No abstract

No abstract

The effects of the mandibular gland secretion of larvae of Plodia interpunctella (Hubner) on the behaviour of conspecific larvae and on its parasitoid, Nemeritis canescens (Gravenhorst) were studied in open chambers and in an olfactometer. The secretion is deposited in the form of droplets on the silk while it is being spun, and as irregular patches on the substratum. Plodia larvae presented with a choice between fresh food and food contaminated with mandibular gland secretion chose fresh food. Those provided with contaminated food only, chose this in preference to starvation. The secretion also caused 'attraction' and stimulation of oviposition movements in female Nemeritis, leading to increased parasitization. The stimulatory effect of the droplets was remarkably persistent and could be detected after storage for at least 5 years at room temperature as well as at 4°C or -7°C. Chemical analysis indicated the presence of two components, the major with an Rf value of 0.6 (empirical formula C&IwO4), and the other with an Rf value of 0.8 (empirical formula C22H3803).Observations on the effect of droplets of mandibular gland secretion on the behaviour of Nemeritis, and on the resulting parasitization were made at 25 f 0.5"C under a ceilingmounted fluorescent light; adult females 3-5 days postemergence were used exclusively. Observations on Plodia larvae were made at the same temperature in semidarkness with the aid of a 40-W red lamp positioned 60 cm from the olfactometer chamber; fifth instar, pre-wandering larvae were used. Response of Plodia larvae to mandibular gland secretion MethodsLarval responses were tested in an olfactometer (Fig. la) based on the design of Varley & Edwards (1953). It was constructed from two sheets of perspex separated by six shallow walls of perspex arranged in the form of a hexagon. The walls were permanently fixed to 0307-6962/80/0600-0165 $02.00 0 1980 Blackwell Scientific Publications 165 11 C, chamber; H, hexagonal plate; B, base of the chamber. The height of the walls of the chamber was 0.8 cm. Three 2.1 cm holes are drilled in the top: one near the outlet for the insertion of the larvae (i.e. at start of tracks in Fig. lb), and one over each odour source for insertion of test materials (i.e. above the squares). During operation these holes were sealed. Stimuli in Figs. l b , 1 and 2 were clean food versus contaminated food; in 3 and 4 , ether extract of cocoons (i.e. plus mandibular gland secretion) versus clean filter paper.

Nephus arcuatusKapur is an important predator ofNipaecoccus viridis(Newstead), in citrus orchards of southwestern Iran. This study examined the feeding efficiency of all stages ofN. arcuatusat different densities ofN. viridiseggs by estimating their functional responses. First and 2nd instar larvae as well as adult males exhibited a type II functional response. Attack rate and handling time were estimated to be 0.2749 h−1and 5.4252 h, respectively, for 1st instars, 0.5142 h−1and 1.1995 h for 2nd instars, and 0.4726 h−1and 0.7765 h for adult males. In contrast, 3rd and 4th instar larvae and adult females ofN. arcuatusexhibited a type III functional response. Constantband handling time were estimated to be 0.0142 and 0.4064 h for 3rd instars, respectively, 0.00660 and 0.1492 h for 4th instars, and 0.00859 and 0.2850 h for adult females. The functional response of these six developmental stages differed in handling time. Based on maximum predation rate, 4th instar larvae were the most predatory (160.9 eggs/d) followed by adult females (84.2 eggs/d). These findings suggest thatN. arcuatusis a promising biocontrol agent ofN. viridiseggs especially for 4th instar larvae and adult females.

ABSTRACT. Larvae of Plodia interpunctella deposit droplets of mandibular gland secretion onto silk filaments connecting particles within the substrate they inhabit, and on to the substrate itself. Active participation of the mouthparts is necessary for both the formation and deposition of these droplets along the filaments and occurs as the silk is spun. Deposition of secretion directly on the substratum does not involve the mouthparts and appears to result from contact between the lower surface of the head and the substratum. Larvae from which the mandibular glands have been removed by excision neither produce droplets on silk nor deposit them on the substratum. Those which are incapable of spinning silk due to cauterization of the spinneret are still able to deposit secretion on the substratum, however. Deposition of secretion on silk webbing does not occur when the setae which regulate formation of droplets on filaments are removed by shaving. Droplets are not characteristic of a particular larval instar but are produced by larvae of all instars as a normal function which does not depend upon intraspecific encounters. Four other Lepidopteran pests, Ephestia elutella, Ephestia cautella, Anagasta kuehniella and Antigasta catolaunalis, were also found to produce droplets of mandibular gland secretion in a similar manner to larvae of P. interpunctella.