A comparison of the host‐searching efficiency of two larval parasitoids of Plutella xylostella

Abstract

Summary1. A host specialist parasitoid is thought to have greater efficiency in locating hosts or greater ability to overcome host defence than a generalist species. This leads to the prediction that a specialist should locate and parasitise more hosts than a generalist in a given arena. The work reported here tested these predictions by comparing the host‐searching behaviour of Diadegma semiclausum (a specialist) and Cotesia plutellae (an oligophagous species), two parasitoids of larval Plutella xylostella.2. Both parasitoids employed antennal search and ovipositor search when seeking hosts but D. semiclausum also seemed to use visual perception in the immediate vicinity of hosts.3. Larvae of P. xylostella avoided detection by parasitoids by moving away from damaged plant parts after short feeding bouts. When they encountered parasitoids, the larvae wriggled vigorously as they retreated and often hung from silk threads after dropping from a plant.4. These two parasitoids differed in their responses to host defences. Diadegma semiclausum displayed a wide‐area search around feeding damage and waited near the silk thread for a suspended host to climb up to the leaf, then attacked it again. Cotesia plutellae displayed an area‐restricted search and usually pursued the host down the silk thread onto the ground.5. Diadegma semiclausum showed a relatively fixed behavioural pattern leading to oviposition but C. plutellae exhibited a more plastic behavioural pattern.6. The time spent by the two parasitoids on different plants increased with increasing host density, but the time spent either on all plants or a single plant by D. semiclausum was longer than that of C. plutellae. Diadegma semiclausum visited individual plants more frequently than C. plutellae before it left the patch, and stung hosts at more than twice the rate of C. plutellae.7. The results indicated that the host‐location strategies employed by D. semiclausum were adapted better to the host's defensive behaviour, and thus it was more effective at detecting and parasitising the host than was C. plutellae.

Biological control of the diamondback moth,Plutella xylostella: A review

“…Sometimes the wasp also follows down the silken thread and stings the suspended larva (Sarfraz, personal observation). A similar behavior was reported for its congeneric species, D. semiclausum (Wang & Keller 2002). Attempts have been made to rear D. insulare in captivity on DBM larvae reared on artificial diet (Sieglaff et al 1998;Johanowicz & Mitchell 2000b) but to date no significant success has been achieved.…”

“…In south Texas, it has been reported to account for /98% parasitism in the field (Legaspi et al 2000). Compared with other parasitoids, it is an efficient host searcher Wang & Keller 2002) and has a significant ability to discriminate previously parasitized hosts (i.e., it avoids multiparasitism and superparasitism) (Bolter & Laing 1983). During a search immediately following contact by a parasitoid, the DBM larva typically moves away wriggling vigorously and drops from the plant suspended by a silken thread.…”

“…Unlike specialist parasitoids, C. plutellae exhibited a fixed host searching behavior, pursued the host(s) down the silk thread and spent a significantly greater proportion of time on the ground (17.79/3.6%) than D. semiclausum (4.79/1.1%) (Wang & Keller 2002). Initially, this wasp was assumed to be a DBM specialist but it has been recorded from or reared on several other lepidopterans (Fitton & Walker 1992) including a naturally occurring hybrid of Nyctemera amica (White) and N. annulata (Boisduval) (Lepidoptera: Arctiidae) (Cameron & Walker 1997).…”

Density dependence and environmental factors affect population stability of an agricultural pest and its specialist parasitoid

“…While specialist parasitoids are more effective at searching for hosts than generalists (Wang and Keller 2002), plant structural complexity plays an important role in determining host-finding (Andow and Prokrym 1990). Mango trees have high structural complexity due to their large size and surface area, and this could lead to variation among infested leaves in the probability of discovery by a parasitoid.…”

Enter the matrix: How to analyze the structure of behavior

“…To gain insight into how the behavior of searching parasitoids is organized, behavioral kinetograms (Field & Keller, 1993;Wang & Keller, 2002) are constructed (see Figure 4). This allowed a visualization of the differences in the behavioral sequences between parasitoids foraging in different environments.…”