Oviposition preference and olfactory response of Diaphania indica (Lepidoptera: Pyralidae) to volatiles of uninfested and infested cucurbitaceous host plants

. The cucumber moth, Diaphania indica (Saunders) (Lepidoptera: Pyralidae), is a major pest of cucurbitaceous plants. The oviposition preference and olfactory response of larvae, mated and unmated male and female adults to volatiles emanating from uninfested and infested plants of four species of cucurbitaceous host plants and odours of conspeci ﬁ cs were recorded. Also the role of experience in the host ﬁ nding behaviour of D. indica was evaluated. The experiments were done using a wind tunnel, olfactometer attraction assays and oviposition bioassays. The results reveal that fewer eggs were laid on infested plants than on uninfested plants. Females signi ﬁ cantly preferred cucumber over squash, melon and watermelon. Cucurbitaceous plants elicited adults of D. indica to ﬂ y upwind followed by landing on the plants. The effect of experience on the olfactory preference of D. indica was dependent on the host plant. Females that had experience of cucumber, squash and melon plants were signi ﬁ cantly attracted to the same plant, but not in the case of watermelon. Larvae of this pest were attracted only to volatiles of uninfested cucumber, squash and melon, whereas volatiles of conspeci ﬁ cs, infested plants and intact watermelon did not attract larvae. This study is an initial attempt to investigate the role of volatile infochemicals in the host-ﬁ nding behaviour of D. indica . These results provide baseline information for the development of new control strategies against D. indica .


INTRODUCTION
The cucumber caterpillar, Diaphania indica (Saunders) (Lepidoptera: Pyralidae), is one of the most important pests of cucurbitaceous plants worldwide (Peter & David, 1991;Namvar & Alipanah, 2002;Nagaraju et al., 2018).The larvae feed on leaves, fruits, fl owers and stem and cause considerable yield loss during an outbreak (Nagaraju et al., 2018).The females prefer young leaves over old leaves, petioles and stems for oviposition (Choi et al., 2003).A previous fi eld study shows that D. indica prefers to lay eggs on sweet melon (Cucumis melo cv Hales Best Jumbo) than on watermelon (Citrullus vulgaris cv Charleston Gray) and cucumber (Cu.sativus cv Alpha Beta) (Ba- Angood, 1979).Currently control programmes largely rely on the application of chemical insecticides.The overuse of chemical control results in the evolution of resistance to insecticides, toxicity to non-target organisms, environmental contamination and insecticide residues in agricultural products (San Choi et al., 2009).To reduce these effects, alternative control methods are required.Herbivorous in-watermelon (Citrullus lanatus) (cv.Saturn) plants were cultivated in individual plastic pots (12.5 diameter × 13.0 cm) containing a 1 : 2 : 1 mixture of organic compost, peat moss and perlite.The plants were grown in a greenhouse, under controlled conditions at 27 ± 2°C, 60-80% RH and a 16L : 8D photoperiod.Supplementary lighting was provided by 400-watt sodium vapour lamps, and seedlings that were about twenty days old (4 to 6 leaf stage) were used in the experiments.Fertilizer was applied to the plants daily in the form of an NPK (20-20-20) fertilizer.To obtain infested plants, a series of 8 seedlings of each cucurbitaceous host plant were introduced into each of a series of smaller screen cages (70 × 70 × 70 cm) kept under the same conditions and infested with either 5 third instar larvae of D. indica, 5 adults of Bemisia tabaci (3 females and 2 males) or 5 adults per plant of T. urticae, 48 h prior to the experiment.At the beginning of the experiment, the insects and mites were removed from the infested plants.To obtain healthy plants, seedlings of each species of Cucurbitaceae were placed in aluminium framed screen cages (100 × 100 × 100 cm) in a separate greenhouse.

Insects
Larvae D. indica were collected from cucumber in greenhouses, in the County Jiroft in the province of Kerman, Iran (28°63´53.58˝Nand 57°82´05.50˝E)and transported to a laboratory.Four separate stock cultures of D. indica were reared and bred on seedlings of each Cucurbitaceae species in each of four aluminium framed screen cages (100 × 100 × 100 cm) kept under the same physical conditions as the plants.Adults were fed by providing them with a piece of cotton wool soaked in honey solution (10%).At least four generations were reared on each type of host plant before starting the experiments.To obtain unmated adults of known age, pupae were separated by gender and kept in separate plastic containers (20 × 17 × 10 cm) until the emergence of the adult insects.To obtain mated adults, pupae of both the sexes were kept in small screen cages (70 × 70 × 70 cm) in an insectary under the same physical conditions as described previously, but with the photoperiod reversed.The newly emerged adults were fed with honey solution as described above.Mated male and female insects, were separated and placed inside a plastic container (5 × 7 cm) with a small piece of cotton wool soaked in a solution of 10% honey and water.Mated 4-5 day old females were used in oviposition preference experiments.

Oviposition bioassay
Long range oviposition experiments were carried out in a wind tunnel made of a transparent acrylic material (180 × 60 × 60 cm) with an airfl ow of 0.5 m/s.The wind tunnel was housed in a condition-controlled room at 27 ± 1°C, 60-80% RH and 16L : 8D photoperiod.In the fi rst four experiments, the responses to the four different host plants each in the following different conditions: 1 -uninfested, 2 -infested with conspecifi c larvae, 3whitefl ies and 4 -two-spotted spider mites, were evaluated.In the last four experiments, the responses to the following four plants: 5 -cucumber, 6 -squash, 7 -melon and 8 -watermelon, were evaluated.All experiments were done during the 8-h dark period, by releasing 5 mated females at a distance of 150 cm from the plants.When all the plants were evaluated simultaneously, insects from each of the four stock cultures were used.In order to avoid the effects of possible learning and adaptation of insects to plants the responses to a particular species of plant or condition of the plant mixtures of moths reared on the other three host plants were used.At the end of each experiment the number of eggs laid on each plant was counted under a binocular microscope.Experiments were replicated 20 times using 100 females for each treatment.The placement of plants in each replication was rotated.al., 2015;Frérot et al., 2017).Chemical signals released by plants vary with plant species and cultivar, plant age and physiology, plant part, climatic factors, air pollution and the species of herbivore (Blande et al., 2014;Moghbeli Gharaei et al., 2014;Frérot et al., 2017).Chemical cues from host plants infl uence host location in various moths, such as Tuta absoluta (Lepidoptera: Gelechiidae) (Proffi t et al., 2011;Megido et al., 2014;Uzun et al., 2015), D. nitidalis (Lepidoptera: Pyralidae) (Peterson et al., 1994), Anticarsia gemmatalis (Lepidoptera: Noctuidae) (Meagher & Landolt, 2010), Plutella xylostella (Lepidoptera: Plutellidae) (Baoyu et al., 2001), Helicoverpa armigera (Lepidoptera: Noctuidae) (Burguiere et al., 2001), Maruca vitrata (Lepidoptera: Crambidae) (Zhou et al., 2015), Epiphyas postvittana (Lepidoptera: Tortricidae) (El-Sayed et al., 2018) and Ostrinia nubilalis (Lepidoptera: Crambidae) (Leppik & Frérot, 2014;Leppik et al., 2014).It is well known that previous feeding experience infl uences the host fi nding behaviour of many herbivorous insects (Anderson & Anton, 2014;Hu et al., 2018).In many studies on lepidopteran species, it is documented that, prior experience can infl uence subsequent responses to plant volatiles (Cunningham et al., 1998;Carlsson et al., 1999;Chow et al., 2005;Pszczolkowski & Brown, 2005;Moreau et al., 2008;Anderson et al., 2013;Megido et al., 2014;Petit et al., 2018).Choosing a suitable host plant for offspring is largely dependent on the oviposition preference of female herbivorous insects (Janz, 2002).In some cases, when suitable food is scarce the larvae of some species of Lepidoptera disperse from the egg-laying site and forage for new host plants.Thus, in so doing they reduce competition, avoid exposure to natural enemies and are less exposed to toxins and plant defence compounds (Singer & Stireman, 2001;Singer et al., 2002;Kakimoto et al., 2003;Singer & Stireman Iii, 2003;Carroll et al., 2006).Understanding the response of D. indica to host plant volatiles is essential for the detection and development of an effective attractant for this pest.In this study, we tested the oviposition preference and olfactory response of mated and unmated males and females and larvae of D. indica to odours emanating from different cucurbitaceous species, both uninfested and infested, eggs, larvae, pupae and adult conspecifi cs.Given that the volatile compounds that are induced by the feeding of conspecifi c and heterospecifi c herbivores can be different and lead to different responses (Rojas, 1999), responses to plants infested with conspecifi c larvae, whitefl ies and two-spotted spider mites, were also evaluated.We also examined the role of experience in the host fi nding behaviour of D. indica females.The purpose of this study was to improve our understanding of the behavioural characteristics, oviposition preference and olfactory responses of D. indica in complex host plant situations, which might be exploited for use in management strategies.

Role of olfactory stimuli and mating status in host fi nding behaviour
To determine the role of olfactory stimuli, sex, and mating status in host fi nding behaviour of D. indica, the olfactory responses of 4-5-day old virgin and mated males and females to uninfested and infested host plants were recorded in the wind tunnel.Wind tunnel and physical conditions were similar to those previously described.One hour before the end of the photo phase, moths were placed individually in a cylindrical plastic tube (3 × 6 cm) closed with gauze, in the wind tunnel room.To avoid contamination from the plant pots, each pot was wrapped in aluminium foil.All experiments were carried out 1-5 h after the onset of the scotophase and two red incandescent light sources (5 watts) above the tunnel provided suffi cient light for observing the behaviour.The four sets of experiments using four different host plants per experiment in different conditions including: (1) uninfested, (2) infested with conspecifi c larvae, (3) whitefl ies and (4) two-spotted spider mites were evaluated.Insects were released from a 10-cm-high platform 150 cm downwind of the odour source.Insects from each of the four stock cultures were used and the control experiments consisted of recording the response of mated and unmated males and females to dry fi lter paper.The following steps in the behavioural sequence were recorded: takeoff (TO: fl ight initiation), oriented fl ight towards the source (OF: fl ight towards the odour source reaching at least half way along the wind tunnel), close to source (CS: oriented fl ight at least 10 cm from the source), and landing (L: contact with source).Each treatment combination was randomly tested 30 times.Each insect was tested only once and if it did not respond within 15 min, it was recorded as a non-response.

Role of experience in host fi nding behaviour
Two-choice olfactory experiments were carried out in the wind tunnel to assess the effect of experience of one species of plant on subsequent attraction to the same and different species of plants.The plants were placed side by side 35 cm apart, at the upwind end of the wind tunnel.Mated females, 4-to-5 days old, were put individually into a cylindrical plastic tube (3 × 6 cm) and released from a 10-cm-high platform 150 cm downwind of the plants.All experiments were done in the dark under the same physical conditions as described previously.Ten mated females were used in each treatment and allowed 15 min for them to respond.A plant was randomly allocated to one side of the wind tunnel at the beginning of each bioassay and replaced after fi ve moths were tested to eliminate potential of positional bias.The duration of the experience was more than fi ve generations.

Olfactory response of larvae
A Y-tube olfactometer with Tefl on tubing, was used to measure the response of larvae of D.indica to different odours.The Y-tube consisted of a 14-cm long stem and two 10-cm long arms, each with an internal diameter of 2 cm.A glass plug at the base of the stem was used to introduce larvae into the Y-tube.At the end of each arm was a glass chamber, of 3.5 cm internal diameter and 17.5 cm long, in which the odour sources were placed.The Y-tube was housed within a temperature controlled room (27 ± 1°C and 60-80% RH) and oriented vertically with the arms 80 cm below fl uorescent lights (~ 1,600 lux).An air pump was used to provide an airfl ow controlled by a flow meter (Testo 425 Hot Wire anemometer) of 300 ml/min in each arm.Airflow entering each arm of the olfactometer was drawn through Tefl on tubing and was humidifi ed by passing it through a 1,000-ml Erlenmeyer fl ask with 500 ml of distilled water and fi ltered by passing it through a 1,000-ml Erlenmeyer fl ask with activated charcoal before entering the glass tube with the odour source or control.An odour source was randomly allocated to one arm of the olfactometer at the beginning of each bioassay and was changed to the other arm after fi ve larvae to eliminate the potential for positional bias.We harvested approximately 3 g of fresh leaves from either infested or uninfested cucurbitaceous host plants for use as odour sources in the olfactometer.Plants were approximately equal in age and size.In order to eliminate the effects of experience of plant volatiles in each test involving a host plant, a mixture of larvae reared on the other three host plants were used.The fourth instar larvae were starved for 2-6 h by keeping them separately in cylindrical plastic tubes (3 × 6 cm) without food under laboratory conditions in order to enhance their response in the olfactometer.After the introduction of larvae at the base of the stem of the olfactometer, each larva was given 600 s to crawl into one of the Y-tube arms and was scored as responsive if it entered either arm.Individuals that did not enter at least one of the arms were scored as unresponsive.At least 30 larvae were tested in each treatment.Before the tests using host plant odours, preliminary tests were conducted to determine whether the two arms of the Y-tube olfactometer were of equal attractiveness in order to exclude the possibility of positional bias, during which the larvae of D. indica were exposed to clean air vs. clean air and also cucumber leaves vs. cucumber leaves.In the fi rst series of assays, leaves of all four species, both uninfested and previously infested (infested by conspecifi c larvae, whitefl ies and two-spotted spider mites separately), were tested individually vs. clean air.In a second series of tests, uninfested leaves were tested against previously infested leaves of the same plant species.In a third series, various conspecifi c cues including 6 adults (3 females and 3 males), 6 larvae, 6 pupae and 30 eggs were tested vs. clean air.After testing, the olfactometer and connecting tubes were washed with detergent and water, and placed in a drying oven (150°C) for at least 2 h between each treatment.

Statistical analysis
Within treatment analyses were carried out after running normality tests on the results of the oviposition bioassays.Differences in the number of eggs laid on different plants were tested using analysis of variance (ANOVA) (SPSS).If signifi cant differences were detected, multiple comparisons were made using Tukey's HSD Multiple Range Test (P = 5%).Percentage of adult insects responding to plant volatiles and the number of larvae of D. indica responding to binary choices in each assay were compared pairwise among experimental treatments using a Chi-square test.

Oviposition bioassays
The results revealed that on uninfested plants D. indica laid an average of 15, 13 and 11 eggs per plant on cucumber, squash and melon, respectively.However, it did not lay any eggs on watermelon and signifi cantly preferred cucumber over squash, melon and watermelon (F 3,76 = 278.20,P < 0.001) (Fig. 1A).Infestation by conspecifi c larvae, whitefl ies and mites, signifi cantly reduced egg laying (F 3,316 = 60.19,p < 0.001) with averages of 3, 4 and 4 eggs per plant laid on plants infested with conspecifi c larvae, whitefl ies and mites, respectively (Fig. 1B).When the host plants in different conditions were evaluated separately, the results revealed that females of D. indica signifi cantly preferred uninfested plants over those infested with conspecifi c larvae, whitefl ies and mites, for cucumber plants (F 3,76 = 6.00, p = 0.001), squash (F 3,76 = 3.38, p = 0.022) and melon (F 3,76 = 278.20,p < 0.001) (Fig. 2).For watermelon plants (F 3,76 = 0.20, p = 0.89) and squash plants infested with whitefl ies (Fig. 2), females did not show any preference for plants in particular conditions.Results revealed that volatiles from host plants in different conditions elicit different responses in D. indica.

Role of olfactory stimuli and mating status in host fi nding behaviour
Role of mating status on behavioural responses of males and females of D. indica to host plant volatiles in the wind tunnel are presented in Fig. 3.The results reveal that mating status has no statistically signifi cant effect on host fi nding behaviour of male insects (Fig. 3B, and D).Also no signifi cant differences were recorded in the take-off response of mated and unmated female moths to volatiles from plants in different conditions.However, the percentages of females of D. indica that responded when close to the source and landed on the source was affected by mating status and also host plant condition (Fig. 3A, and C).The mean percentage landing on uninfested plants and plants infested with conspecifi c larvae, whitefl ies and mites were 70, 33, 40 and 33%, respectively, for mated females, 30, 20, 23 and 27% for unmated females (χ 2 = 75.8,P < 0.001) (Fig. 3C) and 17, 7, 10 and 13% for mated males and 23, 10, 17 and 17% for unmated males (χ 2 = 15.5, P = 0.03) (Fig. 3D).These results indicate that mated females tended to respond more strongly than virgin females to plant volatiles.Mated females signifi cantly preferred uninfested over infested plants (χ 2 = 37.9, P < 0.001) (Fig. 3C), and of the uninfested plants they signifi cantly preferred cucumber over squash, melon and watermelon (Fig. 4A).Unmated females showed no signifi cant differences in their responses to uninfested and infested plants of all the species tested (χ 2 = 3.09, P = 0.37) (Fig. 3C) and no preference for any of the four host plants (Fig. 4B).For mated (χ 2 = 5.28, P = 0.15) and unmated (χ 2 = 6.07,P = 0.10) males, there were no signifi cant differences in their responses to uninfested and plants infested with whitefl ies or mites (fi g. 3D) or in their responses to the four host plants (Fig. 4C and D).

Role of experience in host fi nding behaviour
The results reveal that female insects that had fed only on cucumber, squash or melon plants were signifi cantly attracted to the same plant, but those that were reared on watermelon did not show any preference for watermelon over the other plants (Table 1).Also on watermelon the growth of larvae was not as good as on the other three plants and this strain produced few insects.When the effect of the experience of feeding on a particular species of plant on the subsequent attraction to different species of plants were evaluated, the results reveal that females of D. indica signifi cantly preferred cucumber over squash, melon and watermelon (Table 1).

Olfactory response of larvae
In the preliminary test using clean air (χ 2 = 0.64, P = 0.42) or cucumber leaves (χ 2 = 1, P = 0.31), there were no signifi cant differences in the choice of arms of the olfactometer.This result reveals that both arms of the olfactometer were equally attractive and there was no positional bias in the tests using different odour sources.In comparison with clean air, the larvae of D. indica were attracted to uninfested leaves of cucumber, squash and melon, but not watermelon (Fig. 5).Also larvae did not respond to all of the four cucurbitaceous plants that were previously in-  fested with conspecifi c larvae, whitefl ies and mites (Fig. 5).The second assay reveals that volatiles from uninfested plants of cucumber, squash and melon were more attractive to the larvae of D. indica than those from previously infested plants, but not in the case of watermelon (Fig. 6).Also larvae did not respond to the odour of conspecifi cs, whether adults, larvae, pupae or eggs (Fig. 7).

DISCUSSION
Our results demonstrate that adult females D. indica distinguish among cucurbitaceous host plants and signifi cantly prefer to oviposit on cucumber over squash, melon and watermelon (Fig. 1).Infestation of host plants by conspecifi c larvae, whitefl ies or mites, signifi cantly reduced egg laying and females signifi cantly preferred uninfested over infested plants (Figs 1 and 2).Several previous studies report that damage to plants can affect their attractiveness for mated females and for egg laying.Herbivore-induced plant volatiles can repel or attract conspecifi c or heterospecifi c adult herbivores.Caterpillars induce tobacco to produce volatiles exclusively at night, which are highly repellent to the conspecifi c female moth Heliothis virescens (De Moraes et al., 2001).Mated females of Trichoplusia ni, signifi cantly prefer healthy cotton and cabbage plants for oviposition over plants infested with conspecifi c larvae (Landolt, 1993).Female moths of Spodoptera littoralis lay only a third of the number of eggs on cotton plants infested with conspecifi c larvae than they do on undamaged plants (Anderson & Alborn, 1999).Oviposition choice by females of T. absoluta is infl uenced by the number of conspecifi c larvae on tomato plants and they signifi cantly prefer uninfested plants or those infested with a few larvae (Bawin et al., 2014).In contrast to our results females of the diamondback moth, P. xylostella (Lepidoptera: Plutellidae), lay signifi cantly more eggs on cabbage and canola plants infested with conspecifi c larvae than on uninfested plants (Silva & Furlong, 2012;Wee, 2016).The advantage of choosing healthy plants for egg laying can be little competition between offspring, a lower level of induced defence in the host plant and/or exposure to natural enemies.Table 1.The effect of previous experience on host fi nding behaviour of females of Diaphania indica (n = 10 in each choice, Cu -Cucumber, Sq -Squash, Me -Melon, Wa -Watermelon).The results of the present study on the olfactory responses of adults reveal that mated females had a stronger response than unmated females to the odours of uninfested and infested plants (Fig. 3C), which indicates that the response to host plant volatiles is associated with the physiological state of the female.However, there was no signifi cant difference in the response of mated and unmated males to plant volatiles (Fig. 3D).Both male and female insects were more attracted to uninfested than infested plants.The differences in the responses of mated and unmated females indicate that mated females of D. indica are more responsive to cucurbitaceous plant volatiles than are unmated females and this is important for mated females as their choice of plants determines their fi tness.It is report-ed that physiological changes in female moths after mating enhance the response of gravid females to host plant odours, because they need to lay eggs (Anton et al., 2007;Wee, 2016).Similarly, Saveer et al. (2012) show that mating, modifi es the olfactory physiology of females of the cotton leaf worm, S. littoralis (Lepidoptera, Noctuidae), leading to a shift in olfactory preference from lilac fl owers (Syringa vulgaris) to the green leaves of the larval host plant cotton.Attraction to volatile compounds is not only dependent on their chemical structure, but might change with the physiological status of the recipient (e.g., age, hormone levels, feeding status or mating status) or environmental conditions (Anton et al., 2007;Martel et al., 2009).The odour of tomato leaves elicit an upwind orientation  fl ight followed by landing and egg laying in mated females of the tomato leaf miner T. absoluta, but not in unmated females (Proffi t et al., 2011).Mated females of the moth Pectinophora gossypiella (Lepidoptera: Gelechiidae) are more readily attracted to cotton fl owers than are unmated females or male moths (Wiesenborn & Baker, 1990).Mated females of Lobesia botrana (Lepidoptera: Tortricidae) are attracted to host plant volatiles, but unmated females and mated and unmated males are not attracted (Masante-Roca et al., 2007).It is also reported that mating, increases antennal detection in Dioryctria abietivorella (Lepidoptera: Pyralidae) (Shu et al., 1997).In contrast to our results, mating status in the diamondback moth has little effect on the female's response to host odour and female moths are signifi cantly more attracted to cabbage plants infested with conspecifi c larvae (Wee, 2016).It is also reported that virgin females of S. littoralis (Lepidoptera: Noctuidae) are more responsive to host plant volatiles than mated females (Martel et al., 2009).
The results of the present study indicate that the effect of experience on the olfactory preference of D. indica is dependent on the host plant.Females that had previous experience of cucumber, squash or melon plants were significantly more attracted to the same plant.But females that were reared on watermelon did not show any preference for watermelon over the other plants.Inexperienced females of D. indica, preferred cucumber over squash, melon and watermelon, suggesting that females have an innate olfactory preference for cucumber (Table 1).In other studies the results depend on the plant and insect species.For example, females of H. armigera inherently prefer tobacco for oviposition even after experiencing tomato, cotton or hot pepper plants (Hu et al., 2018).A one generation experience is enough to induce a preference for vanillin in S. nonagrioides, whereas even two generation experience failed to induce a response in adults of Busseola fusca and B. nairobica (Petit et al., 2018).It is reported that larval host plant experience modulates both mate fi nding and oviposition choice in S. littoralis (Anderson et al., 2013).In a variable environment, dependence on experience rather than innate preference could be advantages (Dukas, 2008) in terms of responding to environmental changes and increase in insect fi tness (Anderson et al., 2013).
Few studies report the attractiveness of host plants for larvae.Our bioassays demonstrate that, the larvae of this pest can orient to plant volatiles.The volatiles from leaves of uninfested cucumber, squash and melon in the olfactometer attracted the larvae and enabled them distinguish between these host plants (Fig. 5).However, volatiles emitted by either conspecifi cs, uninfested watermelon or plants infested with either conspecifi c larvae, whitefl ies or mites were not attractive for larvae of this pest (Figs 5,7).When suitable food sources are exhausted the larvae of some species can leave the original oviposition site and forage for other host plants (Singer & Stireman, 2001;Zalucki et al., 2002;Carroll et al., 2006).Larvae can use visual and olfactory cues to fi nd host plants.The role of volatile compounds in the host fi nding behaviour of larvae, has been documented far less frequently than for adult moths.The few studies on their feeding behaviour report similar results for larvae of S. littoralis that are attracted and feed more on undamaged cotton plants than on leaves of herbivore damaged plants (Anderson et al., 2001).It is reported that the larvae of S. exigua prefer undamaged plants to damaged plants and this is due to the leaves producing a feeding deterrent when damaged by larvae (Alborn et al., 1996).In contrast to our results, Carroll et al. (2006) found that both infested and intact maize plants are attractive for larvae S. frugiperda and this pest prefers odours from infested plants over those from uninfested plants.First instar larvae of L. botrana (Lepidoptera: Tortricidae) are attracted by plants infested with the fungus (Botrytis cinerea) (Mondy et al., 1998).Larvae that select an infested host plant may encounter induced plant defence, competition, cannibalism and also natural enemies.
In conclusion, our results indicate that the attractiveness of cucurbitaceous host plants for D. indica depends on the species and condition of the plant (uninfested and infested) and sex, mating status and experience of the insect.This study investigated the effects of plant volatile infochemicals in attracting and determining the oviposition behaviour of D. indica.For improving the monitoring and management of this pest it is now important to identify the behaviourally active volatiles involved and breed more resistant plants.

Fig. 1 .
Fig. 1.Mean (± SE) number of eggs laid by Diaphania indica on uninfested plants of four host plants (A) and on uninfested plants compared to those on host plants infested with conspecifi c larvae, whitefl ies and two-spotted spider mites (B).Columns topped with same letter are statistically similar (Tukey-HSD test, α = 0.05).

Fig. 2 .
Fig. 2. Mean (± SE) number of eggs laid by Diaphania indica on different host plants (cucumber, squash, melon and watermelon) that were either uninfested or infested with either conspecifi c larvae, whitefl ies or two-spotted spider mites.For each plant, columns topped by the same letter do not differ statistically (Tukey-HSD test, α = 0.05).

Fig. 3 .
Fig. 3. Percentage of the responses of mated and unmated females and males of Diaphania indica to uninfested and infested plants in the wind tunnel.The percentage of individuals close to the source (A -females, B -males) and landing on the source (C -females, D -males) is indicated for each treatment.Columns topped by the same letter do not differ statistically (Chi square test, α = 0.05).

Fig. 4 .
Fig. 4. Percentage attractiveness of the different host plants to (A) mated females, (B) unmated females, (C) mated males and (D) unmated males of Diaphania indica in the fl ight tunnel.Columns topped by the same letter do not differ statistically (Chi square test, α = 0.05).