Ovipositional Preferences of Two Squash Bug Species, Anasa tristis and Anasa armigera (Heteroptera: Coreidae), for Different Cultivars and Species of Cucurbitaceae.

The ovipositional preferences of two squash bug species, Anasa tristis (DeGeer) (Heteroptera: Coreidae) and Anasa armigera Say (Heteroptera: Coreidae), were evaluated in paired choice tests of different species and cultivars of plants in the family Cucurbitaceae. Females of A. tristis preferred to oviposit on the cultivar from which they were reared over three other cultivars of the same species. However, females did not show any ovipositional preference for different cultivars when they had no previous exposure to either cultivar. Females of A. tristis were equally likely to oviposit on Cucurbita pepo, Cucurbita maxima, and Cucurbita moschata but were significantly more likely to oviposit on C. pepo than on cucumber and watermelon. Females of A. armigera were equally likely to oviposit on C. pepo or cucumber, regardless of the species they were reared on. When A. armigera was reared on C. pepo, females were more likely to oviposit on C. maxima than on cucumber and less likely to oviposit on C. moschata than on cucumber.

common squash bug, Anasa tristis (DeGeer) (Heteroptera: Coreidae), is a major pest of cucurbit crops in the United States (Doughty et al. 2016). It is found throughout the United States, and in Mexico, Central America, and Canada (Wadley 1920, Beard 1940). It is also a vector of cucurbit yellow vine disease, Serratia marcescens, which can cause severe crop damage (Bruton et al. 2003, Pair et al. 2004, Wayadande et al. 2005). Studies on pest control strategies for squash bugs have included the use of insecticidal sprays, trap crops, mulches, row covers, and biological control (Cartwright et al. 1990, Olson et al. 1996, Pair 1997, Lu et al. 2003, Dogramaci et al. 2004, Decker and Yeargan 2008, Schmidt et al 2014, Cornelius et al. 2016). Research has also explored the possibility of using RNAi techniques for immunosuppression (Shelby 2013).

Several studies have been conducted to evaluate the feeding preferences, fecundity, and nymphal development of A. tristis for different cultivars and species of Cucurbitaceae (Novero et al. 1962, Bonjour and Fargo 1989, Bonjour et al. 1993, Vogt and Nechols 1993, Cook and Neal 1999). Studies found that nymphal development and survival and adult fecundity were higher on Cucurbita pepo L. and Cucurbita maxima Duchesne compared with Cucurbita moschata Duchesne ex Poir-, watermelon, Citrullus lanatus (Thunb.) Matsum.& Nakai, cucumber, Cucumis sativus L., and muskmelon, Cucumis melo L. There is evidence, however, that squash bugs can rapidly adapt to resistant cucurbit species. Nymphal survival of A. tristis on the resistant squash species, Waltham Butternut, increased from about 20% in the first generation to about 45% by the fifth generation (Margolies et al. 1998).

In addition, studies have evaluated the ovipositional preferences of A. tristis for different cultivars and species of Cucurbitaceae. In a field test in Illinois, A. tristis showed an ovipositional preference for C. maxima and C. mixta over C. pepo, C. moschata, and C. ficifolia Bouché (Howe and Rhodes 1976). In Oklahoma, the ovipositional preference of A. tristis for different cultivars and species of Cucurbitaceae was evaluated in field tests. In a comparison of five cultivars of C. pepo and one cultivar of C. moschata, the number of egg masses per leaf was highest for straightneck and crookneck squash, C. pepo. Also, A. tristis showed an ovipositional preference for two cultivars of C. pepo, Yellow Straightneck and Jack O’ Lantern, over cucumber, watermelon, and muskmelon (Bonjour et al. 1990).

In contrast, there are no studies on the biology of the horned squash bug, Anasa armigera Say (Heteroptera: Coreidae). It was mentioned as a pest of squash in several early reports (Parshley 1918, Drake and Harris 1926, Britton 1937, Gould 1944). It is found throughout the eastern United States and as far north as Ontario and Quebec in Canada. It is found as far west as Oklahoma, Kansas, and Texas, and it has been newly recorded in Arkansas (Chordas and Kovarik 2008). An anecdotal report suggested that A. armigera preferred cucumber over squash (Parshley 1918). A. armigera is less common than A. tristis. In a 2-yr field study, A. armigera comprised only 4.3% of wild squash bug egg masses collected in squash fields at the Beltsville Agricultural Center in Maryland (Cornelius, unpublished).

This study examined the ovipositional preferences of A. tristis and A. armigera for different species of Cucurbitaceae in paired choice tests. This study also evaluated the ovipositional preferences of A. tristis for different cultivars of C. pepo and determined if the cultivar on which squash bugs were reared affected their ovipositional preferences for other cultivars.

Materials and Methods

Insect Rearing

A. tristis and A. armigera, were collected from squash, C. pepo, fields at the Beltsville Agricultural Research Center, Beltsville, MD, and maintained in laboratory colonies in cylindrical plastic containers (19.3-cm height by 20.0-cm diameter) (Pioneer Plastics, Inc., Eagan, MN) in an incubator (25°C; 16:8 [L:D] h). Each container had a hole (approximately 14-cm diameter) in the lid covered with a fine mesh screen, a filter paper on the bottom, and two cotton plugged glass shell vials filled with water attached with a rubber band to prevent them from rolling. Both species were maintained on fresh cuttings of cucurbit plants grown in a greenhouse and fruit of either yellow squash or zucchini purchased at a local organic market. A. tristis was reared exclusively on yellow squash (C. pepo cv. Slick Pik YS26). Because there was no published information on rearing A. armigera, this species was divided into two groups: one group was reared exclusively on yellow squash (C. pepo cv. Slick Pik YS26) and the other group was reared exclusively on cucumber (C. sativus cv. Diva).

Ovipositional Preference Tests

Ovipositional preference tests were conducted with squash bugs of both species that were reared exclusively on yellow squash (C. pepo cv. Slick Pik YS26). All A. tristis used in ovipositonal tests were reared on the same cultivar in order to examine whether there was evidence of induced preference for the cultivar on which they were reared. In addition, ovipositional tests were conducted with A. armigera that was reared exclusively on cucumber. Paired choice tests were conducted using different cultivars of C. pepo and different species of Cucurbitaceae (Table 1). All plants used in tests were grown from seed (Johnny’s Selected Seeds, Winslow, ME) in a greenhouse. Ovipositional tests were conducted in 61 × 61 × 61-cm screened cages (Bioquip Products, Rancho Dominguez, CA) with lumite screening (Lumite, Inc. Alto, GA) in a temperature controlled room (25°C; 12:12 [L:D] h). For each replicate, two potted test plants of the same age were placed in opposite corners of a cage. Each test plant was either a different species or a different cultivar of Cucurbitaceae from the other test plant. For each replicate, fivemating pairs were collected from cages and released into the center of the screened cage. Mating pairs were used in order to ensure that all of the females in each replicate had mated. After 48 h, plants and mating pairs were removed from the screened cage. For each replicate, new test plants and new mating pairs were introduced into the screened cage. The position of the two test plants (different cultivars or species) in each corner was rotated between replicates. There were at least eightreplicates for each test. . After 48 h, the number of egg masses and the total number of eggs per mass were counted on each test plant. Egg masses deposited on the screened cage were not counted. Paired t-tests were used to compare the number of egg masses and the total number of eggs deposited on each test plant.

Table 1.

Host plant cultivars and species in the family Cucurbitaceae used in paired choice oviposition tests with the common squash bug, A. tristis, and the horned squash bug, A. armigera

Species	Cultivar	Fruit
C. pepo	Slick Pik	Yellow straight neck squash
C. pepo	Yellow Crookneck	Yellow crookneck squash
C. pepo	Zephyr	Yellow summer squash
C. pepo	Plato	Zucchini
C. pepo	Tigress	Zucchini
C. pepo	Dunja	Zucchini
C. pepo	Magda	Zucchini
C. pepo	Sunburst	Yellow patty pan
C. pepo	Spaghetti Squash	Spaghetti squash
C. pepo	Jack O’ Lantern	Pumpkin
C. moschata	Waltham Butternut	Butternut squash
C. maxima	Burgess Buttercup	Buttercup squash
C. sativus	Diva	Cucumber
C. lanatus	Crimson Sweet	Watermelon

Results

Anasa tristis

When different cultivars of C. pepo were compared, females were more likely to oviposit on Slick Pik, the cultivar they were reared on, than on Plato, Dunja, or Tigress, but not Yellow Crookneck (Fig. 1). However, there was no difference in ovipositional preference of females for Yellow Crookneck compared with any of the other cultivars tested (Fig. 2).

Fig. 1.

The ovipositional preferences of A. tristis, reared on the cultivar Slick Pik, for the cultivar Slick Pik compared with other cultivars of the same species, C. pepo. Test plants: 1) Plato, 2) Dunja, 3) Tigress, and 4) Yellow Crookneck. (A) Mean number (± SE) of egg masses per plant. (B) Mean number (± SE) of eggs per plant. For each paired choice test, bars followed by the same letter were not significantly different (Paired t-test: P > 0.05).

Fig. 2.

The ovipositional preferences of A. tristis, reared on the cultivar Slick Pik, for the C. pepo cultivar, Yellow Crookneck, compared with other cultivars of the same species, C. pepo. 1) Plato, 2) Tigress, 3) Jack O Lantern, 4) Sunburst, 5) Zephyr, 6) Magda, and 7) Spaghetti Squash. (A) Mean number (± SE) of egg masses per plant. (B) Mean number (± SE) of eggs per plant. There were no significant differences.

In paired choice tests, comparing oviposition behavior on C. pepo (cultivar: Yellow Crookneck) with other species of Cucurbitaceae, females did not show a preference for C. pepo over either butternut C. moschata or buttercup C. maxima. Females did show a preference for C. pepo over cucumber and watermelon (Fig. 3).

Fig. 3.

The ovipositional preferences of A. tristis, reared on the cultivar Slick Pik, for the C. pepo cultivar, Yellow Crookneck, compared with other cucurbit species. Test species: 1) butternut (C. moschata), 2) buttercup (C. maxima), 3) cucumber (C. sativus), and 4) watermelon (C. lanatus). (A) Mean number (± SE) of egg masses per plant. (B) Mean number (± SE) of eggs per plant. For each paired choice test, bars followed by the same letter were not significantly different (Paired t-test: P > 0.05).

Anasa armigera

In the laboratory, A. armigera was reared successfully from first instar through adulthood on both squash (C. pepo cv. Slick Pik YS26) and cucumber (C. sativus cv. Diva). In paired choice tests, females reared on cucumber were equally likely to oviposit on either cucumber or C. pepo (Fig. 4). Females reared on C. pepo had no ovipositional preference for C. pepo over cucumber for either cultivar of C. pepo tested. Females reared on C. pepo were significantly more likely to oviposit on cucumber than on C. moschata but were significantly more likely to oviposit on C. maxima than on cucumber. There was no significant difference in the ovipositional preference of A. armigera for cucumber over watermelon (Fig. 5).

Fig. 4.

Mean number (± SE) of egg masses and eggs per plant in a paired choice test evaluating the ovipositional preferences of A. armigera, reared on the C. sativus cultivar Diva, for the C. sativus cultivar Diva compared with the C. pepo cultivar Slick Pik.

Fig. 5.

The ovipositional preferences of A. armigera, reared on the C. pepo cultivar Slick Pik, for the C. sativus cultivar, Diva, compared with other cucurbit species. Test species: 1) Slick Pik and Dunja (C. pepo), 2) butternut (C. moschata), 3) buttercup (C. maxima), 4) cucumber (C. sativus), and 5) watermelon (C. lanatus). (A) Mean number (± SE) of egg masses per plant. (B) Mean number (± SE) of eggs per plant. For each paired choice test, bars followed by the same letter were not significantly different (Paired t-test: P > 0.05).

Discussion

Females preferred to oviposit on the cultivar on which they were reared in paired choice tests with three of the four cultivars tested. However, females did not show any ovipositional preference for different cultivars when they had no previous exposure to either cultivar. These results suggest that squash bugs are capable of rapidly developing an ovipositional preference for the cultivar on which they were reared. This shift in ovipositional preference may enable them to adapt more quickly to less preferred cucurbit species. There is evidence that squash bugs can adapt to a resistant host species within five generations (Margolies et al. 1998).

There was no ovipositional preference for Yellow Crookneck, C. pepo, and either C. maxima or C. moschata. There have been conflicting results concerning the susceptibility of C. maxima to squash bugs. Although some studies found that C. maxima is susceptible to squash bugs (Novero et al. 1962, Howe and Rhodes 1976), survivorship was significantly lower on C. maxima than on C. pepo in another study (Vogt and Nechols 1993). In contrast, C. moschata has been consistently reported as a resistant species (Novero et al. 1962, Howe and Rhodes 1976, Bonjour et al. 1990, Vogt and Nechols 1993).

Females preferred to oviposit on Yellow Crookneck over either cucumber or watermelon. These results were consistent with another study demonstrating that females showed an ovipositional preference for cultivars of C. pepo over both cucumber and watermelon (Bonjour et al. 1990). Also, Cook and Neal (1999) found that squash bug nymphs could not complete development on cucumber. The squash bugs used in the current study were collected from C. pepo fields and reared on C. pepo. Adult females from this laboratory colony did not deposit any eggs on watermelon in paired choice tests. However, there is evidence that there may be regional differences in the preferences of A. tristis populations for different cucurbit crops. For instance, A. tristis is a serious pest of watermelon in Texas and Oklahoma (Edelson et al. 2002, 2003; Dogramaci et al. 2004, 2006). Adult squash bugs collected from watermelon would most likely exhibit different host plant preferences from those collected in squash fields. These findings indicate that there may be regional differences in the host plant preferences of squash bug populations for different species of Cucurbitaceae.

This study represents the first experimental evidence of the host plant preferences of A. armigera. Anecdotal evidence suggested that A. armigera preferred cucumber over squash (Parshley 1918). However, A. armigera was reared successfully in the laboratory on both squash and cucumber. Also, females did not display any ovipositional preferences for either squash or cucumber, regardless of which species they were reared on. When A. armigera was reared on C. pepo, females showed a significant ovipositional preference for C. maxima over cucumber and a significant ovipositional preference for cucumber over C. moschata. This study provides the first experimental evidence that both squash and cucumber can serve as suitable hosts for A. armigera.

Conclusion

There were differences in the ovipositional behavior of the two squash bug species. Both squash bug species oviposited readily on C. pepo and C. maxima. A. armigera was able to successfully complete development on both cucumber and yellow squash and was equally likely to oviposit on both host species. Cook and Neal (1999) found that second-instar A. tristis nymphs did not gain more weight when fed cucumber than when fed water alone. Therefore, A. armigera appears to be better adapted to cucumber than A. tristis. There were also differences between the two species in their ovipositional behavior toward watermelon. A. tristis did not deposit any egg masses on watermelon in a paired choice test, whereas A. armigera was equally likely to lay egg masses on watermelon compared with cucumber. Although A. tristis showed a significant ovipositional preference for the cultivar on which it was reared over three other cultivars, there was no evidence that A. armigera females showed an ovipositional preference for the cultivar on which they were reared in paired choice tests with cucumber and two cultivars of C. pepo.