with a fine brush to make it wriggle backward. We measured the
 straight-line distance between the larval head position before and after
 the wriggling movement. Each larva was measured five times. The longest
 and average wriggling distances were compared between parasitized (n = 40)
 and unparasitized (n = 40) larvae. In addition, to compare the wriggling
 ability of parasitized DBM larvae with respect to parasitism progression
 by <em>C. vestalis</em>, we compared the longest and average
 wriggling distances between parasitized larvae from which the parasitoid
 emerged within 1 day (i.e., &lt; 1 day before emergence; n = 21) and
 after that time (i.e., &gt; 1 day before emergence; n = 19).
 <strong>Hanging ability</strong>
 We fixed a 1 cm × 1 cm cabbage leaf square horizontally in the
 air with wire and placed a parasitized or unparasitized fourth instar DBM
 larva on the upper leaf surface. The larval head was mechanically
 stimulated several times with a fine brush. The number of stimulus times
 it took for the larva to hang from the leaf, and also the length of the
 silk thread from the leaf to the larva, were recorded. We compared 1) the
 proportion of larvae that successfully hung down, 2) the number of
 stimulation events before hanging, and 3) the silk thread length between
 parasitized (n = 40) and unparasitized (n = 27) larvae. Larvae that failed
 to hang down (i.e., that fell off) were excluded from the analysis for
 parts 2 and 3.
description: # Can parasitized diamondback moth larvae avoid ant attacks? Dataset DOI:
 [10.5061/dryad.fttdz0953](10.5061/dryad.fttdz0953) ## Description of the
 data and file structure This study compares the locomotor performance of
 parasitized and unparasitized diamondback moth, *Plutella xylostella*, by
 the parasitoid wasp *Cotesia vestalis*. ### Files and variables #### File:
 All\_data\_(revised).xlsm **Description:** In the worksheet titled
 **"wriggling ability"**, the data indicate the distance (mm)
 each larva wriggled backward in response to physical stimuli. Each larva
 was tested until it had wriggled five times. The **"wriggling
 ability"** cells record the distances wriggled successively by each
 larva, in the order they occurred. The worksheet also includes calculated
 values for the average** **and the longest wriggling distances for each
 larva. In the worksheet titled **"hanging ability"**, the data
 include the number of stimulation events required for a larva to hang down
 itself from the edge of a leaf square, as well as the length of silk
 thread spun during the response. In the hanging ability experiment, the
 number of tested larvae differed between parasitized and unparasitized
 groups; therefore, some cells contain "null" values to reflect
 this difference in sample size. ## Code/software No software is needed to
 view our data.